Rice in China - IRRI books - International Rice Research Institute

Progressin IrrigatedRice ResearchSelected papers and abstracts from theInternational Rice Research Conference21 - 25 September 1987Hangzhou, Chinasponsored byInternational Rice Research InstituteChina Academy of Agricultural SciencesChina National Rice Research Institute1989International Rice Research InstituteP.O. Box 933, Manila, Philippines

The International Rice Research Institute (IRRI) was established in 1960 by theFord and Rockefeller Foundations with the help and approval of the Governmentof the Philippines. Today IRRI is one of the 13 nonprofit international researchand training centers supported by the Consultative Group on InternationalAgricultural Research (CGIAR). The CGIAR is sponsored by the Food andAgriculture Organization (FAO) of the United Nations, the International Bank forReconstruction and Development (World Bank), and the United Nations DevelopmentProgramme (UNDP). The CGIAR consists of 50 donor countries, internationaland regional organizations, and private foundations.IRRI receives support, through the CGIAR, from a number of donorsincluding the Asian Development Bank, the European Economic Community, theFord Foundation, the International Development Research Centre, the InternationalFund for Agricultural Development, the OPEC Special Fund, theRockefeller Foundation, the United Nations Development Programme, theWorld Bank, and the international aid agencies of the following governments:Australia, Belgium, Canada, China, Denmark, Finland, France, Federal Republicof Germany, India, Italy, Japan, Mexico, The Netherlands, New Zealand,Norway, the Philippines, Saudi Arabia, Spain, Sweden, Switzerland, UnitedKingdom, and United States.The responsibility for this publication rests with the International RiceResearch Institute.Copyright © International Rice Research Institute 1989All rights reserved. Except for quotations of short passages for the purpose ofcriticism and review, no part of this publication may be reproduced, stored inretrieval systems, or transmitted in any form or by any means, electronic,mechanical, photocopying, recording, or otherwise, without prior permission ofIRRI. This permission will not be unreasonably withheld for use for noncommercialpurposes. IRRI does not require payment for the noncommercial useof its published works, and hopes that this copyright declaration will not diminishthe bona fide use of its research findings in agricultural research and development.The designations employed and the presentation of the material in thispublication do not imply the expression of any opinion whatsoever on the part ofIRRI concerning the legal status of any country, territory, city, or area, or of itsauthorities, or the delimitation of its frontiers or boundaries.ISBN 971-104-184-7

ContentsForewordRice in China 1Minister He KangRice research: learning from China 5M.S. SwaminathanGLOBAL RICE PRODUCTIONThe global rice situation 9C.C. DavidProblems arising from the Indonesian success in rice production 25D.S. Damardjati, S.R. Tabor, I.N. Oka, and C.C. DavidPHYSIOLOGICAL ASPECTSImproving yield potential in tropical rice 41S. AkitaABSTRACTSImproving the yielding ability of rice 74B. Venkateswarlu and B.S. VergaraHigh-yielding rice cultivars in Japan 75I. NishiyamaHigh-yielding rice cultivars in South Korea 75S.H. Park and S.Y. ChoHigh-yielding rice cultivars in the U.S. 76C.N. Bollich, J.N. Rutger, and D.M. BrandonHigh-yielding rice Cultivars in Peninsular Malaysia 76E. Yusoff and C.Y. TayHigh-yielding rice cultivars in China 77Wu Guangnan and Tsiu JilingHigh-yielding rice varieties in Vietnam 77Dao The Tuan

PEST MANAGEMENTMultiple disease and insect resistance for increased yield stability in rice 79G.S. KhushDurable resistance to rice diseases in irrigated environments 93E.J. Lee, Qi Zhang, and T.W. MewDurable resistance to insect pests of irrigated rice 111R.C. SaxenaEmerging weed control technology for broadcast seeded rice 133S.K. De Datta, P.C. Bernasor, T.R. Migo, M.A. Llagas,and P. NantasomsaranABSTRACTSChemical control of rice sheath blight in Japan 148T. YamaguchiPest control in irrigated rice in West Africa 148E.A. Akinsola and M. Agyen-SampongWeed problems in irrigated rice and their control in Africa 149O. AkobunduNUTRIENT MANAGEMENTDynamics of soil nitrogen and its management 151Zhu ZhaoliangManagement of farm-grown nutrient sources for rice 165Wen QixiaoNutrient kinetics and availability in flooded rice soils 173H.U. Neue and P.R. BloomABSTRACTSIntegrated nitrogen management in irrigated rice 191S.K. De Datta and R.J. BureshManagement of acid sulfate rice soils in South China 192Li Jinpei and Huang YunianNutrient management in saline, acid sulfate, and other problem soils of Vietnam 192Vo-Tong XuanWATER MANAGEMENTIrrigation system principles and practices for reliable and efficient water supply to ricefarms 193S.M. MirandaABSTRACTSIncreasing water-use efficiency on irrigated rice farms 203S.I. Bhuiyan and K. PalanisamiRelationship of drainage practices to rice yield 203Zhang Wei and Situ SongFARMING SYSTEMSIntegrating women’s concerns into farming systems research 205Pudjiwati Sajogyo and T. ParisABSTRACTSCollaborative research on cropping patterns testing in irrigated areas of Asia 216V.R. CarangalRice - wheat rotation: constraints and future directions 217D. SaundersRice - azolla - fish cropping system 217Liu Chungchu

INNOVATIVE BREEDINGHybrid rice: achievements and outloook 219Yuan Longping, S.S. Virmani, and Mao ChangxiongUsing chemical male gametocides in hybrid rice breeding in China 237Tu Zengping and Hu DawenDNA-mediated transformation in rice protoplasts 245H. UchimiyaUsing rapid generation advance with single seed descent in rice breeding 253K. MaruyamaGenetic variation in rice/sorghum hybrids and their application in rice breeding 261Chen Shanbao, Duan Xiaolan, and Fu JunluaABSTRACTSBiotechnology for rice varietal improvement 269A.A. App, G.H. Toenniessen, and R.W. HerdtEconomic efficiency of hybrid and conventional rice production in Jiangsu Province,China 270He Guiting and J.C. FlinnApplication of photoperiod-sensitive genic male sterility in hybrid rice breeding 270Lu Xinggui, Zhou Jixian, Wang Jilin, Fang Guochen,Zhou Wenhua, and Yang ShiyuanDiversification of cytoplasmic male sterility in hybrid rice 271Wan BanghuiTissue culture in rice improvement 271F.J. Zapata and L.B. TorrizoSomaclonal variation in rice improvement 272Xiong Zhenmin and Zheng KangleShuttle breeding for rice improvement 272Min Shaokai, Lu Zitong, and G.S. KhushTrends in breeding rice for high yield 273Yang Shouren and Chen WinfuRole of indica/japonica hybridization in rice improvement 273M.S. BalalWide hybridization for rice improvement 274K.K. Jena and G.S. KhushGene transfer in rice using protoplast fusion and recombinant DNA technology 274E.C. CockingGRAIN QUALITYPhysicochemical and economic aspects of rice grain quality 275B.O. Juliano and L.A. GonzalesABSTRACTScreening for quality of parboiled rice 291K.R. BhattacharyaMACHINERY AND POSTHARVESTIncreasing rice production efficiency through mechanization 293Zhang Baozhao, I. Manalili, and E. BautistaABSTRACTSSmall farm modernization policy: the efficiency-equity trade-off 311P.L. Pingali and B. DuffInnovations in grain drying technologies 311Yong Woon Jeon, L.S. Halos, and A.R. Elepaño

Mechanization of small rice farms in developing countries 312A.G. RijkMechanization of rice farming in China 312Feng BingyuanSmall farm machinery requirements for irrigated rice in East Africa 313G.C. MremaExperience on mechanization technology transfer 313Chak Chakkaphak and B. CochranINTERNATIONAL COLLABORATIONThe need for a global rice research system 315H.M. BeachellInternational collaboration on conservation, sharing, and use of rice germplasm 325T.T. Chang. Y.S. Dong, R.S. Paroda, and C.S. YingFindings from the international irrigated rice nurseries, with special reference to China 339D.V. Seshu and Zhang YihuaABSTRACTSIRRI and national agricultural research systems: challenges and opportunities 357K. KanungoChina’s collaborative relationship with IRRI 357Zhang Yihua and D.L. UndiEducational technology and its implications for rice technology transfer 358D.R. MinnickInternational linkages in rice farming systems 359V.R. Carangal and Guo YixianComputer networking in international agricultural research 359G.N. LindseyMultilanguage copublication: IRRI design and policies 360T.R. Hargrove, V.L. Cahanilla. R.C. Cabrera,and L.R. PollardHighlights and recommendations 361Participants 377Varietal index 383

ForewordThe annual International Rice Research Conference (IRRC) is traditionally a timewhen rice scientists from around the world gather to discuss progress in research toimprove rice production in the many environments in which the crop is grown. Inrecent years, each IRRC has focused on a specific research area of concern. Rainfedlowland rice was intensively discussed in 1985. For 1987, irrigated rice was thechosen focus.Irrigated rice culture is the most widely practiced, covers the largest area, andproduces the highest yields. More than 70% of the world’s rice is produced from the50% of the world’s ricelands that are irrigated.Papers and discussions focused on the global rice situation, physiologicalaspects of the yielding ability of rice, pest management, and nutrient and watermanagement, as well as farming systems, farm machinery, and postharvestmanagement. Special attention was paid to progress in innovative breedingtechniques made possible by recent breakthroughs in hybrid rice breeding andbiotechnology.In alternate years, the conference has been held away from IRRI. IRRC 1987was held in Hangzhou, China, co-sponsored by the Chinese agencies thatcollaborate in research with IRRI. A highlight of that conference was the dedicationof the experimental laboratories and farm of the China National Rice ResearchInstitute at Huang-Tian-Fang, Zhejiang Province.IRRC 1987 was organized and managed by two committees. For IRRI: D. L.Umali, chairperson; S. K. De Datta, J. C. Flinn, G. S. Khush, S. S. Virmani, and B.S. Vergara. For China: Zhang Yihua, chairperson; Wu Shangzhong, Gan Xiaosong,Fei Huailin, and Jiang Yuming. This collection of key papers and abstracts from theproceedings was edited by L. R. Pollard, with the assistance of E. Cervantes.KLAUS LAMPEDirector General

Rice in ChinaMINISTER HE KANGMinistry of Agriculture, Animal Husbandry, and FisheryThe People’s Republic of ChinaRice has always been one of the most important food crops in the world. It isestimated that 40% of the world’s population take rice as their major source of food;1.6 billion people in Asia take rice as their mainstay food. Rice is produced in 111countries in the world. The developing countries, especially the Asian countries—theregions with high population density and the most rapid population growth—produce and consume the most rice.During recent decades, world rice production has experienced comparabledevelopment. It is very encouraging to recall the 40% increase in world output of ricein the 1960s, the additional 30% increase in the 1970s, and the further annual increaseof 3.1% since the beginning of the 1980s. However, present world population hasreached 5 billion, and its growth is still rapid. How to fill the need of futurepopulations for food, especially rice, is still a very intense problem.The Food and Agriculture Organization of the United Nations (FAO) and theInternational Food Policy Research Institute (IFPRI) calculate that in a number ofcountries, the total output of rice up to the year 2000 can only meet 92-97% of therequirement. Hence, global efforts in developing rice production should beintensified.I present here some background on rice production and research in China.China is the world’s largest producer and consumer of rice. Rice has always been themost important food crop in the country. Since the People’s Republic was foundedin 1949, the Chinese Government has attached great importance to rice productionand has adopted a series of policies and measures to promote it. Rice accounts forabout 30% of the area planted to grain crops and about 45% of grain production. In1986, the total area planted to rice was 31.7 million hectares, 123.5% more than in1949. Total output was 169.9 million tons, 3.5 times that of 1949. Average yield perhectare reached 5.35 tons, 2.8 times that of 1949.The increase in food production since 1979 has been particularly striking.Although the total planted area decreased somewhat, to give more land todiversified farming, favorable conditions were created for the development offorestry, animal husbandry, fishery, and sideline occupations in the countryside.

2 He KangChina’s attainment of fairly rapid development of rice production can besummed up as relying on policy, science, and increases in agroinputs. We can singleout a number of contributing factors.Relationships between aspects of production have been reformed and adjusted.After the People’s Republic was founded, land reform throughout China boostedagrarian mutual aid and cooperation. In 1979, we began to implement a series ofreforms centered on a system of contracted household responsibility that linkspayments for output to the collective economy, thus greatly increasing the incentivefor the vast rural population.Economic policies conducive to developing food production have beenimplemented. To guarantee food supplies and to speed economic reconstruction, in1953, an overall policy of planned purchase and sale of grains was introduced. Thegovernment set minimum quotas and prices for grain purchases in each area;farmers could sell their surplus to the state at a higher price. In 1979, the governmentincreased the price for purchasing farmers’ surplus grain by 50%. In 1985, plannedpurchase was replaced by contract purchases, with farmers free to sell their surplusgrain in the market. When market prices for grain are lower than the state prices forplanned purchase, the government intervenes to purchase all the grain in the marketat state prices. This guarantees normal income for the farmers and protects foodproduction, thus keeping farmers’ incentive for grain production high.The state has helped farmers improve production conditions by investing incapital construction for soil improvement and water conservation. Facilities forflood control, irrigation, and drainage have been constructed. After more than 3decades’ work, the area under effective irrigation has been enlarged from 18.5% ofthe total cultivated area in 1952 to 45% in 1986, with practically all ricefields havingirrigation facilities. This has increased the ability of ricefields to resist drought andwaterlogging. Improving low-yielding fields has increased field fertility andproductivity.The agroindustries developed have helped create favorable conditions for riceproduction. Average application of chemical fertilizer in 1985 was 124.4 kg purenitrogen/ha; for rice, application is usually 20% higher. Production of pesticides in1985 was 211,000 t, more than half of it used in rice production. The level of farmmechanization rose sharply, with total use increasing from 250,000 hp in 1952 to 284million in 1985. Rural consumption of electric power increasing from 50 millionkWh in 1952 to 50.89 billion in 1985. All these developments have led to increasedagroproduction.We have made vigorous efforts to reform cropping systems and raise themultiple cropping index. Because we have a low land-to-people ratio, advantages innatural resources have been more fully tapped by expanding multiple cropping.Beginning in the 1950s, the emphasis in reforming the cropping system was onchanging from a single annual crop of rice to two crops. In consequence, the areaunder two crops of rice expanded beyond the previous northernmost limit of the28th parallel to the 33rd parallel. China’s area under two rice crops a year was only3.6 million ha in 1949—14% of the total area planted to rice. It covered 9.7 million hain 1985—33.3% of the total rice area and 2.7 times more than in 1949. During the last

Rice in China 3few years, adjustments have increased the area under other crops. Althoughsomewhat reduced, the area under two rice crops a year is close to the 1985 level.We have attached great importance to the selection and popularization of goodvarieties. Around the end of the 1950s and the beginning of the 1960s, the firstsemidwarf high-yielding varieties, such as Ai-jiao-nan-te and Guangchang Ai, wereevolved in Guangdong Province. Thereafter, several short-, medium-, and longduration,semidwarf, high-yielding indica varieties and medium- and long-durationcombinations were selected and developed. The indica semidwarf gene wasintroduced into japonica rice, and as a result, a group of semidwarf, high-yieldingjaponica rice varieties was released.The successful development and popularization of hybrid rice in the mid-1970smarked another important breakthrough in China’s rice production. By 1973, Chinahad achieved the combination of WA sterile indica rice lines and maintainer lines.Good IRRI varieties were used as restorer lines to develop the indica hybrid ricesthat were popularized over large areas by 1976. Because hybrid rice normally yields15% more than conventional varieties, the area planted to hybrid rice expandedrapidly to reach more than 1/4 the total area planted to rice. The adoption in the lastfew years of such biological techniques in rice breeding as tissue culture has greatlyincreased breeding efficiency and has led to the development of such high-yieldingrice varieties as Zhekeng 66, Zhonghua 8, and Zhonghua 9, which have beenintroduced on a large scale.Integrated utilization of ricefields and greater ecological efficiency have beenencouraged. Vigorous efforts have been made over the last few years to use ricefieldscomprehensively, with emphasis on integrating farming with livestock or fishery.Raising fish in ricefields is a case in point. In 1984, the area of ricefields where fish areraised was 5.58 million ha; that increased to 6.23 million ha in 1985. Under suchcomprehensive use, a hectare usually produces a 10% higher rice yield and 250-400kg of fish. Meanwhile, headway has been made on raising ducks in ricefields,growing winter rapeseed or green manure between rice crops, or growing azolla inricefields. Such integrated use of ricefields, plus a scientific cropping system and useof organic manure, especially fermented rice stalks and green manure, has notablyimproved ecological conditions for sustained increases in rice production.Although we have reaped good harvests for several years and have achievedbasic self-sufficiency in grain, we must improve grain quality along with steadilyincreasing food production to further raise our people’s living standards. Thisdepends mainly on the development of scientific technology, aside from makingcorrect policies and further increasing agroinput. The need is to ensure that vigorousefforts are made to rapidly popularize the already-achieved scientific research resultsand advanced technology and to earnestly strengthen our rice scientific researchwork.New rice varieties and new combinations with high-yield potential, goodquality, and multiple resistance must be selected and developed; studies should bemade to open up sources of fertilizers; fertilization methods should be improved; theefficiency of fertilization should be enhanced; and techniques for raising highyieldingpaddy soil fertility need to be improved. Integrated management of

4 He Kangmedium- and low-yielding ricefields needs to be implemented and the componentcultivation technology for minimizing adversities needs to be popularized.Techniques for comprehensive prevention and elimination of rice diseases, insectpests, and weeds should be summed up and further studied. Research on farmingsystems in rice-producing regions must be further intensified. Rational farmingsystems suitable for agroindustries in different ecological conditions are needed. Thestructure of the planting industry should be reformed, and integrated high-yieldingcomponent cultivation technology should be developed. Ricefield mechanizationand postharvest processing must be studied to enhance productivity. In somerice-producing regions in North China, physiological studies of drought toleranceshould be carried on, irrigation methods improved, and water-saving cultivationtechniques popularized. Moreover, we expect to open up a new phase of riceproduction through new research techniques, such as biotechnology.All rice-growing countries are facing new challenges in the development of riceproduction and scientific research. This conference will play an important role infurther strengthening the international scientific and technical exchanges and insolving new problems. As a developing country and a major rice producer, Chinahas started good scientific exchanges and cooperations with various other countries,especially Asian-Pacific countries, and the International Rice Research Institute(IRRI). We hope that these academic exchanges and cooperations can be furtherstrengthened.This conference centers on the high and sustained production of irrigated rice.The in-depth discussion will surely be conducive to the development of irrigated ricescientific technology and production, and to better understanding and friendshipamong the scientists from various countries. I hope that this International RiceResearch Conference will be a new starting point for China to expand into moreextensive cooperation with the rice-growing countries of the world and with IRRI,for scientific and technical research and for academic exchanges. This will furtherdevelop the cooperation that already has had marked effect and will make greatercontributions to world rice production and science.

Rice research: learning from ChinaDIRECTOR GENERAL M. S. SWAMINATHANInternational Rice Research instituteWe are grateful to the Chinese Academy of Agricultural Sciences (CAAS) and theChina National Rice Research Institute (CNRRI) for cosponsoring this year’sInternational Rice Research Conference (IRRC). In recent years, China has maderemarkable progress in improving the productivity and production of rice. China isnot only the center of origin of considerable genetic variability in both indica andsinica (japonica) rices, but is also the home of many innovations in rice research andimprovement.The semidwarf varieties that helped initiate a new era in the breeding of indicarices capable of responding to good soil fertility and irrigation management comefrom China. Chinese scientists also made the dream of many plant breeders—ofexploiting hybrid vigor on a commercial scale in a self-pollinated plant—come true.The art and science of the use of biofertilizers like azolla have been perfected byChinese scientists and farmers. Above all, we find in this country a symbiotic linkagebetween research and extension, with the result that there is little gap betweenpotential and actual yields in farmers’ fields.It is therefore appropriate that the IRRC is being held in China, at a time whenthere is again concern in the world about the stability of national food securitysystems in developing countries where the fate of rice production is influencedgreatly by monsoon behavior.Most parts of South and Southeast Asia are experiencing abnormal rainfallconditions this year. In large areas of several countries, including India, Sri Lanka,Thailand, Cambodia, Vietnam, and the Philippines, there is severe drought. In otherareas, like Bangladesh and eastern India, there are serious floods. We do not yetknow the ultimate impact of the unfavorable monsoon conditions on total riceproduction this year. It seems possible there could be an 8-10% reduction in overallglobal rice production.Considering that international trade in rice covers less than 4% of totalproduction, this degree of loss could be serious. The fragility of the food securitysystems in many developing countries is evident: even a 5% increase or decrease infood grain production often makes the difference between an uncomfortable glutand acute scarcity. Fortunately, many developed and some developing countries

6 M.S. Swaminathanhave substantial grain reserves just now. Hence, famine can be avoided ifappropriate intervention programs are formulated and implemented.These unfavorable seasonal conditions do provide an opportunity for launchingcontingency plans and compensatory production programs. This is possible becauseof the availability of short-duration rice varieties that are photoperiod insensitive.Wherever seeds are available for implementing compensatory crop productionprograms, we can offset to some extent the losses suffered due to drought or floods.However, to take advantage of this opportunity, reserves of appropriate seeds areimportant. Just as food grain reserves are essential for food security, seed reservesare essential for achieving a certain measure of stability in production.World per capita food supplies, measured as dietary energy, rose by 12%—from 2,340 to 2,830 kcal/d—during the 18-yr period between 1961-63 and 1979-81.Although the gap between developed countries and developing countries stillremains wide, it has narrowed. The introduction of high-yielding rice and wheatvarieties in the mid-1960s played an important role in narrowing the gap.Yet FAO’s The fifth world food survey (FAO 1987) indicates that, despite theprogress made in production, the average inhabitant of a developed country hadnearly two-thirds more to eat in 1979-81 than the average inhabitant of a low-incomedeveloping country. The Fifth Survey also indicates that, with accelerating growth inper capita food supplies in the developing market economies, the proportion of thepopulation suffering from undernutrition has declined, even though the absolutenumber of undernourished people has increased (the result of even more rapidpopulation growth).The carrying capacity of land in many developing countries is under severestress because of increasing pressure from human and animal populations. Land foragriculture is also a shrinking resource, due to competing demands for land use.Within this context, we see a growing emphasis on sustainable food production. Theissues involved have been articulated recently by the World Commission onEnvironment and Development (1987).The economic viability and ecological sustainability of the production processare assuming importance from the point of view of technology development andpublic policy. Can rice researchers face these challenges? I would like to highlightthree important areas that will need increasing attention from rice scientists in theyears ahead.First, I would like to see all nations afford the highest priority to fighting what Icall the ecological fire raging in most parts of the world. Through mechanisms ofdeforestation, soil erosion, desertification, water pollution, and overpopulation,developing countries are being ravaged by this fire. Developed countries sufferequally, through atmospheric pollution, acid rain, contamination of water by toxicwastes, and the spread of environmental mutagens and carcinogens. Certainphenomena—loss of biological diversity, destruction of the ozone layer, andpotential climate changes that may result from carbon dioxide accumulation in theatmosphere and ocean warming—will affect us all, irrespective of the geographicorigin of the problem.

Learning from China 7Today we are concerned with fighting fires in buildings and forests. We do notyet seem to be aware of the vast dimensions and potential impact of the ecologicalfire that is affecting our basic life support systems: land and water, flora and fauna,and the atmosphere.The International Rice Research Institute (IRRI) is reorganizing theInternational Network on Soil Fertility and Fertilizer Evaluation in Rice(INSFFER) into a network that will give special attention to monitoring soil fertilityand to the sustainability of rice production; it is the International Network on SoilFertility and Sustainable Rice Farming (INSURF).The second area that needs common action is the creation of what I would liketo christen a “symphonic” agricultural system, based on principles of ecologicalsustainability, economic viability, and equity. A symphonic research and productionsystem based on harmony among the various links in the production - marketing- consumption chain would impart dynamism coupled with stability to agriculture.All too frequently, the concept of sustainable agricultural production is used toplead for a status quo, or even a reversion to old practices in productiontechnologies. What we need is a dynamic concept of sustainability that helps us meetthe changing human needs of our expanding population, while maintaining andenriching our natural resources base.Fortunately, many developing countries have a large, untapped crop yieldreservoir, even at currently available levels of technology. For example, time andagain, it has been demonstrated that, right now, given an optimum blend ofpackages of economically viable technology; services that can enable all farmers toderive benefit from new technologies, irrespective of their innate input-mobilizingand risk-taking capacities; and government policies on agrarian reform and on inputsupply and output pricing and marketing that are designed to stimulate bothproduction and consumption, we can double the average yields in many countriesthat have chronic food deficits. This is a lesson we can learn from China.Third, steps need to be taken to promote the efficiency of small farmmanagement. Small farms lend themselves to intensive cropping, as has beenelegantly demonstrated by research in the Asian Rice Farming Systems Network(ARFSN). Scientists can show how available land, labor, water, and credit resourcescan be utilized most effectively to increase yield, income, and employment.Although a small farm does not preclude the adoption of new technologies, asmall farmer faces severe handicaps in access to appropriate technologies. Scientistscan develop technologies for small farms, but only the political administration canhelp small farmers overcome their handicaps and derive economic benefit from newtechnologies. Only when the small farmer is enabled to adopt new technologies andimprove the efficiency of management do we find that small farm productivityreaches its potential.Finally, we should take advantage of emerging technologies, such as geneticengineering and other components of biotechnology, for increasing further the yieldpotential of the rice plant under different agroecological conditions. For thispurpose, we will have to increase total biomass production per day while

8 M.S. Swaminathanmaintaining a favorable harvest index. We also need to transfer genes that canconfer more enduring resistances to pests and diseases as well as soil stresses.Breeding varieties for adverse soil and climatic conditions deserves high priority, intandem with efforts in genetic enhancement. All other aspects of the productionprocess, such as agronomy, crop protection, and farm implements, need concurrentattention.A fascinating panorama of new opportunities is now unfolding. In this context,I would like to congratulate the Chinese Ministry of Agriculture, AnimalHusbandry, and Fishery for its vision in establishing CNRRI. We at IRRI feelhighly privileged to have been associated with this important initiative. Dr. RobertF. Chandler, the founding director of IRRI, described the history of IRRI as Anadventure in applied science (1982). I am confident that CNRRI will not only be anexciting adventure in applied science, but will become a world leader in thedevelopment of symphonic rice production systems.The challenges ahead are many and complex. Achieving the growth rates in riceproduction necessary to meet the demands of growing populations is not going to beeasy. The task will require both innovation and dedication on the part of scientistsand total commitment to achieving national food and nutrition security on the partof governments. Both these ingredients are strongly developed in China. I amconfident that all of us participating in this conference will return home charged witha sense of enthusiasm and hope for the future.Before I conclude, I would like to refer briefly to the fine research collaborationwe have with our Chinese colleagues. Collaboration between CAAS and IRRI iswide-ranging and far-reaching. It serves as an outstanding example of the power ofpurposeful scientitic partnership.CAAS has established one of the world’s finest genetic resource conservationcenters in Beijing and is actively participating in the Rice Genetic EngineeringCooperative sponsored by the Rockefeller Foundation. Last year, the HunanAcademy of Agricultural Sciences and IRRI organized an International Symposiumon Hybrid Rice. This year, the Fujian Academy of Agricultural Science and IRRIorganized an International Training Course in Azolla at Fuzhou. The ChineseAcademy of Agricultural Mechanization Sciences and IRRI plan to organize aMonitoring Tour cum Workshop on Farm Machinery for Women in 1988.Academia Sinica and IRRI have useful collaboration in tissue culture and geneticresearch. China participates actively in the three major international researchnetworks, the International Rice Testing Program, INSFFER, and ARFSN.With the establishment of CNRRI, the bonds of collaboration will be furtherstrengthened.References citedChandler R F (1982) An adventure in applied science. International Rice Research Institute, P.O. Box933, Manila, Philippines.FAO—Food and Agriculture Organization (1987) 1985 The fifth world food survey. Rome, Italy. 75 p.World Commission on Environment and Development (1987) Our common future. Oxford UniversityPress, U.K.

The global rice situationC. C. DAVIDWorld rice prices, adjusted for inflation, are lower now than they havebeen for the last 50 yr. Factors that contributed to low prices include anincrease in world rice production (above long-term trends) in the 1980s,increasing substitution of wheat for rice, and reduced global imports.Policy decisions such as the U.S. Food Security Act, increased agriculturalprotectionism in the developed world, and a change in comparativeadvantage for rice production between traditional importing and exportingcountries with the adoption of modern variety rice technology have furthercontributed to stagnant international rice prices. Short- to medium-termforecasts predict continuing low world rice prices. However, the samemodels demonstrate how sensitive prices are to such shocks in the systemas the Asian drought in 1987. A major concern is that continuing lowworld prices will threaten public investment in rice research anddevelopment, slowing the long-term growth in rice production needed tomeet the food needs of Asia’s and the world's expanding population.The primary issue confronting rice-growing countries has shifted in recent years,from the problem of coping with food shortages prevalent during the 1970s to theproblem of disposing of surpluses. This was triggered by the collapse of the worldrice market, where official prices for top-quality Thai 5% brokens, FOB, Bangkokhave fallen to U.S.$200/t from peak prices of nearly $550/t in 1973 and $480/t in1981 (Fig. 1). The price at which trade actually takes place is reportedly lower and theprice differential between high- and low-quality rice has widened. World prices havebeen depressed for the fifth consecutive year, and in real terms have reached theirlowest level, not only for the postwar period but also during this century (Fig. 2).While all grain prices are low at present, rice prices have declined more relative to allother grains. The ratios of rice prices to wheat prices, which had an upward trendbeginning with the turn of the century, ranged from 2.0 to 3.0 in the 1970s but arenow around 1.25 (Fig. 3).What are the underlying causes of this sharp drop in world prices? Is this ashort-run phenomenon or a long-term trend? What is the price outlook in eithercase? Who are the gainers and who are the losers?

10 C.C. David1. Trends in world rice price of Thai 5% brokens in nominal terms, FOB, Bangkok.2. Trends in world rice price in real terms (1964-66 prices).Why the world rice market collapsedThe collapse of the world rice market was caused by both short-run supply anddemand factors and long-run macroeconomic and agriculture-specific events.Trends in world rice production since 1983 indicate abundant supplies (Fig. 4).World rice production has been above the trend line by 20-30 million t, resulting in abuildup of stocks that reached world record levels by the end of the 1985-86 cropseason (Fig. 5). Favorable weather conditions and low world prices of urea wereundoubtedly major factors in these large global production gains.

Global rice situation 114. Trends in world rough rice production.World rice imports dropped sharply, from nearly 14 million t in 1981 to 11million t in 1986. This may be explained in part by the very rapid growth in riceproduction of importing countries compared to production of major exportingcountries (USA, Thailand, Burma, and Pakistan), which were barely above trendlines (Fig. 6).Macroeconomic eventsAnalyzing the economic events of the 1970s helps us understand the underlyingreasons for the substantial weakening of import demand in the face of growing

12 C.C. David6. Trends in rough rice production of rice importers (a) and of major rice exporters Burma, Pakistan,Thailand, and U.S. (b).

Global rice situation 13export surpluses that eventually led to the collapse of the world rice market. In asimulation analysis that used the econometric model of the world grains andsoybeans market of the U.S., Mitchell (1987) found changes in macroeconomicvariables such as income, exchange rates, and fertilizer prices to be more importantin determining long-term price movements than agricultural factors such as drought,policy shifts, and others. The major exception is the sharp price rise in 1973 (Fig. 7),which was caused by a policy decision in the USSR to import large amounts ofwheat. Trends in global production and imports during the early 1970s do not seemto warrant such sharp increases. (The strength of linkages between rice and grainmarkets has become stronger in recent years, as preference for wheat increased athigher income levels in many rice-consuming countries.) Mitchell further arguedthat, although these agricultural factors can cause sharp price fluctuations during a1- or perhaps 2-yr period, they do not appear to have long-run significance.Stepwise simulation of individual effects of various macroeconomic eventsshow that the sharp increases in fertilizer price associated with the oil price shocks in1973 and again in 1979 were the most important factors behind the unprecedentedhigh rice prices during the 1970s (Fig. 8). Comparisons of trends in world prices ofrice and urea indicate a high correlation, R 2 = 0.79 (Fig. 9, 10). Adoption of flexibleexchange rates by many countries during the 1970s weakened the value of the dollarrelative to other currencies and lowered the price of grains for non-USA importersand exporters during the 1970s. That stimulated import demand while reducingexport supplies. Rapid growth of income in oil-exporting countries (Indonesia,Nigeria, Mexico, Middle East) and of newly industrializing countries (Korea,Hongkong, Singapore, Brazil) induced changes in consumption patterns that raisedimport demand for rice and other grains.7. Trends in world rice imports.

14 C.C. David8. Results of simulation analysis distinguishing the impact of macroeconomic versus agricultural factorson world rice price (Mitchell 1987).9. Results of simulation analysis of the impact of specific macroeconomic and agricultural events onworld rice price of Thai 5% brokens, FOB, Bangkok (Mitchell 1987).Agriculture-specific causesThe combined effects of the macroeconomic events explain most of the generallyhigh world rice prices during the 1970s. However, the decline in fertilizer prices to thepre-oil boom level as the OPEC cartel lost control over oil prices and the overalldeceleration of world economic growth have contributed in recent years, albeit to a

Global rice situation 1510. Trends in world price of urea, FOB, Rottendam.more limited extent than in the previous decade, to depressed world market prices ofrice. Aside from purely weather factors, at least three agriculture-specific eventstended to reduce world prices.1. The implementation of the U.S. Food Security Act of 1985. This lawprovides for the maintenance of a relatively high target price for rough rice; areduction in the loan rate for rice and the introduction of a new system ofloan repayment that allows farmers to repay their loans at a rate linked toworld market prices; and the continuation of deficiency payments and, ifneeded, of a big area reduction program. The net effect of this package ofpolicies is to reduce effective loan rates by 20%. That could be used to reducethe prices of rice sold in the world market. Indeed, within a week after thenew policy was announced, U.S. export prices of rice declined by 30-35%. Inaddition, several other programs, such as the Export Guarantee Programsand PL480, that effectively subsidized exports boosted U.S. exportshipments.2. Strong agricultural protectionism in the developed countries. Those policiesdirectly and indirectly reduce world rice prices. The growing protection ofrice markets in Japan, Taiwan, and Korea curtails world import demand.High protection of wheat and other grains in developed countries lowerswheat imports and leads to dumping of surpluses. That eventually depressesthe world price because of the strong linkage among the grain markets. Sinceagricultural protectionism is a major factor in the general collapse ofagricultural commodity markets, it exacerbates the foreign exchangeconstraints many developing countries encounter when importing rice.3. Shifting comparative advantage in rice production as a result of modern ricetechnology (Siamwalla and Haykins 1983). These may be permanent supplyshifts contributing to further thinning of the world rice market.

16 C.C. DavidShifts in comparative advantageThe impact of modern rice technology on Asia rice productivity is now well known.The annual growth rate of rice production rose from 2.3% before 1965 to 3.6% in1965-85, exceeding the 2.3% growth rate of population (Fig. 11). The primary basisof growth changed from crop area expansion to yield increases. Yield increase ratedoubled, from l%/yr in 1955-65 to 2.5% after 1965. That increased rate accountedfor 15% of the growth in rice production in 1966-86, compared to only 40% in1955-65.Modern varieties, fertilizer, and irrigation contributed equally to the increase inyield (Herdt and Capule 1983). Increases in crop area planted to rice slowed from1.3%/yr to 1.0% and its contribution to growth in rice production declined fromalmost 60% to only 25%. Without such remarkable growth in productivity,population pressure on limited land would have resulted in a higher rice productioncost and higher rice prices to consumers in the region.Environmental factors, especially the degree of water control, have been foundto be most important in explaining differential adoption of modern rice technology.Agricultural technologies are highly location-specific, thus the scope for technologytransfer across regions is inherently limited. The differential effect of the newtechnology across environmental conditions can be observed by comparing riceproductivity growth across continents, among Asian countries, and within acountry.11. Trends in population, rough rice production, area, and yield, South and Southeast Asia, 1955-84.

Global rice situation 17Across continentsWhile nearly 60% of the rice area in Asia is irrigated, upland rice is dominant inAfrica and Latin America. Even if China is excluded, the 40% portion of the areathat is irrigated in the rest of Asia is high compared to only about 25% in Africa andLatin America. If the shallow rainfed areas where significant modern varietyadoption has taken place in the past decade are included, the proportion of the areagenerally favorable to the new technology in Asia rises to nearly 70%.The contrast in production performance across the three continents is shown inFigure 12. While the growth rates of rice production are fairly close, yields remainessentially stagnant in Africa; they grow at a substantially lower rate in LatinAmerica than in Asia. Increases in crop area accounted for much of the growth inrice production in Africa and Latin America over the past 2 decades. Although this12. Trends in rough rice production (a) and yields (b), by region.

18 C.C. Daviddifference in sources of growth in output need not mean a loss in comparativeadvantage (land is relatively abundant in these regions), analysis of the changes intrading patterns indicate/that this may be so.Across and within Asian countriesTable 1 shows the production and yield performance of selected Asian countrieswith varying rates of irrigation and modern variety adoption. Countries with lowadoption rates are those where less than 30% of rice area is irrigated (Thailand,Burma, and Bangladesh). In these countries, rice is cultivated in large deltaic areaswhere the cost of developing an effective water control system is high. In Nepal, asignificant part of rice area is in the hills and mountainous regions. Even in thelowland areas, only 30% of the rice area is irrigated. Except for Bangladesh, thesecountries have traditionally exported rice because of relatively high land:populationratios and natural comparative advantages in producing rice relative to other crops.Countries with high modern variety adoption rates are also those where theproduction cost is relatively cheap and the ratio of irrigated area high. They havetraditionally imported rice primarily because the supply of land is low relative to thepopulation.The differential impact of modern rice technology may be observed from thepattern and growth of yield and production. In Bangladesh, Thailand, and Nepal(where modern varieties had the least impact), not only are growth performances inrice production and yields low, they declined markedly after 1965. In contrast,growth rates in yield and production in traditionally importing countries have risendramatically, particularly in Indonesia. In Burma, the policy reforms and vigorousproduction program that have accelerated modern variety adoption since the late1970s have been mainly responsible for the improvement in production growth.Differential adoption of modern varieties has also widened the disparity inyields between irrigated and nonirrigated areas within a country. Figure 13 showstrends in yields by environmental conditions (based on available categories in publicstatistics) in India, Bangladesh, Indonesia, and the Philippines. Yields remainedessentially stagnant at 1.0-1.5 t/ha in the unfavorable areas, in contrast to increasingyields in the more favorable areas.Table 1. Proportion of area irrigated, adoption of modern varieties, and changes ingrowth rate of yield and production in selected Asian countries.Country1983-85 Annual growth rate% area % area planted YieldProductionirrigated to MVs1955-65 1965-85 1955-65 1965-85Bangladesh 15 b 27 b 1.9 1.5 3.1 2.1Burma 19 b53 a0.6 3.3 2.5 3.2Thailand 24 b 13 a 3.2 0.4 5.4 2.5India 46 a 57 b 0.8 2.4 2.0 3.0Philippines 56 c 87 c 0.7 3.6 2.1 4.0Indonesia 71 a 87 c 0.2 4.1 1.2 5.6a 1983, b 1984, c 1985. Sources of basic data: FAO production yearbook (1955-85).

Global rice situation 1913. Trends in rough rice yields, by environmental condition, in selected Asian countries. Figures inparentheses are percentages of area.Changing patterns of tradeBecause the early modern varieties have been best suited to irrigated conditions andbecause of the strong political desire for self-sufficiency in importing countries, theregional impact of the adoption of modern varieties has been to lower the cost perkilogram of producing rice in Asia more in traditional importing countries than intraditional exporting countries. As traditional importers moved closer to rice selfsufficiencyin the late 1970s, the level and pattern of international trade changed.Changes in consumption preferences, policy factors, and political events alsoinfluenced the structure of world rice trade.In 1960, Asia produced a net surplus of rice, with Burma, China, and Thailandas leading exporters (Table 2). Nationalization of international and domestic tradeand the consequent adoption of price policies that depressed farm incentives led tothe collapse of Burma’s rice exports. Together with increasing import demand, Asiahad small net exports of rice by 1970.These trends have reversed during the past 15 yr. The increase in the level andshare of rice exports in Asia was principally accounted for by Thailand andPakistan. Stronger demand for Basmati rice in the Middle East and modern

20 C.C. DavidTable 2. Changes in the structure of rice trade by country and region.Quantity (million t) Share (%)1959- 1969- 1979- 1984- 1959- 1969- 1979- 1984-61 71 81 86 61 71 81 86World TradeExports 6.76 8.86 12.64 12.08Burma 1.67 0.66 0.64 0.60 25 7 5 5China a 1.16 2.01 1.17 1.17 17 23 9 10Pakistan 0.10 0.33 1.12 1.19 2 4 9 10Thailand 1.29 1.23 2.87 4.39 19 14 23 36United States 0.84 1.71 2.83 2.16 13 19 22 18Subtotal 5.06 5.94 8.63 9.51 76 67 68 79Asia 5.03 5.44 7.82 7.91 74 61 62 66Imports 6.56 8.78 12.90 11.53Asia 4.04 5.63 4.80 2.81 60 64 37 24Middle East 0.18 0.47 1.78 2.16 2 5 14 19Africa 0.51 0.71 2.24 2.46 8 8 18 21Developed 0.69 0.91 1.69 2.31 11 10 13 20MarketsDeveloped 0.76 0.58 1.17 0.67 12 7 9 6CPEsa lncluding Taiwan. Sources of basic data: FAO trade yearbook (1959-86). FAOproduction yearbook (1955-85).technology adoption in the Sind area, where ordinary unscented rice is planted infully irrigated areas, explain the growing importance of Pakistan in world trade.The decline of Asia’s role in import trade is more dramatic. Productivity growthfrom modern technology and accelerated public investments in irrigation and othersupport services turned traditionally importing countries (India, Philippines, SriLanka, Malaysia) closer to self-sufficiency. With the withdrawal of Japan and SouthKorea from the world market as a result of trade and price policies, Asia’s level andshare of rice imports declined to 37% in 1980 (Table 3). This dropped further, to 24%in recent years, as Indonesia, which was the single largest rice importer in the 1970s,attained self-sufficiency.The macroeconomic events of the 1970s are the major underlying forces thatshaped these structural changes in the world rice market. The unprecedented highworld rice prices in the 1970s strengthened political commitment to attainingself-sufficiency in most large countries in Asia. Availability of modern varietiesfurther boosted the social profitability of public investments in irrigation and otherproduction infrastructure and programs. Greater availability of foreign loans andgrants from recycled OPEC funds (and in the case of Indonesia, oil receipts)provided the revenues to finance these efforts.In Africa and Middle East, on the other hand, the same events led to increasedshares in import trade. Growth in import demand, primarily for high-quality rice,was most rapid in the Middle East where the oil boom produced the highest incomegrowth. While Africa’s economic growth may have been concentrated in a fewoil-exporting countries, the substitution of rice for coarse grains significantlyincreased its import share, from 8% in 1970 to 22% in 1985.

Global rice situation 21Table 3. Changes in the structure of rice imports in Asia, by country.CountryQuantity (million t) Share (%)1959-61 1969-71 1979-81 1984-86 1959-61 1969-71 1979-81 1984-86AsiaBangladesh 0.41 0.37 0.23 0.23 6India 0.54 0.64 0.07 0.19 8Indonesia 0.96 0.69 1.49 0.16 15Philippines 0.06 0.12 – 0.24 1Malaysia 0.53 0.31 0.24 0.40 10Hongkong 0.37 0.35 0.36 0.38 6Singapore 0.11 0.28 0.19 0.20 2Sri Lanka 0.53 0.40 0.18 0.13 8Total60World 6.56 8.78 12.90 11.6347814435642112–2321372212332124Sources of basic data: FAO trade yearbook (1959-85).Price outlookBecause of the thin, residual nature of the world rice market, the international priceof rice historically has been characterized by a high degree of instability, second onlyto sugar among all agricultural commodities. Therefore, predicting future world riceprices is extremely difficult.In the short run, the outlook is for some recovery in world rice prices. FromJanuary to July 1987, world prices rose slightly (10-15%). There have been efforts inthe major exporting countries to reduce support to rice production and to encouragediversification. In 1986, the rice crop area in Thailand fell by 10% in the dry seasonand by 4% in the wet season. Except for Basmati rice in Pakistan, farm supportprices in real terms were allowed to decline and the supply of subsidized inputs wascurtailed in Burma, Pakistan, and Thailand. In the U.S., rice hectarage was reducedby 8% but yield increases resulted in only a 3% decline in rice output. In manydeveloping countries, the area planted to rice also has been decreasing, following thereduction of input subsidies, irrigation, research and extension budgets, a fall in realprices, and promotion of crop diversification.The generally poor weather conditions worldwide at the beginning of thecurrent wet season will put further pressure on world prices. Newspapers havereported that India, suffering from the worst drought in decades, may lose 20 milliont of its main rice crop, although there are still 23 million t in food grain reserves.Widespread flooding in Bangladesh has caused extensive damage to newlytransplanted ricefields in the northern districts. In Thailand, Kampuchea, Vietnam,Philippines, and Indonesia, delayed planting due to late rains may reduce the harvestpotential. The U.S. crop is expected to be lower by 7 million t as a result of sheathblight infestation in Arkansas and less hectarage planted in Texas. FAO has beenmore cautious about reporting the impact of these events; its August forecast of the1987 rough rice output still puts it at 1.6%, about the 1986 level. The USDA,however, projects world rice output in 1987-88 to decline by more than 3% from lastyear's, the lowest production since 1982-83.

22 C.C. DavidOver the long term, several analysts, including the World Bank, predict acontinuation of current low world prices (Mitchell 1987). The Stanford ResearchTeam that sponsored a meeting to assess the implications of the global rice situationin Indonesia listed potential shocks that could occur to raise future prices.“A severe infestation of disease or pests attacks on MVs; a largeincrease in the price of petroleum, leading to the increases in the fertilizerand fuel costs of producing rice and to import demands in oil-exportingcountries; a severe drought in major producing countries, especiallyThailand; a reduction in the support (target) price of rice in the U.S.; areduction in Japanese rice protection and entry of Japan into the importmarket; a major upheaval in China; reducing rice output; domesticinstability in important countries, such as Bangladesh or the Philippines; aliberalization of world agricultural trade through GATT negotiation; anda new source of import demand, for example from centrally plannedeconomies or Brazil.”They further noted that, although the possibility of any one of these eventshappening is small, their joint probability is fairly high.In all of these price forecasts, the dynamic effect of low world rice prices onfuture production growth and self-sufficiency levels of major rice-consumingcountries are basically ignored. Yet the major reason for the weak import demand inthe 1980s was the success of the modern rice technology, rapid investments inirrigation, and fertilizer price subsidies. Low world rice prices will threaten longtermgrowth in productivity if government production policies respond to thesetrends. The removal of the fertilizer price subsidy alone would significantly reduceIndonesian rice production, as nearly half of the growth over the past decade hasbeen due to this policy instrument (Jatileksono 1986, Timmer 1985). Hayami andKikuchi (1975) have reported a high positive correlation between trends in world riceprices and irrigation investments in the Philippines. The publication of rice researchresults has also been found highly responsive to price fluctuations in theinternational rice market (Hayami and Morooka 1987).Projections of future demand and supply of rice into the year 2000 (Barker andHerdt 1985, FAO 1981) predict global as well as Asian shortfalls in rice productionrelative to consumption that will raise real world prices. Hence, efforts in developingcountries to sustain growth in productivity must continue. Notwithstanding theuncertainty of the occurrence of shocks, when public investments in the agriculturalproduction infrastructure is induced by cyclical price changes rather than by longtermtrends of social profitability, recurrent food shortages and oversupplies recur ina cobweb manner. Wide fluctuations in world rice prices will result.ConclusionWhile low world rice prices are most desirable from an importer/consumerviewpoint, the economic welfare and farm incentives of exporting countries andoften of rice farmers in importing countries will be reduced. In Asia, which accountsfor about 90% of global production and consumption, the bulk of the rice consumed

Global rice situation 23Table 4. Distribution of world rice production and consumption by region.CountryWorld production (%) World consumption (%)1959-61 1969-71 1979-81 1984-86 1959-61 1969-71 1979-81 1984-86Asia 92.36 90.86 90.33 91.37 91.81 90.99 89.11 89.88Africa 1.95 2.44 2.12 2.00 2.14 2.50 3.03 2.88Middle East 0.65 0.66 0.60 0.50 0.76 0.89 1.25 1.20North America 1.48 1.77 2.29 1.82 1.14 1.12 1.40 1.37South America 2.72 3.16 3.38 3.12 2.64 2.99 3.40 3.14Europe 0.68 0.60 0.47 0.45 1.08 0.84 0.75 0.78Sources of basicdata: FAO production yearbook (1955-85).is produced domestically by farmers belonging to the lower rung of the incomebrackets (Table 4). Low world prices will not benefit Asian countries, except perhapsHongkong, Singapore, and Brunei, but will mostly benefit developed countries thatimport the greater part of their domestic rice supply. On the other hand, low-incomecountries cannot afford to protect their farmers as developed countries do.It is unfortunate that a number of large Asian countries achieved selfsufficiencyat the same time that the world rice market collapsed. To protect ricefarmers, rice stocks had to be accumulated at high cost rather than at a loss. It isironic that as these countries apparently gained comparative advantage in riceproduction, they immediately lost it under the new world price regime. Based on thenew prices, the social cost of self-sufficiency suddenly appears too high and the netbenefit of maintaining production infrastructures too little.Speedy resource adjustment is the most efficient way to respond to thechanging comparative advantage resulting from differential technical innovationsand changing factor endowments, demand patterns, and other real market forces.However, it is unfair that low-income countries must bear the burden of adjustmentto the market distortions arising from rice price and trade policy in the U.S. andJapan, specifically, and from agricultural trade protectionism generally.References citedBarker R, Herdt R W (1985) The rice economy of Asia. Resources for the Future, Washington, D.C. andInternational Rice Research Institute, P.O. Box 933, Manila, Philippines.FAO—Food and Agriculture Organization (1955-85) FAO production yearbook. Rome, Italy. (variousissues)FAO—Food and Agriculture Organization( 1959-86) FAO trade yearbook. Rome, Italy. (various issues)FAO—Food and Agriculture Organization (1987) Food outlook. June and August issues. Rome, Italy.Hayami Y, Kikuchi M (1975) Investment inducements to public infrastructure: irrigation in thePhilippines. IRRI Agric. Econ. Dep. Pap. 75-15. P.O. Box 933, Manila, Philippines.Hayami Y, Morooka K (1987) The market price response of world rice research. IRRI Agric. Econ. Dep.Pap. 87-21. P.O. Box 933, Manila, Philippines.Herdt R W, Capule C (1983) Adoption, spread and production impact of modern rice varieties in Asia.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Jatileksono T (1986) Equity implication of technology changes in the Indonesian rice economy. Ph Ddissertation, University of the Philippines, Diliman.

24 C.C. DavidMitchell D O (1987) Rice market prospects to the year 2000. Paper presented at the Seminar on Recentand Future Movements in World Rice Prices, 13-14 Jan 1987, Jakarta, Indonesia.Siamwalla A, Haykins S (1983) The world rice market: structure, conduct, and performance. IFPRI Res.Rep. 39. Washington, D.C.Timmer C P (1985) The role of price policy in rice production in Indonesia: 1968-1982. HIIDDevelopment Discussion Paper 196. Harvard Institute for International Development, Cambridge,Massachusetts.NotesAddress: C. C. David, Department of Agricultural Economics, International Rice Research Institute, P.O. Box 933,Manila, Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Problems arising fromthe Indonesian successin rice productionD. S. DAMARDJATI, S. R. TABOR, I. N. OKA, AND C. C. DAVIDFrom being one of the world’s largest rice importers, Indonesia increasedrice production remarkably within 2 decades and achieved rice selfsufficiencyin 1985. But changing world economic conditions have createdproblems in maintaining that self-sufficiency. The collapse of the worldrice market has raised its support price and discouraged further investmentsin rice production. The decline in oil prices has reduced theresources available for development and price subsidies. To maintain abalance between production and consumption in light of growing ricerequirements, the new rice development strategy must shift away fromheavy reliance on short-run policy instruments, such as input pricesubsidies and price supports, toward greater use of long-term policyinstruments that increase the country’s capacity for sustainable growth inrice production. Public investments in land development and technologydevelopment and transfer must continue to be pursued vigorously, withincreasing emphasis on minimizing the risk of pest outbreaks and onimproving product quality.Rice plays a dominant role in the Indonesian economy. It is the staple food,accounting for more than 55% of total calorie and approximately 60% of totalprotein consumption. It is the major source of employment and income for most ofthe 70% of the population that reside in rural areas. Rice is produced primarily bysmall farmers, 65% of whom cultivate less than 1 ha. The annual area harvested isabout 9.8 million ha, slightly more than 60% of the total area of food crops. Thetwo-thirds of the rice area that is irrigated contributes 85% of the total riceproduction.Since 1985, Indonesia has shifted from being one of the world’s largest riceimporters—averaging 1-2 million t throughout the 1970s—to becoming selfsufficient.This was the result of remarkable performance in rice production over 2decades. Up to the late 1960s, the population grew at a faster rate (2.3%) than riceproduction (1.8%). Since that time, the growth of rice production has more thandoubled (5.6%) while rice consumption rose from 99 kg per capita in 1969 to 137 kgin 1985.

26 Damardjati et alAchieving rice self-sufficiency has provided the nation with what many perceiveto be adequate food security, a political objective closely interwoven with nationalsecurity interests. Maintaining the balance between rice production and consumptionis a top priority of the Ministry of Agriculture.The problems associated with maintaining rice self-sufficiency have been mademore difficult by the changing world economic environment. The world rice marketcollapsed when prices dropped to less than US$200/t, compared to $300-400 in the1970s. This has raised the cost of supporting a floor price, because surpluses can onlybe exported at a loss. The apparently low opportunity cost of imported rice hasdiscouraged, at least in the short run, the investments in irrigation and rice researchwhich would make possible long-term productivity.Changing conditions in the world petroleum market also have substantiallyreduced the resources available to the Indonesian Government for developmentexpenditures. The bulk of the efforts directed toward rice self-sufficiency took placeduring a post oil-boom period, during which the Indonesian Government had ampleresources to finance liberal farmer subsidy programs. At present, far fewer resourcesare available to farmers as direct subsidies—and to government bodies asdevelopment budgets—to maintain rice self-sufficiency.This paper discusses the issues emerging from Indonesia’s success in riceproduction and suggests broad policy directions for maintaining the country’sself-sufficiency in rice. First, the changing nature of production growth, the cost offertilizer and rice price subsidies, and future rice requirements and developmentstrategy are discussed. The second part of the paper presents four issues related tothis strategy: a) public investments in land development; b) pest problems associatedwith narrow varietal base, continuous cropping, and high use of fertilizer andpesticides; c) increasing expenditures for rice research and extension; and d)improving grain quality.Changing nature of production growthThe introduction of modern rice technology, the government’s policy focus on rice,world market trends in rice, and the size of oil revenues essentially shaped the natureof the Indonesian rice production under the New Economic Order of Governmentbeginning in the late 1960s. (This discussion draws extensively from Jatileksono andDavid 1986.) Rice production growth in the 1950s and 1960s was relatively slow andwas achieved primarily by expansion of crop area planted to rice (Table 1). Riceproduction growth accelerated to 3.8%/yr from 1969 to 1977, and has been evenmore rapid (7%/yr) in recent years. Intensification of land use rather than expansionof the cultivated area has been the major source of recent growth. Average yields,which stagnated at about 2 t/ha in the 1950s and 1960s, doubled to 4 t/ha by 1986.Yield increases accounted for nearly 80% of the growth in rice production.Adoption of modern varieties, increased use of fertilizer, and improvements inirrigation have been the basis of growth in yields and of expansion of crop area. It isdifficult to separate the impact of these factors because they are highlycomplementary. Modern varieties raise profitability of both irrigation and fertilizer.

Indonesian rice production 27Table 1. Growth rate of production, area, and yield of rice in Indonesia, 1955-82.PeriodGrowth rate (%)Production Area Yield1955-67 1.84 1.34 0.501969-77 3.79 0.862.931977-837.02 1.42 5.60Source: Jatileksono and David (1986).Greater availability and lower costs of irrigation and fertilizer induce higher MVadoption. From 1969 to 1976, yield increases were achieved primarily through theMVs released in 1967 and disseminated nationwide in 1969-70 as a key componentof the BIMAS (mass intensification) extension-credit programs (Fig. 1). Adoptionwas fairly rapid up to 1974, when it reached 33% of the harvested area. But as theviability of early MVs suffered from serious outbreaks of brown planthopper (BPH)infestation, adoption rates slowed. The release of IR36, which is early maturing andresistant to BPH biotype 2, pushed MV adoption after 1975. Within 2 yr of itsintroduction, IR36 was planted on 36% of the rice crop area.1. Rice production growth in Indonesia, 1963-86 (Satari 1983b, Sekretariat Badan Pengendali Bimas1987).

28 Damardjati et alBy the mid-1970s, it became clear that more attention was needed to boost riceproduction further. Growth in demand continued to outpace growth in domesticproduction. The oil boom in 1973 and the second oil price shock in 1977-78 providedthe necessary government revenues to heavily assist rice farmers. Rice price policyshifted from implicitly taxing producers (20-30% from 1969 to 1976 when worldprices were unprecedentedly high) to slightly subsidizing farm prices (5-10% as worldprices declined by the early 1980s). Heavy subsidies on fertilizer reduced thenitrogen-rough rice price ratio from an average of 3 between 1969 and 1976 to 1.5between 1978 and 1985. The domestic price of urea was 36% below the world pricefrom 1979 to 1983. Pesticides were also heavily subsidized; domestic pricesrepresented only 10-20% of the full economic cost of the most widely used pesticides.Table 2 presents the distribution of subsidized fertilizer and pesticides for theintensification programs. Average annual irrigation investment from 1977 to 1983was 230 billion rupiahs in 1980 prices, more than double the annual investment levelsfor 1970-76. In separate studies, Timmer and Jatileksono concluded that fertilizerprice policy alone accounted for about half of the very rapid growth in riceproduction during this period (Jatileksono 1986, Timmer 1985).Costs of food securityThe costs of providing positive economic incentives to rice production through aguaranteed floor price for farmers and subsidized fertilizers, however, have becomea heavy burden to the government. Such production-support programs requiredTable 2. Distribution of subsidized fertilizers and pesticides for Indonesian IntensificationProgram, 1969-86.YearUrea KCI Z.A. Insecticides Fungicides Rodenticides(t) (t) (t) (kg) (kg) (kg)1969 202,434 – – – – –1970 307,936 – – – – –1971 171,672 – – – – –1972 405,841 – – – – –1973 480,200 – – – – 70,5431974 668,332 – – 1,371,332 – 46,7521975 670,184 – – 2,362,332 7,507 84,7521976 665,648 – –3,440,572 20,280 159,1091977 919,011 – – 4,202,161 41,152 113,0321978 975,322 – – 3,998,808 19,875 121,0321979 1,146,767 – 23,317 4,133,790 10,140 79,0301980 1,679,015 8,782 53,896 6,369,731 43,416 73,7561981 1,991,668 19,853 99,198 9,006,532 128,935 119,2741982 2,152,599 69,357 294,208 11,255,599 94,463 94,7141983 2,117,422 169,692 359,210 13,982,490 276,011 171,2461984 2,531,316 230,415 385,910 13,907,377 300,946 88,0201985 2,552,689 296,832 455,922 14,979,795 213,442 82,3511986 2,612,842 295,567 470,177 17,236,570 439,431 85,946Source: Sekretariat Badan Pengendali Bimas (1987).

Indonesian rice production 33As the potential for crop intensification through improved irrigation, use ofmodern varieties, fertilizer, and pesticides reached the limits of sustainable growth inrice production in Java, the government also changed the focus of land investments.Beginning in the late 1970s, transmigration programs, investments in marketinfrastructure, and irrigation development were accelerated in the outer islands.Irrigation investment per hectare was higher in Java and other favorable areas in theearly 1970s; the outer islands received a higher rate of irrigation investment perhectare in the last decade (Jatileksono 1986).The growth in rice production required to maintain a balance betweenproduction and consumption without increasing the real rice price can come from anincrease in productivity and/or crop area expansion. A 1.3%/yr growth rate of riceyields between 1986 and 2000 would require an expansion of about one millionadditional hectares of rice land, obtained either by double cropping throughirrigation or by opening new land for cultivation. If no increases in crop area areforthcoming, rice productivity will have to increase by nearly 3%/yr from 1986 to2000 to keep pace with population and income growth. Such high growth rates inproductivity may be difficult to generate because a high proportion of farmers arealready using modern varieties and complementary inputs. Moreover, the level ofcrop intensification—continuous cropping, high fertilizer, and pesticide use—isalready threatening the ecology and therefore the long-term sustainability of riceproduction. Development of market and irrigation infrastructure and transmigrationprograms in the outer islands will be a necessary component in the effortsto supply the growing rice requirements.Pest risks associated with narrow varietal basesModern rice technology has undoubtedly been instrumental in Indonesia’s achievingself-sufficiency in rice. Yet, such technology has also raised the risk of massive croplosses due to disease and pest disturbance. Important pests now include the greenleafhopper, BPH, whitebacked planthopper, rice blast, bacterial leaf blight, sheathblight, rice tungro virus (RTV), grassy stunt virus, and ragged stunt virus, rice stemborers, stink bugs, leaffolders, gall midge, and rats (Table 6). Preharvest losses due todiseases, pests, and rodents are estimated to range from 19 to 24% of production(Sumardi 1976). Serious outbreaks of BPH occurred in 1976, 1977,1978, and 1986.In 1976-77, more than 450,000 ha of rice land were damaged due to BPH. Thiscaused a production decline of about 370,000 t of rice valued at more than $100million (Oka 1979). Even during good production years, pest and disease problemsstill cause considerable losses.Several factors contribute to the preharvest losses problem. Dependence on afew modern varieties planted over a wide area increases the risk that pest and diseaseattacks will destroy a significant share of the crop. Modern rice varieties accountedfor about 94% of total rice production in 1986. The Directorate General of FoodCrops reported that Cisadane and IR36 occupied about 66% of the area planted tomodern rice varieties (Table 7).West Java is one of the provinces that have a high degree of dependence on athin varietal base. In 1986, the Central Bureau of Statistics reported that 84% of all

34 Damardjati et alTable 6. Occurrence of major rice pests and diseases in different agroecosystemin Indonesia.Pests and diseasesIrrigatedLowlandrainfedTidalswampNontidalswampUplandPlant and leafhoppersStem borersGall midgeBugsArmy wormsLeaffoldersRodentsBirdWeedsVirusFungiBacteriaAdverse soils++++++++++++++++++++++++-++++++++++++++++++++++++- + -+++ ++ -+++ ++ -+ - -- - --- -+++ +++ ++++++ ++ +++ +++ -+ + ++++ + ++++ + -+++ ++ ++++++ very frequent, ++ frequent, + less frequent, - almost not or less frequent.Source: Satari (1987).rice farmers used Cisadane (a smooth, moderate-amylose, high-yielding variety).This variety accounted for 88% of total provincial production. That same year,problems of BPH resistance to Cisadane were reported and the dangers of massivecrop loss necessitated a large-scale campaign in 1987 to induce farmers to switchvarieties.Other factors contributing to increased preharvest losses are 1) continuedplanting of nonresistant varieties; 2) planting of modern varieties with a small geneticbase for resistance to certain pest species (thereby triggering development of newraces or pest biotypes); 3) continuous year-round planting (thereby increasing therisk of pest buildup because a permanent food source and shelter are provided thepests); 4) high fertilizer use enhancing the development of many pest species; and5) overdependence on pesticides, with pest resistance, pest resurgence, andsecondary pest outbreak consequences (Oka 1982).An important issue that needs to be addressed is the tradeoff betweenrequirements for production growth and the need to reduce the risk of varietalbreakdown. The recent removal of pesticide subsidies and reduction of fertilizersubsidies will improve sustainability, but may result in short-run sacrifice inproduction growth. Adoption of integrated pest management that combinesadoption of pest-resistant varieties, more efficient use of pesticides, and adoption ofbiological control would minimize the tradeoff between growth and sustainability ofrice production. This implies a vigorous research and extension system.Research funding prioritiesThe Indonesian Government has successfully established a strong research system inthe Agency for Agricultural Research and Development (AARD). In 1986-87,however, the budget for agricultural research was sharply curtailed, following the

lndonesian rice production 35Table 7. Distribution of area planted to modern rice varieties in Indonesia, 1985-86.VarietyPlanting area (ha)1985-86 WS 1986 DSTotalPercentageIR36CisadaneKrueng AcehIR42IR46SemeruIR54CipunegaraKelaraSadangBaritoIR38BahbolonIR32IR50CitanduyIR52Cikapundung1,518,1761,552,577321,300274,361109,025144,95996,75775,91853,92850,88937,66034,90045,37543,51041,38433,87320,610759,987884,867184,962137,015171,81882,37866,72862,34963,70543,52440,86329,16061,6722,278,1632,437,444506,262411,376280,843227,337163,485138,267117,63394,41378,52364,06061,67245,37543,51041,38433,87320,61032.334.67.25.84.03.22.32.01.71.31.10.90.90.60.60.60.50.3100.07,044,230Source: Directorate General of Food Crops.decline in petroleum revenues in 1985 and 1986, and it now constitutes less thanone-eighth of 1% of the retail value of the rice crop. Investment in agriculturalresearch (AARD budget) by the Government of Indonesia declined from $39.5million in 1985-86 to $29.9 million in 1986-87. This decline has been offset byincreasing external donor contributions to agricultural research. Total externaldonor contribution to agricultural research increased from $22.4 million in 1985-86to $40.2 million in 1986-87. External financing accounts for nearly 60% of totalresearch expenditures for 1986-87 and a far higher proportion of researchdevelopment expenditures.This high degree of dependence on external sources to finance agriculturalresearch has meant that research priorities have been largely linked to donor projectinitiatives. Since the gestation period of an externally assisted project is normallyseveral years, present research investment in fact reflects priorities established whenIndonesia was experiencing dramatic growth in rice production, that is, during theearly 1980s. At that time, donor-emphasis was shifted from a focus on irrigatedlowlands to research for the uplands, on other food crops, and for disadvantagedareas off Java. With a predominant share of research development funds accountedfor by external donor investment, a relatively small share of the research budget isbeing directly invested in lowland rice research.Exact figures on the distribution of research funds by crop are difficult toassemble for Indonesia. However, one sign of the underfinancing of rice research isthe decline in the research budget for the Sukamandi Rice Research Institute in West

36 Damardjati et alJava, the only one of the major research institutes with a first-priority mandate tofocus on irrigated lowland rice research. The budget for research activities atSukamandi Research Institute declined from approximately 735,000 rupiah in1984-85 to 380,000 rupiah in 1987-88 (Table 8). Of this, external assistance accountsfor approximately three-fourths of the operational research budget.It is difficult to forecast with any precision the consequences of such grossunderfinancing of the national rice research program. To a certain degree, otherresearch institutes (notably Bogor, Sukarami, and Maros Research Institutes) alsoconduct important rice research. Although the focus on unfavorable areas in theseinstitutes complements the move to open new cultivated land on the outer islands,the general underfinancing of rice research is likely to limit the nation’s capacity toreact to pest and disease outbreaks, to design new cultivation programs, to developappropriate technologies for improving postharvest management and grain quality,or, in the aggregate, to continually replenish the strong technological shelf requiredto support sustained growth in output. The current shift in the main mission of riceintensification activities from encouraging adoption of new technology packages toencouraging more efficient use of farm resources or fine-tuning production practicesrequires even more public support for research and extension. Far more skill andknowledge are required to promote better seed selection, correct fertilizermanagement, integrated pest management, and proper postharvest handling andpractices.The possible neglect of rice research in Indonesia in recent years can be partlycompensated for by the progress made by universities and international institutionssuch as IRRI. Developing technological opportunities for rice production growth inthe future continues to rely heavily on support from external bodies.The quality problemWith the attainment of self-sufficiency in rice, the problem of rice quality has gainedimportance. Price premiums for quality in the world market are substantial and havewidened as the world rice market has collapsed. In the domestic market, demand forrice quality also has increased with increasing consumer income. Improving ricequality is an option to raise the value of rice production.An important form of the quality problem is the lack of correspondencebetween the qualities of rice being produced and those desired by the consumingpublic. Recent consumer surveys conducted by the Directorate of Food CropsEconomics, Department of Agriculture, in major urban centers of Java show thatconsumers overwhelmingly prefer the taste of traditional rice varieties and wouldbuy such rice if they could afford to do so. Nearly 95% of national rice production isnow in modern varieties, and although some of the more recently released modemvarieties incorporate desirable taste characteristics (such as Cisadane and IR64), theprice premiums paid for traditional varieties (or mixes) sharply exceed the price ofgood-taste characteristics of modern rice varieties. In the Jakarta market, forexample, the price of traditional varieties (or mixes incorporating some traditionalvarieties) are more than twice the price of modern varieties. With income growth, a

Indonesian rice production 37Table 8. Budget for research activities of Sukamandi Research Institute for FoodCrops, Indonesia.Government budgetYearOperational('000 Rp)Material andadministration('000 RP)Foreignaid b('000 Rp)Total('000 Rp)1980-811981-821982-831983-841984-851985-861986-871987-88168,175172,250293,900337,408367,500367,844278,48484,656249,825407,750356,100322,243292,500292,15671,51635,34475,00032,98473,902260,000418,000580,000650,000659,651735,000692,984423,902380,000a Routine maintenance and salaries not included. b From ASEAN – EEC, USAID,World Bank.greater share of the consumer population are demanding, and are able to afford, ricewith desirable taste characteristics.Another important dimension of quality relating to physical (rather thanchemical) characteristics is influenced primarily by postharvest handling andprocessing rather than by variety characteristics. Poor quality of rough rice results inhigh postharvest losses and waste in the food system, lower farm gate prices, andhigher administrative costs for operating the public stockpiles.Problems of postharvest handling, drying, and storage have worsened becauseof the dramatic rise in the volume of rice harvested during the main wet seasonmonths. Postharvest losses are even higher when the crop is harvested duringadverse climatic conditions (Damardjati and Barrett 1986). Estimates of postharvestlosses vary considerably by survey and by definition. According to routine wastemonitoringsurveys of the Department of Agriculture, farm-to-retail market lossrates are on the order of 11-13% of total rice production (Table 9). This would implythat nationally, about 2.8 million t of rice is lost in the postharvest processing anddistribution system.Table 9. Postharvest losses in West Java, 1983-84 and 1985-86.Postharvest practicesHarvestingThreshingTransportationCleaningDryingSource: Winarno (1987).Postharvest losses (%)1983-84 1985-862.7 2.35.1 2.62.2 2.02.2 2.24.016.22.912.0

38 Damardjati et alThe impact of poor physical rice quality may be reflected by the rate of ricerejected by the public procurement system. The National Logistics Bureau(BULOG) buys rice (rough and milled) at quality standards designed for safe storageof up to 6 mo. The Logistics Bureau procurement standards have been more strictlyenforced since 1985 (post-self-sufficiency), although in general these standards areless discriminating than those in other major producing nations (Table 10).Although the sharp increase in the amount of rice rejected by the National LogisticsBureau is due to the more rigid enforcement of its quality standards in 1985 and1986, it is a sign that the quality of rough rice harvested during the wet season isgenerally below that required for minimum-term storage. For example, betweenMarch and July 1986, a total of 700,000 t of rice was offered for sale to the LogisticsBureau. Of this, 118,700 t (17%) was rejected on quality grounds. More than half ofthis rice was rejected because of high moisture levels or undermilling. Other qualityproblems included discolored and damaged grains and an excess of brewers andbroken grains. The loss to the government from a high rejection rate can bemeasured in terms of higher administrative costs for operating the public stockpiles.To the farm community, a high rejection rate is reflected finally in lower farm gateprices.A number of programs have been introduced to improve farmer’s threshing,drying, and cleaning technologies. The rate of adoption of improved drying andTable 10. Rice procurement quality standard for the Indonesian national stockpile compared toquality standard in other countries.Degree Moisture Broken Chalky Yellow & ForeignYear Quality of milling content grain Brewer grain damaged matterlevel(%) (%) (%) (%) (%) grain (%) (%)Indonesia1969-701970-711971-721972-731973-741974-751975-761976-771977-781978-791979-801980-811981-821982-831983-841984-851985-86Philippines20% brokensThailand15% brokensBBBBBBBBBBBBBBBBB1/11/11/11/190%90%90%90%90%90%90%90%90%90%90%90%90%1414141414141414141414141414141414353530253535353535353535353535353522211222222222222–––333333333333330.50.50.531333333333333202020101010101010101010101110.05100%100%14 20 – 5 114 15-17 – 3 20.50.2Source: Silitonga (1986).

Indonesian rice production 39cleaning technology has been less than satisfactory, due largely to the lack offarm-level economic incentives to adopt such innovations. Quality-based incentivesin the domestic rice market are more linked to consumer taste characteristics and lessto the properties associated with long shelf-life that are the case with governmentstocks. Preferred eating qualities have been successfully bred into more recentlyreleased modern varieties, but more can be done.ConclusionsBetween 1986 and the year 2000, Indonesia will likely require an additional 10-11million t of rice to maintain self-sufficiency. Growth in harvested area will be limitedby the rising costs of irrigation and opening new land. Hence, productivity will haveto grow by at least 1.3%/yr, not an easy task when input and product price subsidiesare also being reduced. The costs of stockpiling large quantities of rice have grownprohibitively large, as have the costs of maintaining artificially low fertilizer andpesticide prices—a burden on the government budget.The new rice development strategy must shift away from a heavy reliance onthese short-run policy instruments to raise farm incentives toward greater use oflong-term policy instruments that increase the country’s capacity for sustainablegrowth in rice production. Public investments in land development and technologydevelopment and transfer must not be influenced by short-run fluctuations in worldprices. Neglecting the production infrastructure will lead to a more rapiddepreciation, and ultimately higher costs for rebuilding. Indeed, if future worldprices continue to be low, greater investments will become necessary to maintain thelong-term goal of balancing production and consumption. There are disturbingsigns that Indonesia’s national rice research program is being seriously underfunded.Clearly, the need to raise productivity by 2-3%/yr while reducing the risk of pestinfestation and improving product quality will require continuous researchadvances.We have neglected to discuss two serious problems peripherally related to rice.The first is the problem of crop diversification. Success in rice has stimulated a callfor an equal level of attention and success in other food crops. In 1986, campaignswere mounted to achieve self-sufficiency in soybean and maize. These twocommodities were given priority as part of the government’s campaign for food cropdiversification. Certainly, many positive features are associated with the government’scampaign to increase the production of other food crops. However, there alsoremains the possibility that greater attention to production of soybean and maizewill divert attention and resources away from rice production. In 1986, for example,there is evidence that lands were shifted out of dryland rice to soybean. Seriousgovernment attention to food crops diversification is a relatively new phenomenonin Indonesia; as such, it would be premature to speculate on the likely effects on rice.Throughout the 1970s, growth in rice production was a major force instimulating employment opportunities in the rural areas. On an annual per hectarebasis, rice cultivation provides nearly 80% more employment than does the mostintensive mixture of nonrice food crops. Demand for rice will continue to grow

40 Damardjati et althrough the end of the century, but much slower than during the early 1970s tomid-1980s. Even assuming that production growth can keep pace with growth indemand, there will be appreciably less new employment generated in the rice sectorrelative to growth in the labor force than was the case during the last decade. Thesocial implications of a major slowdown in the rice sector-generated employment areclear. Without strong compensatory growth in other rural activities, wage ratescould fall and rural-to-urban migration rates could rise. Both would likely reduce thegrowth rate of the economy as a whole. This implies that careful choices must bemade in designing the next generation of rice technologies to minimize the possibledisruptive influences on what is most likely to be slow growth in rice sectoremployment.References citedBULOG—National Logistics Bureau (1979-87) BULOG statistics. Jakarta. (various issues)Central Bureau of Statistics (1986) The statistical yearbook of Indonesia. Jakarta. (various issues)Damardjati D S, Barrett D M (1986) Improving and maintenance of rice quality in Indonesia. Indon.Agric. Res. Dev. J. 8(2):45-50.Directorate of Food Crops Economics (1987) Supply and demand study for food crops. (mimeo.)The Falcon Team Report (1985) Rice policy in Indonesia, 1985-1990: the problems of success. Jakarta.Jatileksono T (1986) Equity implication of technology changes in the Indonesian rice economy. Ph Ddissertation, University of the Philippines, Diliman.Jatileksono T, David C C (1986) Equity implications of technical change in the Indonesian rice economy.IRRI Agric. Econ. Dep. Pap. 86-01.Oka I N (1979) Feeding population of people versus population of insects: the example of Indonesia andthe rice brown planthopper. Pages 23-30 in Proceedings of the symposia, IX International Congressof Plant Protection. Vol. I. Plant protection fundamental aspects. Burgess Publishing Co.,Minnesota.Oka I N (1982) The potential for the integration of plant resistance agronomics. Biological/mechanicaltechniques and pesticides for pest control in farming systems. Pages 173-184 in CHEMRAWN II.International Conference on Chemistry and World Food Supplies: The New Frontiers. InternationalUnion of Pure and Applied Chemistry and International Rice Research Institute, Manila,Philippines.Satari G (1983a) Integrated control program on major rice pests in Indonesia status, problems andprospects. (mimeo.)Satari G (1983b) Prospects of increasing rice production in Indonesia. Pages 1-8 in Proceedings of theworkshop on rice research: problems and research results on rice, Bogor, 22-24 March 1983. CentralResearch Institute for Food Crops, Bogor, Indonesia.Sekretariat Badan Pengendali Bimas (1987) Maintain self-sufficiency of rice production in the year 2000.Ministry of Agriculture, Jakarta.Silitonga C (1986) Policy on handling of rice surplus. Paper presented at a Workshop on Development ofRice Processing Industry in Indonesia. Bogor Agricultural University, Indonesia. 17 p.Sumardi (1976) Economical impacts of pest and diseases control on rice production. Paper presented at aSymposiumon the Role of Plant Pest, Diseases and Weed Management, 5-7 Jul 1967, Jakarta. 10 p.Timmer C P (1985) The role of price policy in rice production in Indonesia: 1968-1982. HIIDDevelopment Discussion Paper 196.Winarno F G, ed. (1987) Present status: post-harvest handling of food crops. Ministry of Agriculture,Jakarta.NotesAddresses: D. S. Damardjati, Sukamandi Research Institute for Food Crops, AARD, Jalan Raya No. 9, SukamandiSubang, West Java, Indonesia; S. R. Tabor, Directorate General of Food Crops, Ministry of Agriculture, Jakarta,Indonesia; I. N. Oka, Bogor Research Institute of Food Crops, JI. Cimanggu, Bogor, Indonesia; C. C. David,Agricultural Economics Department, International Rice Research Institute, P.O. Box 933, Manila, Philippines.Citation information: International Ria Research Institute (1989) Progress in irrigated ria research. P.O. BOX 933,Manila, Philippines.

Improving yield potentialin tropical riceS. AKITAHighlights of findings so far in our program to identify viable strategies forimproving rice yields are 1) grain yield of high-yielding indica varieties andlines grown with favorable management in the dry season at IRRl is about9.5 t/ha, that of F 1 hybrids is almost 20% higher; 2) sink capacity ofshort-duration IR varieties shows significant seasonal variation and isnegatively related to temperature at the vegetative stage; 3) spikeletformation efficiency and sink size per absorbed nitrogen before headingvary with growth duration, heterosis, and growing season; spikeletformation efficiency of short-duration varieties in the dry season at IRRl iscomparable with that reported in northern Japan; 4) despite the adverseeffect of high temperature at the vegetative stage for sink formation in thetropics, dwarf indica varieties at IRRl had grain yield and spikelet formationefficiency similar to those of some high-yielding japonica varieties intemperate regions, indicating that the yield potential of indica dwarfvarieties is high; 5) F 1 hybrids show less heterosis in biomass productionthan in grain yield under favorable management; better yields of F 1 hybridsbred at IRRl are mainly attributed to higher harvest index; higher spikeletformation efficiency due to sustained advantage of early seedling vigor isresponsible for this; 6) the highest total biomass production (22 t/ha) wasobtained in a high-nitrogen water culture with a medium-duration variety,although final total biomass was not significantly higher than that of ricegrown in the field with favorable management; this was close totheoretically calculated biomass; 100-d growth gave the highest yield inthe high-nitrogen water culture; 7) lower dry matter production per unitsolar radiation at ripening stage is closely associated with faster leafsenescence due to higher translocation of substances from the leaf to thegrain; faster leaf senescence is partly due to higher sink activity, whichactivates mobilization of substances for translocation; 8) based on thesefindings, the target yield in IRRl's dry season is estimated to be 15 t/ha.Further improvement of sink formation efficiency is the primary factor foryield improvement in the tropics. Significant variation in sink formationefficiency among varieties and by planting months indicates potential forimprovement of this characteristic. Improvement of sink formationefficiency and ripening by decreasing maintenance respiration, leaferectness, and slow senescence would help in reaching yield potential.Most traditional rice varieties cultivated in the tropics and subtropics arephotoperiod sensitive and mature in 160-170 d (long growth duration). In general,they are tall, with a harvest index around 0.3. At nitrogen rates exceeding 40 kg/ ha,yields of many cultivars decline due to severe lodging and overgrowth.

42 S. AkitaSemidwarf varieties were developed to improve resistance to lodging withhigher nitrogen application. IR8, the first IRRI semidwarf variety released in 1966,has erect leaves and is high tillering, photoperiod insensitive, and more responsive tonitrogen than traditional varieties. IR8, IR20, IR24, IR26, and IR42 mature in125-140 d (medium growth duration) and have 0.4 harvest indexes. Dwarfnessimproved not only lodging resistance, but also the rate of partitioning ofphotosynthates to grain. The semidwarf varieties doubled the yield potential oftropical rice.Short-duration varieties like IR36, IR52, and IR64 mature in 110-125 d; veryshort-duration varieties like IR28 and IR58 mature in less than 110 d. Underoptimum conditions, yield potential of very short-duration varieties compares to,and at times is slightly lower than that of medium- and short-duration varieties.Short-duration varieties like IR36 have been widely accepted in rice-growingcountries of Asia because of their high yield, yield stability, and photoperiodinsensitivity. Short-duration varieties enable farmers to increase their croppingintensity because two or three crops of rice can be grown annually where only onewas possible before. This has improved annual yield potential remarkably.Since the release of IR8, high yields in favorable rainfed and irrigatedenvironments have been a major target of varietal improvement at IRRI. Half theworld’s riceland, producing three-fourths of the world’s total rice, is irrigated andfavorable rainfed environment. Unfortunately, the yield potential per crop ofreleases since IR8 has not increased significantly, except in F 1 hybrids. While riceproduction in many countries is now temporally sufficient, a continuous gain in ricegrain yield is essential to meet increasing food demands and to more efficiently useland.Several experiments in plant physiology at IRRI in the last 2 yr have exploredstrategies for obtaining higher yields. One physiologically characterizes existinghigh-yield varieties by a modified, more reliable growth analysis technique (V.Coronel, F. Parao, and S. Akita, IRRI, unpubl.). Grain yield on the IRRI farm hasbeen declining (Ponnamperuma 1979). An adequate analysis of this situation suffersfrom a lack of reliable databases on growth and yield in previous years, which in turnhampers appropriate physiological analysis. In addition, we need a continuousaccumulation of reliable databases on physiological characteristics such as growthand yield for each newly developed high-yielding variety and line.Some factors involved in the physiological mechanism for yield determinationremain unknown. IRRI’s monthly planting experiment is a method we are using toanalyze the yield determination process (Parao and Akita 1987; F. Parao and S.Akita, IRRI, unpubl.). Seasonal variations in yield, yield components, and growthprovide a large amount of information (Evans and De Datta 1979, Moomaw et a11967, Osada et al 1973). A field and water culture experiment is being used toevaluate potential biomass production and yield response to higher nitrogenapplication (Q. Shi and S. Akita, IRRI, unpubl.). Through the water culturetechnique we hope to elucidate physiological reactions of plants to controllednutrient management, which is difficult in soil-grown crops.Another research thrust is in hybrid rice. This program has increased the yieldpotential of rice 10-20% over the best tropical pureline rice varieties (Virmani 1982).

Improving yield potential 43While the practical use of F 1 hybrids in farmers’ fields in the tropics is stillcontroversial, studies on the physiological bases of heterosis in rice not only enrichthe hybrid rice breeding program, but also may lead to the identification of criteriafor selecting for higher grain yield potential in pureline varieties (L. Blanco et al; K.Katayama and S. Akita, IRRI, unpubl.).Stable high yields will be obtainable only when the yield determining processesoperating throughout the growth stages are in balance. We hope to explain themajor physiological characteristics of each yield determining process and the extentto which these processes can be extended.Biomass production, grain yield, and harvest indexof recent IRRl varieties and linesThe growth characteristics of traditional varieties and some of the early IRRIvarieties are already well documented (Tanaka et a1 1968, Yoshida and Parao 1976).Here we summarize only the data on biomass production and yield of recent IRlines. Pooled data on biomass production and grain yield of 30 high-yielding IRvarieties and lines and F 1 hybrids obtained during the 1986-87 dry season underfavorable management are summarized in Figure la. Biomass production was 20-21t/ ha for medium-duration varieties, at planting densities of 50 hills/ ha and nitrogenapplication of 150 kg N/ ha. This is close to the highest biomass production reported1. Total biomass production, grain yield (a), and harvest index (b) of recently developed IRRI varieties,lines, and F 1 hybrids with 105 kg N/ ha. Data were collected from 2 experiments in the 1986 and 1987 dryseason. Average solar radiation and temperature during cropping season in 1986 and 1987 were 17.7 and20.2 MJ/m 2 /d and 26.4 and 26.2 °C, respectively.

44 S. Akitafrom IRRI so far and is almost equal to the highest biomass production reported intemperate rice (Ministry of Agriculture and Forestry 1982). Lower biomassproduction was obtained from shortduration varieties.The biomass production of recently developed high-yielding varieties (HYV)and lines and F l hybrids was slightly higher than that of traditional varieties like Petaand Binato when lodging of traditional varieties was artificially prevented. Grainyields of recent HYVs ranged from 7.5 to 9.5 t/ha (14% moisture content), higherthan yields of traditional varieties. That grain yield was consistent and independentof growth duration, except for a slightly lower yield of very short-duration varieties.Stable yield independent of growth duration is attributed to higher nitrogenuptake rates, especially at early growth stages, by recently developed high-yieldingshort-duration varieties (Fig. 2). That resulted in higher spikelet formationefficiency. In most of the F 1 hybrids tested, grain yield was higher than that of thehigh-yielding pureline varieties. During the dry season, the F 1 hybrids showed10-20% higher yield than the best check variety, often with yields of more than10 t/ha.Decline of biomass with growth duration and the almost constant level of grainyield irrespective of growth duration result in a higher harvest index (HI) (the ratioof grain weight to total biomass produced) for short-duration varieties (Fig. 1b). AHI higher than 0.55 is often observed in very short-duration varieties. Dwarfness andheterosis are the primary factors responsible for improved HI, independent ofgrowth duration. However, improvement of HI using heterosis in indica varietieswas lower than that using dwarf genes.In the water culture experiment, the highest biomass produced was about22 t/ha with IR29723-143-3-2-1. Cultivars like IR44 and IR56, which have a canopyof droopy leaves, showed lower biomass production than IR29723-143-3-2-1 andIR58, which have erect leaves (Table 1). These results show the importance of leaferectness for higher biomass production.Vigorous growth at early stages due to high nitrogen in the culture solution wasalways followed by a sharp decline in growth at later stages due to enhanced darkrespiration. The result was little significant improvement in biomass over that fromgrowth in the field under favorable agronomic practices. The highest crop growthrate (CGR) was around 40 g/m 2 per d, maximum leaf area index (LAI) was morethan 20, and total nitrogen uptake was 3540 g N/m 2 in rice grown at higher nitrogen(Fig. 3). Identical materials grown under favorable management in the field showeda CGR of only 30 g/m 2 per d, a maximum LAI of less than 10, and nitrogen uptakeof 20-21 g N/m 2 . Grain yield in high-nitrogen water culture often declined markedlydue to overgrowth. Usually, the grain yield decline of long-duration varieties in highnitrogen was more than that of short-duration varieties, and yield decreases weresignificantly different among varieties (Table 1).When biomass production approaches its potential limit, increased biomassdoes not always result in increased yield. In our experiment on the effect of a 6-mowet season fallow on yield, with 150 kg N/ha applied in the dry season, only theshort-duration varieties showed increased spikelet numbers and yield with increasedtotal biomass (Table 2). The increased biomass is due to the increased nitrogen

2. Nitrogen uptake rate by some recently developed IR varieties and lines (a) and the relation between total nitrogen uptake andtotal biomass production (b) (L. Blanco and S. Akita, unpubl. data).

Table 1. Comparison of biological yield, grain yield, and yield components of selected high-yielding IR cultivars grown in high-nitrogen culture solutionwith materials grown under favorable management in the field. IRRI, 1987 dry season (Q. Shi and S. Akita, unpubl. data). aGrown in culture solution with 80 Ppm NIR58 103 1727 (106) 684 (85) 40 60.7 (129) 970 (104) 70 23lR56 b 110 1703 (101) 613 (77) 36 43.4 ( 94) 892 (118) 73IR64 113 1877 (104) 543 (69) 29 38.6 ( 97) 892 (118) 61 18lR29723-143-7-2 129 2197 (115) 499 (57) 23 47.5 (112) 800 (110) 53 12IR44 b 133 1825 ( 99) 257 (36) 14 30.8 ( 75) 460 ( 56) 48 8Grown in field with 150 kg N/haIR58 106 1622 801 49 47.0 930 90 35lR56 b 112 1694 796 47 46.4 82IR64 117 1717 790 46 39.7 753 89 26lR29723-143-3-2-1 133 1915 881 46 42.3 730 90 24lR44 b 131 1837 721 39 41.0 820 81 23aAll the data are on dry weight basis. Planting density was 50 hills/m 2 . Culture solution of 80 ppm N was changed once a week. Figures in Parenthesesare values relative to field-grown materials. b Has droopy leaves. c Dry weight increase from panicle initiation to heading.Duration(d)Biologicalyield(g/m 2 )Grain HarvestSpikelets/m 2 Wr cFilled CGR atyield index(X 10 3 )(g/m 2 grain heading)(g/m 2 ) (%)(%) (g/m 2per d)

Improving yield potential 473. Growth curves of IR29723-143-3-2-1 (medium-duration) grown in high-nitrogen water culture and inthe field with favorable management, 1987 dry season (Q. Shi and S. Akita, unpubl. data).supply at early stages. Medium-duration line IR29723-143-3-2-1 showed increasedtotal biomass, but yield decreased due to reduced ripening, despite a small increase inspikelet numbers. Initial higher nitrogen application or absorption was effective inimproving yield only for short-duration cultivars.Our recent high-nitrogen water culture experiment clearly indicates thatgrowth duration and nitrogen level affect grain yield significantly. Kawano andTanaka (1968) pointed out that the growth duration giving the highest yield vanes

48 S. AkitaTable 2. Comparison of the effect of 6-mo fallow and continuously cropped conditions on yieldand yield components of selected IR cultivars. IRRI, 1987 dry season (V. Coronel and S. Akita,IRRI, unpubl. data). aVarietyGrowthduration(d)Totalbiomassproduction(g/m 2 )Grainyield(g/m 2 )Spikelets/m 2 Grain 1,000-filling grain(X 10 3 )(%) weight (g)CroppedIR58IR64lR29723-143-3-2-1FallowIR58IR64lR29723-143-3-2-110311412713851385184566060079036.127.838.581.889.986.822.424.023.51081151 2615701660201068066072041.834.839.075.780.879.521.623.623.2a Total biomass production, grain yield, and 1,000-grain weight were measured at 0% moisture.Planting density was 50 hills/m 2 , 150 kg N/ha was split-applied in both plots.with nitrogen level, from 0 to 150 kg N/ha, and suggested that at 120-150 kg N/ha,the optimum growth duration is about 120 d. In our experiments using 150 kg N/hawith a plant density of 50 hills/m 2 , grain yield of recent IR varieties and lines variedlittle with growth duration between 110 and 140 d; grain yield of very short-durationcultivars was slightly lower.A possible cause of the differences in the relationship between grain yield andgrowth duration between our results and previous reports (Vergara et al 1966,Tanaka et al 1966) is the different nitrogen absorption abilities of the cultivars used.Most of the latest IRRI lines have early vigor (Chang and Vergara 1972). Nitrogenuptake rate at early stages in our experiments was high; uptake may be limited inearlier lines (Fig. 2).In our experiment using extremely high nitrogen in water culture, optimumgrowth duration was about 100 d. Usually, optimum growth duration for high yieldwill be shorter with increasing nitrogen. However, the optimum growth durationalso will vary with the nitrogen uptake ability of varieties used.Biomass productionHigh biomass production often is closely associated with high yield. Hoshino et al(1983) compared the productivity of japonica varieties developed in southern Japanwith that of indica varieties; they found that lower yields of japonica varieties weredue to lower biomass production. They also observed that the improved yield ofnewly developed high-yielding variety Akenohoshi, which has genes from IRvarieties (Shinoda et al 1982), was mainly attributable to increased sink capacity dueto increased biomass production. When sink formation efficiency is constant, highbiomass production at heading will result in higher sink capacity (except with severeovergrowth).Canopy architecture and nutrient uptake ability have been improved in mostcurrent high-yielding varieties. The biomass production ability of high-yielding

Improving yield potential 49indica varieties is high. In our recent high-nitrogen water culture experiment, thehighest total biomass production was 22 t/ha. It did not increase significantly, evenwhen lodging was artificially prevented, over rice grown in the field under favorablemanagement. In high-nitrogen water culture, medium-duration IR29723-143-3-2-1showed high biomass (20 t/ha) about 100 d after sowing (Fig. 3). This implies that itmight be possible to increase the biomass production of shortduration varietieswhose biomass potential is below 20 t/ha (Fig. 4).Biomass production in the tropics has a clear disadvantage due to hightemperatures during later growth stages. A high biomass of 29 t/ha (Xu 1984) canhardly be expected (Fig. 4). In our water culture experiment, dark respiration rate atheading was more than 40 g dry wt/m 2 per d when 20 t/ha biomass was obtained at4. Growth curves obtained from various locations when high yield was observed. Grain yield is shown bythe adjusted value for 14% moisture content.

50 S. Akitaheading—almost equivalent to the highest CGR. The growth curve showed littleincrease after heading. This higher dark respiration rate is strongly limiting biomassproduction potential in the tropics. However, 22 t total biomass/ ha in the dry seasoncan be a realistic target for potential biomass production at IRRI farm; biomassproduction potential computed on the basis of recent information is also close to theobserved maximum (Table 3).Higher photosynthesis does not guarantee higher biomass production; it is notdifficult to get a CGR as high as 40 g/ m 2 per d at early stages. However, higher CGRat early stages caused rapid decline in CGR at later stages because of increasedrespiration. Consequently, the final biomass produced by manipulating photosynthesiswith nitrogen did not increase much.Photosynthetic rate per unit leaf area under saturated light with favorablegrowing conditions (Pmax) has been studied extensively as a means of increasingbiomass production potential (Akita 1980, Ohno 1976). But the high Pmaxmeasured under favorable condition sometimes is inversely correlated with yield.Varietal response to Pmax measured under favorable conditions often fails tocorrelate with yield or CGR. The primary reason for this minimal contribution ofPmax to CGR is the dominant effect of leaf area on CGR at earlier stages.Higher leaf area development ability is commonly associated with lowernitrogen content per unit leaf area, which in turn is closely related to lower Pmax,This explains why cultivars with higher leaf area development ability, such as F 1 ricehybrids, have higher yields, even though little advantage in Pmax is observed(Yamauchi and Yoshida 1985). This is reinforced in the extremely dwarf cultivars:they have higher Pmax due to lower leaf area development ability but often turn outto be poor yielders (Hayashi 1972).The contribution of Pmax to CGR is diminished at middle growth stages whenthe leaf is erect and the canopy is more dense. Each leaf in a dense canopy with erectleaves utilizes lower radiation. Light utilization efficiency at low light is becomingmore limiting for canopy photosynthesis rate than is Pmax. Thus, higherphotosynthetic efficiency at rate-limiting light intensity (E) can be an importantfactor in increasing crop growth rate (Horie 1981), especially in a canopy with erectdense leaves.So far, little varietal response in E value has been observed in the rice seedlingcanopy (Akita and Saito 1984). The avenues open here are to improve growth rate ininitial stages, as in F 1 rice hybrids; to improve photosynthetic efficiency per nitrogenuptake, as in C 4 plants; or to increase the ratio between photosynthesis rate andrespiration loss. Efforts to screen rice materials with low photorespiration have beenunsuccessful (Akita 1980a), and the possibility of incorporating C 4 characteristicsinto rice seems low. Efforts to identify rice genotypes with lower maintenancerespiration were made with Lolium (Wilson 1982); further improvement of leaferectness in later growth stages (Tanaka et al 1969) and slow senescence would beworthwhile.Even among high-yielding varieties, leaf erectness in some varieties (like IR44and IR56) is not sufficient for higher biomass production. As far as present yield(which is far from the potential) is concerned, leaf erectness is not a strongly

Table 3. Calculation of biomass production potential of rice with 130 d growth duration in IRRl’s dry season condition.3020.12900.880.120.970.4012.417708541884Ripeningstage3020.83000.850.120.450.202.751761962080Vegetativestage IVegetativestage IIReproductivestageNumber of days aAverage daily solar radiation b (MJ/m 2 )Photosynthetically active radiation duringthe period c (MJ/m 2 )Average light interception by the canopy dPhotosynthetic energy conversion efficiency eCorrection for light saturation lossCorrection for respiration loss gFixed energy (MR/m 2 )Conversion for dry weight h (g CH 2 O/m 2 )Correction for inorganic content i (g/m 2 )Total biomass (g/m 2 )2511.41370.150.120.700.601.0466743017.32500.880.120.850.6013.468619561030a Growth duration of the variety was assumed 130 d. Seedling period is 15 d.b Transplanted on 1 Jan. The average daily solar radiation was obtainedcfrom the 10 yr average from 1977 to 1986 in IRRI. Photosynthetically active radiation = 0.48 X av daily solar radiation (Kanda 1975).d Estimatedbased on LAI-light interception relation by Kanda (1975). Average LAI used for each period was 0.50, 5.5, 15.0, and 8.0, respectively, from our watereculture experiment on IR29723-143-3-2-1. Quantum yield in normal air at 30 °C of 0.0524 mole CO 2 /absorbed einstein reported by Ehleringer andfBjorkman (1977) was used. Similar quantum yield of 18 was used for wheat by Austin (1982). Based on the determination of canopy photosynthesisof rice (Tsuno and Kitakado 1970). Saturation loss, the daily integrated rate of canopy photosynthesis divided by daily canopy photosynthesis rateunder no light saturation of photosynthesis were calculated. After heading due to senescence, 0.45 was tentatively used. g Based on our data at lRRlcondition and in agreement with the measurement by Tanaka and Yamaguchi (1968) and Yamaguchi (1978). h 64.0 g DW/MJ was used for conversioni(Murata et al 1968). Mineral content of 11% was used.

52 S. Akitayield-limiting factor. However, when potential yield level is the aim, leaf erectnesswill play a much more important role (Table 1).Harvest indexWhen room for improving biomass production potential is limited, as is observed inthe high-nitrogen water culture experiment (Table 1), the only way to increase yieldwould be to manipulate the yielddetermining process to give a higher HI. Even iftotal biomass production remains the same, grain yield varies significantly with theprocess by which total biomass is attained.The key growth factors determining HI are dry weight at heading (DWh) andcrop growth rate around heading (CGRh). DWh is closely related to sink capacity,CGRh eventually determines ripening percentage. The product of DWh and CGRhwould be a rough prediction of the grain yield of a variety. Usually, DWh and CGRhare inversely related. Excess nitrogen gives higher DWh, but CGRh simultaneouslybecomes low, causing a yield decline due to reduced ripening percentage (Fig. 3).This situation is often referred to as overgrowth.Increasing initial growth by agronomic management, giving higher DWh andmaximizing the value of CGRh × DWh, has been the usual path for increasing yieldof a given variety and condition. Chang and Vergara (1972) referred to DWh as“early vigor” and CGRh as “late-sustained vigor” and discussed the participation ofthe different genes that control them. However, the relationship of CGRh and DWhby physiological interaction is primarily an inverse correlation.To get a higher HI, CGRh has to be higher, in order to keep a high ripeningpercentage. The ideal way to maintain a high CGRh and better ripening is to reduceDWh to as low as possible without sacrificing sink capacity. Yield improvement hasbeen accomplished by improving sink size per DWh, or more precisely, sink capacityper unit nitrogen absorbed before heading (sink formation efficiency). In the tropics,high temperatures during the vegetative and ripening stages cause overgrowth andpoor ripening. Higher sink formation efficiency and better ripening play crucial rolesin improving yield.The HI of short-duration varieties (110-120 d) varied from 0.40 to 0.50 (Fig. 1),far below the proposed limit for HI of wheat (Austin et a1 1980). In calculating HI,several expressions have been used. Here, HI is calculated as the ratio of rough riceto total biomass production, including roots. Austin used the ratio of grain weight todry weight of upper ground parts.The ratio of dehulled grain weight to total biomass needs to be calculated tocompare the HIS of rice and wheat. Usually the rice grain weight we use includes hullweight; in wheat, the hull is not included. Assuming that maximum root weight is 5%of total biomass, the HI of 0.60 proposed as the limiting value for wheat isrecalculated at 0.57. The present HI of short-duration rice varieties is recalculated to0.34-0.42 (equivalent to 0.40-0.50 in the ratio of rough rice weight to total biomass).It has often been claimed that rice hull weight is almost 20% of rough riceweight, much higher than that of wheat, and that the partitioning of photosynthate

Improving yield potential 53among organs is different between wheat and rice. However, when the ratio ofdehulled grain weight to panicle weight is compared, that of rice is slightly higher.The rachis of wheat may be much heavier than that of rice.Another factor that needs to be considered is the higher partitioning ofphotosynthates to vegetative organs in the tropics than in the temperate climateswhere wheat is grown. It would be expected that the limiting value of HI for rice inthe tropics would be much lower than 0.57. Even if the limiting value of 0.50,equivalent to 0.60 in rough rice to total biomass, is taken (that is equivalent to thehighest value observed in our no-nitrogen plot in the dry season), the present HI of0.34-0.42 for short-duration rice varieties is far below the limit. An accurate estimateof the limiting HI for rice in the tropics needs to be established.Two physiological processes are involved in improving HI: sink formation andripening. When the contribution to grain of each yield-determining process wasevaluated, the contribution of spikelet number was highest in short-durationvarieties (Parao and Akita 1987, Yoshida and Parao 1976). Osada et al (1373)reported a higher contribution of ripening to yield with medium-duration varieties.In the monthly planting experiment using short-duration varieties IR58 andIR64, grain yield and temperature during vegetative period were correlatednegatively (Table 4). Grain yield and solar radiation during ripening were correlatedpositively (Table 4). In a previous monthly planting experiment using mediumdurationvarieties, solar radiation during the reproductive and ripening stages andyield were correlated positively (Evans and De Datta 1979, Osada et a1 1973). Theinfluence of climate on the yield-determining process may vary with growthduration.Table 4. Correlation coefficients among grain yield of short-duration cultivars,average temperature, and solar radiation at different growth stages and two nitrogenlevels. Monthly planting experiment, IRRI, 1986 dry season (Parso and Akita1987). a IR58 IR640 kg N 120 kg N 0 kg N 120 kg NTvTpTrRvRpRr–0.46–0.39–0.31–0.30–0.100.24–0.76** –0.54–0.59* –0.33–0.28 –0.08–0.57*–0.150.44–0.64*–0.260.08–0.26 0.31–0.01 0.270.51 0.65*a Tv, Tp, Tr - average temperature during vegetative, reproductive, and ripeningstages, Rv, Rp, Rr - average solar radiation during vegetative, reproductive, andripening stages. Experimental condition: Fifteen-day-old seedlings were transplantedat the beginning of the month. Spacing was 20 X 20 cm. Two levels ofnitrogen, zero and 120 kg N/ha, were given. * - Significant at the 5% level, ** -significant at the 1% level.

54 S. AkitaSink formation processYoshida and Parao (1976) reported that more than 80% of the seasonal variation inyield of short-duration varieties at IRRI was attributable to variation in spikeletnumbers per m 2 . In our recent experiment, variations in grain yield across seasonsand with different fertilizer levels were attributed mainly to variations in sinkcapacity. In many cases, the sink formation process limits grain yield.Sink capacity is defined as the product of panicle number per unit land area,spikelet number per panicle, and average spikelet weight. In this paper, sink capacityis the product of grain weight and spikelet number per unit land area.Wide variation in potential weight of grain has been observed among varieties,with as high as 73 mg rough rice weight reported (Takita 1983). Because of poorgrain filling in extremely large grains, most varieties with higher yield potential havegrain weights in the 25-35 mg range. Within this range, varieties with higher grainweight tend to show higher yield potential. Usually, there is a high negativecorrelation between grain size and spikelet number per unit land area.Two processes are involved in spikelet formation: panicle number determinationand determination of spikelet numbers per panicle. Usually, panicle numberdetermination precedes spikelet number determination. But in short-durationvarieties, the two processes occur almost simultaneously, at panicle initiation.Initially, a large number of tillers and spikelets are differentiated. The final numberof panicles and of spikelets per panicle are determined by the availability ofphotosynthate and nutrients during the succeeding stage.Kumura (1956) found a high correlation between leaf nitrogen content at thereproductive stage and spikelet numbers per panicle. Wada and Matsushima( 1962)reported that spikelet formation is strongly affected by both nitrogen uptake and theavailability of carbohydrate during the reproductive stage. CO 2 enrichment andshading during the reproductive stage (Akita 1980b, Yoshida and Parao 1976) andthe high positive correlation between solar radiation during the reproductive stageand grain yield (De Datta and Zarate 1970, Evans and De Datta 1979, Murata andTogari 1972) also indicate the strong effect on sink size of photosynthetic activityduring the reproductive stage. These observations indicate that higher nitrogen inthe plant tissue favors higher differentiation of spikelets and that a higher supply ofphotosynthates would be required to minimize spikelet degeneration during thereproductive stage.On the other hand, Murayama (1967) and Yoshida (1981) observed that sinksize in warmer region cannot be increased, even if nitrogen content before heading isincreased. If that is the case, the chances for improvement of yield in the tropics arelow.We examined the relation between spikelet number and nitrogen absorbedbefore heading in two experiments. In a recent monthly planting experiment, higherdry matter production or higher nitrogen uptake before heading was always relatedto higher sink formation in the same months. But across months, sometimes therelationship was negative. This can be explained by differential spikelet formationefficiency in different months (Fig. 5).When productivity among varieties and seasons is compared, the concept ofsink formation efficiency needs to be introduced as a factor in evaluating differential

Improving yield potential 555. Relation between spikelet no./m 2 and nitrogen absorbed before heading (V. Coronel, F. Parao, L.Blanco, and S. Akita, IRRI, unpubl. data).ability to produce sink. Sink formation efficiency can be evaluated in different ways.One way is by sink capacity per biomass at heading (DWh) or by sink capacity perabsorbed nitrogen before heading (Nh) (Murayama 1967). Sink capacity per Nhwould be a more precise indication, because DWh involves starch, which isphysiologically inactive.Another way is through sink capacity per leaf weight at heading (Suzuki 1980).Differential productivity among varieties was found to be due to differential sink sizeto DWh. In a wet season in which the temperature at early stage is high, DWh is alsohigh. But sink size is inversely related to temperature, and sink size per DWh in a wetseason becomes smaller.We found that spikelet formation efficiency (spikelet numbers per unit nitrogenabsorbed before heading) was related negatively to mean air temperature during thevegetative stage (Fig. 6). A higher negative correlation between grain yield andtemperature during vegetative stage was found (Table 3). An almost 7% increase ofsink size occurred with a decrease of 1 °C within the temperature range 24-28 °C.

56 S. Akita6. Effect of temperature during vegetative stage on spikelet formation rate of IR64 with 120 kg N/ha.Spikelet formation rate is shown as spikelet no./m 2 divided by number of days from transplanting topanicle initiation (F. Parao and S. Akita, IRRI, 1987).The average yield gap between dry season and wet season crops is almost 30% atIRRI (IRRI yield trial data, unpubl.). Almost the same order of difference in sinksize was observed. This yield gap can be attributed primarily to the difference in sinksize due to temperature effect.Assuming that this relationship holds even at 20 °C, the common meantemperature during the vegetative stage in temperate regions, a nearly 30% highersink size than that in the dry season crop at IRRI can be expected (although highersolar radiation in the dry season may reduce this gap). A major cause for higheryields of indica high-yielding varieties in temperate regions would be the higherspikelet numbers produced by lower temperature in the vegetative stage. WhenKorean indica-japonica high-yielding varieties are grown in a tropical environment,yields are far below those possible in Korea (Akita et al, unpubl.).Based on results of the correlation study and the physiological development ofthe panicle, temperature around panicle initiation would be expected to be the mostinfluential for spikelet formation in short-duration varieties. Higher meantemperature at the vegetative stage was related to faster initial tillering and leafgrowth (Yoshida 1973). When excessively high tillering was observed in the wetseason, nitrogen content in the sheath at the panicle initiation stage was lower(Fig. 7). Higher tillering at early stages was related negatively to effective tillerpercentage (Fig. 7).

Improving yield potential 577. Relation between no. of tillers at 20 d after transplanting and nitrogen content in sheath at panicleinitiation (a) and between no. of tillers at 20 d after transplanting and no. of effective tillers (b) of IR58with 120 kg N/ha (F. Parao and S. Akita, IRRI, unpubl. data).Low nitrogen content in the sheath may be detrimental to development of leafnumbers per tiller. Limited leaf development per tiller may cause higher numbers ofineffective tillers, because a minimum number of leaves is required for a tiller to beeffective at panicle initiation (Matsushima 1980). Thus, in short-duration varieties,mean temperature at panicle initiation was negatively correlated with paniclenumber. In turn, panicle number was positively correlated with spikelet number.Higher spikelet formation efficiency, which is parallel to panicle numberformation efficiency, is closely related to higher response to fertilizer application(Fig. 8). In those months when spikelet formation efficiency is high, the yielddifference between 0 nitrogen plot and 120 kg N/ha was higher. That is, nitrogenapplication in the month when higher spikelet formation efficiency is obtained iseffective for increasing grain yield.In short-duration varieties, the process of determining spikelet number perpanicle occurs at the same time. Low temperature also may be effective in increasingspikelet numbers per panicle by preventing spikelet degeneration (Yoshida 1973).Higher dry season yields in the tropics have been attributed to favorable solarradiation during reproductive and ripening stages (Evans and De Datta 1979). But ahigher supply of photosynthates will not always increase yield, because sink size hasbeen determined at the preceding stage.Suzuki (1980) reported a high negative correlation between spikelet number toleaf weight at heading and mean air temperature during the 6 wk before heading. DeDatta and Zarate (1970) found a high negative correlation between yield and meantemperature at the vegetative stage in one variety tested. These results support ourobservation. In principle, sink formation efficiency is determined by the balance ofthe partitioning of nitrogen and photosynthate for sink formation and for vegetativeorgans. Studies on the mechanism of nitrogen in the sheath and its relationship withthe spikelet formation process need to be intensified.

58 S. Akita8. Effect of N application on grain yield and panicle number of IR58 and IR64 in different transplantingmonths, IRRI, 1985-86.Effectiveness offertilization =Yield at 120 kg N/ha - Yield at 0 NYield at 0 NMurayama (1967) pointed out that spikelet formation efficiency (evaluated asspikelet number per unit nitrogen absorbed before heading) is higher in coolerclimates than in warmer regions. Yoshida et al (1972) confirmed this using IRRIcultivars. But our recent results showed that more recently developed short-durationIR varieties grown in the dry season, when temperature during the vegetative stage islow, had a spikelet formation efficiency per unit nitrogen absorbed before headingsimilar to that of varieties grown in northern Japan (Fig. 6).Two factors are involved in these observations. One is the effect of temperatureon spikelet formation efficiency, the other the effect of growth duration on spikeletformation efficiency. Recent results at IRRI show that short-duration varieties havehigher spikelet formation efficiency than long-duration varieties. One physiologicalexplanation for the higher spikelet formation ability of short-duration varietiescould be higher nitrogen content in the sheath at panicle initiation. Usually thedecrease of nitrogen content in the tissue with time after transplanting follows asimilar pattern, irrespective of variety. A shorter period from transplanting to

Improving yield potential 59panicle initiation, as in a short-duration variety, naturally gives higher nitrogencontent at panicle initiation.The similar level of sink formation efficiency observed in the dry season atIRRI, where mean temperature in the vegetative stage is about 24 °C, with thatobserved in northern Japan, where mean temperature during the vegetative stage isabout 20 °C, clearly indicate that the potential spikelet formation efficiency of anindica high-yielding variety is higher than that of a japonica variety. The significantyield improvement in Korea (Kim 1978) and the recent breeding of a high-yieldingvariety in Japan (Shinoda et al 1982) by introducing an indica dwarf gene may alsoprove the higher potential of the indica dwarf gene for spikelet formation.Spikelet formation also is strongly affected by nitrogen content in plant tissueduring the reproductive stage (Kumura 1956). In addition, some short-durationvarieties have higher nitrogen uptake rates (NUR) at early stages. With optimumfertilizer rates, total nitrogen uptake at harvest by some short-duration, highyieldingvarieties was similar to that of medium-duration varieties (Fig. 2). In thetropics, where temperature at early crop stages is high, development of shortdurationvarieties whose spikelet formation efficiency is higher has been areasonable way to compensate for the adverse effect of high temperature. As spikeletformation efficiency increases, it becomes easier to keep high sink size per unit dryweight increase (which is highly desirable in tropical rice cultivation).Higher NUR also was expressed by faster initial growth in F 1 hybrids. Amongthe IRRI varieties, IR8 still belongs to the group having the highest initial growth(Akita et al, unpubl. data). However, some materials show higher initial growth thanIR8. It will be necessary to look for the possibility of incorporating genes that givehigher initial growth coupled with higher sink formation efficiency to improve yieldsof short-duration varieties.One common perception is that higher initial growth at the individual plantlevel does not contribute to improving the yield potential of a total crop. Increasedinitial crop growth can easily be obtained by increasing planting density or byapplying higher levels of basal fertilizer. These management practices cancompensate for the advantage of higher initial growth at the individual plant level asfar as CGR or energy fixation ability by the canopy is concerned. Besides, higherCGR or canopy photosynthesis at the initial stage does not always favor higher sinkformation, as was the case in our fallow experiment with medium-duration varieties(Table 2).However, biomass production of short-duration varieties is still low even whenplanting density and nitrogen applied are high. The dominant factor for higher sinkformation is more initial growth coupled with higher sink formation efficiencydetermined at the individual plant level. The advantage of F 1 hybrids for highergrain yield is mainly due to these characteristics. Attention needs to be given tohigher initial growth with adequate sink formation efficiency at the individual plantlevel.A higher ratio of leaf weight to total dry weight at heading was observed in themonthly planting experiment transplanted under short-day condition. Thisincreased partitioning of photosynthates to leaf was related to reduced spikelet

60 S. Akitanumbers per m 2 , although reduced spikelet numbers in August and Septemberplantings were effective in keeping ripening high under low solar radiation (Table 5).On the other hand, it is known that exogenously applied gibberellic aciddecreases partitioning of photosynthates to leaf (Katayama and Akita 1987) andthat gibberellic acid concentration in a plant is under photoperiodic control (Suge1971). Taguchi et al (1952) also observed photoperiodic variation in tillerdifferentiation. Photoperiodic variation in the partitioning of photosynthates orgrowth that may be controlled by some plant hormone sensitive to daylength mayeventually affect spikelet formation efficiency.These examples show that grain yield can be increased by fine-tuning theprocesses related to partitioning of nitrogen and photosynthate for sink formation.Genetic improvement for higher sink formation ability, such as that in shortdurationvarieties, has high potential for increasing yield.Assuming 22 t biomass/ha and a HI of 0.5 dehulled rice to total biomass,equivalent to 0.6 rough rice to total biomass, as the potential level under IRRI’s dryseason conditions, 15 t grain yield/ ha (13 t/ha dry weight basis) can be expected asthe target yield. To reach this goal, at least 6.5 t/ha increase in dry weight may haveto be obtained after heading (assuming 30% of grain weight is due to translocationfrom other plant parts). Then, the key factor would be whether sink size is enough toget 15 t grain/ ha from 15 t dry weight/ha at heading. The spikelet number requiredfor this would be 65 × 10 3 /m 2 , assuming grain weight of 24 mg dry weight and 85%ripening. Current spikelet numbers are always below 50 × 10 3 /m 2 . To get 15 t dryweight/ ha at heading is easy (Fig. 3). But to keep 65 × 10 3 /m 2 spikelets with 12 t dryweight/ha at heading is not possible now, even if the highest spikelet formationefficiency observed in IRRI is considered. This clearly shows how important it is toimprove spikelet formation efficiency in tropical rice for yield improvement.Ripening processSpikelets formed during the reproductive stage may not all fill. Some will not befertilized, others will not develop after being fertilized. Ripening involves two majorprocesses: effective sink size determination (ripening percentage determination) andgrain growth to fill the determined effective sink capacity.When sufficient sink is not formed before heading, ripening rarely limits yield.When environmental factors at ripening are unfavorable, the ripening processseverely limits yield despite higher sink formation.High temperature during ripening is a common factor in tropical ricecultivation. High temperature reduces CGR and shortens the ripening period, sothat ripening often limits yield of long-duration varieties and yield of cultivated wetseason crops. On the other hand, ripening rarely limits yield of a short-durationvariety grown in the dry season at IRRI because high solar radiation in ripeningcompensates for the adverse effect of high temperature.In our monthly planting experiment, ripening percentage was low in wet seasonrice transplanted in May, June, and July, while initial vegetative growth was highdue to higher temperature at the vegetative stage and low solar radiation at ripening.

Table 5. Growth yield and its components of IR64 in 120 kg N/ha in dry weight basis in monthly planting experiment. IRRI, 1985-86 (Parao andAkita, unpublished).0.420.400.390.430.440.4 10.310.320.300.320.320.2793081057075086071580086010201040960875PlantingmonthGrainyield(g/m 2 )Panicle no./ Spikelet no./ Filling(m 2 ) (m 2 x 10 3 ) (%)1,000-Leaf weight/ BiomassHarvestgrainbiomass at at headingindexweight heading (%) (g/m 2 )AugSepOctNovDecJanFebMarAprMayJunJul54845926950649466669852851443826245434229430433445341844544140336926729925.521.821.624.625.932.434.337.629.031.623.822.486.386.955.682.580.879.284.164.275.762.048.483.524.924.322.824.823.526.024.222.123.422.422.724.20.470.450.320.490.450.470.480.390.410.360.240.43

62 S. AkitaHowever, in rice transplanted under short-day conditions in August and September,the ripening percentage was extremely high despite low solar radiation and low dryweight increase at ripening. Yield was also higher (Table 5).Reducing the energy used for excess spikelets would be helpful for high yield inthe wet season. The self-regulation of a spikelet formation system sensitive tophotoperiod appears to be an adaptation for expected inferior ripening conditions.Better ripening of short-duration varieties transplanted in some months in the wetseason cannot be explained by the information available. This indicates that thereare still unknown mechanisms involved in the ripening process.9. Relation between ripening percentage and dry weight increase after heading (a) and between grain yieldand dry weight increase after heading (b) of IR64 (F. Parao and S. Akita, IRRI, unpubl. data).

Improving yield potential 63The high correlations between grain yield and solar radiation (Moomaw et al1969, Munakata et al 1967, Nishiyama 1986) and between grain yield and dry weightincrease during ripening (Wr) (Osada et al 1973, Tanaka et al 1966) that have beenreported suggest that ripening percentage is determined by the photosynthate supplyduring the entire ripening period. But in our monthly planting experiment, ripeningpercentage varied from 50 to 90% in both short-duration varieties used (Fig. 9).Ripening percentages as high as 90% were observed even in months when the solarradiation and Wr were extremely low and the correlation between yield or ripeningpercentage and Wr was not high (Fig. 10).In months when ripening percentage per Wr was higher, grain yield per Wr wasalso higher. This may indicate that once a spikelet is fertilized, it may have highability to attract substances by internal translocation in rice. In addition, the relationbetween dry weight increase and solar radiation during the ripening stage showedhigher hysteresis (Fig. 10) (which was not observed at the reproductive stage).Matsuura et al (1969) also reported an inverse relationship between yield and Wr.We attributed seasonal variation of ripening percentage to the CGR 5 d beforeand after heading (Fig. 11). In the high-nitrogen water culture experiment, ripeningpercentage was also strongly correlated with CGR during heading. Rahman andYoshida (1984) reported little change of ripening percentage even when droughtstress was imposed after complete anthesis. These results indicate that photosyntheticactivity during the short period before and after heading is critical for spikeletdevelopment and for fertilization of each spikelet.10. Relation between average solar radiation and dry weight change (Wr) at ripening of IR64 with 120 kgN/ha (F. Parao and S. Akita, IRRI, 1987).

64 S. Akita11. Relation between crop growth rate per spikelet at 5 d before and after heading and filling percentage(a) and between no. of spikelets per panicle and filling percentage (b) of IR64 (F. Parao and S. Akita,IRRI, unpubl. data).Togari (1957) considered that solar radiation during the 15 d before and afterheading significantly affects ripening. In the tropics, the critical period would bemuch shorter. This may be the reason for the more significant effect of CGR duringthe 5 d before and after heading on ripening in our experiment. Reserved starch inthe culm can be remobilized to substitute for lower current photosynthesis aroundheading, but this may not be directly involved in determining ripening percentage.The correlation between CGRh and ripening percentage is found even in longdurationvarieties having higher carbohydrate reserves in the culm at heading. Anyapproach that produces high CGRh may improve yield by improving ripeningpercentage.

Improving yield potential 65Canopy photosynthesis at heading when LAI is highest is affected morestrongly by canopy structure and by dark respiration than by Pmax. Akita et al(1980) observed a significant advantage of leaf erectness in their deep placementfertilization experiment with Milyang 23, an indica variety bred in Korea. Keepingleaves erect around heading and lowering maintenance respiration would be highlyhelpful in keeping CGRh at a higher level. Ito et al (1987), in a growth cabinetexperiment, reported that lower temperature after complete heading was highlyeffective in increasing ripening. That may be attributed to increased CGR due toreduced respiration at lower temperatures. At present, there is no practical way toreduce dark respiration except to lower the temperature. However, if varietaldifferences in maintenance respiration after heading do exist, screening materials forlow maintenance respiration would be helpful, especially in the tropics.Moriya and Fukada (1974) evaluated varietal differences in ripening abilityusing the ratio of ripening percentage to spikelet number per m 2 . They reportedsignificant differences in ripening ability among varieties cultivated in warmerregions of Japan. The higher ripening ability in their experiment needs to beexamined further.Another factor controlling ripening percentage is the number of ineffective orincomplete spikelets. In our monthly planting experiment, extremely low ripeningpercentage was observed for crops transplanted in June and July. Ripeningpercentage was correlated negatively with spikelet number per panicle (Fig. 11).When extremely low ripening is observed, the number of ineffective spikelets will behigher.Conditions that favor development of higher spikelet number per panicle tendto enhance production of ineffective spikelet, especially at the secondary rachisbranch (Matsushima 1980). The physiological activity of spikelets may be dependenton photosynthate availability during the last phase of vegetative growth. Therefore,CGR even before heading significantly affects ripening percentage.Low effect of deep-placed nitrogen at panicle initiation in high-tillering IRRIvarieties grown in the tropics has been reported (Akita et al 1986). The poor responseto deep-placed nitrogen also may be explained by the higher number of ineffectivespikelets found in the secondary rachis branches. Efforts to increase the number ofpotentially active spikelets would be worthwhile.Once the effective sink size is set, the weight of each grain will be determined bythe grain growth process. Grain growth is defined by grain growth rate and durationof the effective filling period. Usually, grain growth follows an exponential curve. Inthe tropics, grain weight shows little increase during the first 5 d, then increasesalmost linearly to reach its maximum about 25 d after anthesis (Chowdhury andWardlow 1978). Anthesis in a panicle or among panicles usually is completed within5 d, so that at 28 °C, ripening is completed in about 30 d. The period during whichripening is affected negatively and linearly by temperature ranges from about 30 d at28 °C to 65 d at 18 °C (Ministry of Agriculture, Fisheries, and Forestry 1982).High temperature during grain growth causes a higher growth rate and ashorter filling period. But the increased grain growth rate caused by highertemperature often is not enough to compensate for the reduction in filling period, so

66 S. Akitathat grain weight tends to decline (Nagato et al 1966). However, within normaltemperature ranges, the variation in rice grain weight is relatively smaller than it is inother crops (Chowdhury and Wardlow 1978, Evans and Wardlow 1976). Tajima etal (1961) pointed out the advantage for higher yield of a prolonged ripening periodcaused by lower temperature at ripening. That was primarily due to increasedripening percentage and increased grain weight. Reduced grain weight at highertemperatures is, of course, detrimental to yield in tropical rice. It would be helpful toidentify varieties whose grain growth is less affected by high temperature.In the monthly planting experiment, grain weight showed significant seasonalvariation and was correlated negatively with temperature at ripening. Grain weightalso was highly correlated with ripening percentage. This may indicate that spikeletdevelopment before heading limits grain size by determining hull size. Lower grainweight can be attributed to conditions during filling as well as at later reproductivestages. The range of variation was ± 10% average grain weight.The relatively small variation in grain weight of rice in the presence ofsignificant variation in environmental factors during ripening may indicate that onceripening percentage is determined during heading, the developing grain will attain itsgiven capacity irrespective of environmental conditions, so long as they are notextreme. One physiological reason for this would the be higher translocation abilityof rice: its ability to move substances from another organ to grain.Two physiological processes are involved in grain growth: utilization ofphotosynthates through current photosynthesis, and remobilization and translocationof substances accumulated before anthesis. After effective sink size isdetermined, if the supply of current photosynthate during ripening is limited, theeffective sink will trigger accelerated translocation of photosynthates from leaf,sheath, and culm. Cock and Yoshida (1971) reported that about 20% of the graincarbohydrate is from previously stored carbohydrate. In our dry season experiment,we often found that short-duration varieties accumulated minimal carbohydratebefore anthesis. However, in the monthly planting experiment, grain carbohydratederived from previously stored carbohydrate showed marked seasonal variation.Even in early short-duration varieties, a high proportion of grain weight wassupplied by translocation, especially in months when current photosynthate supplyduring ripening was limited. The relatively small reduction in grain weight understress (Kato 1986, Rahman and Yoshida 1984) may support the conclusion thateffective sink has a high ability to attract stored substances when unfavorableenvironmental conditions prevail.If grain growth is an unstable process, significant variation in grain weightshould be observed under different environmental conditions and grain weightshould show continuous distribution between filled and unfilled grains across time.But the grain weight distribution curve for rice at maturity, even under undesirableripening condition, shows clear discontinuity between unfilled and filled grains.Thus, the grain growth process, a highly compensating and stable process, may beless limiting to grain yield than other yield-determining processes.Higher translocation of carbohydrate and nitrogenous compounds from leafand sheath naturally accelerates senescence of leaves and sheath. In months whentranslocation plays a significant role in grain filling, dead leaves increased (Fig. 12).

68 S. Akitawould be apparent when high sink size is kept. However, in our monthly plantingexperiment, when sink size was limited compared to available carbohydrate forgrain filling, higher grain weight was observed in varieties transplanted in August orSeptember, when senescence is highest.The faster leaf senescence of indica varieties than of japonica is well known.One cause of this may be the large effective sink size of recently developed highyieldingindica varieties. When grain yield was high, it was often accompanied byincreased nitrogen uptake after heading (Murata 1969, Tanaka et al 1964).The findings of Matsuura et al (1969) contradict those observations. Usually,root activity at ripening is higher in plots with nitrogen deep-placed at panicleinitiation. High yield with deep-placed nitrogen was obtained in the plot where thelowest Wr was observed. This may indicate that higher root activity during ripeningis not always required for high yield. To conclude that higher nitrogen uptake due toimproved root activity during ripening is contributing to high yield is an openquestion.Faster senescence is sometimes an indication of bigger sink size. However,slower senescence with bigger sink size is desirable. Lai and Hou (1986) suggestedthat poor root activity at ripening is involved in the faster senescence of indicavarieties. Oritani (1987) also suggested that leaf senescence is closely related tohormonal balance.The cause of senescence may not be a single factor. Further analysis of thesenescence mechanism is required. Efforts to reduce senescence of materials withsufficient sink size would be helpful in increasing yield through increased grainweight.Another condition that can contribute to high yield during ripening is staggeredflowering of cultivars with large numbers of spikelets per panicle, as in Akenohoshi,a high-yielding variety from southern Japan (Shinoda et al 1982), or as in the panicleweight-type indica varieties bred in Korea. That would lead to less competition forphotosynthates at heading, and thus is a desirable characteristic for higher ripeningpercentage, although nonuniform ripening may cause lower grain quality.Advantages of short-duration varietiesin tropical rice cultivationThe advantages of short-duration varieties, which have high nitrogen responsiveness,have been intensively incorporated into commercial varieties worldwide (Dalrymple1986, Johnston et al 1972). Consequently, growth duration has been shortened from135 d to 110 d without sacrificing yield (Fig. 1). Recently developed very shortdurationvarieties also show high yield, although slightly lower than short-durationvarieties. In addition, annual productivity of very short-duration varieties is muchhigher than that of short- or medium-duration varieties.Higher sink formation efficiency due to spikelet differentiation at highernitrogen concentrations and to higher NUR at early growth stages is the primaryadvantage of high-yielding, short-duration varieties developed recently at IRRI.Previously, higher NUR was considered the criterion for low nitrogen responsiveness

lmproving yield potential 69(Murata 1969). The opposite is the basis for higher nitrogen responsiveness as far assemidwarf short-duration varieties are concerned (Chang and Vergara 1972).The advantage of higher NUR is limited to short-duration varieties. For longormedium-duration varieties, higher NUR at early stages is hazardous to high yieldunder well-fertilized conditions; it causes overgrowth, even in the semidwarf planttypes. The reduced NUR during earlier stages of recent medium-duration varieties,such as IR29723-143-3-2-1, IR29512, and IR54752 used in our experiment, may becharacteristic of the ability of longer duration varieties to adapt well to highnitrogen. Higher NUR, which tends to cause overgrowth, may not be beneficial forlong-duration varieties but reduced NUR could be desirable for increased and stableyields.Another important advantage for higher ripening ability of short-durationvarieties in the tropics is minimized dark respiration at heading. The limitedvegetative growth of short-duration varieties prevents overgrowth through the fastershift from vegetative to reproductive growth, thereby minimizing excessively highdark respiration around heading.Short-duration high-yielding varieties also do not require the sophisticatedfertilizer management, such as late deep placement (Tanaka et al 1970), splitapplication, and V-shaped application (Matsushima 1980), that have been proposedto avoid overgrowth in medium- and long-duration varieties. Higher yield can beobtained by promoting canopy photosynthesis through dense planting and highnitrogen application and by introducing higher NUR. Besides, a short-durationvariety is beneficial in introducing multiple cropping.When trends in irrigated rice cultivation techniques, such as labor-savingmanagement, increased fertilizer application, direct seeding, etc., are considered,short-duration varieties have many advantages. Serious drawbacks are poor lodgingresistance and inferior grain quality. The higher HI of short-duration cultivars isusually accompanied by lower partitioning of photosynthates to the culm, which inturn lowers lodging resistance. Lodging resistance is often correlated with hightillering ability. Most of the short-duration, high-yielding varieties from IRRIpossess the high tillering ability that establishes an efficient canopy more quickly(Dalrymple 1986). High tillering may be desirable in short-duration varietiesbecause it is associated with higher initial growth, providing rapid canopydevelopment for a more efficient canopy structure (Yoshida 1981).However, high tillering is not always necessary for higher initial growth. Higherinitial growth can be achieved with increased planting density through directseeding. That practice is gaining wide acceptance in tropical rice cultivation.Combining medium tillering with sufficient initial growth and lodging resistance is amore rational approach to stabilizing yield potential. Such is the case with F 1hybrids and some recent Korean panicle weight-type varieties that show higheryields with reduced tiller numbers and bigger panicles (Akita et al 1980, Virmani1986).Inferior grain quality or eating preference quality is a common characteristic ofshort-duration varieties bred at IRRI. This is partly due to the limited time duringwhich short-duration varieties have been developed. The grain quality of short-

70 S. Akitaduration IR varieties already has been improved remarkably, without sacrificingyield. The best quality varieties in Japan, Koshihikari and Sasanishiki, are alsoamong the high yielders. This reinforces the finding that quality can be improvedindependently of yield.However, if higher yield of short-duration varieties that mature under highnitrogen is inevitably related to poor grain quality, the strategies for improving yieldpotential need to be modified. Physiological studies of the relationship betweengrain quality and grain growth under high nitrogen need to be intensified.The ability for high yields in short-duration varieties is expressed only under thelimited conditions of well- fertilized, densely planted, and favorable solar radiation.But the main rice-growing season in the tropics is the wet season. And sufficientfertilizer is not always available. Under those circumstances, suitable varieties andtechniques for producing high yields should be developed on the basis of the findingsreported here.ConclusionThe scope for improving biomass production beyond 22 t/ha at IRRI is limited aslong as the present energy balance between photosynthesis and respiration ismaintained. A better regulation of photosynthesis and respiration would be helpfulin increasing biomass production, but this may not be realized in the near future.Under these circumstances, the way to improve grain yield is to increase the HI.Higher temperatures during vegetative and ripening stages in tropical rice cultivationstrongly limit HI. High temperature during the vegetative stage promotes initialgrowth but reduces sink size due to reduced spikelet formation efficiency. Hightemperature during ripening will cause poor ripening by reducing the CGR.The way to improve these disadvantages in the tropics has been to developvarieties with high sink formation efficiency, such as short-duration dwarf varietiesand those grown in cooler regions. This approach has been successful; the spikeletformation potential of recent high-yielding indica varieties is higher than that ofhigh-yielding japonica varieties. The inverse relationship between temperatureduring the vegetative stage and sink size observed at IRRI and the higher spikeletnumbers and yield of high-yielding indica varieties grown in temperate climatessupport this view.Progress in breeding for higher yields in rice has been associated primarily withimprovement in HI. The HI of short-duration varieties that gave the highest yields atIRRI was a 0.4-0.5 ratio of rough rice weight to total biomass. This is a 0.34-0.42ratio of dehulled grain weight to total biomass. Compared with a proposed HI limitof 0.57, the ratio of dehulled grain weight to total biomass for wheat (Austin 1980),scope still exists for increasing the HI of rice in the tropics.A short-duration variety has many physiological advantages in increasing andstabilizing yields in tropical rice cultivation. In varieties that do not showovergrowth, higher initial growth and faster nitrogen uptake, as are observed in F 1hybrids, could be the target of research for higher yields. In medium- and longdurationvarieties, slower initial growth, which prevents overgrowth, would bepreferable for higher, more stable yields.

Improving yield potential 71The primary characteristic for yield improvement in tropical rice varieties ishigher sink formation efficiency. Further efforts to increase effective sink size byincreasing spikelet formation efficiency would be the primary step to increase HI toclose to 0.60 kernel weight-to-biomass ratio.At present sink size, the ripening process rarely limits yield in dry seasoncultivation at IRRI, where solar radiation is high. However, increasing the sink sizemay require improving ripening. Improved ripening would entail a better plant type,with erect leaves, lower maintenance respiration, and slower senescense afterheading. Efforts to improve sink size and ripening will translate into grain yieldsclose to the target 15 t/ha in IRRI’s dry season (estimated on the basis of a target22 t/ha biomass production and 0.6 HI).References citedAkita S (1980a) Studies on the differences in photosynthesis and photorespiration among crops. I. Thedifferential responses of photosynthesis, photorespiration and dry matter production to oxygenconcentration among species. Bull. Natl. Inst. Agric. Sci. D31:1-58.Akita S (1980b) Studies on the differential responses of photosynthesis and photorespiration amongcrops. II. The differential responses of photosynthesis, photorespiration and dry matter productionto carbon dioxide concentration among species. Bull. Natl. Inst. Agric. Sci. D31:59-94.Akita S, Coronel V, Parao F T (1986) The physiological response of rice to light and nitrogen through latedeep placement fertilization. Pages 81-91 in Weather and rice. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Akita S, Fujimaki H, Tanaka I (1980) Effect of deep placement fertilization on yield and yieldcomponents of some rice varieties [in Japanese]. Proc. Crop Sci. Soc. Jpn. 49 (extra issue) 1:11-12,Austin R B (1982) Crop characteristics and the potential yield of wheat. J. Agric. Sci. Camb. 98:447-453.Austin R B, Bingham J, Blackwell R D, Evans L T, Ford M A, Morgan C L, Taylor M (1980) Geneticimprovements in winter wheat yields since 1900 and associated physiological changes. J. Agric. Sci.Camb. 94:675-689.Blanco LC, Akita S, Virmani S S (1986) Growth and yield of F 1 rice hybrids in different levels of nitrogen.Jpn. J. Crop Sci. 55 (extra issue) 1:12-13.Chang T T, Vergara B S (1972) Ecological and genetic information on adaptability and yielding ability intropical rice varieties. Pages 431-453 in Rice breeding. International Rice Research Institute, P.O.Box 933, Manila, Philippines.Chowdhury S I, Wardlow F I (1978) The effect of temperature on kernel development in cereals. Aust. J.Agric. Res. 29:205-223.Cock J H, Yoshida S (1971) Accumulation of C14 labelled carbohydrate before flowering and itssubsequent redistribution and respiration in the rice plant. Proc. Crop Sci. Soc. Jpn. 41:226-234.Dalrymple D G (1986) Development of high-yielding rice varieties in developing countries. Agency forInternational Development, Washington, D.C.De Datta S K, Zarate P M (1970) Environmental conditions affecting the growth characteristics, nitrogenresponse and grain yield of tropical rice. Biometeorology 4:71-89.Ehleringer J, Bjorkman O (1977) Quantum yields for CO 2 uptake in C 3 and C 4 plants. Plant Physiol.59:86-90.Evans L T, De Datta S K (1979) The relation between irradiance and grain yield of irrigated rice in thetropics, as influenced by cultivar, nitrogen fertilizer application and month of planting. Field CropsRes. 21-17.Evans L T, Wardlow J F (1976) Aspects of the comparative physiology of grain yield in cereals. Adv.Agron. 28:301-359.Hayashi K (1972) Efficiencies of solar energy conversion in rice varieties. Bull. Natl. Inst. Agric. Sci.D23:1-68.Horie T (1981) System ecological studies on crop-weather relationships in photosynthesis, transpirationand growth. Bull. Natl. Inst. Agric. Sci. A28:1-181.Hoshino T, Yagi T, Tezuku T (1983) Genecological studies on yielding ability of rice plant in warmerregions-varietal differences in dry matter production and its components. Jpn. J. Crop Sci. KyushuBranch Rep. 50:20-22.

72 S. AkitaIto N, Tesuka T, Matsubara T (1987) Effect of night and day temperature on ripening of rice [inJapanese]. Jpn. J. Crop Sci. 56 (extra issue):275-296.Johnston T H, Jadon N E, Bollich C N, Rutger J N (1972) The development of early maturing andnitrogen responsive rice varieties in the United States. Pages 61-76 in Rice breeding. InternationalRice Research Institute, P.O. Box 933, Manila, Philippines.Kanda M (1975) Efficiency for solar radiation energy utilization. JIBP Synth. 11:187-198.Katayama K, Akita S (1987) Effect of exogenously applied gibberellic acid on initial growth of ricecultivars. Jpn. J. Crop Sci. 56 (extra issue) 2:173-174.Kato K (1986) Effects of the shading and rachis-branch clipping on the grain-filling process of ricecultivars differing in the grain size. Jpn. J. Crop Sci. 55(2):252-260.Kawano K, Tanaka A (1968) Growth duration in relation to yield and nitrogen response in the rice plant.Jpn. J. Breed. 18:46-51.Kim I H (1978) Green revolution in Korea [translated into Japanese by T. Katayama]. Zenkoku NogyoFukyu Kyokai, Tokyo.Kumura A (1956) Studies on the effect of internal nitrogen concentration of rice plant on theconstitutional factor of yield. Proc. Crop Sci. Soc. Jpn. 24:177-180.Lai K L, Hou C R (1986) Differentiation of physiological characteristics between indica and japonica rice.Jpn. J. Crop Sci. 55:98-102.Matsuura K, Iwata T, Hasegawa T (1969) Studies on the effect of deep layer application of fertilizers inrice plant. I. Proc. Crop Sci. Soc. Jpn. 38:215-221.Matsushima S (1980) Rice cultivation for the million. Japan Scientific Society Press, Tokyo.Ministry of Agriculture (1982) Efficient use of solar energy in plant population of C 3 , C 4 and CAM plantgroups [in Japanese]. Interim report. Agriculture, Forestry and Fisheries Research Council, Tokyo.Moomaw J C, Baldazo P G, Lucas L (1967) Effects of ripening period environment on yields of tropicalrice. Newsletter. 18 p.Moriya K, Fukada K (1974) A view on the growth habits and yielding abilities of short height and tilleringhabit varieties of rice in Kagoshima Prefecture. Bull. Kagoshima Agric. Exp. Stn. 2:1-11.Munataka K, Kawasaki T, Kariya K (1967) Quantitative studies on the effects of the climatic factors onthe productivity of rice. Bull. Chugoku Agric. Exp. Stn. Ser. A14:59-95.Murata Y (1964) On the influence of solar radiation and air temperature on the local differences in theproductivity of paddy rice in Japan. Proc. Crop Sci. Soc. Jpn. 33:59-63.Murata Y (I 969) Physiological responses to nitrogen in plants. Physiological aspects of crop yield. Eastinet al, eds. American Society of Agronomy, Wisconsin.Murata Y, Miyasaka A, Munakata K, Akita S (1968) On the solar energy balance of rice population inrelation to the growth stage. Proc. Crop Sci. Soc. Jpn. 37:685-691.Murata Y, Togari Y (1972) Analysis of the effect of climate factors upon the productivity of rice atdifferent localities in Japan. Proc. Crop Sci. Soc. Jpn. 41:372-387.Murayama N (1967) A discussion on the leveling-off trend of rice yield in Japan and measures to level itup. Jpn. Soc. Plant Physiol. 6:25-32.Nagato K, Ebata M, Kishi Y (1966) Effects of high temperature during ripening period on the qualities ofindica rice. Proc. Crop Sci. Soc. Jpn. 35:239-244.Nishiyama I (1985) Relation between rice yield and photosynthetically active solar radiation during seedripening stage in selected prefectures in Japan. Jpn. J. Crop Sci. 54(1):8-14.Ohno H (1976) Varietal differences of photosynthetic efficiency and dry matter production in indica rice.Tech. Bull. Trop. Agric. Res. Cent. 9:1-72.Oritani T (1987) Effect of nitrogen applied at different growth stage of photosynthesis, hormonal leveland yield of rice cultivars, Nanjing 11 and Myliang 23 [in Japanese]. Jpn. J. Crop Sci. 56 (extra issue)2:73-74.Osada A, Nara M, Chakrabandhu H, Rahong M, Gesprasert M (1973) Seasonal changes in growthpattern of tropical rice. II. Environmental factors affecting yield and its components. Proc. Crop Sci.Soc. Jpn. 42(3):351-361.Parao F T, Akita S (1987) Effect of temperature on the growth and yield of IR cultivars. Jpn. J. Crop Sci.56 (extra issue) 1:6-7.Ponnamperuma F N (1979) Soil problems in the IRRI farm. Paper presented at the IRRI ThursdaySeminar, International Rice Research Institute, Los Baños, Philippines.Rahman M S, Yoshida S (1984) Effect of water stress on grain filling in rice. Soil Sci. Plant. Nutr.31(4):497-551.Shinoda H, Ogawa T, Okamoto M (1982) Chugoku No. 91, the first bred line which has high yieldpotential [in Japanese]. Kinki Chugoku Noken Houkoku 64:3-5.Suge H (1971) Physiology of flowering in rice plants. IV. Proc. Crop Sci. Soc. Jpn. 40:115-119.

Improving yield potential 73Suzuki M (1980) Studies on the physiological characteristics in yield determining process of rice inwarmer region. Bull. Kyushu Agric. Exp. Stn. 20:429-494.Taguchi R, Kawai M, Ikemoto S (1952) After effect of photoperiodism in relation to development andyield of rice plant. III. Proc. Crop Sci. Soc. Jpn. 21:215-216.Tajima K, Funayama K, Ota Y, Nakamura H (1961) Studies on ripening of rice. III. Effect of differentlocations on the ripening. Proc. Crop Sci. Soc. Jpn. 30:93-96.Takita T (1983) Breeding of rice line extraordinarily large grains as a genetic source for high yieldingvarieties. JARQ 17:93-97.Tanaka A, Kawano K, Yamaguchi J (1966) Photosynthesis, respiration and plant type of the tropical riceplant. Effect of various factors on growth and grain yield. Tech. Bull. 7:19-24.Tanaka A, Navasero S A, Garcia C V, Parao F T, Ramirez E (1964) Growth habit of rice plant in thetropics and its effects on nitrogen response. IRRI Tech. Bull. 3:1-80.Tanaka A, Yamaguchi J (1968) Growth efficiency in crops [in Japanese]. Agric. Hortic. 43:907.Tanaka A, Yamaguchi J, Shimazaki Y, Shibata K (1968) Historical changes in plant type of rice varietiesin Hokkaido. J. Sci. Soil Manure Jpn. 39(11):526-534.Tanaka M, Soma T, Shimada T (1970) Studies on deep placement of fertilizer and practical techniques inlowland rice crop [in Japanese]. (1)-(4). Agric. Hortic. 44(7)-45(8).Tanaka T, Matsushima S, Kojyo S, Nitta H (1969) Analysis of yield-determining process and itsapplication to yield prediction and culture improvement of lowland rice. XC. On the relationbetween the plant type of rice plant community and the light-curve of carbon assimilation. Proc.Crop Sci. Soc. Jpn. 38:287-293.Togari Y (1957) Differential effect of solar radiation on growth with growth stage [in Japanese]. Pages71-72 in Food crops. Yokendo, Tokyo.Tsuno Y, Kitakado K (1970) Ecophysiological study on high yielding rice. VII. Considerations in canopyphotosynthesis. Proc. Crop Sci. Soc. Jpn. 39 (extra issue) 1:11-12.Vergara B S, Tanaka A, Lilis R, Puranabhavung S (1966) Relationship between growth duration andgrain yield of rice plants. Soil Sci. Plant Nutr. 12(1):31-39.Wada G, Matsushima S (1962) Analysis of yield-determining process and its application to yieldprediction and culture improvement of lowland rice. LXIII. Proc. Crop Sci. Soc. Jpn. 31:23-26.Wilson (1982) Response to selection for dark respiration rate of mature leaves in Lolium perenne and itseffects on growth of young plants and simulated Swards. Ann. Bot. 49:303-312.Xu H, Pan Q, Qi Y (1984) The Ganhua No. 2 population with a yield potential beyond 1800 jin per muand its control technique. Sci. Agric. Sin. 5:12-17.Yamaguchi J (1978) Respiration and the growth efficiency in relation to crop productivity. J. Fac. Agric.Hokkaido Univ. 59(1):59-129.Yamaguchi M, Yoshida S (1985) Heterosis in net photosynthetic rate, leaf area, tillering and somephysiological characters of 35 F 1 rice hybrids. J. Exp. Bot. 36:274-280.Yoshida S (1973) Effects of temperature on growth of the rice plant ( Oryza sativa L.) in a controlledenvironment. Soil Sci. Plant Nutr. 19(4):299-310.Yoshida S (1981) Fundamentals of rice crop science. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Yoshida S, Cock J H, Parao F T (1972) Physiological aspects of high yields. Pages 459-469 in Ricebreeding. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Yoshida S, Parao F T (1976) Climatic influence on yield and yield components of lowland rice in thetropics. Pages 471-494 in Climate and rice. International Rice Research Institute, P.O. Box 933,Manila, Philippines.NotesAddress: S. Akita, International Rice Research Institute, P.O. Box 933, Manila, Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstracts 75High-yielding rice cultivars in JapanI. NISHIYAMAThe superhigh-yielding rice project was initiated in Japan in 1981. In ourstudies of the physiological characteristics of different varieties, we foundthat 1) Japonica varieties grown in high-yielding trials in northern Japanyielded approximately the same as indica varieties grown in southernJapan; 2) Korean indica-japonica crosses and the newly releasedAkenohoshi variety produced a large number of spikelets withoutexhibiting excessive growth; 3) Withering occurred in rice plantscontaining smaller amounts of carbohydrates in the culms and leafsheaths; 4)Treatment with growth regulators improved Akenohoshi planttype and resulted in higher yields; 5) Analysis of carbohydrate contentindicated that three aspects should be considered in breeding superhighyieldingvarieties—accumulation of carbohydrates at heading, dry matterproduction during ripening, and effective translocation to panicles;6) Studies on root morphology showed that the high-yielding indica andindica-japonica varieties have deeper root systems and a higher ratio ofthe transectional area of the metaxylem to leaf area, indicating higherwater-supplying ability.I. Nishiyama, Tropical Agriculture Research Center, Owashi, Tsukuba, lbaraki 305, Japan.High-yielding rice cultivars in South KoreaS. H. PARK AND S. Y. CHOAnnual rice production in Korea increased to more than 5 million t duringlast 2 decades, providing national self-sufficiency. The yield increase wasachieved while the area planted to irrigated rice remained almostunchanged. The increase is due largely to continuous breeding of new,high-yielding varieties suitable for different regions of the country. Thenew cultivars are associated with such morphological and physiologicalcharacters as erect leaves in the upper canopy, with increasing leaf angletoward the base; reduced plant height, with high nitrogen response andlodging resistance; increased number of spikelets per unit area; highphotosynthetic efficiency; optimum leaf area indexes (7-9 for indica/japonica and 5 for japonica varieties); high harvest index; and optimumgrowth durations for different regions.S. H. Park and S. Y. Cho, Crop Experiment Station, Rural Development Administration, Suweon,Korea.

76 AbstractsHigh-yielding rice cultivars in the U.S.C. N. BOLLICH, J. N. RUTGER, AND D. M. BRANDONRice production in the U.S. is highly mechanized; all rice is direct-seededand irrigated. Yields on a total of 1 million ha average about 6 t/ha.Characteristics that contribute to high yields include lodging resistance,early maturity, and disease resistance. Lodging resistance and associatedN-responsiveness of new cultivars have had the largest effect on yield.Lodging resistance has been achieved by breeding for short stature,through quantitative gene action and through the major semidwarfinggene sd1. The semidwarfs (which have been studied most) produce 15-25% higher yields due to a combination of improved lodging resistanceand production of more panicles/unit area. Additional physiologicalcharacteristics that can raise yield levels further have not yet been definedadequately for rice breeders to put them to work in breeding new cultivars.C. N. Bollich, U.S. Department of Agriculture, Agricultural Research Service, Route 7, Box 999,Beaumont.Tx 77706, USA; J. N. Rutger, U.S. Department of Agriculture, Agricultural ResearchService, Agronomy Department, University of California-Davis, Davis, CA 95616, USA; D. M.Brandon, California Cooperative Rice Research Foundation, Inc.. P.O. Box 306, Biggs, CA95917, USA.High-yielding rice cultivarsin Peninsular MalaysiaE. YUSOFF AND C. Y. TAYCurrent rice yields in Peninsular Malaysia are highly variable, butindications are that this situation will improve with broader adoption ofmodern crop management practices, improvement in infrastructure, andincreased adoption of modern varieties. In the field, leaf area index (LAI)and spikelet number/m 2 limit yield. These limitations are dictated more bythe current subsidized fertilizer rate and currently recommended plantdensity than by limitations in varietal response per se. If yields in excess of5 t/ha are to be achieved, it is imperative that LAI be increased throughincreased plant density/m 2 and higher fertilizer rates. This approachwould be in line with current emphasis on increased mechanization.Current plant type may need to be remodeled to meet operational andmanagement requirements. In this context, serious consideration shouldbe given to plant height reduction and judicious use of short-durationvarieties. Short-duration varieties would be especially useful in controllingdeviations in cropping schedules. Physiological characteristics of varietiesalready released have not been fully tapped.E. Yusoff and C. Y. Tay, MARDl Rice Research Division. Bumbung Lima Station, Kepala Batas,Seberang Perai, Penang, Malaysia.

Abstracts 77High-yielding rice cultivars in ChinaWu GUANGNAN AND TsIu JILINGHigh-yielding rice cultivars in China have 4 basic physiological characteristics:1. Growth pattern-high total biomass accumulation; moreassimilates translocated into grain; 0.50-0.55 harvest index; and mediumgrowth duration (130-150 d). 2. Sources of photosynthates—highoptimum leaf area index (9-10); low extinction coefficient (less than 0.4);small leaf angle inclination (8-12 for flag leaf); semidwarf (culm length90-100cm); high photosynthetic rate (Pn) of a single leaf (high chlorophyllcontent, high Pn under shaded conditions, etc.). 3. Sink capacity—largepanicle extends grain filling for receiving more assimilates; higherspikelet-leaf ratio (number of spikelets/cm 2 leaf area) promotes photosynthesis.4. Nitrogen and mineral nutrition—high N, P 2 O 5 , and K 2 Ocontent in leaves; strong N, P 2 O 5 , and K 2 P absorption ability. High-yieldingcultivars absorb more N and minerals and metabolize them at a higherlevel.Wu Guangnan and Tsiu Jiling, Institute of Agrobiological Genetics and Physiology, JiangsuAcademy of Agricultural Sciences, Nanjing. Jiangsu 210014, China.High-yielding rice varieties in VietnamDAO THE TUANYield increases in high-yielding rice varieties seem to have reached aplateau. Maximum yields in a given year depend more on meteorologicalfactors than on management. A mathematical model of the yield formationprocess shows that both sink and source contribute to yield increases.Improving sink size by selecting for large-panicle varieties increases yield,but not in proportion to sink size because source becomes a limiting factor.Improving source size by selecting for high photosynthetic rate increasesyield response to nitrogen. High-yielding varieties tolerant of acid soils bycrossing high-yielding varieties with tolerance for AI toxicity, Fe toxicity,and P deficiency are needed to extend the area of high-yielding varietiesthat respond to limited inputs.Dao The Tuan, Vietnam Agricultural Science Institute, Hanoi, Vietnam.

Multiple disease and insectresistance for increasedyield stability in riceG. S. KHUSHNumerous diseases and insects can attack rice, and crops are morevulnerable now to attacks because of better management practices andreduced genetic variability. Several epidemic outbreaks of diseases andinsects have occurred in different parts of the rice-growing world duringthe last 20 yr. To combat disease and insect problems, many breedingprograms emphasize the development of varieties with multiple resistance.Sources of resistance have been identified and breeding methodologieshave been refined, and many varieties with multiple resistance arewidely grown. Their greater yield stability has helped stabilize riceproduction at higher levels than ever before.Rice around the world is host to more than 60 diseases and more than 100 insectpests, some of which are of major international importance. The major changes thathave occurred in rice varietal composition and cultural practices during the last 20 yrhave made the crop more vulnerable.Today, high-yielding varieties are planted in approximately 60% of the 146million hectares planted to rice in the world. These varieties are early maturing,photoperiod insensitive, of short stature, high tillering, and have dark green, erectleaves. A relatively small number of improved varieties have replaced literallythousands of traditional cultivars, reducing the genetic variability of the crop.In the wake of the introduction of improved plant type varieties, farmers havestarted using improved cultural practices, such as more fertilizer and higher plantdensity. Development of irrigation facilities and availability of early-maturing,photoperiod-insensitive varieties have enabled farmers in large areas of tropical Asiato grow successive rice crops throughout the year.The reduced genetic variability, improved cultural practices, and continuouscropping intended to increase rice production have increased the geneticvulnerability of the crop. Within the last 15 yr, serious outbreaks of diseases andinsect pests have affected rice crops in several countries. Very little research has beendone on chemical control of rice diseases in the tropics. Chemical control of insectpopulations for prolonged periods in tropical climates where insect generationsoverlap through the year is very expensive. Social and economic conditions presentadditional obstacles to chemical control.

80 G.S. KhushUsing host plant resistance to control diseases and insects is the most logicalapproach to overcoming these production constraints. Rice improvement projectsat the International Rice Research Institute (IRRI) and in national programs havebeen placing major emphasis on developing germplasm with multiple resistance tomajor diseases and insects. Varieties and breeding lines with resistance to as many asfive diseases and five insect species have been developed.Major diseases and insects of riceIn most rice-growing areas, more than one disease or insect cause serious yield losses.In Latin America, blast, hoja blanca, and Sogatodes oryzicola limit rice production.In Africa, blast and stem borers take serious toll of rice yields. In Asia, where 92% ofthe world’s rice is produced and consumed, more than a dozen diseases and insectscause losses of epidemic proportions. Disease and insect problems are most seriousin tropical Asia because the year-round favorable climate and a long history of ricecultivation are conducive to the development of many diseases and pest organisms.One year, there may be an epidemic of bacterial blight; the next year, greenleafhopper (GLH) and tungro may cause serious damage; the third year, anoutbreak of brown planthopper (BPH) and grassy stunt may occur.To minimize yield losses from diseases and insects, varieties with multipleresistance to most of the major diseases and insects are needed. Five diseases (blast,sheath blight, bacterial blight, tungro, and grassy stunt) and five insects (BPH, GLH,whitebacked planthopper (WBPH), stem borer, and gall midge) commonly occur inmost countries of tropical and subtropical Asia. Scientists are focusing breedingprogram attention on developing germplasm with multiple resistance to these majordiseases and insects.Recent pest outbreaksReports of disease and insect outbreaks on rice are numerous. The most well knownis the 1942 brown spot outbreak in Bengal; yield losses there led to the famine of 1943(Padmanabhan 1973). In 1954, a serious outbreak of bacterial blight occurred inEastern India (Bihar State). In recent years, BPH outbreaks of devastating intensityhave been frequent. In Indonesia, outbreaks of BPH occurred in different parts ofthe country almost every year between 1968 and 1977. In 1974-75, as many as283,888 ha of ricefields were hopperburned (Dyck and Thomas 1979). Since 1978, avery high proportion of the rice area in Indonesia has been planted to BPH-resistantvarieties and outbreaks have been minimized. Even so, an outbreak of BPH in NorthSumatra Province in 1981 hopperburned 40,000 ha; in 1987, 50,000 ha of the crop inJava was destroyed.Serious outbreaks of BPH occurred in Kerala State, India, from 1973 to 1976;as much as 50,000 ha of the rice crop was destroyed in 1973. Outbreaks also haveoccurred in Tamil Nadu, Andhra Pradesh, Orissa, and West Bengal (Dyck andThomas 1979). BPH outbreaks were common in the Philippines in the early 1970s.In 1973, thousands of hectares of ricefields were destroyed in Laguna Province; in1976, it happened in Mindanao. Other countries reporting BPH outbreaks are

Multiple disease-insect resistance in rice 81Bangladesh, China, Fiji, Japan, Korea, Malaysia, Nepal, Papua New Guinea,Solomon Islands, Sri Lanka, Thailand, and Vietnam.Tungro outbreaks occur regularly in major rice-growing countries. In a serioustungro outbreak in the Philippines in 1970, 250,000 ha of riceland were completelydestroyed. Outbreaks of somewhat lesser magnitude occurred in different provincesin 1975, 1978, 1981, and 1985. In Indonesia, tungro outbreaks are common in West,East, and Central Java as well as in South Sulawesi. In India, outbreaks haveoccurred in Bihar, West Bengal, and Orissa. The most recent outbreak, in TamilNadu in 1985, completely destroyed more than 50,000 ha. Other countries reportingtungro outbreaks are Bangladesh and Malaysia.Outbreaks of grassy stunt have occurred in the Philippines (1974), Kerala(1974), Sri Lanka (1973), and Indonesia (1973-1976). In the Philippines, grassy stuntcompletely destroyed about 20,000 ha in Laguna Province in 1974.Blast, another serious disease, causes considerable damage in some areas,particularly where cooler temperatures prevail at the flowering stage. The mostrecent blast outbreak was in Korea in 1978; yield losses on the order of 30-40% werereported.Sources of resistanceRice scientists consistently screen rice germplasm collections for resistance to themajor diseases and insects, and have identified sources of resistance to most of them.High levels of resistance to blast (Ou et al 1975), bacterial blight (Ou et al 1971),tungro (Ling 1969), BPH (Heinrichs et al 1985, Pathak 1972), GLH (Cheng andPathak 1972), and WBPH (IRRI 1977) have been found among cultivatedgermplasm. Resistance to grassy stunt was not found among the cultivated varieties,but one accession of Oryza nivara was found highly resistant (Linget al 1970). Highlevels of resistance to stem borer and sheath blight have not been found. Varietieswith moderate levels of resistance to stem borer have been identified (Chaudhary etal 1983, Pathak et al 1971). Several programs have identified sources of resistance togall midge (Heinrichs and Pathak 1981, Khush 1977b).Improving sources of resistanceMany resistance donor parents have the plant type typical of tall traditional varietiesof the tropics. As a first step, genes for resistance are transferred into cultivars ofimproved plant type by crossing donors with improved parents. Several improvedpest-resistant lines with good grain quality are selected from those crosses.BlastResistance breeding programs emphasize the use of diverse resistance sources(breeding lines derived from such parents as H105, Dawn, Carreon, Gam Pai 15,Colombia 1, Sigadis, and Tetep). Crosses involving TKM6 and O. nivara also haveyielded several blast-resistant lines. Normally, improved progeny lines are tested atleast 2 or 3 times/yr for several years to expose them to numerous prevalent blastraces. Only lines that show resistance for several years are selected and used in the

82 G.S. Khushcrossing program. Many highly resistant breeding lines were selected from crossesthat include Tetep and Gam Pai 15.In recent years, strategies in breeding for blast resistance have been modified.Breeding lines with partial disease resistance and slower disease development arepreferred because the resistance is more durable. Several upland rice varieties such asMoroberekan, and even lowland varieties such as IR36, have excellent levels ofpartial resistance. This type of resistance is being incorporated into new lines.Bacterial blightResistance breeding programs have produced several successful varieties andbreeding lines that are now widely grown in Asia and that have served as parents innumerous crosses at IRRI and in national programs. Bacterial blight-resistant IR20and IR22 were released in 1969; IR26 in 1973; IR28, IR29, and IR30 in 1974; andIR32 and IR34 in 1975. The Philippine Government has released several otherresistant breeding lines (IR36, IR38, IR40, IR42, IR44, IR46, IR48, IR50, IR52,IR54, IR58, IR60, IR62, and IR64). These IR lines are widely grown in manycountries. The varieties all have the single dominant resistance gene Xa-4.Although bacterial blight races compatible with Xa-4 have evolved in thePhilippines and Indonesia, no serious epidemics of bacterial blight have occurred onthese varieties so far. Other genes with broader spectrum resistance to bacterialblight, such as xa-5 and Xa-7, are being incorporated into the newer breeding lines.TungroPeta, Intan, Sigadis, TKM6, HR21, Malagkit Sungsong, Gam Pai 15, PTB18,Pankhari 203, BJI, Utri Merah, and Utri Rajapan were used as donor parents tobreed improved lines with tungro resistance. Seven IR varieties are moderately tohighly resistant to tungro. IR20, IR26, and IR30 inherit their moderate resistancefrom TKM6. Gam Pai 15 is the donor parent of highly resistant IR28, IR29, IR34,IR50, IR52, IR54, IR56, and IR60. In our hybridization program, IR36, IR38,IR40, IR42, and IR48 inherit those resistance sources.Strong resistance to tungro vectors also protects the crop from the ravages ofthat disease. Many vector-resistant breeding lines screened by artificial inoculationtechniques show high tungro susceptibility, but escape disease infection in the field.Grassy stuntThe only known source of resistance to grassy stunt virus is O. nivara, a wild plantwith weak stems, spreading growth habit, shattering panicles, long awns, redpericarp, and low yield potential. In 1979, O. nivara was crossed with IR8, IR20, andIR24. The F 1 plants from those crosses were backcrossed four times, using IR8,IR20, and IR24 as recurrent parents. In each successive backcross, F 1 plants thatmorphologically resembled the recurrent parents were selected. By late 1970, grassystunt-resistant lines were obtained that resembled IR8, IR20, and IR24. But becausethose lines lacked other desirable traits, such as BPH and tungro resistance, theywere used as parents in numerous other crosses.

Multiple disease-insect resistance in rice 83On the basis of rigorous field screening, numerous grassy stunt-resistant lineshave been selected that are resistant to several other pests and that have desirableagronomic traits and grain quality. The first grassy stunt-resistant varieties—IR28,IR29, and IR30—were released in 1974; IR32 and IR34 were released in 1975. ThePhilippine Government released grassy stunt-resistant IR36 and IR38 in 1976; IR40and IR42 in 1977 (Khush et al 1977); IR48 in 1978; IR50, IR52, and IR54 in 1980;IR56 in 1982; and IR58 and IR60 in 1984.In 1982, a new strain, grassy stunt 2, appeared in the Philippines (Hibino et al1985). All the improved varieties, including those with genes from O. nivara, aresusceptible. Several thousand accessions from the germplasm bank at IRRI havebeen screened but no good source of resistance to this strain has been found.Brown planthopperIR26 (released in 1973) was the first BPH-resistant variety. It has Bph-1 forresistance. However, its resistance broke down in 1976 with the development of anew BPH biotype. Varieties with bph-2 —1R32, IR36, IR42, IR58, IR50, IR52, andIR54—released then have been widely cultivated for the last 10 yr.In 1981, a biotype capable of attacking varieties with the bph-2 gene wasdetected in isolated areas in North Sumatra (Indonesia) and Mindanao(Philippines). Although that new biotype has not spread to other areas, new varietiesIR56, IR60, IR62, and Kelara with Bph-3 gene for resistance have been released inthe Philippines and Indonesia.IR46 and IR64 have partial resistance to all known BPH biotypes. Improvedbreeding lines with bph-4 also have been developed. Recently, resistance to allknown biotypes of BPH has been transferred from O. officinalis to O. sativa.Green leafhopperPeta, FB24, Tjeremas, and Sigadis were used as parents in early crosses at IRRI.Later lines from those crosses were found resistant to GLH (Cheng and Pathak1972). Many progeny of those crosses, including IR5, IR8, IR20, and IR24,inherited that GLH resistance. Those varieties and many breeding lines with GLHresistance have been used as resistance sources in crossing programs.Most IRRI crosses made after 1969 had at least one parent with GLHresistance. Progeny from those crosses were rigorously screened, and only thoseshowing resistance were saved. All IR varieties except IR22 and all the IR linesnamed by the Philippine Government are GLH-resistant. Of the seven known genesfor GLH resistance, four have been incorporated into improved varieties. We havealso backcrossed some GLH-resistance genes from O. glaberrima to O. sativa.Whitebacked planthopperSeveral improved breeding lines with resistance to the whitebacked planthopper(WBPH) have been developed using N22 and IR2035-117 as sources of resistance.Resistance also has been incorporated into breeding lines with multiple resistance.Five known genes for resistance to WBPH have been transferred to an isogenic

84 G.S. Khushbackground by backcrossing to IR36 four times. However, the insect occurs onlysporadically. None of the improved varieties being planted currently are resistant.Gall midgeGall midge is a major pest in some endemic areas in most South and Southeast Asianrice-growing countries. India, Thailand, and Sri Lanka have strong breedingprograms for resistance to all midges. IRRI has developed some improvedgermplasm using PTB18 and CR94-13 as resistance sources. The segregatingpopulations were screened in India. IR32, IR36, IR38, IR40, and IR42 are resistantto gall midge at several locations in India. Resistant varieties Kakatiya, Shakti,Vikram, Phalguna, and Surekha in India and BG400-1 and BG2767-5 in Sri Lanka(Khush 1984) are widely grown.Stem borersTKM6 has been widely used as a source of resistance to striped borer. Manybreeding lines and IR20, IR26, IR30, IR32, IR36, IR38, and IR42 inherit theirmoderate resistance to striped stem borer from TKM6. Sources of yellow borerresistance include breeding lines IR1820-52-2, IR1917-3-19, and IR1539-823-1-4,and varieties W1263, MNP119, and PTB18. IR36 has good resistance to yellowborer and striped borer.Developing germplasm with multiple resistanceResistance to only one or two rice diseases and insects is not enough. Modern ricevarieties must have multiple resistance to most of the pests prevalent in the areaswhere they are to be grown. Improved germplasm with multiple resistance to asmany as four diseases and four insects has been developed (Table 1). To combineresistances, improved lines with resistance to one or two pests were intercrossed,with numerous topcrosses and double crosses. The segregating populations wereextensively screened to identify multiple-resistance lines.In 1969, about 85% of the entries in IRRI replicated yield trials were eithersusceptible to 6 diseases and insects (blast, bacterial blight, tungro, grassy stunt,BPH, GLH) or resistant to only 1. Only 2% were resistant to 3 diseases and 3 insects.The proportion of entries with multiple resistance has been gradually increased, andin the 1974 replicated yield trials, 90% of the entries were resistant to 5 or 6 diseasesand insects (Khush 1977a).This proportion of multiple-resistance entries has been maintained in thereplicated yield trials. Many multiple-resistance IR varieties (IR28, IR36, IR42,IR46, IR50, IR54, IR62, and IR64) are widely grown. About 85% of the rice area inthe Philippines is now planted to multiple-resistance varieties. Large areas areplanted in Indonesia and Vietnam. Many other multiple-resistance lines have beenreleased as varieties by national programs. Several multiple-resistance lines serve asrestorer parents in hybrid rice breeding programs in China and elsewhere.

Multiple disease-insect resistance in rice 85Table 1. Disease and insect resistance of varieties named by IRRl (IR5 to IR34) and of IRRllines named as varieties by the Philippine Government (IR36-IR65).IR varietyReaction aBlast Bacterial Grassy Tungro GLH BPH biotype Stem Gallblight stunt 1 2 3 borer midgeIR5 MR S S S R S S S MS SIR8 S S S S R S S S S SIR20 MR R S MR R S S S S SIR22 S R S S S S S S S SIR24 S S S S R S S S S SIR26 MR R MR MR R R S R MR SIR28 R R R R R R S R MR SIR29 R R R R R R S R MR SIR30 MS R R MR R R S R MR SIR32 MR R R MR R R R S MR RIR34 R R R R R R S R MR SIR36 R R R R R R R S MR RIR38 R R R R R R R S MR RIR40 R R R R R R R S MR RIR42 R R R R R R R S MR RIR44 R R S R R R S MR SIR46 R R S MR MR R S R MR SIR48 R R R R R R R S MR –IR50 MS R R R R R R S MR –IR52 MR R R R R R R S MR –IR54 MR R R R R R R S MR –IR56 R R R R R R R R MR –IR58 R R R R R R R S MR –IR60 R R R R R R R R MR –IR62 MR R R R R R R R MS –lR64 MR R R R R R MR R MR –IR65 R R R R R R R SIR66 MR R R R R R R RMSMR––a s = susceptible, MS = moderately susceptible, MR = moderately resistant, R = resistant. Reactionswere based on tests conducted in the Philippines for all diseases and insects except gallmidge conducted in India.Breeding methodsThe pedigree method of breeding is usually used to develop germplasm with multipleresistance. Selection is based on comprehensive records of each line’s pest reactions;for F 4 and later-generation lines, selection also is based on the reaction of ancestrallines. The bulk method of breeding does not permit concurrent screening for anumber of pests. The backcross method does not permit the development ofgermplasm with diverse genetic backgrounds.Backcrossing is used to transfer genes for resistance from primitive or wildgermplasm, as was the case with O. nivara for grassy stunt resistance. Fourbackcrosses were made with IR24 to transfer the Gs gene for resistance to a desirableagronomic plant type. These lines were used as donors for resistance in a pedigreebreeding program to develop multiple-resistance lines (Khush et al 1977).

86 G.S. KhushWhen resistance is governed by major genes, the pedigree method of breeding iseminently suited to disease and insect resistance programs. (Most resistance traits inrice are under the control of major genes.) But pedigree breeding is not suitable fortraits governed by polygenes. Resistance to rice stem borers and sheath blightappears to be under polygenic control. For those traits, the male sterile-facilitatedrecurrent selection method (Chaudhary et al 1981) is being used.The possibility of using the single seed descent method to improve the traitsgoverned by polygenic variation also needs to be explored. Early generationpopulations from multiple crosses involving three or four parents with minorresistance genes may be propagated in bulk. Three or four generations can be easilygrown in one year. Selection should not be practiced during that year. At the F 5 or F 6stage, the bulk population may be exposed to targeted pest pressure to identifyindividual plants with better resistance levels. Those can be grown in progeny rowsfor further evaluation.Breeding strategiesThe breeding strategies being followed involve incorporating diverse major genes forresistance into progeny with improved plant type, then combining those progenywith major resistance genes for other pests. If cultivars with a particular gene becomesusceptible because new biotypes develop, varieties with a second gene should beavailable. This sequential-release strategy has been used for BPH resistance.Five BPH-resistant varieties with the Bph-1 gene (IR26, IR28, IR29, IR30, andIR34) were released in 1973-74. In 1976, those varieties became susceptible at somePhilippine locations. But by that time, multiple-pest-resistance varieties IR36, IR38,IR42, IR50, and IR54 with the bph-2 gene for BPH resistance had become available.They were released as replacements for varieties with Bph-1 for resistance and arenow widely grown in countries where the new biotype of BPH originated (thePhilippines, Indonesia, and Vietnam). In 1982, other biotypes of BPH were detectedin isolated areas of North Sumatra in Indonesia and the Mindanao area in thePhilippines. IR56, IR60, and IR62 with the Bph-3 gene for resistance to the newbiotype were released.Another strategy is to pyramid two or more major genes for BPH resistance.Bph-1 and Bph-2 are closely linked but cannot be combined; so are Bph-3 and bph-4.The genes Bph-1 and Bph-3, and Bph-1 and bph-4, bph-2 and Bph-3, and bph-2 andbph-4 segregate independently of each other and can be combined. We predict thatvarieties with two resistance genes will have a longer useful life (Khush 1979).Another approach for disease or insect control is to develop multiline varieties.They have been used in the U.S. to control crown rust of oats (Frey et al 1973).Multiline varieties are a mixture of 8-10 isogenic lines, each having a distinct gene fordisease or insect resistance. The availability of 8-10 genes for resistance is aprerequisite to the adoption of this strategy.For traits that are under polygenic control, such as stem borer resistance, malesterile-facilitated recurrent selection is more suitable. Several parents with low levelsof resistance are crossed with a recessive male sterile line. The F 2 seeds from thesecrosses are mixed to establish an intermating bulk population. Seeds set on sterile

Multiple disease-insect resistance in rice 87plants resulting from outcrossing are harvested to plant the next generation bulkpopulation. The bulk populations are exposed to the target disease or insect pressureduring the intermating cycles. Selection for resistance leads to the accumulation ofminor genes for resistance and genotypes with higher level of resistance are selected(Chaudhary et al 1981).inheritance of resistanceInformation on the genetics of resistance is useful in determining the breedingmethod to be used, the size of the segregating populations to be grown, and thebreeding strategy to be adopted. Only scanty information was available on thegenetics of pest resistance when IRRI’s resistance breeding program was initiated.Since then, a fairly large amount of knowledge on the genetics of resistance has beenaccumulated.Blast. Most of the work on the genetics of blast resistance has been conducted inJapan (Kiyosawa 1972, 1974). Ten loci of major genes for resistance have beenidentified. Some are characterized by a multiple allelic series. Some of the loci havebeen assigned to their respective linkage groups by linkage analysis (Toriyama 1972).In independent studies, Atkins and Johnston (1965) identified two genes whichthey designated Pi1 and Pi6. Hsieh et al (1967) identified three dominant genes forresistance in japonica strains, designated Pi4, Pi22, and Pi25. Investigations are nowunder way at IRRI to identify major resistance genes for tropical blast races.Bacterial blight. The inheritance of resistance to Japanese isolates of thebacterial blight organism was investigated by Sakaguchi (1967) and Ezuka et al(1970, 1975). Three resistance genes were identified: Xa-1, Xa-2, and Xa-3. SeveralIRRI studies on the inheritance of resistance to Philippine isolates of the bacteriumled to the identification of several new genes for resistance (Librojo et al 1976,Olufowote et al 1977, Petpisit et al 1977, Sidhu et al 1978, Sidhu and Khush 1978a,Singh et al 1983). Those new genes have been designated Xa-4, xa-5, Xa-6, Xa-7,xa-8, and xa-9, Xa-1 and Xa-2 are linked, with a crossover value of 3%. Xa-4 andXa-3 are very closely linked. Recent investigations (Ogawa et al 1986a,b) haveshown that Xa-3, Xa-6, and xa-9 are allelic to each other. Two new genes, Xa-10 andXa-11, were recently identified. Xa-10 conveys resistance to Philippine race 2(Yoshimura et al 1983) and Xa-11 conveys resistance to Japanese races (Ogawa andYamamoto 1986).Grassy stunt. A single dominant gene Gs conveys grassy stunt resistance in O.nivara (Khush and Ling 1974). Gs segregates independently of Bph-1, the dominantgene for resistance to BPH (the vector of grassy stunt).Brown planthopper (BPH). Two genes for BPH resistance identified by Athwalet al (1971) are designated Bph-1 and bph-2. These two genes are closely linked, norecombination between them has been observed. Lakshminarayana and Khush(1977) identified Bph-3 and bph-4, which also are closely linked (Sidhu and Khush1978b). TKM6 from India is susceptible to BPH, but when crossed with othersusceptible varieties, yields some resistant progeny in the segregating populations.Martinez and Khush (1974) showed that TKM6 is homozygous for Bph-1 as well asinhibitory gene I-Bph-1, which inhibits Rph-1. Khush et al (1986) identified a new

88 G.S. Khushrecessive gene, designated bph-5, which conveys resistance to the Bangladeshpopulation of BPH. Kabir and Khush (1988) have identified Bph-6 and bph-7,which also convey resistance to the Bangladesh population of BPH.Green leafhopper (GLH). Inheritance of GLH resistance was investigated byAthwal et al (1971). Three dominant genes that segregate independently of eachother were identified and designated Glh-1, Glh-2, and Glh-3. Two more genes wereidentified by Siwi and Khush (1977). One is recessive and is designated glh-4; theother is dominant and is designated Glh-5. Two more dominant genes designatedGlh-6 and Glh-7 were recently reported by Rezaul Karim and Pathak (1979). IR28was found to possess another dominant gene which is nonallelic to and independentof Glh-1, Glh-2, Glh-3, glh-4, and Glh-5. However, its allelic relationships with Glh-6and Glh-7 have not been determined (Avesi and Khush 1984).Whitebacked planthopper (WBPH). A single dominant gene for WBPHresistance identified by Sidhu et al (1979) was designated Wbph-1. This gene hasbeen incorporated into progeny with improved plant type. Angeles et al (1981)identified another dominant gene for WBPH resistance, designated Wbph-2. Somevarieties appear to have an additional recessive gene for resistance. Two new genesfor resistance recently identified by Hernandez and Khush (1981) were designatedWbph-3 and wbph-4. Wu and Khush (1985) identified another dominant gene forresistance in N’Diang Marie, designated Wbph-5.Gall midge. Gall midge resistance is also under major gene control. Satyanarayanaiahand Reddi (1972) showed that one dominant gene in the variety W1263governs resistance to gall midge. Sastry and Prakasa Rao (1973) postulated theexistence of three recessive genes for resistance. Two independent dominant genesdesignated Gm-1 and Gm-2 were identified by Chaudhary et al (1986).Variation in disease and insect organismsExistence of races or strains of disease organisms and insect biotypes complicatesresistance breeding. Race and biotype differences have been detected for most of theimportant rice pests. Race variability of the blast fungus has been well recognized.Many races of the fungus often are present in a country, and the races differ fromcountry to country (Ou 1972).Strains of bacterial blight also differ from country to country, and often withincountries. Five distinct strains are known to occur in Japan (Horino et al 1981); sixoccur in the Philippines (Mew and Vera Cruz 1979). Because of differences instrains, varieties resistant in one country are often susceptible in another. Thus,varieties with Xa-4 are resistant to race 1 of bacterial blight in the Philippines but aresusceptible in Indonesia.Extensive studies on variations in the tungro virus organism have beenconducted. Some varieties, such as Gam Pai 15, which are highly resistant inIndonesia and the Philippines, are susceptible in India. That suggests straindifferences from country to country. Within India, variation in tungro strainpathogenicity has been noted (Anjaneyulu and John 1972).Occurrence of grassy stunt has been recorded in Indonesia, Philippines,Vietnam, Thailand, India, and Sri Lanka. Varieties and breeding lines having the Gs

Multiple disease-insect resistance in rice 89gene for resistance from O. nivara are resistant to the original strain in all thosecountries. However, a new strain designated grassy stunt 2 has been identified in thePhilippines; O. nivara is susceptible to this strain.Two BPH biotypes were present, one in East and Southeast Asia and the otherin South Asia, before BPH-resistant varieties were introduced and widely grown. Anew biotype appeared in the Philippines, Indonesia, and Vietnam in 1976, afterlarge-scale cultivation of IR26 which has Bph-1 gene for resistance. That newbiotype was designated biotype 2 to distinguish it from the original East andSoutheast Asian biotype 1 (Khush 1977b). Another BPH biotype (biotype 3) isknown only in the laboratory. Additional biotypes of BPH have appeared inisolated pockets in North Sumatra (Indonesia) and Mindanao (Philippines).Biotype variation in GLH has been suspected for some time (Khush 1977b).Rezaul Karim (1978) showed that varieties with Glh-1, Glh-2, Glh-3, and Glh-5genes, which convey resistance to Philippine GLH biotypes, are susceptible inBangladesh. That clearly demonstrates the existence of distinct biotypes of GLH.The occurrence of gall midge biotypes also has been known for some time. Atleast two are known in India. Biotypes in Thailand, India, and Sri Lanka differ, as isshown by differential reactions of resistant varieties in those countries (Heinrichsand Pathak 1981).Multiple resistance and yield stabilityThe importance of multiple resistance for yield stability can hardly be overemphasized.Multiple-resistance and susceptible varieties have been evaluated inreplicated yield trials at IRRI for the last 12 yr. As Figure 1 shows, the yield of1. Yields of IR8, IR36, and IR42. Yields of multiple-resistance IR36 and IR42 show little year-to-yearvariation; yield of susceptible IR8 fluctuates widely. Dry season replicated yield trials at IRRI.

90 G.S. Khushsusceptible IR8 fluctuates from year to year, depending on disease or insectincidence. If there is a disease or insect attack, yield is drastically reduced. However,if disease or insect incidence is low, yield is high. The multiple-resistance varieties,such as IR36 and IR42, show only minor yield fluctuations from year to year, andthus have greater stability.References citedAngeles E R, Khush G S, Heinrichs E A (1981) New genes for resistance to whitebacked planthopper inrice. Crop Sci. 21:47-50.Anjaneyulu A, John V T (1972) Strains of rice tungro virus. Phytopathology 62:1116-1119.Athwal D S, Pathak M D, Bacalangco E H, Pura C D (1971) Genetics of resistance to brown planthopperand green leafhopper in Oryza sativa L. Crop Sci. 11:747-750.Atkins J G, Johnston T H (1965) Inheritance in rice of reaction to races 1 and 6 of Pyricularia oryzae.Phytopathology 5:993-995.Avesi G M, Khush G S (1984) Genetic analysis for resistance to the green leafhopper, Nephotettixvirescens (Distant), in some cultivars of rice, Oryza sativa L. Crop Prot. 3:41-51.Chaudhary R C, Heinrichs E A, Khush G S (1981) Increasing the level of yellow stem borer resistancethrough male sterile facilitated recurrent selection in rice. Int. Rice Res. Newsl. 6(5):7-8.Chaudhary R C, Khush G S, Heinrichs E A (1983) Varietal resistance to rice stemborers in Asia. InsectSci. Appl. 5:447-463.Chaudhary B P, Srivastava P S, Shrivastava M N, Khush G S (1986) Inheritance of resistance to gallmidge in some cultivars of rice. Pages 523-528 in Rice genetics. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Cheng C H, Pathak M D (1972) Resistance to Nephotettix virescens in rice varieties. J. Econ. Entomol.65:1148-1153.Dyck V A, Thomas B (1979) The brown planthopper problem. Pages 3-17 in Brown planthopper: threatto rice production in Asia. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Ezuka A, Horino O, Toriyama K, Shimoda H, Morinaka T (1975) Inheritance of resistance of rice varietyWase Aikoku 3 to Xanthomonas oryzae. Tokai Kinki Nogyo Shinkenko Kenkyo Hokoku28:128-130.Ezuka A, Watanabe Y, Horino O (1970) Varietal resistance of rice to bacterial leaf blight. 2. Resistance inWase Aikoku 3 group. Nippon Shokubutso Byori Gakkaiko 36:174-175.Frey K J, Browing J A, Simmons M D (1973) Management of host resistance genes to control diseases. Z.Pflanzenkr. 80:160-180.Heinrichs E A, Medrano F G, Rapusas H R (1985) Genetic evaluation for insect resistance in rice.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Heinrichs E A, Pathak P K (1981) Resistance to the rice gall midge, Orseolia oryzae in rice. Insect Sci.Appl. 1:123-132.Hernandez J E, Khush G S (1981) Genetics of resistance to whitebacked planthopper in some rice ( Oryzasativa L.) varieties. Oryza 1844-50.Hibino H, Cabauatan P, Omura T, Tsuchizaki (1985) Rice grassy stunt virus strain causing tungro likesymptoms in the Philippines, Plant Dis. 69:538-541.Horino 0, Mew T W, Khush G S, Ezuka A (1981) Comparison of two differential systems fordistinguishing pathogenic groups of Xanthomonas campestris pv. oryzae. Ann. Phytopathol. Soc.Jpn. 17:1-14.Hsieh S C, Lim M H, Liang H L (1967) Genetic analysis in rice. VIII. Inheritance of resistance to races 4,22, and 25 of Pyricularia oryzae. Bot. Bull. Acad. Sin. 8:255-260.IRRI—International Rice Research Institute (1977) Annual report for 1976. P.O. Box 933, ManilaPhilippines. 584 p.Kabir M A, Khush G S (1988) Genetic analysis of resistance to brown planthopper in rice, Oryza sativa L.Plant Breed. 100:54-58.Khush G S (1977a) Breeding for resistance in rice. Ann. New York Acad. Sci. 287:296-308.Khush G S (1977b) Disease and insect resistance in rice. Adv. Agron. 29:265-341.Khush G S (1979) Genetics of and breeding for resistance to brown planthopper. Pages 321-332 in Brownplanthopper: a major threat to rice in Asia. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Khush G S (1984) Breeding for resistance to insects. Prot. Ecol. 7:147-165.

Multiple disease-insect resistance in rice 91Khush G S, Ling K C (1974) Inheritance of resistance to grassy stunt virus and its vector in rice. J. Hered.65:134-136.Khush G S, Ling K C, Aquino R C, Aguiero V M (1977) Breeding for resistance to grassy stunt in rice.Paper presented at the 3d Congress, Society for the Advancement of Breeding Researches in Asiaand Oceania Working Group on Plant Genetic Resources, 12-13 Feb 1977, Canberra, Australia.Khush G S, Rezaul Karim A N M, Angeles E R (1986) Genetics of resistance of rice cultivar ARC 10550to Bangladesh brown planthopper biotype. J. Genet. 64:121-125.Kiyosawa S (1972) Genetics of blast resistance. Pages 203-206 in Rice breeding. International RiceResearch Institute, P.O. Box 933, Manila, Philippines.Kiyosawa S (1974) Studies on genetics and breeding for blast resistance in rice. Natl. Inst. Agric. Sci. Jpn.Ser. D. Misc. Publ. 1. 58 p.Lakshminarayana A, Khush G S (1977) New genes for resistance to the brown planthopper in rice. CropSci. 17:96-100.Librojo V, Kauffman H E, Khush G S (1976) Genetic analysis of bacterial blight resistance in fourvarieties of rice. SABRAO J. 8:105-110.Ling K C ( 1969) Testing rice varieties for resistance to tungro disease. Pages 277-291 in The virus diseasesof the rice plant. The Johns Hopkins Press, Baltimore, Maryland, USA.Ling K C, Aguiero V M, Lee S H (1970) A mass screening method for testing resistance to grassy stuntdisease of rice. Plant Dis. Rep. 56:565-569.Martinez C R, Khush G S (1974) Sources and inheritance of resistance to brown planthopper in somebreeding lines of rice, Oryza sativa L. Crop Sci. 14:264-267.Mew T M, Vera Cruz C M (1979) Variability of Xanthomonas oryzae. Specificity in infection of ricedifferentials. Phytopathology 69:152-155.Ogawa T, Yamamoto T (1986) Inheritance of resistance to bacterial blight in rice. Pages 471-480 in Ricegenetics. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Ogawa T, Yamamoto T, Khush G S, Mew T W (1986a) The relationship between genes Xa-3 and Xa-6for resistance to rice bacterial blight. Rice Genet. Newsl. 3:79-80.Ogawa T, Yamamoto T, Khush G S, Mew T W (1986b) Inheritance of resistance to bacterial blight inSateng - a reinvestigation. Rice Genet. Newsl. 30:80-82.Ou S H (1972) Rice diseases. Commonwealth Mycological Institute, Kew, Surrey, England. 368 p.Ou S H, Ling K C, Kauffman H E, Khush G S (1975) Diseases of upland rice and their control throughvarietal resistance. Pages 126-135 in Major research in upland rice. International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Ou S H, Nuque F L, Silva J P (1971) Varietal resistance to bacterial blight of rice. Plant Dis. Rep.55:17-21.Olufowote J O, Khush G S, Kauffman H E (1977) Inheritance of bacterial blight resistance in rice.Phytopathology 67:772-775.Padmanabhan S Y (1973) The great Bengal famine. Annu. Rev. Phytopathol. 11:11-26.Pathak M D (1972) Resistance to insect pests in rice varieties. Pages 325-341 in Rice breeding.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Pathak M D, Andres F, Galacgac N, Raros R (1971) Resistance of rice varieties to striped borers. IRRITech. Bull. 11. P.O. Box 933, Manila, Philippines. 69 p.Petpisit V, Khush G S, Kauffman H E (1977) Inheritance of resistance to bacterial blight in rice. Crop Sci.17:551-554.Rezaul Karim A N M (1978) Varietal resistance of rice to green leafhopper, Nephotettix virescens(Distant): sources, mechanism, and genetics of resistance. Ph D thesis, University of the Philippinesat Los Baños, Philippines. 162 p.Rezaul Karim A N M, Pathak M D (1979) New genes for resistance to green leafhopper, Nephotettixvirescens (Distant) in rice, Oryza sativa L. Crop Prot. 1:483-490.Sakaguchi S (1967) Linkage studies on the resistance to bacterial leaf blight Xanthomnonas oryzae (Uyedaet Ishiyama) Dowson in rice. Bull. Natl. Agric. Sci. Jpn. Ser. C. 16:1-18.Sakaguchi S, Suva T, Murata N (1968) Studies on the resistance to bacterial leaf blight Xanthomonasoryzae (Uyeda et Ishiyama) Dowson, in the cultivated and wild rice. Bull. Natl. Agric. Sci. Tokyo,Jpn. Ser. D. 18:1-29.Sastry M V S, Prakasa Rao P S (1973) Inheritance of resistance to rice gall midge Pachydiplosis oryzae(Wood-Mason). Curr. Sci. 42:652-653.Satyanarayanaiah K, Reddi M V (1972) Inheritance of resistance to insect gall midge Pachydiplosisoryzae (Wood-Mason) in rice. Andhra Agric. J. 19(1&2):1-8.Sidhu G S, Khush G S (1978a) Dominance reversal of a bacterial blight resistance gene in some ricevarieties. Phytopathology 68:461-463.

92 G.S. KhushSidhu G S, Khush G S (1978b) Genetic analysis of brown planthopper resistance in twenty varieties ofrice, Oryza sativa L. Theor. Appl. Genet. 53:199-203.Sidhu G S, Khush G S, Medrano F G (1979) A dominant gene in rice for resistance to whitebackedplanthopper and its relationship to other plant characters. Euphytica 28:227-232.Sidhu G S, Khush G S, Mew T W (1978) Genetic analysis of bacterial blight resistance in seventy-fourvarieties of rice, Oryza sativa L. Theor. Appl. Genet. 53:105-111.Singh R J, Khush G S, Mew T W (1983) A new gene for resistance to bacterial blight. Crop Sci.23:558-560.Siwi B H, Khush G S (1977) New genes for resistance to green leafhopper in rice. Crop Sci. 17:17-20.Toriyama K (1972) Breeding for resistance to major rice diseases in Japan. Pages 253-281 in Ricebreeding. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Wu C F, Khush G S (1985) A new dominant gene for resistance to whitebacked planthopper in rice. CropSci. 25:505-509.Yoshimura A, Mew T W, Khush G S, Omura T (1983) Inheritance of resistance to bacterial blight in ricecultivar CAS 209. Phytopathology 73:1409-1412.NotesAddress: G. S. Khush, Plant Breeding Department, International Rice Research Institute, P.O. Box 933, Manila,Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Durable resistance to rice diseasesin irrigated environmentsE. J. LEE, QI ZHANG, AND T. W. MEWDurable resistance is retrospective rather than prospective. Level ofdurability of resistance cannot be determined from screening in thegreenhouse or in field nurseries. The definite longevity required fordurable resistance is not predetermined and probably cannot be determined.Resistance can be called durable only if the resistance of onecultivar remains effective while another succumbs to an epidemic. Theprimary problem encountered in breeding for durable resistance is that themechanism of resistance durability is not yet fully understood, particularlyin its epidemiological and genetical aspects. Components of durableresistance remain obscure. Inheritance of durable resistance has not yetbeen clearly demonstrated. When these questions are answered, abreeding program for durable resistance could be of practical value. Theprocess required for durable resistance in breeding is continued fieldscreening for extended periods at diverse geographical locations. Fromavailable information, it appears that many rice cultivars possess durableresistance to rice diseases, either in wide geographical regions or inspecific regions. Such cultivars should be carefully characterized for theirresistance to specific diseases. We also note the level of resistancedurability is different for different diseases and for the same disease underdifferent environments. Partial resistance is durable for blast in tropicallowland irrigated rice, but in a temperate region, no clear-cut evidence wasobtained. A major gene Xa-4 for bacterial blight seems to be durable; thegene from O. nivara for grassy stunt resistance also seems durable.Rice is attacked by about 100 diseases (Ou 1982). Distribution of these diseasesvaries with geography and agroecosystem (Table 1). The economic importance of adisease will be different in different rice-growing environments, even though the ricecrop is irrigated in all. In East Asia, blast, sheath blight, and bacterial blight are themost destructive; in tropical Asia, viral diseases, bacterial blight, and sheath blightare of major concern.Disease epidemics bear close relationships to crop intensity and cropmanagement, in addition to varietal susceptibility and pathogen virulence. In Korea,where rice is grown exclusively under irrigation, yield losses to diseases are 4.0%annually. The environments and the cultural practice used by the Korean farmers,

94 Lee et alTable 1. Number of rice diseases identified in different countries.Country Fungi Bacteria Virus Mycoplasma Nematode Others TotalKorea 35 4 31 4 47Japan 45 4 5 14 34 93USA 43 – 23 2 50Philippines 24 4 5 –2 3 38–including heavy nitrogen application, favor disease development, especially blast. InChina, where more than 90% of the rice crop is grown with full irrigation, yield lossesto major diseases range from 10 to 20% annually, and sometimes are as high as 30%(Wu 1986).In tropical Asia, no realistic estimation of yield loss due to diseases has beenmade, but the environment is highly favorable. If irrigation water is available, cropsat different growth stages coexist in a given area. Where irrigation water is notadequate, there are always voluntary rice, ratoon rice, or rice stubble in fields.Asynchronous planting prolongs a disease cycle; the availability of host plantsenables the inoculum to survive for continuous infection. To reduce losses, EastAsian farmers depend heavily on extensive use of expensive chemicals.Loss may be reduced, but production cost is increased. Resistance may providethe most economical means of disease control, yet with the shift in virulence in areaswhere cropping intensity is high, resistance is often short-lived. To develop diseaseresistantvarieties, major genes (vertical resistance) are used because they are easy torecognize and to incorporate into breeding lines. Many cultivars with verticalresistance to blast, bacterial blight, and viral diseases have been developed andreleased to farmers. Like their counterparts in other food crop improvementprograms, rice scientists search for long lasting resistance. Durable resistance againstthe major diseases in rice was described by Johnson (1982) as “resistance thatremains effective during its prolonged and widespread use in an environmentfavorable to a disease.” Buddenhagen (1982) tried to analyze some pathosystems inrelation to durable resistance in the tropics.As agriculture has moved to a new scenario in Asia, many traditional ricevarieties have been rapidly replaced by improved, high-yielding modem varieties.Analysis of traditional varieties, which potentially possess attributes for durableresistance after hundreds of years of selection by farmers, is helpful to national andinternational rice improvement programs. It is imperative that scientists in varietalimprovement programs study how such resistance can be assessed and utilized.Rice disease epidemics in KoreaIn 1978, seven yr after Tong-il-type rice cultivars were released, a blast epidemicoccurred in Korea (Chung and Heu 1980). Before 1972, blast and stripe virus werethe two major diseases constraining production in japonica varieties with heavynitrogen application. Tong-il was the first semidwarf improved rice variety resulting

Durable resistance to rice diseases 95from indica-japonica hybridization. It became popular in Korea because of its highlevel of resistance to blast and stripe and its high yield (4.8 t/ha, compared with3.4 t/ha with traditional japonica varieties) (Crill et al 1982). Varieties with suchresistance were free from blast and stripe symptoms in farmers’ fields from 1971 to1977. By 1977, more than 54% of Korea’s riceland was planted to these Tong-il-typevarieties.In 1976, a race virulent to Tong-il began to appear in the southern mountainousparts. The 1977 typhoons spread it throughout the country. The first sign of theepidemic was leaf blast at early growth stages; neck blast later became severe.Weather data showed that in August 1978, temperature and humidity were high,frequency and amount of rainfall were also high, but solar radiation was less thannormal (Lee and Park 1979). A disease such as blast would become epidemic notonly because the environmental conditions were favorable, but also because thevirulence of the disease race matched the resistance of the varieties.It was obvious that blast resistance in Tong-il-type varieties was no longereffective. The useful life of a variety, or group of varieties with similar, if notidentical, resistance had come to an end in 5 yr.The story has not ended here; virulence of the pathogen continues to evolve tosubsequent replacement varieties.Rice disease epidemics in ChinaSince the 1960s, major changes have occurred in the varietal composition of andcultural practices for rice in China. The high-yielding varieties planted all over thecountry are characterized by early maturity, semidwarf plant type, high yield, andstrong tillering. Several hundred improved plant-type varieties have replaced mostof the tall traditional varieties (Lin 1986a).Research on the control of diseases through host resistance has beenincreasingly emphasized during the last 20 yr. The many improved resistant varietiesdeveloped have played important roles in increasing food production. But resistancein those varieties was overcome by pathogen races, either before or shortly after theircommercial release. Cultivar Zhai Ye Qing 8, which was highly resistant to blast, waswidely grown in South China and the Yangtze River Valley in the 1970s, covering anarea of more than 530,000 ha. It was severely damaged by blast in 1975 (Wu 1986).Previously resistant hybrid rice Shan-You 2 was grown widely for several years inSichuan Province. The area of cultivation had increased to more than 2,000,000 hain 1985, when about 600,000 ha of the total area unexpectedly was severely attackedby blast, with an estimated yield loss of 400,000 t. It was observed that the populationof a predominant blast race had changed from ZG to ZB, which was virulent againstShan-You 2 (D. Q. Feng, pers. comm.). In Fujian Province, early indica resistantvariety Hong 410 planted in about 275,000 ha (70% of the total cultivated area)became susceptible to blast in 1981 (Lin 1986b). In Northeast China, in DonggouDistrict, Liaoning Province, medium-duration japonica rice variety Zhong dan 2(pi-ta 2 ) was severely attacked by the newly emerged race ZA 61 in 1982.

96 Lee et alRice disease epidemics in South and Southeast AsiaIn South and Southeast Asia, rice tungro and other viral diseases have affectedirrigated rice production for more than 10 yr. The first improved modern rice varietyshowing resistance to rice tungro was IR20; the most recent one was IR66 in thePhilippines. Although there were questions about whether these cultivars weremerely resistant to the vector instead of to the virus, resistance of IR36 wasovercome, followed by IR42, then IR64. From 1982 to 1986, tungro alone affectedthousands of hectares of rice in India, Indonesia, Malaysia, and the Philippines.Current commercial cultivars either lack proper resistance or the resistance isshort-lived.Durable resistanceUsing both genetical and epidemiological concepts, Van der Plank (1968) classifiedhost plant resistance into vertical (VR) and horizontal resistance (HR). MonogenicTable 2. Terminology for types of resistance.Type of resistanceDefinitionResistanceevaluationAuthorHorizontal or racenonspecificPartial orincompleteRate reducingor slow blastingFieldDurableDilatoryEqually effectiveagainst all races ofa pathogenReduced rate ofepidemic developmentdespite the presenceof susceptible lesionsSlow diseasedevelopment due toreduced infection rateLow-level resistancecan be observed in thefield but cannot bedetected by proceduresfor differentiation ofpathogenic racesResistance remainseffective duringprolonged and widespreaduse in anenvironment favorableto the diseaseRetarded rate ofdisease developmentMeasurement of r Van der Plank(infection rate) (1968)Measurement of Parlevlietlatent period, (1979)infection frequency,spore production,and AUDPCDetermination of Nelson (1978)disease efficiency,lesion size,sporulationcapacity, andAUDPCMeasurement of r Kiyosawa(1970)Determining inter- Johnsonmediate levels (1981)of disease developmentacross time(retrospectivejudgment).Measurement of r Marchetti(1983)

Durable resistance to rice diseases 97VR is effective against specific races. It delays a disease by reducing the amount ofeffective inoculum. Polygenic HR is equally effective against all races of a pathogen.When a disease has started, it lowers its degree by reducing the apparent infectionrate, It is believed that reduction of apparent infection rate is associated with lastingresistance of a variety and that it can be measured quantitatively. Several terms areused to refer to this resistance type (Table 2).Scientists working with various crops have proposed using the different typesor terms of resistance, such as horizontal, field, or dilatory, as means of measuringrate of disease development. Others proposed that partial or incomplete resistance,also known as rate-reducing or slow blasting, be used to measure the components ofdisease development, including latent period, infection frequency, spore production,or lesion size.Johnson (1982), working on yellow rust of wheat during the epidemic inBritain, proposed the term durable resistance. Winter wheat cultivar Joss Camberwas felt to have adequate but incomplete (quantitative) resistance to yellow rustbefore 1972. It was considered then that Joss Camber possessed the type ofresistance that reduced the rate of disease development. The 1972 yellow rustepidemic proved that Joss Camber was highly race-specific. Resistance of wheatcultivar Cappelle-Desprez survived the 1972 epidemic and its resistance remainedeffective for many years.Although Johnson could not show that Cappelle-Desprez was not race-specificand that its resistance would be permanent, it was obvious that its resistance wasmore durable than that of Joss Camber. Johnson defined durable resistance as“resistance that has remained effective while a cultivar possessing it has been widelycultivated in an environment favoring the disease. This characteristic of resistance isrecognized retrospectively.”Durable resistance in riceBacterial blightUsing the criteria defined by Johnson, many successful examples of durableresistance are found in rice, with resistance to bacterial blight effective for manyyears and planting extended to a wide area. Using host resistance to control bacterialblight is efficient. Despite differential pathogenicity of the bacterial pathogenreported in China, the resistance of some varieties is stable. A japonica variety,Nongken 58, introduced from Japan in 1958 has been planted widely in the YangtzeRiver Valley and Shandong, Anhui, Hubei, Hunan, and Sichuan Provinces since1963. The total growing area has increased to at least 4 million hectares. Resistancehas remained effective for more than 24 yr. Nongken 58 is not only widely grown, itis also used as a resistance donor. Many improved varieties derived from it, such asNonhu 6, Zhekeng 66, Aikeng 23, Luwan 4, Jarhu 5, Erwan 5, and Zhijing Non,have been planted widely (Zhang et al 1986). In 1960, varieties Bao Tai-ai and BaoXuan 2 derived from a Guangdong wild rice Zhong Shan Hong (bred by Ding Yin in1929) became commercial cultivars in Guangdong and Guangxi Provinces. BaoTai-ai was grown on about 5,322,000 ha from 1976 to 1980 and was still planted on150,000 ha in 1986. The variety is moderately resistant to bacterial blight and is also

98 Leeet alresistant to planthoppers (S. Y. Sun, pers. comm.). Its multiple resistance may bederived from the wild parent Zhong Shan Hong.In the Philippines, varieties with the Xa-4 gene for resistance to bacterial blighthave been widely planted since the early 1970s. The resistance, although incomplete,has been matched by virulence of race 2, which is widespread in the country. Butbecause of the background of resistance in varieties developed through multiplecrosses and adequate field screening, no major epidemic has been reported (Mew,unpubl. data). There are indications, however, that incidence of bacterial blight isincreasing.BlastNumerous varieties have been reported to have stable resistance. In China, earlyindica varieties Zhen Shan 97 and Zhen Luon 13 have been widely planted for about10 yr in regions where blast used to be severe. Some varieties also have been widelygrown for 10-16 yr in environments highly conducive to disease development. Indicavariety Fu She 94, introduced to Xiy Yiong District, Sichuan Province, in 1973, hasbeen used by the farmers for 14 yr, even though its resistance is moderate. Earlyjaponica resistant variety Shuang-Feng 4 has been grown in Anhui Province for13 yr, with no information to show that resistance has broken down. Tall traditionalvariety Majigu was grown for more than 30 yr in Xiy Yiong District, SichuanProvince, where blast was a major disease, until it was replaced by Fu She 94 becauseof its low yield. None of the traditional varieties have been analyzed for resistance.Observations in China indicate that field resistance is associated with durableresistance. In Donggou District, Liaoning Province, Northeast China, where blast isa major problem, no varieties could be grown for more than 3-5 yr. However,Jingyue 1, a widespread cultivar in the region, has a relatively long history ofcultivation, about 18 yr (Lin 1986b). Although it is frequently attacked by blast, ithas rarely suffered severe damage. Highly blast-resistant Xiang Ai Zao 9(IR8 / Xiang Ai Zao 4) released in 1970 was cultivated on about 670,000 ha in Hunan,Fujian, Guangdong, Guang Xi, and Shan Xi Provinces by 1979. It is susceptible toinfection but pathogen reproduction is reduced.Many rice varieties have been recorded across the history of China. Some arestill being used today. Huan Sheng zheng, in his book Li-seng-ju-jing published inthe 16th century, described many cultivars. Zao Bai Dao, Xue Li Dong, Mai ZhengChang, San Zhao Qi, Zi Mang Tao, Eai Nou, Qing Gan Nou, and Xiang Kang arestill being grown in Zhejiang Province after 700-800 yr (Yio 1986). Because blast hasalways been a major disease problem in this province, these varieties must possessattributes that make their resistance durable.Lin (1986b) analyzed minor genes for resistance in some japonica varieties.Reimei, which was introduced into Northeast China from Japan more than 15 yrago, still shows resistance there. But it became extremely susceptible in Koreashortly after its introduction. Inheritance of its resistance was found to bequantitative, with additive and partially dominant effects of minor genes. Thebroad-sense variability hb 2 estimated for the RRI (relative resistance index) ofMokotou/ Reimei was 66.26%. It was estimated that six pairs of genes controlled theresistance of Reimei.

Durable resistance to rice diseases 99The irrigated rice environment in tropical Asia is not as conducive to blast asenvironments in temperate regions. Under irrigation, IR36, which has partialresistance to blast, is stable to the disease (Bonman 1985). Since the release of IR8,blast has not been a serious disease in the Philippines. Although IR8 is no longer apopular commercial variety, its resistance to blast in such an environment has notbeen broken down. Other improved varieties with adequate blast resistance showsimilar results, in contrast to their performance in upland environments or intemperate regions.Viral diseasesThe agents responsible for viral diseases appear to be relatively more stable thanbacterial pathogens. The number of strains with different virulences is less than thatof bacterial pathogens. Resistance is also more long-lasting. When Tong-il was firstreleased to farmers, it was not only highly resistant to blast but also possessed a highlevel of resistance to stripe virus, then a major disease problem in rice. Although theresistance of Tong-il types to blast was overcome, their resistance to the stripe virusremains effective (Chung and Heu 1980). In the tropics, grassy stunt virus used to bea serious biological constraint to rice production. Epidemics were reported inSoutheast Asia in the early 1970s. After the incorporation of a resistance genederived from Oryza nivara, resistance was effective for nearly 10 yr, until a new strainwas found in the late 1970s (Hibino et al 1985). O. nivara carries a major gene forresistance to grassy stunt (Khush and Ling 1974). There is information, however,that the O. nivara resistance gene may not be effective across all of South andSoutheast Asia (H. Hibino, pers. comm.).Screening proceduresBlastIn Korea, the breakdown in 1976 of Tong-il sister varieties such as Nopung andRaegyeong to races KI-307, KI-315, and KI-413 has shifted breeding from verticalresistance to a more durable type of resistance. Since then, all recommendedvarieties have been evaluated for lasting resistance.General characteristics of 10 cultivars. The degree of resistance to leaf and neckblast of five Tong-il sister lines and five japonica varieties was evaluated in thegreenhouse, blast nursery, and multilocational trials (Table 3). The varieties hadbeen grown by farmers for 7 yr, including a 2-yr regional adaptation test. Samgang,Seomjin, Shinsunchal, Taebaeg, Milyang 30, and Milyang 40 exhibited resistanceassumed to be durable. About 17% of the total rice area in Korea was planted tothese varieties in 1986. When they were inoculated with representative races of theblast fungus, they showed race-specific reactions (Table 4).Greenhouse test. Recommended cultivars were inoculated with 10 representativeraces of blast fungus. Based on lesion count, they were classified into fivegroups (Table 5). Twenty-seven varieties with low lesion numbers, includingSeomjin, Shinsunchal, and Bongkwang, were classified as group II and group III.Milyang 30, Milyang 42, and IR36 (from the Philippines) consistently showedlow disease levels in farmers’ fields. Measurement of the components of resistance

100 Lee et alTable 3. Degree of resistance to blast disease in 10 rice varieties grown in commercialfields.VarietyYearreleasedAreacultivated(ha)Degreeofresistance aIndica/japonicaTaebaeg (S287)Samgang (M55)Milyang 30Milyang 42Milyang 23JaponicaShinsunchal (I 355)Seornjin (I 353)Bongkwang (Minehikare)Nagdong (M15)Chucheong (Aki-bare)19801983197719791976198319831974197519726,540143,7343,6067473,3594,98292,87513,16157,910290,018RMRMRMRSMRMRMSSa R = resistant, MR = moderately resistant, S = susceptible.Table 4. Varietal reaction to representative races of P. oryzae.VarietyKJ101KJ105KJ KJ201 301Varietal reaction a toKI1117KI307KI313KI315aKI KI315b 401Indica/japonicaTaebaegSamgangMilyang 30Milyang 42Milyang 23JaponicaShinsunchalSeornj inBongkwangNagdongChucheongRRRRRSSSSSRRRRRSSSSSRRRRRSRRSSRRRRRSRRSSRRRRRSSSSSRRSRSRRRSRRRRRSRRRSSRSSSSRRRSRRSSSSRRRSRRRRRSRRRSSa R = resistant, S = susceptible.Table 5. Some major varieties grouped on the basis of number of lesions per tillerproduced by 10 races of P. oryzae.I II Ill IV V(0 tiller) (1-10 tillers) (11-20 tillers) (21-40 tillers) (41 tillers)Daeseong Samgang Daechang Unbong SobaegYoungsan Shinsunchal Seornjin Seonlag NongbaekNorin 1 Kwangmyoung Sangju 6 Bongkwang DobongSangju 5 Youngdug Suweon 342 Chucheong CheonmaTaebaeg Iri 372 Sangju 6 Nagdong Yeomyeongbyeo

Durable resistance to rice diseases 101showed that they have lower relative disease efficiency, lesion size, and sporulationcapacity than susceptible IR50 (from the Philippines), M59, and S264 (Table 6). Thelatent period did not seem to be an important component in this test, as had beenreported by Villareal (1981).Blast nursery test. The varieties were classified into 5 groups on the basis of testsconducted in 20 blast nurseries; 24 of them, including Shinsunchal, Seomjin, andBongkwang, exhibiting reaction types 3-5 (IRRI SES), were classified in groups IIand III (Table 7). In the 5-yr blast nursery test at Icheon, low average reaction typesincluded Milyang 30 and Milyang 42 (Table 8). Reaction type 1 was seldomobserved.The disease progress curves for Shinsunchal, Seomjin, and Bongkwang werelow compared with susceptible varieties (Fig. 1). The same low disease progresscurve was observed with Milyang 30 and Milyang 42 tested in the IRRI blast nursery(Fig. 2).Field screening for leaf blast. On the basis of multilocational tests for leaf blastof 81 recommended cultivars and elite lines, 42 cultivars with 0.1-1.0% diseased leafTable 6. Relative infection efficiency, lesion size, sporulation capacity, and latent period of sixrice varieties inoculated with isolates of Pyricularia oryzae. aCultivarRelative infection efficiency bSporulation(lesion/100 cm 2 ) Lesion capacity dsizeFully extended Partially extended (mm 2 ) c Per Per 10-mm 2 Latentfifth leaf sixth leaf lesion lesion period eMilyang 42 5.0 A 102.2 A 1.3 A 315 A 2610 A 6.3 ABIR36 2.6 A 133.6 A 1.6 A 332 A 2244 A 5.7 CMilyang 30 11.4 B 142.0 A 2.0 AB 422 A 2404 A 6.2 BSuweon 264 28.8 C 225.6 B 4.8 C 1596 B 4638 B 6.4 AMilyang 57 31.5 C 232.9 B 4.1 BC 1271 B 4003 AB 6.2 BIR50 31.4 C 344.8 C 4.1 BC 1052 B 3745 AB 5.7 Ca In a column, cultivar means followed by a common letter are not significantly different (P £0.05) by Duncan’s multiple range test. Analysis of variance showed no isolate X cultivar interaction.b Means of 4 P. oryzae isolates; all other values are means of 3 isolates. c Data from 9 dafter inoculation. d Mean number of conidia from samples taken 6, 9, and 12 d after inoculation.e Days to 50% lesion appearance calculated by the formula of Shaner et al (1978).Table 7. Some major rice varieties grouped on the basis of average reaction type(0-9) at 20 blast nurseries.I II Ill IV V(0-2) (3) (4-5) (6-7) (8-9)Daeseong Unbong SobaegSongjeon YeomyeongbyeoTaebaeg Namyang Nongbaek Seolag HwaseongChilseong Shinsunchal Dobong Chiag ChucheongBaegYang Youngmun Bongkwang GihoNagdongSamgang Cheongcheong Seomjin Dongjin

102 Lee et alTable 8. Reaction of major rice varieties to blast (0-9 scale) in 20 blast nurseries, 1981-85. aVariety 1981 1982 1983 1984 1985lndica/japonicaTaebaeg 0.8 (0-2) 1.1 (0-3) 0.8 (0-3) 0.7 (0-2) 0.7 (0-2)Samgang 0.8 (0-3) 0.9 (0-3) 0.7 (0-4) 1.0 (0-4) 1.1 (0-3)Milyang 302.5 (0-6) 1.9 (0-4) 1.5 (0-4) 2.3 (0-7) 2.7 (0-7)Milyang 422.0 (0-5) 1.9 (0-6) 1.2 (0-5) 1.6 (0-4) 1.3 (0-4)Milyang 23 4.1 (1-8) 3.9 (1-7) 3.0 (0-6) 3.8 (1-7) 6.8 (1-7)JaponicaShinsunchal 2.7 (0-4) 3.1 (0-6) 2.8 (1-5) 3.8 (1-6) 3.3 (2-5)Seomjin 4.7 (1-7) 4.6 (1-8) 4.2 (1-7) 5.0 (2-7) 48 (1-7)Bongkwang 4.2 (1-8) 5.5 (2-9) 3.9 (0-7) 5.6 (1-9) 5.5 (1-9)Nagdong 8.1 (3-9) 8.7 (4-9) 8.2 (5-9) 8.6 (7-9) 8.4 (5-9)Chucheong7.5 (1-9) 8.4 (5-9) 8.2 (5-9) 8.3 (6-9) 8.2 (5-9)a Figures given are means of 20 blast nursery readings based on the IRRl standard evaluationsystem. Figures in parentheses are ranges of minimum to maximum scoring based on Standardevaluation system for rice (IRRI 1980).1. Leaf blast disease progress curves for Korean commercial varieties and elite lines at Icheon blastnursery, 1986.area were classified under groups II and III (Table 9), again including Seomjin,Samgang, Shinsunchal, and Bongkwang. Low percentage of diseased leaf area alsowas observed in these cultivars during 7-yr trials at lcheon (Table 10).Field screening for neck blast. The multilocational trial for neck blast (Table 11)and the 7-yr neck blast test at Icheon (Table 12) showed similar trends of lowpercentage neck blast infection for Seomjin, Shinsunchal, and Samgang.

Durable resistance to rice diseases 1032. Disease progress curves for rice cultivars infected by Pyricularia oryzae in an upland nursery, IRRI.Table 9. Some major rice varieties grouped on the basis of diseased leaf area in thefield at 7 locations. aI(0)II(0.1-0.5)Ill IV V(0.51-1.0) (1.01-5.0) (5.0)Iri 372Iri 373Sangju 5Milyang 82DeeseongSeomjinSamgangShinsunchalYoungsanTaebaegKwanagBongkwangYoungdugWonpungJangseongMilyang 8NongbaekDobongOdaeBaegamSeolagGihoBongkwangCheonmaNagdongChucheongSeonamPalgeuma Figures in parentheses are % diseased leaf area,Blast control in durable-resistance varieties. Seomjin, which consistentlyexhibited resistance with lower reaction types, was tested under high nitrogen andchemical application to control leaf and neck blast. High nitrogen did not affect thelow leaf and neck blast infection of Seomjin in the field; susceptible varietiesChucheong and Jinju were greatly affected. The combined effect of high nitrogenand chemical treatment was negligible for Seomjin (Table 13, Fig. 3).Five experiments tested durability of resistance in 13 varieties and elite lineswith low disease level (Table 14). After 7 yr in the field, these cultivars continue to

104 Lee et alTable 10. Reaction of rice varieties to leaf blast at lcheon 1980-86.Diseased leaf area (%)1980 1981 1982 1983 1984 1985 1986Indica/japonicaTaebaegSamgangMilyang 30Milyang 42Milyang 23JaponicaShinsunchalSeomjinBongkwangNagdongChucheong0.01-00.010.34---0.360.25000.130.030.230.010.030.3 13.141.300000.01000.051.950.6200000.0300.020.1 32.451.1600000000.010.260.350000000.030.011.090.380.020.02---0.070.220.0361.2541.68Table 11. Some major rice varieties grouped on the basis of neck blast infection(%) at 7 locations. aIII Ill IV V(0) a (0.1-5.0) (5.1-20.0) (20.1-50.0) (50.1)Seomjin Shinsunchal Nongbaek Nobaeg BongkwangTeebaeg Daecheong Daeseong OdaeCheonmaIri 377 Youngsan Bongkwang Songjeon BaegarnIri 372 Samgang Chilseong UnbongYoungdug Kwanag Youngmun Yeomyeongbyeoa Figures in parentheses are % neck blast incidence.Table 12. Neck blast infection (%) in varieties tested at lcheon 1981-86.Neck blast incidence (%)1980 1981 1982 1983 1984 1985 1986Indica/japonicaTaebaegSarngangMilyang 30Milyang 42Milyang 23JaponicaShinsunchalSeomjinBongkwangNagdongChucheong0.4-1.121.391.8---28.816.4003.22.428.7001.414.611.7000.92.00.3005.643.927.700.44.32.411.85.31.04.713.516.0000.700.41.406.50.53.4000.3701.011.5202.572.032.42010.0---001.58.532.1

Durable resistance to rice diseases 105Table 13. Leaf and neck blast incidence on three varieties grown under differentnitrogen levels.VarietyDiseased leaf area (%) Panicles infected (%)Low N High N Low N High NSeomjin 0.04 0.07 0 0Chucheong 0.16 0.71 8.1 52.8Jinju 0.31 1.14 21.6 82.13. Effect of varietal resistance and N level on reducing leaf blast in protected and unprotected plots.Table 14. Some varieties and elite lines identified as possibly having durable resistanceto blast fungus.Degree ofresistanceVarietyElite lineHigh Seornjin, Daeseong, Youngsan, M80, M82, Sangju 5Shinsunchal, Shinkwang, Taebaeg Iri 377,S341, Sangju 6ModerateLowNorin 1, Baegunchalbyeo, Gaya,Jungweon, Cheongcheong, SamgangSobaeg, NongbaekS342show less disease and evidently possess more durable resistance. They will be usefulfor blast management.Bacterial blightIn general, bacterial diseases are known to be difficult to control with chemicals.Host plant resistance to combat bacterial blight is most efficient and economical(Kozaka 1969). Epidemics of the disease are host- and environment-dependent. A

106 Lee et alnumber of studies of cultivar resistance have been done in many countries (Kozaka1969, Mew 1987, Ou 1982, Son 1981), and many resistant cultivars have beendeveloped. But resistance soon becomes ineffective because of the presence ofvirulent races in many countries. Although such a phenomenon is common in fungaldiseases (Van der Plank 1968), there are few examples in bacterial diseases.Considering such a situation, work on resistance to bacterial blight in rice is focusedon resistance which may be more durable. Field resistance has been proposed (Andoet al 1973, Horino 1978, Lee 1979).Unlike the blast fungus, the bacterial blight pathogen Xanthomonas campestrispv. oryzae is relatively stable, and fewer races have been identified with a limitednumber of differentials. Pathogen variation and varietal resistance were reviewedrecently (Mew 1987). Different types of resistance are identified in germplasmscreening, such as seedling resistance, adult plant resistance based on crop growth,qualitative and quantitative resistance based on level of disease development afterinfection, and differential and nondifferential resistance based on race response. Noexperimental data shows genetically and epidemiologically which type is moredurable. The International Rice Research Institute (IRRI) follows a procedure thatappears to be adequate for screening for durable resistance in the field (Mew et al1987). All plants of the F 2 population are inoculated in the field with an indigenousvirulent isolate. At 2-3 wk after inoculation, susceptible plants are rogued. Theseprocedures continue to the F 3 and F 4 . Because of the compound crosses and thescreening procedure as such, many lines and IR varieties have been found to possessdifferent levels of background resistance. The background resistance apparentlyinteracts with the major gene Xa-4 to result in resistance that appears durable (Mew,unpubl. data).Field resistance. Field resistance or quantitative resistance to bacterial blighthas been investigated in Japan. A number of major genes govern varietal resistance,but not to pathotype IV. Ando et al (1973) demonstrated high correlations amongthe quantitative resistance of Kinmaze group varieties to pathotypes I, II, and III,and also of Kogyoku group varieties to bacterial groups II and III. Sato (1978)reported that field resistance of Asominori was race nonspecific and showed lowdisease development.In Korea, Gaya is known to be susceptible to both K1 and K3 races andSeomjin susceptible to K3 and resistant to K1 race. These varieties have race-specificresistance. When both cultivars were tested in the field, levels of disease developmentwere much lower than those of Chucheong and Milyang 23 (Table 15). Whether theypossess durable resistance can only be evaluated when they have been grown in wideareas for many years.Adult plant resistance. Seedling resistance to bacterial blight is common. Ingeneral, resistance at the seedling stage is correlated with that at the flag leaf stage;this is known as seedling or overall resistance (Mew 1987). Some workers havereported significant variation of resistance with growth stage (IPE 1968). Ezukaet al(1974) observed a difference in expression of resistance to bacterial blight betweenseedlings and adults of Wase Aikoku group varieties which they called adultresistance or mature plant resistance.

Durable resistance to rice diseases 107Table 15. Durable resistance to BLB pathogen in field of current commercial cultivarsin Korea (1986, Rural Development Administration-IRRI).VarietyDifferential reaction aLesion area (%) whento raceinoculated with raceK1 K3 K1 K3Gaya S S 5.9 5.2Seomjin R S 0.171.7Chucheong S S20.026.4Milyang 23 S S 27.9 21.5a S = susceptible, R = resistant.According to Zhang and Mew (1984), Malagkit Sungsong, Zenith, and lineIR1695 have the Xa-6 gene for resistance to bacterial blight. These lines were verysusceptible at the seedling stage but resistant on leaf 11-12 (except MalagkitSungsong, which was resistant on earlier leaves). In staggered plantings tosynchronize inoculation date, Malagkit Sungsong and Zenith expressed increasingresistance with ascending leaf position to four races of the bacterial blight pathogen.Most cultivars become more resistant when they mature. Those that have true adultplant resistance are always susceptible at adult plant stages (Mew 1987).In a collaborative Rural Development Administration and IRRI study of 69Korean and IRRI germplasm against all three races, percent diseased leaf area wasrelatively low as plants matured (Table 16). All the lines and varieties showingresistance at the seedling stage were resistant at maximum tillering and the flag leafstage to all three races (Table 17). However, some lines susceptible at the seedlingstage showed resistance at maximum tillering and flag leaf stage, or both. In acomparison of disease progress curves of Gaya and Chucheong inoculated by thespraying method in the field, Gaya (known to have durable resistance) showed slowdisease development (Fig. 4). Asominori, known to have field resistance in Japan,showed very low disease development at different growth stages (Fig. 5) (Lee 1979).Detailed genetic and epidemiological analysis of these varieties may provide insightsinto durable resistance to bacterial blight.Table 16. Disease severity in 69 rice germplasm inoculated with 3 BLB races atdifferent growth stages.Growth stageLesion area (%)K1 K2 K3Seedling 31.3 49.4Maximum tillering 13.325.6Flag leaf9.1 a64.223.613.9a Not tested.

108 Lee et alTable 17. Classification of rice germplasm for varietal resistance to 2 Korean BLBraces by growth stage.Reaction a atVarieties (no.) classified byinoculation with BLB racesSeedling Maximum Flag leaftillering K1 K3R R R 37S S S 7S R R 4S S R 1011111421a R = resistant, S = susceptible.4. Symptom development, by season, of current commercial cultivars in Korea inoculated in the field byspraying with BLB pathogen (1985, IAS-IRRI).ConclusionDurable resistance is a retrospective concept as R. Johnson defined it. Following hisdefinition, the level of durability of resistance cannot be determined on the basis ofscreening in the greenhouse or in field nurseries. The longevity required for durableresistance cannot be predetermined. Resistance of a variety can only be calleddurable if the resistance of one variety remains effective while another succumbs toan epidemic. The main problem encountered in breeding for durable resistance isthat the mechanism of resistance durability is not yet fully understood, particularlyits epidemiological and genetical aspects. Components of durable resistance remainobscure. Inheritance of durable resistance has not yet been clearly demonstrated.When such questions are answered, breeding programs for durable resistance wouldbe of practical value. One process that is always required in breeding for durableresistance is continuous field screening for extended periods at diverse geographicallocations.

Durable resistance to rice diseases 1095. Change of quantitative resistance in rice cultivars to four isolates of bacterial leaf blight.I — 1 Jun II — 6 Jul III — 8 Aug IV — 11 Sep V — 20 Sep(seedling stage) (tillering stage) (about panicle (flag leaf stage) (about harvesting)bearing stage)From the available information, it is clear that many rice cultivars appear topossess durable resistance to rice diseases, either across wide geographical regions orin specific regions. Such cultivars should be carefully characterized for theirresistance to specific diseases.We also note that a variety may have short-term resistance to one disease anddurable resistance to another. The level of durability is different for different diseasesand for the same disease under different environments. Partial resistance to blast isdurable in tropical lowland irrigated rice; in temperate regions, no clear-cut evidenceis available. The major gene Xa-4 for bacterial blight seems to be durable. The genefrom O. nivara for grassy stunt resistance also seems to be durable.References citedAndo T, Yamamoto T, Yamada M (1973) The quantitative resistance of rice varieties to bacterial blight[in Japanese]. Proc. Assoc. Plant Prot. Hokuriku 21:32-35.Bonman J M (1985) Recent progress in international research on blast resistance. Biological stresses withspecial emphasis on blast. Paper presented at the Second International Upland Rice Conference, 4-8Mar, Indonesia.Buddenhagen I W (1982) Disease resistance in rice. Pages 401-428 in Durable resistance in crops. F.Lambed, J. M. Waller, and N. A. Van der Graaf, eds. Plenum Press, New York. 454 p.Chung G S, Heu M H (1980) Status of japonica-indica hybridization in Korea. Pages 135-152 inInnovative approaches to rice breeding. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Crill P, Ham Y S, Beachell H M (1982) The rice blast disease in Korea and its control with race predictionand gene rotation. Pages 123-130 in Evolution of the gene rotation concept of rice blast control.International Rice Research Institute, P.O. Box 933, Manila, Philippines.

110 Lee et alEzuka A, Watanabe Y, Horino O (1974) Difference in resistance expression to Xanthomonas oryzaebetween seedlings and adults to Wase Aikoku group rice varieties.Hibino H, Cabauatan P Q, Omura T, Tsuchizahi T (1985) Rice grassy stunt virus strain causingtungro-like symptoms in the Philippines. Plant Dis. 69:538-541.Horino O (1978) Distribution of pathogenic strains of Xanthomonas oryzae (Uyeda et Ishiyama)Dowson in Japan in 1973 and 1975 [in Japanese, English summary]. Ann. Phytopathol, Soc. Jpn.44:297-304.IPE—Institute of Plant Environment, Office of Rural Development (1968) Annual report for 1967 [inKorean]. Suweon, Korea.IRRI—International Rice Research Institute (1980) Standard evaluation system for rice. InternationalRice Testing Program, P.O. Box 933, Manila, Philippines.Johnson R (1981) Durable resistance: definition of genetic control and attainment in plant breeding.Phytopathology 71:567-568.Johnson R (1982) Genetic background of durable resistance. Pages 5-26 in Durable resistance in crops. F.Lamberti, J. M. Waller, and N. A. Van der Graaf, eds. Plenum Press, New York. 454 p.Khush G S, Ling K C (1974) Inheritance of resistance to grassy stunt virus and its vector in rice. J. Hered.65:134-136.Kiyosawa S (1970) Comparison among various methods for testing blast resistance of rice varieties [inJapanese, English summary]. Ann. Phytopathol. Soc. Jpn. 36:325-333.Kozaka T (1969) Control of rice diseases with resistant varieties [in Japanese]. Agric. Hortic. (NogoOyobi Engei) 44:208-212.Lee E W, Park S Z (1979) Interpretation on the epidemic outbreak of rice blast disease in Korea, 1978. J.Korean Soc. Crop Sci. 24:l-10.Lee S G (1979) Studies on the field resistance of rice cultivars to bacterial blight incited by Xanthomonasoryzae. MS thesis, Seoul National University, Korea.Lin S C (1986a) Breeding for disease resistance in rice. In Rice crop of China. Agriculture Publishing,Beijing.Lin S C (l986b) Genetic analysis of minor gene resistance to blast in japonica rice. Pages 451-469 in Ricegenetics. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Marchetti M A (1983) Dilatory resistance to rice blast in USA rice. Phytopathology 73:545-649.Mew T W (1987) Current status and future prospects in research on bacterial blight of rice. Annu. Rev.Phytopathol. 25:359-382.Mew T W, Reyes R C, Vera Cruz C M (1987) Screening rice for resistance to bacterial blight( Xanthomonas campesrris pv. oryzae ). In Methods in phytobacteriology. Klement et al, eds. (inpress)Nelson R R (1978) Genetics of horizontal resistance to plant diseases. Annu. Rev. Phytopathol.16:359-378.Ou S H (1982) Rice diseases. Commonwealth Mycological Institute, Kew, Surrey, England. 368 p.Parlevliet J E (1979) Components of resistance that reduce the rate of epidemic development. Annu. Rev.Phytopathol. 17:203-222.Sato T (1978) Field resistance to bacterial leaf blight of rice [in Japanese]. Plant Prot. 32:187-192.Shaner G, Ohm H W, Finney R E (1978) Response of susceptible and slow leaf-rusting wheats toinfection by Puccinia recondita. Phytopathology 68:471-475.Son J K (1981) Pathogenic variability in Xanthomonas oryzae (Uyeda et Ishiyama) Dowson andinheritance of resistance to the pathogen in rice. Res. Rep. D D A (Soil Fert. Plant Prot. Mycol.23:36-61.Van der Plank J E (1968) Disease resistance in plant. Academic Press, New York. 206 p.Villareal R L, Nelson R R, MacKenzie D R, Coffman W R (1981) Some components of slow-blastingresistance in rice. Phytopathology 71:608-611.Wu S Z (1986) Rice diseases. In Rice crop of China. Agriculture Publishing, Beijing.Yio X L (1986) The history and development of rice crop in China. In Rice crop of China. AgriculturePublishing, Beijing.Zhang Qi, Lin S C (1986) Analysis of resistance to some strains of X. c. pv. oryzae in rice commercialcultivars of China [in Chinese]. Sci. Agric. Sin. (in press)Zhang Qi, Mew T W (1984) Characterization of adult plant resistance of rice to bacterial blight. Paperpresented at a Saturday Seminar, 28 Apr 1984, International Rice Research Institute, Los Baños,Philippines.NotesAddress: E. J. Lee, Qi Zhang, and T. W. Mew, International Rice Research Institute, P.O. Box 933, Manila, Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. BOX 933,Manila, Philippines.

Durable resistance to insect pestsof irrigated riceR. C. SAXENAResistant rice varieties are needed to reduce losses caused by insect pestsin irrigated rice. The stability of resistance depends on the geneticinteraction between the rice host and the insect herbivore. Methods forevaluating levels of resistance, including tolerance, are described.Although plant morphology contributes to resistance, most rice-plantinteractions are determined by biochemical factors, particularly byallelochemicals. Their identification and inheritance will help in breedingfor insect resistance; failure to recognize the occurrence and evolution ofpest biotypes can frustrate that breeding. Systematic surveillance forbiotypes will help in adjusting breeding strategies. Considering thebuffering effect of plant resistance on insect pest populations in thecontext of integrated pest management would lead to better appreciationof even moderate levels of resistance and tolerance and emphasize theimportance of natural enemies. The goals of breeding for maximum yieldand for resistance durability need to be in balance. Programs that take fulladvantage of host plant resistance in insect management shouldencompass a broad range of basic and applied research.The expression and long-term stability of resistance to a herbivore insect in a plantspecies depend on the genotype of the host, the genotype of the insect, and theinteraction between the plant and the insect under different environmentalconditions (Gallun and Khush 1980). Consequently, understanding the heterogeneityin the host plant and in the insect and the dynamics of plant-insectinterrelationships, and applying that knowledge to developing durable pest-resistantvarieties, have become important in modern agriculture. Deployment of varietieswith diverse resistance backgrounds has become the cornerstone of the achievementof long-term stability against rapidly evolving insect pests.Durability does not imply that resistance has to be effective against all variantsof an insect pest. Durable resistance will have given effective control for many yearsand is still effective (Russell 1978). Durable resistance should be considered in thecontext of pest management systems, not in isolation.Rice, with its tremendous antiquity, genetic diversity, seasonality, range, andincreased intensity of cultivation, has proven to be a vast substrate of interactionwith insect pests that is ideal for their diversification (Saxena and Rueda 1982). Weare just beginning to understand the central role that genetic variability or

112 R.C. Saxenauniformity of rice varieties plays in regulating insect pest populations that in turnaffect the health and productivity of rice varieties.As we increase our knowledge about plant-insect interactions, we must ask hownew information can be used to better manage the rice crop. We should alsorecognize that plant resistance acts as the filter against which to select pests unable toattack. But the survivors may interbreed, to produce a new biotype or host race thatcan successfully colonize and attack previously resistant hosts.The early success of the first brown planthopper (BPH)-resistant variety IR26against the pest’s general population, in the Philippines in 1973-75 and in Indonesiain 1974-76, was real and spectacular. So was the devastation when this popularvariety succumbed to a new selection or biotype of the BPH. The rapidity with whichthe defenses of resistant cultivars can be overcome is a matter of serious concern,because it sometimes can take much longer to produce a new resistant variety than ittakes a new biotype of a pest to evolve.Insect pests vs resistant rice varietiesMore than 100 insect species attack rice. Of these, 20 are major pests of irrigated rice.Taken together, they infest all parts of the rice plant at all growth stages. A few, suchas leafhoppers and planthoppers, also transmit viral diseases. Losses to insect pestsin Asia have been estimated to be 31.5% (Cramer 1967). In 117 experiments at IRRIfrom 1964 to 1979, yield losses caused by insects averaged 40% (Pathak andDhaliwal 1981).Planting high-tillering varieties with heavy fertilization and growing ricethroughout the year with improved irrigation has favored buildups of pestpopulations and pest attacks. High-yielding rice varieties grown in the tropics withmodern technology often have more severe pest problems than do traditionalvarieties planted in poorly managed peasant farmers’ fields. Development ofappropriate pest management technology is the challenge.Host plant resistance is the key component in integrated control of rice insectpests. The increasing problems involved in insecticidal control further emphasize theneed for resistant varieties. Resistant varieties provide an inherent pest control thatinvolves no additional cost and no environmental pollution problems. Their use iscompatible with other methods of insect control and is not subject to the vagaries ofweather. In certain situations, the use of resistant varieties is the only effective meansof pest control.Plant resistance is especially valuable in developing countries, where the ricecrop is planted on small holdings and where economic constraints and lack oftechnical knowledge limit the proper use of insecticides. Also, resistant varietiescontrol pests at low densities; the use of insecticide is justifiable only when pestdensity reaches an economic injury threshold. Incorporating insect resistance intoimproved varieties has become a necessity in international and national rice breedingprograms in the tropics. Within the last 25 yr, significant progress has been made inbreeding for resistance; rice varieties resistant to key insect pests are now beinggrown on millions of hectares (Table 1).

Table 1. Varietal resistance against major insect pests of irrigated rice (Heinrichs 1986, Pathak and Saxena 1980).–––––+++–++–+–––––––––––––+??+––+––––––––Common name Scientific nameStatus of resistance aSources Varieties Genes Biotypesidentified released identified encounteredStriped stem borerYellow stem borerAfrican white stem borerLeaffolderCasewormBrown planthopperWhitebacked planthopperSmall brown planthopperRice delphacidGreen leafhopperZigzag leafhopperWhite leafhopperGall midgeWhorl maggotStalkeyed flyRice stem maggotRice bugBlack bugRice water weevilRice hispaRice thripsChilo suppressalisScirpophaga incertulasMaliarpha separatellaCnaphalocrocis medinalisNymphula depunctalisNilaparvata lugensSogatella furciferaLaodelphax striatellusSogatodes orizicolaNephotettix virescensRecilia dorsalisCofana spectraOrseolia oryzaeHydrellia philippinaDiopsis macrophthalmaAtherigona oryzaeLeptocorisa oratoriusScotinophara coarctataLissorhoptrus oryzophilusDicladispa armigeraStenchaetothrips biformis+ ++ ++ –+ o+ –+ ++ ++ ++ ++ ++ ++ –+ ++ ++ o+ –+ –+ o+ –+ –+ –a o = Resistant breeding lines available, ? = biotypes suspected.

114 R.C. SaxenaTechniques for evaluating varietal resistanceSuccess in breeding for resistance depends on effectively identifying resistance andincorporating it into varieties that also have other desirable agronomic characters.Efficient methods of screening are therefore essential to properly identify and utilizeresistant germplasm.Resistance is normally identified by exposing plants or plant parts to the insects(Metcalf and Luckman 1975). The effect is evaluated in terms of insect responses,such as orientation and settling, feeding, assimilation of food, growth, adult survivaland egg production, and oviposition, during the process of insect establishment onplants (Saxena 1969, Saxena et al 1974). Resistance to egg hatchability is alsoimportant against leafhoppers and planthoppers that lay their eggs within the planttissue (Saxena and Pathak 1977).Evaluating resistance on the basis of plant injuryFree-choice (FC) seedling bulk test. The FC seedling bulk test, or standard seedboxscreening test (SSST), is routinely used to mass screen rice germplasm for resistanceto leafhoppers and planthoppers (Pathak and Saxena 1980). The method isrelatively simple and fairly reliable on highly susceptible and highly resistantgermplasm. Test varieties are sown in seedboxes, along with a susceptible check anda resistant check. At 1 wk after seeding, several thousand 2d- and 3d-instarleafhopper or planthopper nymphs are uniformly scattered on the seedlings. Thatinfestation level is sufficient to kill the susceptible varieties. Damage is recorded assoon as the susceptible check is killed. Final grading is done after all susceptibleplants are killed.No-choice (NC) seedling bulk test. In the FC seedling bulk test, the nymphstend to move over to the susceptible check shortly after seedlings are infested,causing an imbalance in the infestation of test varieties (Saxena and Khan 1984). Theescape of a test variety may be misconstrued as true genetic resistance. Varietiesshowing pseudoresistance due to host evasion, induced resistance, and escape areuseful, but should be distinguished from varieties showing resistance across a widerrange of environments (Painter 1951).In the NC test, varieties are sown and infested as in the FC test. But each row ofseedlings is separated from the others by an intervening mylar partition, to preventselective accumulation of nymphs on the susceptible variety. That forces nymphs tofeed on the test varieties. Damage is scored as in the FC test.Resistance to S. furcifera of 10 genetically diverse rice varieties, scored by FCand NC seedling bulk tests, were compared (Table 2). Podiwi A8 and N22 weremoderately resistant and resistant in the FC test, but susceptible and moderatelysusceptible in the NC test.Modified seedbox screening test (MSST). The SSST technique selects varietieson the basis of insect damage to seedlings. Thus, regardless of major genes or majorand minor genes, in SSST, varieties are discarded if resistance is not expressed at theyoung seedling stage.Minor genes provide polygenic resistance, which is generally more effectivethan major gene resistance against genetically plastic pests (Simons 1972). Major

Durable resistance to rice insect pests 115Table 2. Resistance a of rice seedlings to infestation by S. furcifera nymphs in freechoice( FC ) and no-choice ( NC ) tests (Saxena and Khan 1984).Variety Resistance gene FC NC Differences bADR52ARC10239ColombolR2035-117-3Muskhan 41N22N32Podiwi A8TN1 (S check)Wbph-3Wbph-2Wbph-1 + recessive?Wbph-1 + WbPh-2Wbph-1Wbph-1Wbph-1wbph-4no resistance gene1.0 0.61.4 1.11.1 1.00.6 0.91.0 0.90.8 2.21.0 1.32.6 7.89.0 9.00.4 NS0.3 NS0.1 NS–0.3 NS0.1 NS–1.4**–0.3 NS–5.2**0.0 NSa Scored on 0-9 scale: 0 = highly resistant, 9 = highly susceptible. b NS = not significant,** = significant at 0.01 level of probability.gene resistance is qualitative; polygenic resistance is quantitative, the equivalent offield resistance (Takase 1962) or horizontal resistance (Van der Plank 1968).Mature plant resistance or field resistance results from the cumulative effect ofminor genes for resistance as plants grow older (Russell 1978), regardless of whetherthe resistance is evaluated in the greenhouse or in the field. Field-resistant varietieswith horizontal or low-level resistance to all biotypes should continue to resistbiotypes capable of overcoming major-gene resistance.A technique recently developed at the International Rice Research Institute(IRRI) evaluates breeding lines for field resistance (Velusamy et al 1986, ZhangZhi-tao et al 1986, Medrano et al 1987). Using this technique, several rice varietieshave been identified which are resistant to N. lugens at both the vegetative andreproductive phases in the field and as 30d-old plants in the greenhouse. UsingSSST, 7- to 10-d-old seedlings of those varieties were evaluated as susceptible.Occasionally, field-resistant varieties evaluated by SSST on the day the susceptiblecheck plants are killed are rated as moderately resistant. If damage is evaluated later,those moderately resistant varieties are rated susceptible.The design and methods used for MSST are the same as for SSST, except thateach seedling is infested at 10 DAS with 3-5 2d- or 3d-instar nymphs instead of 8-10nymphs. In SSST, the nymphs kill susceptible varieties 8-9 d after infestation. InMSST, the F 1 progeny of initially infesting insects kill the susceptible check 25-28 dafter infestation.In SSST, Kencana was found to be moderately susceptible to N. lugensbiotypes 1,2, and 3 at IRRI and in Bangladesh, Solomon Islands, and Sri Lanka. InMSST, it was found to be resistant at IRRI (Table 3) (Medrano et al 1987). In SSST,IR46 and IR26, with the major resistance gene Bph-l, were susceptible at alllocations. In MSST, however, IR46 was resistant to biotype 2 and the SolomonIslands population; IR26 was susceptible. In IRRI field tests, IR46 was resistant tobiotype 2. Utri Rajapan and Triveni also had lower damage ratings in MSST than inSSST at all locations. At IRRI, Utri Rajapan rated 7.5 in SSST and 1 in MSST forbiotype 2. It showed tolerance for biotype 2 after the seedling stage in bothgreenhouse and field tests. Utri Rajapan and Triveni showed field resistance to N.lugens at all locations.

116 R.C. SaxenaTable 3. N. lugens damage in selected rice varieties in standard (SSST) and modifiedseedbox screening tests (MSST) (Medrano et al 1987). aVarietyBiotype 1 Biotype 2 Biotype 3SSST MSST SSST MSST SSST MSSTSinna SivappuKencanaIR26IR46ASD7Utri RajapanTriveniTN 11.5 a6.5 bc3.0 a1.5 a2.0 a6.0 b8.0 cd9.0 d1.0 a2.5 ab2.5 ab1.5 ab1.0 a2.0 ab3.0 b9.0 c1.5 a6.0 a8.5 d8.0 d3.5 b7.5 cd8.5 d9.0 d1.5 a 1.0 a 1.5 a1.5 a 6.0 bcd 3.0 ab8.5 c 3.5 ab 4.0 ab1.5 a 4.0 bc 3.5 ab1.5 a 8.5 d 8.5 c1.0 a 6.5 cd 4.5 ab5.0 b 7.5 d 6.5 bc9.0 c 8.0 d 9.0 ca SES scale 0-9: 0 = no damage, 9 = plants killed. In a column, means followed bya common letter are not different at the 5% level by DMRT.Utri Rajapan is being used as a donor of field resistance to N. lugens in IRRIbreeding programs. It also has high tolerance for N. lugens and S. furcifera andresistance to rice tungro virus.Field screening for resistance. The stability of resistance in breeding lines andvarieties identified in the greenhouse needs to be tested under different agroclimaticconditions and pest (biotype) situations. Field screening is convenient if pestnumbers are high or if accessible pest hot spots can be identified. Resurgenceinducinginsecticides also have been used as a tool in field-screening against N.lugens (Heinrichs et al 1978). Damage scores and the percentage of hopperburnedplants can identify varieties with moderate levels of field resistance. An InternationalRice Brown Planthopper Nursery is being grown in many cooperating Asiancountries to monitor N. lugens biotypes in different geographical regions and toidentify new sources of resistance.Regional monitoring of virulent strains of N. virescens and evaluating thesusceptibility of selected breeding lines and varieties to tungro virus are being done inthe Philippines. In Midsayap, North Cotabato, varieties with high pest infestationlevels generally had higher tungro incidence (Table 4), except Utri Merah. Thatvariety supported a high pest density but had a very low tungro incidence. Somevarieties resistant to the pest also had low tungro incidence. Others, despite the lowpest population carried, had relatively higher tungro incidence. IR29 is used as theresistant check against N. virescens at IRRI, but it seems to have lost its resistance tothe pest in North Cotabato.Evaluating resistance by insect responseDifferences in insect feeding, growth, and population increase on different ricevarieties reflect relative varietal susceptibility or resistance.Ingesting and assimilating food. Newly emerged leafhoppers or planthoppersare weighed individually and enclosed singly in parafilm sachets on a leaf or leafsheath of a resistant or susceptible rice plant (Pathak et al 1982, Saxena and Pathak1977). The control insect is enclosed with only a moist cotton swab, and used to

Durable resistance to rice insect pests 117Table 4. N. virescens infestation levels on selected varieties and breeding lines andincidence of rice tungro virus (RTW at 30 d after transplanting, Midsayap, NorthCotabato, Philippines, Aug 1987. aVarietyAdults andnymphs(no./10 hills)RTV(%)VarietyAdults andnymphs(no./10 hills)RTV(%)IR8120IR26111IR29103IR36155IR42147IR5632IR6219IR6498IR66192IR28224-32-3-214lR28228-12-31-1-2 21lR31868-64-2-533 107lR32429-47-32-265lR32453-20-32-232ARC1155414a Av. of 4 replications.991009999100485010099122210093132ASD7BabaweeModdai KaruppanMudgoPalasithariPankhari 203PTB8PTB 18PTB33Rathu HeenathiTAPL796TriveniUtri RajapanUtri MerahTN150 9944 9849 9955 9611 821 015 5615 7315 3540 7832 2062 8237 995 4136 100assess weight loss due to katabolism. After 24 h, each female and its excreta areweighed separately. The amount of food assimilated is calculated as(C1 - C2)Food assimilated = WI × + (W1 - W2)C1where W1 and W2 are the initial and final weights of test insects and C1 and C2 arethe initial and final weights of control insects. Food ingested = food assimilated +weight of excreta. Saxena and Pathak (1977) used this method to demonstratedistinct differences in food intake by three N. lugens biotypes feeding on differentrice varieties.Locating feeding sites. Knowledge of the mode of leafhopper and planthopperfeeding on the rice plant is useful in evaluating and elucidating the mode of varietalresistance to these pests and the viral diseases transmitted. Using safranine, a dyehighly selective to lignin that is translocated in xylem vessels, Khan and Saxena(1984a) monitored the feeding behavior of N. virescens, N. lugens, and S. furcifera.The honeydew excreted by the hoppers on treated and untreated plants wascollected on filter paper disks and the filter paper treated with 0.1% ninhydrinacetonesolution. On safranine-treated seedlings, red honeydew spots indicatedxylem feeding, bluish amino acid spots indicated phloem feeding.Other methods to quantify insect feeding. The feeding activity of riceleafhoppers and planthoppers on resistant plants also has been quantified bycollecting honeydew on filter paper disks, staining them with ninhydrin (Paguia et al1980) or bromocresol green (Pathak and Heinrichs 1982), and measuring the area(mm 2 ).

118 R.C. SaxenaElectronically recorded insect feeding. McLean and Kinsey (1964) devised amethod of recording aphid feeding. The insect and the plant are connected to anelectronic recorder. Voltage fluctuations produced during insect probing, salivation,and phloem or xylem feeding are amplified and recorded. With this device, distinctdifferences in feeding by S. furcifera (Khan and Saxena 1984b), N. lugens (Velusamyand Heinrichs 1986a), and N. virescens (Khan and Saxena 1985a,b) on resistant andsusceptible varieties were demonstrated (Fig. 1). S. furcifera and N. lugens fedexclusively from the phloem; N. virescens fed from both the phloem and the xylem.On susceptible varieties, the insects probed readily and fed longer; on resistantvarieties, they probed briefly but repeatedly, reducing the effective ingestion period.Growth index. Growth is measured by the number of nymphs that becomeadults and the time taken to reach the adult stage on resistant and susceptible plants.An insect's growth index is calculated as the ratio of percentage on nymphsdeveloping into adults to mean growth period in days (Saxena et al 1974). The higherthe growth index, the more suitable the variety for insect growth.Population increase. A host plant’s suitability is reflected in total insectpopulation. That total represents the combined effect of feeding, metabolism ofingested food, growth, survival, fecundity, and hatchability of eggs (Heinrichs andRapusas 1983, Khan and Saxena 1985c). Thirty-d-old resistant and susceptiblepotted plants covered with mylar cages are infested with a specified number of pairsof newly emerged males and females. If infested plants start showing symptoms ofhopperburn, the insects are transferred to fresh plants of identical age. Individualinsects that fall to the soil and die are counted every week and pooled with the rest ofthe progeny. Differences in the increase of leafhopper and planthopper populationson resistant and susceptible varieties are marked.Basis of resistanceIn developing pest-resistant varieties, it is important to understand the basis ofresistance and consider possible effects on other pests (Chapman and Bernays 1977).In an uncoordinated breeding program, an anomalous situation could arise in whichfactors tending to both favor and suppress a pest would be developed simultaneously.For practical use, resistance characteristics that render one varietyunsuitable or less suitable to an insect that is adapted to a nonresistant variety of thesame plant species are important. Both morphological and biochemical factorscontribute to plant resistance.Morphological factorsMorphological or biophysical resistance factors in plants interfere with insect vision,orientation, locomotion, feeding, mating, and oviposition. Biophysical resistance isa general, more stable type of resistance than biochemical resistance. Traditional ricevarieties differ more widely in their stature, shape, stem diameter, presence orabsence of trichomes, awns, etc., than do modern high-yielding varieties, whichconform to a more or less typical plant type.

Durable resistance to rice insect pests 1191. Waveforms recorded during S. furcifera feeding on susceptible TN1 (a) and resistant IR2035-117-3 (b)and during N. virescens feeding on susceptible TN1 (c) and resistant ASD7 (d) rice varieties using anelectronic monitoring device (Khan and Saxena 1984b; 1985a,b).Resistance to striped stem borer was found in varieties with leaf sheaths tightlywrapped around the stem, closely packed vascular bundles, and a thicksclerenchymatous layer (Patanakamjorn and Pathak 1967). Those characters deterlarval boring activity. The mandibles of larvae feeding on rice varieties containinghigh silica wear out faster. Variety Dahanala 2220, which has a vestiture of long andshort hairs (375/cm 2 ) on the abaxial surface, is resistant to rice thrips. Nira, aglabrous variety (28 hairs/cm 2 ), is highly susceptible (Fig. 2) (R. C. Saxena and E. B.Medina, IRRI, unpubl.). The most spectacular example of morphological resistanceagainst rice bug feeding is in the variety Saathi, which has a panicle completelyenclosed in the leaf sheath of the flag leaf. Whether genes that confer morphologicalresistance are closely linked with biochemical resistance factors is not known.

120 R.C. Saxena2. Scanning electron micrographs of a) rice variety Dahanala 2220 having a vestiture of long and shorthairs on the abaxial surface, and b) Nira, a glabrous variety. Dahanala 2220 is resistant to rice thrips, Nirais susceptible (Saxena and Medina, IRRI, unpubl).Biochemical factorsBiochemical factors in plants are far more important than morphological factors inimparting resistance. They confer a range of resistance, from general to highlyspecific. Once a pest species adapts to a variety’s biochemical factors, or if a variety isgrown in an area where an already adapted virulent biotypes exists, resistance breaksdown. The factors may be nutritionally based or may include nonnutritionalchemicals, called allelochemicals, that affect insect behavior, growth, health, orphysiology.Saxena (1986) reviewed the effect of rice plant allelochemicals on the behaviorand physiology of C. suppressalis, N. lugens, S. furcifera, and N. virescens. Steamdistillate extract of plants of resistant variety TKM6 inhibited striped stem boreroviposition, hatching, and larval development. Extract of susceptible varietyRexoro induced oviposition. The oviposition inhibitor in TKM6 was identified aspentadecanal. Extracts of susceptible varieties attracted N. lugens females, those ofresistant varieties repelled them (Saxena and Okech 1985). Fewer individuals settledand fed on susceptible TN1 plants sprayed with extracts of resistant ARC6650 andPTB33 varieties than on plants sprayed with TN1 extract. Applying extract ofresistant ASD7 (Khan and Saxena 1985a) and of resistant IR2035-117-3 (Khan andSaxena 1986) to TN1 plants reduced feeding by N. virescens and S. furcifera females,respectively.Extracts of resistant varieties and nonhost barnyard grass applied topicallykilled more adults than did extracts of susceptible plants (Saxena 1986). N. lugensbiotypes differed in their relative vulnerabilities to extracts of resistant varieties. Gaschromatographic analysis of resistant and susceptible plant extracts showedqualitative and quantitative differences in volatiles (Fig. 3) (Saxena and Okech1985). Major amino acids differed quantitatively in Mudgo, ASD7, and TN1; theirability to stimulate feeding by different biotypes of N. lugens also differed.Volatile compounds from resistant host plants may penetrate the insect’s bodythrough the cuticle or spiracles during feeding and respiration. Leafhopper andplanthopper nymphs and stem borer larvae, particularly young instars that have a

Durable resistance to rice insect pests 1213. Gas chromatograms of volatiles of leaf sheaths of rice varieties susceptible (TN1) and resistant to N.lugens. biotype 1 (Saxena and Okech 1985).vestiture of poorly chitinized cuticle and relatively larger surface area because oftheir smaller size, are more vulnerable to volatiles emanating from resistant riceplants.ToleranceTolerance is an inherent or acquired capacity to endure a physical or biologicalstress. In the context of plant-insect interactions, tolerant plants do not resist a pest;they are susceptible to infestation. But possibly because of their innate vigor, theycan withstand infestation, and yield losses are not incurred. Without inhibiting pestpopulations and without exerting severe selection on the pest, the tolerant varieties

122 R.C. Saxenaaccomplish the same net result, as far as crop damage or yield loss is concerned, asactive resistance mechanisms. They help minimize selection of new biotypes of a pest(Horber 1980).Although little is known about the sources of tolerance, certain plants orvarieties do seem capable of enduring more pest pressure longer. That plantendurance exposes the insect pests for a longer time to their natural enemies andother abiotic factors that limit pest populations. Because tolerance traits are alsoheritable, they are of practical value. Increased utilization of tolerance in breedingprograms is expected to minimize the biotype problem (Tingey 1981, Velusamy andHeinrichs 1986b).Tolerance for insect pests is being increasingly sought in rice varieties. Hiraoand Todoroki (1975) reported that greenhouse and field tests showed the indicavariety Mudgo was tolerant of N. lugens. In India, breeding line 57-5-1 from a crossof IR8/PTB20 was reported to be tolerant of N. lugens; it gave higher yields eventhough it supported a population that caused hopperburn in susceptible varieties(Nair et al 1978). Ho et al (1982) reported that Triveni was tolerant of N. lugensdamage at both the vegetative and mature growth stages. Yield reduction was only40% on 35-,50-, and 70-d-old Triveni plants infested with 400 hoppers; it was 100%on susceptible TN1 .Panda and Heinrichs (1983) determined the levels of tolerance and antibiosis inrice varieties having moderate resistance to N. lugens. Tolerance was measured asplant weight loss due to insect feeding (functional plant loss index [FPLI]); antibiosiswas measured as dry weight of the total insect population. Utri Rajapan wasconsidered tolerant of N. lugens biotype 2 because it had a significantly lower FPLI(55%) even though it supported a population equivalent to that which damagedsusceptible IR26 (FPLI = 90%). Moderately resistant Triveni, Kencana, and IR46had lower FPLIs than IR26 because they had both tolerance and antibiosis. UtriRajapan was more tolerant of N. lugens than other moderately resistant varieties.Based on pooled regression estimates of FPLI on N. lugens weight, Utri Rajapanwas classified as tolerant and IR46, Kencana, and Triveni as moderately resistant(due to low levels of antibiosis). In field trials, IR26 plants had a damage rating of 9and were completely hopperburned, resulting in total yield loss. Although UtriRajapan had a field population of N. lugens equal to that on susceptible IR26, yieldreduction was only 25%, indicating tolerance.With an electronic device, Velusamy and Heinrichs (1986b) monitored feedingby N. lugens biotype 3 females on resistant IR56; field-resistant IR36, IR42, and UtriRajapan; and susceptible TN1. Distinct differences in waveforms for probing,salivation, ‘A’ waveform (reflecting attempted localization of sieve elements ofphloem), and ingestion were observed on resistant and susceptible varieties. N.lugens probed repeatedly, salivated for a long time, and ingested little from thephloem of resistant IR56. Phloem ingestion from Utri Rajapan was significantly lessthan from susceptible TN1, but significantly more than from resistant IR56 andfield-resistant IR36 and IR42 (Table 5). Phloem ingestion decreased significantly onolder IR36, IR42, and Utri Rajapan plants.Although fewer N. lugens biotype 2 females settled on and fed significantly lesson tolerant Utri Rajapan than on susceptible TN1, the insect’s growth and

Durable resistance to rice insect pests 123Table 5. Electronically recorded events during 180-min feeding bouts by N. lugensbiotype 3 females on various rice varieties (Velusamy and Heinrichs 1986). aVarietyProbes Salivation ‘A’ waveform(no.) (min) (min)Phloemfeeding(min)IR56 69 a 84 a 53 a9 eIR36 44 b 49 b 43 b46 dIR4243 b 44 c 41 b 51 cUtri Rajapan 37 c 39 c 36 c 73 bTN1 (S check) 15 d 15 d 11 d 131 aa Means of 7 replications, each replication using a new insect and a new plant.Within a column, means followed by a common letter are not significantlydifferent at the 5% level by DMRT.development, longevity, fecundity, and rate of population increase were as high onUtri Rajapan as on TN1 (R. C. Saxena and V. F. Magalit, IRRI, unpubl.). Theallelochemical and nutritional factors that influence N. lugens behavior on UtriRajapan are being investigated.Utri Rajapan also has field resistance to S. furcifera (E. A. Heinrichs and N.Panda, IRRI, unpubl.) and is resistant to rice ragged stunt and tungro viruses,transmitted by N. lugens and N. virescens, respectively (Panda et al 1984). Althoughsome Utri Rajapan plants became infected with tungro virus, symptoms were mildand disappeared as the plant matured. Of the two tungro-associated viruses, onlyrice tungro bacilliform virus was present in Utri Rajapan. Velusamy et al (1987)studied the inheritance of field resistance to N. lugens in Utri Rajapan and Triveni.Reactions of F 1 , F 2 , and F 3 populations from the crosses of Utri Rajapan andTriveni with TN1 showed that two independently segregating recessive genes governthe field resistance in both varieties. They have common genes for field tolerance.In the past, breeding for tolerance or field resistance received less attentionbecause appropriate identification techniques were lacking, tolerant varieties mayserve as reservoirs of the insect vectors of viruses, and information on inheritance oftolerance in crop plants was meager. These gaps are being overcome as far as rice isconcerned.The tolerance character will increasingly be used to supplement othermechanisms of insect resistance in rice. In new varieties, tolerance for a pest willprovide greater stability against dynamic insect pests and the viral diseasestransmitted by them.BiotypesBiotypes occur in nature as products of a survival mechanism for the persistence ofinsect species. It is well known that phytophagous insects can be highly selective andspecialized in the hosts they consume. Diversification and specialization of an insectspecies into well-adapted biotypes enable it to keep pace with the evolution andescalation of the defenses of the host plant, either through natural selection or bymanipulation of the host plant genome through planned breeding (Saxena and

124 R.C. SaxenaRueda 1982). Failure to recognize the existence of insect biotypes in nature can havefar-reaching and frustrating consequences in pest management (Diehl and Bush1984).Among rice insect pests, biotypes have been identified in N. lugens, N.virescens, and O. oryzae. Occurrence of biotypes in S. furcifera and S. orizicola issuspected. The threat of N. lugens biotypes to the stability of resistant varieties isparticularly serious because of its marked genetic plasticity and wide range ofdistribution. The possibility of N. lugens biotypes was anticipated as early as 1969,soon after discovery of pest-resistant variety Mudgo. At present, N. lugens biotypesare identified principally by the differential reactions of host rice varieties to the pestin greenhouse screening and field-planted test nurseries at a wide range of locations.Repeated collection and rearing of field populations on resistant varieties since1971 has culminated in the selection of three distinct N. lugens biotypes, designatedbiotype 1, biotype 2, and biotype 3 (IRRI 1976). Biotype 1 infests only varietieslacking genes for N. lugens resistance. Biotype 2 can thrive on varieties having theBph-1 resistance gene and on those susceptible to biotype 1. Biotype 3 can infestvarieties having bph-2 gene and those susceptible to biotype 1. However, none ofthese biotypes thrive on varieties with Bph-3 and bph-4 resistance genes, nor onPTB33 with two unidentified genes.IR26, the first BPH-resistant, major gene variety released, effectivelysuppressed the general BPH population (predominantly biotype 1) in the Philippinesin 1973-75 (Fig. 4, Pathak and Khush 1979) and in Indonesia in 1974-76 (Harahap1979). But IR26 became susceptible when biotype 2 evolved in the Philippines.Reports of widespread hopperburn indicated a shift in the predominant N. lugenspopulation because of the extreme selection pressure exerted by intensive cultivationof IR26. It also confirmed that N. lugens populations are genetically plastic.IR36 and IR42, with the bph-2 gene, were released in 1976 and 1977 and werewidely grown for 7-8 yr, during which time their resistance held in most areas. But in1982, both were damaged in North Sumatra and Mindanao (IRRI 1983). Ingreenhouse tests at IRRI, the Mindanao biotype also killed IR26, indicating that thisbiotype differed from biotypes 2 and 3 (Medrano and Heinrichs 1985). By 1982,IR56 and IR60 with the Bph-3 gene were available. IR56 was resistant to N. lugens inboth North Sumatra and Mindanao. Lines with bph-4 genes for resistance also havebeen developed, and recently new resistance genes bph-5 and Bph-6 have beenidentified (IRRI 1986a). Resistance to all biotypes from wild Oryza officinalis hasalso been transferred to O. sativa.A new population of N. lugens was recovered from the common weed grassLeersia hexandra in the Philippines (Domingo et al 1983, Heinrichs and Medrano1984) and neighboring countries. Although this biotype can infest and kill theLeersia host, it did not survive on any of the rice varieties tested so far. Conversely,the rice-infesting biotypes failed to survive on Leersia.Biotypes 1, 2, and 3 and the Leersia grass-infesting biotypes can bedistinguished as distinct populations on the basis of rostral, tarsal, and antennalcharacters (Fig. 5) (Saxena and Rueda 1982, Saxena et al 1983, Saxena and Barrion1985). This shows that considerable genetic variation may be concealed inapparently morphologically alike individuals and populations of N. lugens.

Durable resistance to rice insect pests 1254. Total number of N. lugens macropters caught in 3 light traps at IRRI. Intensive cultivation of resistantvarieties has contributed to adecline of N. lugens populations since mid-1973 but has also caused a shift inbiotype populations (Saxena and Barrion 1985).5. Discriminant scores of biotype of N. lugens from L. hexandra and of biotypes 1, 2, and 3 based onrostral, leg, and antennal characters of macropterous females (Saxena et al 1983).Cytological, electrophoretic, and hybridization studies also support the view that N.lugens species can diversify into biotypes.Three-dimensional spatial relationships of 19 N. lugens populations originatingfrom Australia, South, Southeast, and East Asia (based on discriminant functionanalysis of morphometric data on rostral, tarsal, and antennal characters) showed

126 R.C. Saxenathat the allopatric populations have a higher magnitude of segregation than thesympatric populations (Fig. 6) (IRRI 1986b).Pankhari 203, ASD7, ASD8, and IR8 are resistant to N. virescens in thePhilippines but susceptible in Bangladesh, suggesting two different biotypes(Rezaul-Karim and Pathak 1982). Significant differences in the morphornetrics ofmale and female genital and abdominal characters in the two biotype populationshave been recorded (Saxena et al 1985).Differential varietal reactions to O. oryzae populations in India, Indonesia, SriLanka, and Thailand point to the occurrence of biotypes (Pathak and Saxena 1980).Deployment of host plant resistanceDespite the nagging problem of pest biotypes, host plant resistance will remain a keycomponent in pest management. Breeding insect-resistant varieties is an essentialfeature of rice varietal improvement programs, and vast areas will continue to beplanted to insect-resistant varieties. Although IR26, the first BPH-resistant variety,succumbed early, IR36 continued to be successfully planted for nearly a decade. In1982, IR36 was planted on almost 11 million ha.IR26 has a simple pedigree, with BPH resistance inherited only from TKM6.IR36 and other varieties, such as IR56, IR60, and IR62, have many resistant parentsin their ancestry, including wild rice Oryza nivara. IR36, IR46, and IR56 also havemultiple resistance to other pests and tolerance for some soil problems. Because thenatural defenses of varieties with monogenic (major gene) resistance eventuallybecome vulnerable to new pest biotypes, the future strategy is to widen the geneticbase of resistance to include both major and minor genes. Current strategies inbreeding insect-resistant cultivars are both short term and long term (Khush 1979).Identification of new genes and donorsNarrowing genetic diversity by cultivating only varieties that derive their pestresistance from a limited gene pool would not portend well for the future. Theidentification of new genes and donors is of utmost importance. More than 45,000O. sativa accessions and 435 accessions of wild rices have been screened at IRRI inpursuit of new sources of resistance to the BPH. Of these, more than 400 cultivatedrices and about 200 wild accessions have been found resistant to one or more of thethree N. lugens biotypes at IRRI. Trials in 1986 showed that 40% of the elite linespossessed combined resistance against all 3 biotypes in the dry season; 70% hadcombined resistance in the wet season. New resistance genes bph-5 and Bph-6recently were identified.Sequential release of varieties with major genesThe nature of the genetics of resistance should not be so complex that plant breederscannot easily manage to combine resistance with other desirable characters. Theconsequence is that single major resistance genes are incorporated into improvedplant types and that resistant varieties are made available to farmers sequentially.IR26, IR28, IR29, and IR30 with the Bph-1 gene were grown in the Philippines in

Durable resistance to rice insect pests 1276. Three-dimensional spatial relationships of nineteen populations of brown planthopper N. lugensmacropterous females based on discriminant function analysis (IRRI 1986b).1973-76. When N. lugens biotype 2 emerged in 1974-76, IR36 and IR42 with thebph-2 gene were released. IR56 and IR60 with Bph-3 were already available in 1982,when IR36 and IR42 were damaged in North Sumatra and Mindanao. Lines withthe bph-4 gene for resistance have already been developed, although IR56 and IR60are still holding against N. lugens. Resistance also has been transferred from wildrice O. officinalis to cultivated rice and similar efforts to transfer resistance fromother wild species are under way.It may be possible to systematically rotate the same specific resistance gene, if aparticular biotype exists only at a certain time and place. This strategy has not beenused against N. lugens because new sources of resistance are still being discovered.However, varietal rotation and different groups of varieties are being used effectivelyagainst N. virescens biotypes during wet and dry cropping seasons, either singly or incombination (Manwan et al 1987).Pyramiding major genesTwo or more major genes can now be combined in the same improved variety. Bph-1and bph-2 genes cannot be combined because of close linkage, but Bph-3 and bph-4segregate independently of Bph-1 and bph-2. Crosses have now been made tocombine Bph-1 and Bph-3; bph-2 and Bph-1; and bph-4, bph-2, and bph-4. Suchgene combinations may be effective longer and may retard biotype selection.

128 R.C. SaxenaMultiline varietiesThis approach envisages incorporating several major genes into an isogenicbackground, then mechanically mixing the progeny to form a multiline variety.Multiline rice varieties have largely remained untested, partly because appropriatematerials are not yet available. Kampuchean rice farmers have adopted a somewhatsimple but practical approach to multiline varieties. They plant 5-7 varieties thathave different growth durations and grain types, for different household needs andas insurance against pest outbreaks and weather vagaries (Chang 1984).Horizontal resistanceThe concept of using moderate resistance and tolerance to slow down biotypeselection currently is receiving greater attention. The possibility of incorporatingminor genes is being explored at IRRI. The durable resistance of IR36 and IR46against N. lugens is attributed to the presence of minor genes for resistance. Crosseswith tolerant varieties such as Utri Rajapan could yield progeny with stableresistance. But incorporating horizontal resistance is time-consuming because of lowheritability.Wide hybridizationAmong the 19 species of wild rices are some that can serve as valuable sources ofinsect resistance. Resistance to leafhoppers and planthoppers has already beentransferred from the O. officinalis (2n = 24, CC genome) group to O. sativa (2n = 24,AA genome) by using the embryo rescue technique. The progeny are backcrossedwith improved plant types. The next step is to combine these new sources ofresistance with other breeding lines. Protoplast culture and fusion techniques mayeventually solve the problem of prefertilization incompatibility between wild speciesand cultivated species.Future considerationsThe practical benefits to be gained from breeding for insect resistance in rice justifysustained research on all aspects of host plant resistance. The current emphasis ondurability of resistance is part of the fine tuning of the process. Durable resistance isexpected to relieve rice farmers of the need to repeatedly change varieties. Durabilitycombined with multiple pest and disease resistance will further reduce the need toapply pesticides. The buffering effect of plant resistance also should be considered inthe context of integrated pest control. Such an approach would lead to a greaterappreciation of the importance of identifying and utilizing moderate levels ofresistance or tolerance and would favor conservation of a pest’s natural enemies.Goals for attaining maximum yield and durability of rice varieties shouldbalance. Instead of applying inorganic nitrogen, an integrated approach to nutrientmanagement will be needed. Even if varieties are resistant, high levels of inorganicnitrogenous fertilizers increase pest growth and reproduction. For example,although the N. lugens biotype 1 population remained lower on resistant Mudgothan on susceptible TN1, pest progeny was several times greater when high rates of

Durable resistance to rice insect pests 129inorganic nitrogen were applied to Mudgo (Pathak 1977). Insecticidal control alsoneeds to be rationalized to ensure stability. Resurgence-causing insecticidessignificantly increased N. lugens biotype 2 populations, not only on susceptible IR29but also on moderately resistant IR40 and resistant IR42, although the degree ofresurgence varied (Reissig et al 1982).Those measures can be expected to keep pest populations below economicinjury levels. However, they may not altogether stop the evolution of pest biotypes.In both natural and managed systems, more heterogeneity exists in pest populationsthan is generally recognized. A pest’s gene pool is continuously enriched throughmigration, mutation, chromosomal translocations, genic recombinations, and otherevolutionary phenomena. Systematic biotype surveillance in major rice-growingareas will help in adjusting strategies of breeding for insect resistance. All possibleresistance mechanisms, whether governed by major or minor genes, will have to beconsidered. Major gene resistance will help buy time for developing more durableresistance.Increased understanding of the causes of resistance, identification of chemicalsthat confer resistance or susceptibility, and the study of their inheritance wouldgreatly improve breeding for insect resistance. If resistance involves more than onedefense chemical, it may become possible to develop durable resistance. Pests are notlikely to overcome sensitivity to several substances simultaneously.The present generalization of the role of major and minor genes will be resolvedas far as insect pests are concerned. In cucurbits, it has been found that resistance dueto high levels of cucurbitacin is controlled by many loci. But in cotton, change of asingle gene that causes production of one different metabolic enzyme may result inthe production of an array of sesquiterpenes, secondary compounds that affectcotton insect pests (Gould 1983).Programs for insect management that take full advantage of host plantresistance will encompass a broad range of basic and applied research. Developmentof precise and creative methods to enhance natural variation within cultivated ricewill pave the way for ecologically sound and economically rewarding pestmanagement.References citedChang T T (1984) Conservation of rice genetic resources: luxury or necessity? Science 224:251-256.Chapman R F, Bernays F (1977) The chemical resistance of plants to insect attack. Pages 603-643 inStudy week on natural products and protection of plants. G. B. Marini-Bettolo, ed. PontificaAcademia Scientiarum, Casina F10 IV, Citta Del Vaticano.Cramer H H (1967) Plant protection and world crop production. Pflanzenschutz-Nachr. 20:15-24.Diehl S R, Bush G L (1984) An evolutionary and applied perspective of insect biotypes. Annu. Rev.Entomol. 29:471-504.Domingo I T, Heinrichs E A, Saxena R C (1983) Occurrence of brown planthopper on Leersia hexandrain the Philippines. Int. Rice Res. Newsl. 8(4):17.Gallun R L, Khush G S (1980) Genetic factors affecting expression and stability of resistance. Pages 63-85in Breeding plants resistant to insects. F. G. Maxwell and P. R. Jennings, eds. John Wiley and Sons,New York.Gould F (1983) Genetics of plant-herbivore systems: interaction between applied and basic study. Pages599-653 in Variable plants and herbivores in natural and managed systems. R. F. Denno and M. S.Mclure, eds. Academic Press, New York.

130 R.C. SaxenaHarahap Z (1979) Breeding for resistance to brown planthopper and grassy stunt virus in Indonesia.Pages 201-208 in Brown planthopper: threat to rice production in Asia. International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Heinrichs E A (1986) Perspectives and directions for the continued development of insect-resistant ricevarieties. Agric. Ecosyst. Environ. 18:9-36.Heinrichs E A, Medrano F G (1984) Leersia hexandra, a weed host of the brown planthopper,Nilaparvata lugens (Stål). Crop Prot. 3:77-85.Heinrichs E A, Rapusas H (1983) Levels of resistance to the whitebacked planthopper, Sogatella furcifera(Homoptera: Delphacidae), in rice varieties with different resistance genes. Environ. Entomol.12:1793-1797.Heinrichs E A, Viajante V, Aquino G (1978) Resurgence-inducing insecticides as a tool in field screeningof rices against the brown planthopper. Int. Rice Res. Newsl. 3(3):10-11.Hirao J, Todoroki A (1975) Mechanisms of resistance to the brown planthopper in the rice lines bredfrom Mudgo cultivar at the TARC. Proc. Assoc. Plant Prot. Kyushu 21:56-60.Ho D T, Heinrichs E A, Medrano F G (1982) Tolerance of rice variety Triveni to the brown planthopperNilaparvata lugens. Environ. Entomol. 11:598-602.Horber E (1980) Types and classifications of resistance. Pages 15-21 in Breeding plants resistant to insects.F. G. Maxwell and P. R. Jennings, eds. John Wiley and Sons, New York.IRRI—International Rice Research Institute (1976) Selection and studies on sources of resistance:biotypes. Pages 107-108 in Annual report for 1975. P.O. Box 933, Manila, Philippines.IRRI—International Rice Research Institute (1983) One step ahead. Pages 5-6 in Research highlights for1982. P.O. Box 933, Manila, Philippines.IRRI—International Rice Research Institute (1986a) Morphometric variations in brown planthopper.Pages 61-62 in Annual report for 1985. P.O. Box 933, Manila, Philippines.IRRI—International Rice Research Institute (1986b) Pest resistance. Pages 30-31 in Research highlightsfor 1985. P.O. Box 933, Manila, Philippines.Khan Z R, Saxena R C (1984a) Electronically recorded waveforms associated with the feeding behaviorof Sogatella furcifera (Homoptera: Delphacidae) on susceptible and resistant rice varieties. J. Econ.Entomol. 77:1479-1482.Khan Z R, Saxena R C (1984b) Technique for demonstrating phloem for xylem feeding by leafhoppers(Homoptera: Cicadellidae) and planthoppers (Homoptera: Delphacidae) on susceptible andresistant rice varieties. J. Econ. Entomol. 77:550-552.Khan Z R, Saxena R C (1985a) Effect of steam distillate extract of a resistant rice variety on feedingbehavior of Nephotettix virescens (Homoptera: Cicadellidae). J. Econ. Entomol. 78:562-566.Khan Z R, Saxena R C (1985b) Behavioral and physiological responses of Sogatella furcifera(Homoptera: Delphacidae) to selected resistant and susceptible rice cultivars. J. Econ. Entomol.78:1280-1286.Khan Z R, Saxena R C (1985c) Mode of feeding and growth of Nephotetix virescens (Hornoptera:Cicadellidae) on selected resistant and susceptible rice varieties. J. Econ. Entomol. 78:583-587.Khan Z R, Saxena R C (1986) Effect of steam distillate extract of resistant and susceptible rice cultivars onbehavior of Sogatella furcifera (Homoptera: Delphacidae). J. Econ. Entomol. 79:928-937.Khush G S (1979) Genetics and breeding for resistance to the brown planthopper. Pages 321-332 inBrown planthopper: threat to rice production in Asia. International Rice Research Institute, P.O.Box 933, Manila, Philippines.McLean D L, Kinsey M G (1964) A technique for electronically recording aphid feeding and salivation.Nature (London) 202:1358-1359.Manwan I, Sama S, Rizvi S A (1987) Management strategy to control tungro in Indonesia. Pages 92-97 inProceedings of the workshop on rice tungro virus. Ministry of Agriculture, Indonesia.Medrano F G, Heinrichs E A (1985) Response of resistant rices to brown planthoppers (BPH) collected inMindanao, Philippines. Int. Rice Res. Newsl. 10(6):14-15.Medrano F G, Heinrichs E A, Alam S, Jackson Y Y, Senadhira D, Wichramasinghe N (1987) Modifiedseedbox screening test to identify field resistance to brown planthopper (BPH). Int. Rice Res. Newsl.12(3):17-18.Metcalf R L, Luckman W H (1975) Introduction to insect pest management. John Wiley and Sons, NewYork. 520 p.Nair N R, Nair S S, Rambai N (1978) A new high yielding brown planthopper tolerant variety of rice.Oryza 17:161.Paguia P, Pathak M D, Heinrichs E A (1980) Honeydew excretion measurement techniques fordetermining differential feeding activity of biotypes of Nilaparvata lugens on rice varieties. J. Econ.Entomol. 73:35-40.

Durable resistance to rice insect pests 131Painter R H (1951) Insect resistance in crop plants. McMilIan Co., New York. 577 p.Panda N, Heinrichs E A (1983) Levels of tolerance and antibiosis in rice varieties having moderateresistance to the brown planthopper, Nilaparvata lugens. Environ. Entomol. 12:1204-1214.Panda N, Heinrichs E A, Hibino H (1984) Resistance of the rice variety Utri Rajapan to the ragged stuntand tungro viruses. Crop Prot. 3:491-500.Patanakamjorn S, Pathak M D (1967) Varietal resistance of the Asiatic rice borer, Chilo suppressalis(Lepidoptera: Crambidae), and its association with various plant characteristics. Ann. Entomol.Soc. Am. 60:287-292.Pathak M D (1977) Defense of the rice crop against insect pests. Pages 287-295 in The genetic basis ofepidemics in agriculture. R. Day, ed. New York Academy of Sciences, New York.Pathak M D, Dhaliwal G S (1981) Trends and strategies for rice insect problems in tropical Asia. IRRIRes. Pap. Ser. 64. 15 p.Pathak M D, Khush G S (1979) Studies of varietal resistance in rice to the brown planthopper at IRRI.Pages 287-301 in Brown planthopper: threat to rice production in Asia. International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Pathak M D, Saxena R C (1980) Breeding approaches in rice. Pages 421-455 in Breeding plants resistantto insects. F. G. Maxwell and P. R. Jennings, eds. John Wiley and Sons, New York.Pathak P K, Heinrichs E A (1982) Bromocresol green indicator for measuring feeding activity ofNilaparvata lugens on rice varidies. Philipp. Entomol. 11:85-90.Pathak P K, Saxena R C, Heinrichs E A (1982) Parafilm sachet for measuring honeydew excretion byNilaparvata lugens on rice. J. Econ. Entomol. 75:194-195.Reissig W H, Heinrichs E A, Valencia S L (1982) Insecticide-induced resurgence of the brownplanthopper, Niloparvata lugens, on rice varieties with different levels of resistance. Environ.Entomol. 11:165-168.Rezaul-Karim A N M, Pathak M D (1982) New genes for resistance to green leafhopper, Nephottetixvirescens (Distant) in rice, Oryza sativa L. Crop Prot. 1:483-490.Russell G E (1978) Plant breeding for pest and disease resistance. Butterworths, London. 485 p.Saxena K N (1969) Patterns of insect plant relationships determining susceptibility or resistance ofdifferent plants to an insect. Entomol. Exp. Appl. 12:751-766.Saxena K N, Gandhi J R, Saxena R C (1974) Patterns of relationships between certain leafhoppers andplants. I. Responses to plants. Entomol. Exp. Appl. 17:303-313.Saxena R C (1986) Biochemical basis of insect resistance in rice varieties. Pages 142-159 in Naturalresistance of plants to pests: roles of allelochemicals. M. B. Green and P. A. Hedin, eds. AmericanChemical Society, Washington, D.C.Saxena R C, Barrion A A (1985) Biotypes of the brown planthopper Nilaparvata lugens (Stål) andstrategies in deployment of host plant resistance. Insect Sci. Appl. 6:271-289.Saxena R C, Khan Z R (1984) Comparison between free-choice and no-choice seedling bulk tests forevaluating resistance of rice varieties to the whitebacked planthopper. Crop Sci. 24:1204-1206.Saxena R C, Okech S H (1985) Role of plant volatiles in resistance of selected rice varieties to the brownplanthopper Nilaparvata lugens (Stål) (Homoptera: Delphacidae). J. Chem. Ecol. 11:1601-1616.Saxena R C, Pathak M D (1977) Factors affecting resistance of rice varieties to brown planthopper,Nilaparvata lugens (Stål). In Proceedings of the 8th annual conference of the Pest Control Council ofthe Philippines. Bacolod City.Saxena R C, Rueda L M (1982) Morphological variations among three biotypes of the brownplanthopper Nilaparvata lugens in the Philippines. Insect Sci. Appl. 3:193-210.Saxena R C, Soriano M V, Barrion A A (1985) Comparative morphometrics of male and female genitaland abdominal characters in Nephotettix virescens (Distant) population from Bangladesh and thePhilippines. Int. Rice Res. Newsl. 10(3):27-28.Saxena R C, Velasco M V, Barrion A A (1983) Morphological variations between brown planthopperbiotypes and Leersia hexandra and rice in the Philippines. Int. Rice Res. Newsl. 8(3):3.Simons M D (1972) Polygenic resistance to plant disease and its use in breeding resistant cultivars. J.Environ. Qual. 1:232.Takase B N (1962) Tests and screening for resistance in breeding potato varieties resistant to late blight.Recent Adv. Breed. 3:9-17.Tingey W M (1981) The environmental control of insects using plant resistance. Pages 175-197 in CRChandbook of pest management in agriculture. D. Pimentel, ed. CRC Press, Boca Raton, Florida.Van der Plank J E (1968) Disease resistance in plants. Academic Press, New York.Velusamy R, Heinrichs E A (1986a) Electronic monitoring of feeding behavior of Nilaparvata lugens(Homoptera: Delphacidae) on resistant and susceptible rice cultivars. Environ. Entomol. 15:678-682,Velusamy R, Heinrichs E A (1986b) Tolerance in crop plants to insects. Insect Sci. Appl. 7:689-696.

132 KC. SaxenaVelusamy R, Heinrichs E A, Khush G S (1987) Genetics of field resistance to brown planthopper. CropSci. 27:299-300.Velusamy R, Heinrichs E A, Medrano F G (1986) Greenhouse techniques to identify field resistance to thebrown planthopper, Nilaparvata lugens (Stål) (Hornoptera: Delphacidae), in rice cultivars. CropProt. 5:328-333.Zhang Zhi-Tao, Heinrichs E A, Medrano F G (1986) Seedbox screening tests to determine resistance tobrown planthopper (BPH). Int. Rice Res. Newsl. 11(2):10-11.NotesAddress: R. C. Saxena, Entomology Department, International Rice Research Institute, P.O. Box 933, Manila,Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Emerging weed control technologyfor broadcast seeded riceS. K. DE DATTA, P. C. BERNASOR, T. R. MIGO, M. A. LLAGAS, AND P. NANTASOMSARANAsian rice farmers traditionally have depended on land preparation, use oftall cultivars, flooding, and hand weeding to control weeds. When modernsemidwarf rices that respond to high fertilizer rates were introduced, thetime spent on hand or rotary weeding increased tremendously andweeding costs rose. As a result, more farmers turned to herbicides, suchas 2,4-D, MCPA, butachlor, and thiobencarb, for weed control. Increasinglabor costs, expanding irrigated areas, development of early-maturing ricecultivars, and increased availability of low-cost herbicides have encouragedthe adoption of broadcast seeding in Thailand, Malaysia, and thePhilippines. Butachlor is now marketed in 22 countries, thiobencarb in 56countries. These herbicides are the most widely used in broadcast seededrice. In the Philippines, the benefit-cost ratio for weed control usingherbicides is highly attractive. Chemical control has been further improvedby modifying application techniques. Integration of control methods for adiverse weed flora has resulted in sustained control without adverseeffects on the environment.Cultivated rice seems to have originated, and almost certainly was developed, inareas where water was available (Matsunaka 1983). Even in ancient times, ricegrown under submergence was believed to compete with weeds better than uplandrice. Selecting submerged rice culture was considered the first step in traditionalweed control. Transplanted seedlings have an advantage over weeds that emergeafter transplanting. In the tropics, where weeds grow rapidly, older rice seedlings orrapid-growing tall cultivars are used to give rice plants a head start.Many of the practices used in Asian rice production contribute indirectly toweed control (De Datta and Herdt 1983). Land preparation, especially harrowingand puddling, provides weed-free conditions at planting and often reduces weedgrowth in the established crop (Bernasor and De Datta 1987). Keeping waterstanding in the field suppresses weed growth considerably (De Datta et al 1973, Kim1986, Mabbayad 1967). Intermediate tall rice cultivars have been reported to bemore competitive than semidwarf rices (De Datta 1974).In most tropical Asian countries, year-round moderately warm temperaturesand high humidity encourage year-round weed growth. The most common weeds intropical lowland rice in South and Southeast Asia are Echinochloa glabrescensMunro ex Hook. f., Echinochloa crus-galli (Burm. f.) Presl, Sphenoclea zeylanica

134 De Datta et alGaert., Cyperus difformis L., Cyperus iria L., Fimbristylis miliacea (L.) Vahl,Paspalum distichum L., and Scirpus maritimus L. (De Datta 1981).In general, substitutive, preventive, and complementary weed control practiceskeep populations of these weeds to a manageable level. But they do not eliminateweeds. Farmers still must resort to direct methods, such as hand weeding,mechanical weeding, and herbicide use (De Datta 1981).We summarize here information on recent advances in weed control technologyfor tropical lowland rice, focusing on broadcast seeded flooded rice.Weed control in transplanted riceTransplanting is the most common rice culture in the Asian tropics, and probablywill remain so for a long time. In developing weed control technology fortransplanted rice, the focus should be on ecological and economic sustainability.Hand weedingHand weeding is the most common and effective weed control method intransplanted rice. However, it is tedious and time-consuming. Studies show thathand weeding and harvesting are two of the most labor-intensive operations ingrowing modern rice cultivars in South and Southeast Asia (De Datta and Herdt1983). In several IRRI experiments, an average 540 labor hours was required toweed 1 ha twice; 150 labor hours often is adequate for 1 thorough hand weeding and1 spot weeding.Mechanical weedingSimple machines have been developed to suppress weeds, but they can only be usedwhen rice is planted in straight rows. The rotary weeder is by far the most efficient. Itmay be pushed manually or powered by a small gasoline engine (De Datta andHerdt 1983). Human-powered rotary weeding combined with other methods ofweed control is widely used in some Philippine provinces (Smith and Gascon 1979).In Java, Indonesia, progressive farmers with more than 1 ha land use rotary weeders(Syarifuddin et al 1983). Although the labor used in rotary weedings was half thatneeded for two hand weedings, grain yield was lower (De Datta 1981). The slightlylower yield with two rotary weedings perhaps was due to the inability of the rotaryweeder to remove weeds within or close to rice hills.HerbicidesChemical weed control has become popular among rice farmers largely because ofrising labor costs. The area of transplanted rice on which herbicides are used hasbeen increasing steadily in both temperate and tropical Asia (Chang and De Datta1972).Chemical weed control began when the herbicidal property of 2,4-D wasdiscovered. The phenoxy acid herbicides 2,4-D and MCPA have effectivelycontrolled broadleaf weeds and sedges in transplanted rice when applied 2-3 wk afterweeds emerged (Moomaw et al 1968, Mukhopadhyay 1978, Vega 1954). In the

Weed control for broadcast seeded rice 135Asian tropics, 2,4-D and MCPA applied 4-5 d after transplanting (DT) ricecontrolled grasses as well as broadleaf weeds and sedges (De Datta et al 1968, DeDatta and Lacsina 1969). More selective herbicides, such as butachlor andthiobencarb, used as a preemergence (4-5 DT) and postemergence (6-8 DT)treatments, also controlled weeds in transplanted rice.Weed control in broadcast seeded flooded riceIn most of tropical Asia where labor is abundant and inexpensive, transplanting ricehas been the common practice. But in many developed countries, the labor supply islimited and costly. The more efficient practice of direct seeding rice has been adopted(Smith and Shaw 1966). Among the direct seeding methods, broadcast seeding ofpregerminated rice is faster and easier and produces grain yields similar to andoccasionally higher than those obtained by transplanting (De Datta 1986). In acontinuous cropping experiment at IRRI, the average yield of 49 crops (1968-83) ofbroadcast seeded flooded rice was 4.6 t/ha, similar to the 4.8 t/ha yield withtransplanted rice (Table 1) (Cia et al 1984).Although direct seeding has been practiced by farmers in India, Bangladesh,and (particularly) Sri Lanka for many years (De Datta 1981,1986), it has not beenwidely adopted in Southeast Asia because of the poor weed control associated with it(Bernasor and De Datta 1983). Weed control is critical in broadcast seeded floodedrice because the land is exposed during initial crop growth stages (Moorthy andDubey 1979). It is difficult to hand weed during this period because rice seedlings aresimilar to grassy weed seedlings. Hand weeders moving through the fields cannotavoid destroying some rice plants (Chang and De Datta 1974, Subiah andMorachan 1976).Since the late 1970s, broadcast seeded rice has become increasingly importantin Southeast Asia (De Datta and Flinn 1986). With the increase in irrigated area, theavailability of herbicides, the development of early-maturing rice varieties, andimproved fertilizer management taking place amid socioeconomic constraints,many farmers in the Philippines, Thailand, and Malaysia have been encouraged toswitch from traditional transplanted to broadcast seeded flooded rice (De Datta1986). In the dry season in the Philippines, rice is broadcast seeded on at least 30% ofthe irrigated land (De Datta 1986). In Central Luzon, Philippines, where most ricecrops are irrigated, the number of farmers adopting wet seeded rice increased fromless than 2% in 1979 to more than 80% in 1984 (Coxhead 1984, Moody and Cordova1985). In Thailand, at least 0.8 million ha was planted to broadcast seeded rice inTable 1. Yields of transplanted and direct seeded flooded rice at maximum Nrates (av of 49 crops). a IRRl continuous cropping experiment (Cia et al 1984).Planting methodGrain yield (t/ha)TransplantedDirect seededa 294 rice crops and 2 N rates. Dry season N rate = 150 kg; wet season N rate = 90kg.4.84.6

136 De Datta et al1985 (De Datta 1986). In the Muda area of Malaysia, the area planted to directseeded rice increased from 40% in 1983 (De Datta 1986) to 65% in 1986 (Ho 1987).Herbicides for annual weedsHerbicides are now considered indispensable for cost-efficient weed control inlowland rice, particularly broadcast seeded flooded rice. Continuous herbicidescreening trials at IRRI have identified chemicals suitable for weed control inbroadcast seeded flooded rice. Results of IRRI research and trials with cooperatingcountries have encouraged broad use of butachlor in 22 countries (IRRI 1969) andthiobencarb in 56 (IRRI 1970). The herbicides most widely used in the Philippinesare butachlor and thiobencarb (De Datta and Flinn 1986). In Thailand, somecommonly used herbicides (besides butachlor and thiobencarb) are oxadiazon andpiperophos + dimethymetryn (Vongsaroj 1985). In the Muda area, Malaysia, allfarmers use 2,4-D butyl ester applied 25-30 d after seeding (DAS) for broadleaf weedand sedge control (Ho 1984). Chemicals currently being tested are trifluralin,piperophos, pyrazolate, molinate, fluazifop-butyl, butachlor, thiobencarb, andoxadiazon.The continuing screening trials identify promising new herbicides and at thesame time confirm the performance of previously screened herbicides and refineapplication techniques. In the 1984 wet season preliminary screening trial,quinchlorac and MO/butachlor appeared promising for broadcast seeded floodedrice (Table 2) (De Datta and Flinn 1986, IRRI 1985). Quinchlorac controlled weedseffectively, caused only slight crop injury, and was associated with significantlyhigher yields than the thiobencarb/2,4-D check. In the dry and wet season advancedscreening trials, average yields over 3 yr in 75% of the sites (IRRI and the PhilippineBureau of Plant Industry research stations at Maligaya, Bicol, and Visayas) with allherbicide treatments were significantly higher than the untreated check (Table 3)(Bernasor and De Datta 1983, Cia et al 1984, De Datta and Flinn 1986). Butachlorand thiobencarb, earlier reported to be highly selective on broadcast seeded floodedrice (De Datta and Bernasor 1971, 1973; De Datta 1981; De Datta and Herdt 1983),occasionally were moderately toxic to rice when combined with 2,4-D. Thisoccurred most frequently when plots had too much water or when herbicides wereapplied during cold weather (Bernasor and De Datta 1983). However, rice plantsalways recovered from the toxicity-caused injury.Timing of application. Chemical weed control in direct seeded rice calls for amore strict timing of application than in transplanted rice, because direct seeded riceand weed seedlings are in similar growth stages (De Datta and Bernasor 1973).Applying preemergence herbicides earlier than 6 DAS usually results in severe cropinjury; applying later than 8 DAS results in poor weed control. Weed control andcrop safety in broadcast seeded flooded rice were improved by applying someherbicides before seeding. Arceo and Mercado (1981) reported better grass controland higher yields when butachlor was applied 2 d before seeding (DBS) rather thanat 6 DAS. Mabbayad and Moody (1982) obtained similar results at IRRI.In a 1983 dry season experiment, applying a granular formulation of butachlorand piperophos/2,4-D at 3 DBS controlled grassy weeds and improved grain yieldsbetter than at 6 DAS (Table 4) (Migo and De Datta 1983). Weed control and grain

Weed control for broadcast seeded rice 137Table 2. Effect of early postemergence application (6 DAS) of new herbicides on weed control,crop tolerance, and yield of broadcast seeded flooded IR58 a (Adapted from De Datta and Flinn1986).TreatmentWeed biomass (g/m 2 )Rate(kg ai/ha) Broadleaf Grases SedgesweedsToxicityrating bYield(t/ha)Quinchlorac 0.3 0 a 0 a 2 a 2Thiobencarb/2,4-D 1.5 0 a 6 a 54 b 3MO/butachlor 1.0 34 b 13 a 10 ab 4Untreated check – 43 b 69 b 57 b 04.3 a3.3 b3.1 b0 ca Av of 3 replications. In a column, means followed by a common letter are not significantlydifferent at the 5% level. DAS = d after seeding. b Rated on a 0-10 scale 2 wk after herbicideapplication: 0 = no toxicity, 10 = complete kill.Table 3. Effect of herbicides applied 6-8 d after seeding on grain yield of direct seeded floodedrices (IR36 and IR42) at IRRl and at the Philippine Bureau of Plant Industry experiment stationsat Maligaya and Bicol (dry season) a (Bernasor and De Datta 1983).Treatment bRate(kg ai/ha)Yield(t/ha)IRRI Maligaya c Bicol MeanNaproanilide/thiobencarbPiperophos/2,4-D IPEThiobencarb/2,4-D IPEButachlor + 2,4-D IPEBifenox/2,4-D EEUntreated check1.0/0.70.33/0.171.0/0.50.75 + 0.52.0/0.66–4.9 a4.3 a4.6 a4.4 a4.6 a2.6 b4.6 a4.8 a4.2 a4.8 a3.6 a2.3 b5.4 a4.7 ab4.5 ab3.6 bc4.4 ab2.5 c5.0 a4.6 a4.4 a4.3 a4.2 a2.5 ba In a column, means followed by a common letter are not significantly different at the 5% levelby DMRT. b Herbicides were applied as proprietary mixtures. IPE = isopropyl ester, EE = ethylester. + = herbicides were applied one after the other. c Av of only 4 yr.Table 4. Grassy weed biomass and grain yield of broadcast seeded flooded IR36as affected by time of herbicide application a (Adopted from Migo and De Datta1983).HerbicideRate(kg ai/ha)ApplicationTime bWeedbiomass(g/m 2 )Grainyield(t/ha)ButachlorPiperophos/2,4-DUntreated check0.750.750.30.3–3 DBS6 DAS3 DBS6 DAS–6 a103 b12 a180 b62 b4.5 a1.6 b4.4 a2.5 b2.5 ba Av of 4 replications, In a column, means followed by a common letter are notsignificantly different at the 5% level. b DBS = d before seeding, DAS = d afterseeding.

138 De Datta et alyield were similar in the 6 DAS treatments of both herbicides and the untreatedcontrol. Results suggest that some herbicides can be applied before seeding withouthurting broadcast seeded flooded rice. Because they are applied only before weedsemerge, weed control is improved and grain yields are increased.Application technique. The usual method of diluting pesticides with largevolumes of water is inefficient. In the tropics, the only sprayers widely available tofarmers are those that deliver a spray at several hundred liters per hectare; that is aburden to many farmers (Migo and De Datta 1983).During the 1982 dry season, applying 4 herbicides undiluted, using a herbicidecontainer bottle through its modified nippled cap, or diluted to 350 liters/ ha, usingthe conventional knapsack sprayer, were compared for efficiency. All treatmentswere applied 6 DAS. Regardless of application method, oxadiazon, butachlor, and1. Total weed weight at harvest and grain yield of broadcast seeded flooded IR36 as affected by method ofherbicide application (av of 3 replications). Bars with a common letter are not significantly different byDMRT at the 5% level (Migo and De Datta 1983).

Weed control for broadcast seeded rice 139pendimethalin provided adequate weed control and resulted in similar dry weedweights. Resulting rice yields with herbicide were significantly higher than those ofthe untreated check. Diluted thiobencarb gave significantly less dry weed weightthan undiluted (Fig. 1) (Migo and De Datta 1983). But either way, thiobencarbresulted in higher yields than did the butachlor check, undiluted butachlor, anddiluted pendimethalin. All other herbicides, regardless of application method, gavedry weed weights and yields similar to those of the butachlor check.These results suggest that applying undiluted herbicide with a sprinkler bottle isan effective alternative to applying with a knapsack sprayer, without sacrificingweed control and grain yield.Perennial weed controlIn the Philippines and some other tropical Asian countries, perennial weedsP. distichum and S. maritimus pose a serious threat to lowland rice.Cultural control. Often, P. distichum is not a serious weed problem where thereis good tillage and water management (De Datta 1981). In long-term experiments, astillage intensity increased from zero to the conventional 1 plowing + 2 harrowings orfrom 1 harrowing to 3 harrowings, P. distichum stand declined significantly (Fig. 2)(Bernasor and De Datta 1981, 1987). Similar results were reported in other tillagestudies (De Datta 1983, Diop 1982, Manuel et al 1979). S. maritimus growth notcontrolled by thorough tillage (Fig. 2) (Bernasor and De Datta 1987) can be2. Weed population and grain yield of broadcast seeded flooded rice as affected by tillage, cultivar, andherbicide (av of 6 crops). IRRI, 1984-86. Within tillage, cultivar, or herbicide, items with a common letterare not significantly different at the 5% level by DMRT (Bemasor and De Datta 1987).

Table 5. Effect of land and water management on Scirrus maritimus populations in untreated plots (Bernasor and De Datta 1986).473 c16 b0 a452 b172 b4 a21-156**-4*244 c20 b0 a400 b344 b0 a-1 56-3240426 c68 b4 a342 c120 b0 a84-524*Land preparationS. maritimus a (no./m 2 )1974 1975 1976 1977 1978 1979 1980 1981 1982 1983Continuous wetAlternate dry and wetContinuous dry289 b59 a65 a406 b36 a35 a205 c60 b15 aDry season191 b 395 c59 a 26 b26 a 4 a295 a57 b9 a288 b3 a6 aContinuous wetAlternate dry and wetContinuous dry310 b236 b29 a325 b167 a20 a300 b191 b67 aWet season421 b 177 c209 b 53 b35 a 6 a278 b146 b4 a360 b154 b4 aContinuous wetAlternate dry and wetContinuous dry-21-1773681-131*15-95-150-52Difference-230 218-150 -27-9 -217-895-7 2-151**2a Av of two replications. In a column, means followed by a common letter are not Significantly different at the 5% level. l = significant at the 5% level,** = significant at the 1% level.

Weed control for broadcast seeded rice 141minimized by appropriate soil and water management. In a long-term studyinvolving shifting land management and cropping patterns, soil cultivation changedfrom continuous wet to continuous dry. S. maritimus populations in the untreatedcontrols decreased (Table 5) (Bernasor and De Datta 1986). However, culturalcontrol methods often take care of only one or two weed species, leaving others toproliferate.Chemical control. Fenoprop and mecoprop, first found effective in Europe(Arcuset and Pecheur 1967, Baldacci et al 1964, Chiapparini 1966), also providedoutstanding control of S. maritimus in the Philippines (De Datta and Lacsina 1974).Propanil and 2,4-D and their combinations (Madrid and Lubigan 1975, Paller et al1971, Vegaet al 1971), and bentazon (De Datta 1974, De Datta 1977, De Datta andLacsina 1974, Ghosh et al 1973) also controlled weeds effectively.Several studies have shown that the efficacy of herbicides can be improvedthrough timely application (Bernasor 1983, De Datta and Bernasor 1981, Madridand Lubigan 1975). Bentazon and 2,4-D applied 25 DAS provided better weedcontrol than when applied 15 DAS. They also gave significantly higher yields thanthe untreated check, regardless of application time (Table 6) (Bernasor and De Datta1986, De Datta and Flinn 1986, IRRI 1983). However, another herbicide had to beapplied to control grassy weeds.Results of preliminary field screening trials in 1982 showed that bensulfuronmethylapplied 6-8 DAS provided excellent control, not only of S. maritimus butalso of E. glabrescens, E. crus-galli ssp. hispidula, and M. vaginalis (Table 7)(Bernasor and De Datta 1986, IRRI 1983). Herbicides that control both annual andperennial weeds, such as bensulfuron-methyl, would eliminate the need for herbicidecombinations and improve prospects for costefficient weed control technology.Integrated weed controlThe growing concern that using the same method of weed control continuously maylead to a buildup of weed species tolerant of the control method used motivated thedevelopment of integrated control methods (De Datta 1981). The technologycombines tillage, cultivar, seeding rate, N management practices, and herbicide use.Table 6. Effect of time of application of bentazon and 2.4-D on control of Scirpusmaritimus and yield of broadcast seeded flooded lR36 a (Bernasor and DeDatta 1986).TreatmentRate(kg ai/ha)ApplicationTimeS. maritimusbiomass(g/m 2 )Grainyield(t/ha)Bentazon 1.0 15 DAS 41 b 3.9 aBentazon 1.0 25 DAS 6 a 3.8 a2,4-D 0.75 15 DAS 80 c 4.1 a2.4-D 0.75 25 DAS 20 ab 4.2 aUntreated check – – 201 c 1.8 ba Av of 4 replications. In a column, means followed by a common letter are notsignificantly different at the 5% level. Butachlor was applied at 1.0 kg ai/ha 6 dafter seeding (DAS) to all treatments to control annual weeds.

142 De Datta et alTable 7. Effect of bensulfuron-methyl on control of Scirpus maritimus and annual weeds andyield of broadcast seeded flooded IR42 a (Adapted from Bernasor and De Datta 1986).Weed biomass (g/m 2 )ApplicationRate Time b S. maritimus Grasse c Monochoria(kg ai/ha)vaginalisGrainyield(t/ha)Bensulfuron-methyl 0.05 6 DAS 4 a 0 a 0 a 5.0 aUntreated check – – 36 b 11 b 17 b 2.2 bBensulfuron-methyl 0.05 8 DAS 4 a 0 a 0 a 4.7 aButachlor 1.0 6 DAS 128 b 0 a 1 a 2.1 ba Av of 3 replications, In a column, means followed by a Common letter are not significantly differentat the 5% level. b DAS = d after seeding. c Echinochloa glabrescens and E. crus-galli ssp,hispidula.Effect of tillage, cultivar, and herbicide. To evaluate tillage for weed control, itis critical to study it with other cultural practices for more than 1 yr. In a 3-yr(1984-86) study on the long-term effect of tillage, cultivar, and herbicide on weedshift and control in broadcast seeded flooded rice, increasing tillage frequency from1 to 3 harrowings lowered the P. distichum population and increased grain yield, butincreased the S. maritimus stand (Fig. 2) (Bernasor and De Datta 1987). Cultivartype did not affect weed control, indicating that IR36 and IR29723-143-3-2-1 areequally competitive with weeds. Bensulfuron-methyl and propanil + 2,4-D providedadequate control of S. maritimus and the annuals, but P. distichum incidenceincreased.These results emphasize the importance of combined control methods whereweed flora is diverse for effective total weed control.Effect of cultivar, seeding rate, nitrogen management, and herbicide. Goodstand establishment in broadcast seeded flooded rice, using a competitive ricecultivar at an appropriate seeding rate, often substantially minimizes weedcompetition. Further weed control is achieved through appropriate use of herbicidesand other cultural practices. In our study, short-statured IR64 yielded higher thanintermediate-statured IR29723-143-3-2-1 and tall Binato in butachlor-treated plotswhen N was applied in three splits (Table 8) (Llagas et al 1987). In unweeded plots,IR29723-143-3-2-1 gave the highest yield, IR64 and Binato gave similar yields.When N was applied in two splits, IR64 and IR29723-143-3-2-1 had similar yields,which were higher than that of Binato at each weeding regime. Among the threecultivars, only IR64 was affected by N management. In the butachlor-treated plots,IR64 yielded higher when N was applied in three splits. But when weeds were leftuncontrolled, IR64 yielded more when N was applied in two splits.These results suggest that N efficiency is best expressed when weeds areeffectively controlled, particularly with N-responsive varieties.Farm-level constraints trialWe have conducted several on-farm trials in the Philippines to monitor and evaluatefarmers' production practices and to compare these with improved practices.

Weed control for broadcast seeded rice 143Table 8. Effect of cultivar, N management, and weed control on grain yield ofbroadcast seeded flooded rice (Llagas et al 1987).Grain yield (t/ha) aCultivarN management bN 1 N 2 DifferenceIR64lR29723-143-3-2-1BinatoButachlor fb 2,4 D4.4 a3.4 b1.7 cUnweeded1.6 b2.4 a1.3 bDifference2.8**1.0**0.4ns3.5 a3.2 a1.8 b0.9**0.2ns–0.1nsIR64IR29723-143-3-2-1BinatoIR64lR29723-143-3-2-1Binato2.5 a2.6 a1.5 b1.0**0.6*0.3ns–0.9**–0.2ns–0.2nsa Av of 4 replications and 2 seeding rates. b N1 = 1/3 N basal incorporated, 1/3 Nat 30 d after seeding (DAS), 1/3 N 5-7 d before panicle initiation (DBPI); N 2 =2/3 N at 15 DAS, 1/3 N 5-7 DBPI. fb = followed by, * = significant at the 5%level, ** = significant at the 1% level, ns = not significant.In these experiments, the use of a combination of herbicides was found to benecessary to control a single weed vegetation for optimum rice yields (De Datta andFlinn 1986). Our data further showed that improved herbicide weed controlaccounted for about 30% on average of the yield gap over farmers’ weed controlpractices; actual contributions varied enormously across sites and over years (Fig. 3).The benefit-cost ratio of researcher’s weed control compared with farmers’ practiceswas extremely high in the dry season, on average exceeding 20:1.Economics of broadcast seeding in puddled fieldsThe economics of broadcast seeding in puddled fields or in dry soil varies widelyamong Southeast Asian countries (De Datta 1986). Experience in the Philippinesshows that considerably less labor is needed to produce broadcast seeded floodedrice than to produce transplanted rice. In a survey area in Central Luzon, Coxhead(1984) found that only 36 preharvest labor days/ha is needed for broadcast seededflooded rice, compared with 63 for transplanted rice. The most obvious savings arein crop establishment.Considerations leading to a widescale shift from transplanting to direct seedingin Northwest Selangor, Malaysia, were potential savings in production costs,savings in time, timeliness of plantings, and savings in labor due to mechanization.Malaysian data show the incurred labor cost was only US$15/ha with directseeding, compared with US$37/ ha with transplanting.In Philippine constraints research sites, the benefit-cost ratio of weed controlwith herbicides in irrigated areas was 25:1 (Table 9) (De Datta 1986). Usually, a 2.5:1

144 De Datta et al3. Average yields with farmers’ and high inputs, and relative contributions of fertilizer, weed control, andinsect control to improved rice yields on broadcast seeded irrigated farms in 3 provinces in thePhilippines. 1984 and 1985 dry seasons (De Datta and Flinn 1986).Table 9. Comparison of the economics of high levels of weed control and farmers’ current practicesin irrigated wet seeded rice. 1984 dry season, three Philippine provinces (De Datta 1986).ProvinceSites(no.)Weed control cost (US$/ha)Farmers’practiceResearchers’practiceDifferenceProfit ($/ha)Farmers’practiceResearchers’practiceBenefit-costratioBulacanCamarines SurNueva Ecija21511281199971–25412012187143172526> 25benefit-cost ratio is considered adequate for farmer’s field conditions. The 25:1benefit-cost ratio makes chemical weed control technology highly attractive tofarmers.In Thailand, the trend to change from hand weeding to herbicide use isincreasing because of high labor costs. Farm labor wages have increased more than100% within 5 yr, from US$1/labor day in 1978 to US$2.50 in 1983. The shift has notbeen as fast as it might have been because farmers’ acceptance of chemical weedcontrol technology is limited by lack of resources and knowledge of herbicide use(Suwunnamek 1983).

Weed control for broadcast seeded rice 145These findings show that broadcast seeded flooded rice culture is economicallyattractive to many Southeast Asian rice farmers. The practice will be adopted furtherin tropical Asia as production costs increase without commensurate increases in riceprices. Weed scientists and agronomists are challenged to develop and continue toimprove weed control technologies that are economically and ecologicallysustainable.References citedArceo L M, Mercado G L (1981) Improving crop safety of butachlor in wet-seeded rice ( Oryza sativa L.).Philipp. J. Weed Sci. 8:19-24.Arcuset P, Pecheur J (1967) The use of fenoprop to destroy Cyperaceae in rice. Weed Abstr. 17(6):412.Baldacci E, Chiapparini L, Moglia C (1964) Further researches on the use of CDAA alone and inmixtures with DPA and mecoprop for the control of barnyard grass ( Echinochloa sp.) and otherweeds of rice [in Italian, English summary]. Riso 13(1):25-47.Bernasor P C (1983) Effects of 2,4-D on different growth stages of the perennial weed bulrush ( Scirpusrnaritimus L.) and lowland rice ( Oryza sativa L.). MS thesis, University of the Philippines at LosBaños, Laguna, Philippines. 58 p.Bernasor P C, De Datta S K (1981) Long-term effect of reduced tillage on weed shift in lowland rice.Paper presented at the 12th Annual Conference of the Pest Control Council of the Philippines, 13-15May 1981, University of the Philippines at Los Baños, Laguna, Philippines.Bernasor P C, De Datta S K (1983) Integration of cultural management and chemical control of weeds inbroadcast-seeded flooded rice. Pages 137-155 in Proceedings of the 9th Asian-Pacific Weed ScienceSociety Conference. November 28-December 2, 1983. Asian-Pacific Weed Science Society, Manila,Philippines.Bernasor P C. De Datta S K (1986) Chemical and cultural control of bulrush ( Scirpus maritimus L.) andannual weeds in lowland rice (Oryza sativa L.). Weed Res. 26:233-244.Bernasor P C, De Datta S K (1987) Long-term effects of chemical and nonchemical weed control inbroadcast seeded flooded rice. Paper presented at the 18th Annual Conference of the Pest ControlCouncil of the Philippines, 5-8 May 1987, Davao City, Philippines.Chang W L, De Datta S K (1972) Control of weeds in transplanted rice in Taiwan as affected by variousrates and times of applying granular benthiocarb and butachlor. Int. Rice Comm. Newsl. 21(1):8-16.Chang W L, De Datta S K (1974) Chemical weed control in direct-seeded flooded rice in Taiwan. PANS20(4):425-428.Chiapparini L (1966) The weeds of rice fields and their control in Italy. Weed Abstr. 15(5/6):247.Cia B S, Bernasor P C, De Datta S K (1984) Development and spread of modern technology for directseeded flooded rice in tropical Asia. Paper presented at the 15th Scientific Meeting of the CropScience Society of the Philippines, 16-20 May 1984, Batac, Ilocos Norte, Philippines.Coxhead I A (1984) The economics of wet seeding: inducement to and consequences of some recentchanges in the Philippine rice cultivation. M Agric Dev Econ thesis, Australian National University,Canberra, Australia.De Datta S K (1974) Weed control in rice: present status and future challenge. Philipp. Weed Sci. Bull.1(1):1-16.De Datta S K (1977) Approaches in the control and management of perennial weeds in rice. Page 204 inProceedings of the 6th Asian-Pacific Weed Science Society Conference, July 11-17, 1977. Asian-Pacific Weed Science Society, Jakarta, Indonesia.De Datta S K (1981) Principles and practices of rice production. John Wiley & Sons, Inc., New York.618 p.De Datta S K (1983) Perennial weeds and their control in the tropics. Pages 255-272 in Weed control inrice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.De Datta S K (1986) Technology development and spread of direct-seeded flooded rice in Southeast Asia.Exp. Agric. 22:417-426.De Datta S K, Bernasor P C (1971) Selectivity of some new herbicides for direct-seeded flooded rice in thetropics. Weed Res. 11(1):41-46.De Datta S K, Bernasor P C (1973) Chemical weed control in broadcast-seeded flooded tropical rice.Weed Res. 13:351-354.

146 De Datta et alDe Datta S K, Bernasor PC (1981) Integrated control of perennial weed Scirpus maritimus L. in wetlandrice. Pages 219-229 in Proceedings of the 8th Asian-Pacific Weed Science Society Conference,November 22-29, 1981. Asian-Pacific Weed Science Society, Bangalore, India,De Datta S K, Flinn J C (1986) Technology and economics of weed control in broadcast-seeded floodedrice in the tropics. Pages 51-74 in Weeds and the environment in the tropics. Proceedings of the 10thAsian-Pacific Weed Science Society Conference, November 24-30, 1985. Asian-Pacific WeedScience Society, Chiangmai, Thailand.De DattaS K, Herdt R W (1983) Weed control technology in irrigated rice. Pages 89-108 in Weed controlin rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.De Datta S K, Krupp H K, Alvarez E I, Modgal S C (1973) Water management in flooded tropical rice.Pages 1-18 in Water management practices in Philippine irrigation systems: research and operations.International Rice Research Institute, P.O. Box 933, Manila, Philippines.De Datta S K, Lacsina R Q (1969) Promising new herbicides for transplanted tropical rice. Pages 112-128in Proceedings of the 2nd Asian-Pacific Weed Control Interchange, June 16-20, 1969. Asian-PacificWeed Science Society, Los Baños, Philippines.De Datta S K, Lacsina R Q (1974) Herbicides for the control of perennial sedge Scirpus maritimus L. inflooded tropical rice. PANS 20(1):68-75.De Datta S K, Park J K, Hawes J E (1968) Granular herbicides for controlling grasses and other weeds intransplanted rice. Int. Rice Comm. Newsl. 17(4):21-29.Diop A M (1982) Weed control in broadcast-seeded wetland rice ( Oryza sativa L. ). MS thesis, Universityof the Philippines at Los Baños, Laguna, Philippines. 94 p.Ghosh A K, Kim D K, De Datta S K (1973) Germination, growth rate, and control of perennial sedgeScirpus maritimus in tropical rice. Pages 249-256 in Proceedings of the 3rd Asian-Pacific WeedControl Interchange, June 7-12, 1971. Asian-Pacific Weed Science Society, Malaysia.Ho Nai Kin (1984) Weed problems in the direct seeded and volunteer seedling fields in the Muda area.Paper presented at the Forum on Pest and Disease Problems Associated with Direct Seeded RiceCultivation, 1 Sep 1984, Palau Penang, Malaysia.Ho Nai Kin (1987) Direct seeding culture and integrated weed management programme in the Mudaarea. Paper presented at the Annual Meeting of the National Integrated Pest Control Committee ofMalaysia, 12 Mar 1987, Kuala Lumpur, Malaysia.IRRI—International Rice Research Institute (1969) Annual report for 1968. P.O. Box 933, Manila,Philippines. 402 p.IRRI—International Rice Research Institute (1970) Annual report for 1969. P.O. Box 933, Manila,Philippines. 266 p.IRRI—International Rice Research Institute (1983) Annual report for 1982. P.O. Box 933, Manila,Philippines. 532 p.IRRI—International Rice Research Institute (1985) Annual report for 1984. P.O. Box 933, Manila,Philippines. 504 p.Kim J S (1986) Changes in magnitude of weed reserve in lowland rice soils under simulated croppingcondition. Ph Ddissertation, University of the Philippines at Los Baños, Laguna, Philippines. 100 p.Llagas M A, Migo T R, De Datta S K (1987) Integrated weed management in broadcast seeded floodedrice. Paper presented at the 18th Annual Conference of the Pest Control Council of the Philippines,5-8 May 1987, Davao City, Philippines.Mabbayad B B (1967) Tillage techniques and planting methods for lowland rice. MS thesis, University ofthe Philippines at Los Baños, Laguna, Philippines. 110 p.Mabbayad M O, Moody K (1982) Effect of time of application and the use of naphthalic anhydride onbutachlor phytotoxicity in wet-seeded rice. Paper presented at the 13th Annual Conference of thePest Control Council of the Philippines, 5-8 May 1982, Baguio City, Philippines.Madrid M T Jr., Lubigan RT (1975) Evaluation of different 2,4-D formulations for the control of Scirpusmaritimus in lowland rice. Pages 18-21 in Weed science report, 1974-1975. Department ofAgronomy, University of the Philippines at Los Baños, Laguna, Philippines.Manuel J S, Mercado B L, Lubigan R T (1979) Approaches to the control of Puspalum distichum L. inlowland rice. Philipp. Agric. 62:255-261.Matsunaka S (1983) Evolution of rice weed control practices and research world perspective. Pages 5-17in Weed control in rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Migo T R, De Datta S K (1983) Improvement in herbicide application technique and application timingin transplanted and broadcast-seeded flooded rice. Pages 162-175 in Proceedings of the 9th Asian-Pacific Weed Science Society Conference, November 28-December 2, 1983. Asian-Pacific WeedScience Society, Manila, Philippines.

Weed control for broadcast seeded rice 147Moody K, Cordova V C (1985) Wet-seeded rice. Pages 467-480 in Women in rice farming systems. L. J.Unnevehr, ed. Lower Ltd., Hampshire.Moomaw J C, De Datta S K, Seaman D E, Yogaratnam P (1968) New directions in weed control researchfor tropical rice. Proc. 9th Br. Weed Control Conf. 2:675-681.Moorthy B T S, Dubey A H (1979) Uptake of nitrogen by puddle seeded rice and the associated weedsunder different preemergence herbicides. Oryza 17:132-134.Mukhopadhyay S K (1978) Weed control indifferent rice culture systems. I. Weed control in lowland riceunder submergence. In Indian Council of Agricultural Research. National symposium on increasingrice yield in kharif. Central Rice Research Institute, Cuttack, India.Paller E C Jr., Lubigan R T, Vega M R (1971) Evaluation of phenoxy-propanil treatments for the controlof Scirpus maritimus L. in lowland rice. Philipp. Agric. 55:225-231.Smith J, Gascon F E (1979) The effect of the new rice technology on family labor utilization in Laguna.IRRI Res. Pap. Ser. 42. 17 p.Smith R J, Shaw W C (1966) Weeds and their control in rice production. Agric. Handb. 292. USDA,Washington, D.C. 64 p.Subiah K K, Morachan Y B (1976) Efficiency of herbicides in direct-sown short duration rice. MadrasAgric. J. 63:242-243.Suwunnamek U (1983) Profits on weed management and related problems in Thailand. Reportsubmitted to FAO Regional Center for Southeast Asia supporting the training course in advancedweed control, December 8-15, 1983, Prince of Songkhla University, Hat Yai, Thailand.Syarifuddin A K, Sundaru M, Azirin Azis (1983) Farmers’ weed control technology in insular SoutheastAsia. Pages 201-206 in Weed control in rice. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Vega M R (1954) The effect of herbicides on weeds in rice fields. Philipp. Agric. 38:13-47.Vega M R, Paller E C Jr., Lubigan R T (1971) The effect of continuous herbicide applications on weedpopulations and on the yield of lowland rice. Philipp. Agric. 55:204-209.Vongsaroj P (1985) Weeds in paddy-field and their control. Paper prepared for participants of theworkshop at Cholburi Province. Department of Agricultural Extension, Department of Technologyand Economic Cooperation, and Department of Agriculture, Bangkok, Thailand.NotesAddress: S. K. De Datta, P. C. Bernasor, T. R. Migo, M. A. Llagas, and P. Nantasomsaran, International Rice ResearchInstitute, Los Baños, Laguna, Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

148 AbstractsABSTRACTS: PEST MANAGEMENTChemical control of rice sheath blight in JapanT. YAMAGUCHIResearch on rice sheath blight and control methods in Japan can bedivided into four parts. Causal agent—in 1975, the PhytopathologicalSociety of Japan adopted the name Rhizoctonia solani Kuhn for theimperfect stage of the causal fungus. Biology—research on epidemiology.Disease occurrence and distribution—the increase since the 1950s isattributed to changes in the cultivation of irrigated rice (sheath blight isconsidered the second most important rice disease in Japan, next to blast.The area affected covered more than 1 million ha in 1984, accounting formore than 50% of the total rice cultivated area.). Chemical control-thecharacteristics and methods of applying the chemicals important inintegrated rice cultivation in Japan.T. Yamaguchi. Chugoku National Agricultural Experiment Station, Nishi-Fukatsu. Fukuyama,Hiroshima, 721 Japan.Pest control in irrigated rice in West AfricaE. A. AKINSOLA AND M. AGYEN-SAMPONGInsect pests of irrigated rice in West Africa include internal stem feeders,leaf feeders, sap suckers, and panicle pests. Current knowledge of theoccurrence of and damage caused by these pests and current pest controlpractices of farmers, as well as research-based recommendations, aredescribed.E. A. Akinsola, WARDA Upland Rice Research Station,.B.P. 2551, Bouake, Cote D’lvoire; M.Agyen-Sampong, WARDA Mangrove Swamp Rice Regional Station P.M.B. 6784, Freetown,Sierra Leone.

Abstracts 149Weed problems in irrigated riceand their control in AfricaO. AKOBUNDUAnnual and perennial weeds are among the most serious, but largelyunderrated, pests of lowland rice in Africa. Most African farmers spendmore time in weeding than in any other rice production activity. Oryzalongistaminata and red rice mimic cultivated rice at early growth stages, sothat good hand weeding requires a skilled operator who can distinguishthe weed from the crop. A large proportion of rice is grown by smallholderfarmers operating farms of less than 2 ha. They use largely unimprovedweed control practices. Land use frequency is low, so weed pressures arehigh in most lowland ricefields. Farmers also lack the expertise to adoptthe intensive rice production practices used to minimize weed pressure inAsia. Improved weed management in Africa consists of cultural, biological,chemical, and integrated weed control. Transfer of these improved weedcontrol technologies to farmers requires that the acute shortage of trainedweed scientists also be addressed.O. Akobundu, International Institute of Tropical Agriculture, PMB 5320, Ibadan, Nigeria.

Dynamics of soil nitrogenand its managementZHU ZHAOLIANGSources of N in rice plants are divided into soil and nonsoil origin. Thecontributions of seedling N, N derived from nonsymbiotic nitrogen fixation,and soil N are given for the major rice crop in different cropping systems.The N-supplying capacity of irrigated rice soil to rice crops grown indifferent cropping systems in regions of China is presented, and itstentative prediction discussed. Diversities in the contribution of subsoiland nonsoil N to total soil N supply are factors that induce large deviationsin the prediction. In addition, for soils capable of fixing ammonium, therefixation by clay minerals of ammonium mineralized from soil organic Nshould be considered in developing a method for measuring N mineralizationof the soils under anaerobic incubation. Only a semiquantitativeprediction can be made using current techniques. Methods for recommendingN fertilizer application are briefly reviewed. Simulation of soil Nmineralization patterns and the estimation and use of the parametersinvolved in the simulation equation for recommending rate and timing of Nfertilizer application also are discussed.In nature, nitrogen in the soil-plant system is dynamic. A better understanding of thedynamics of soil N is essential for efficient utilization of both soil and fertilizer N inrice production. The following discussion is confined primarily to results of studieson irrigated rice in China.Sources of nitrogen in rice plantsFrom the point of view of agronomy, two aspects of soil N supply are of interest—Nsupplyingcapacity and N-supplying pattern. Soil N-supplying capacity, also calledsoil N supply, usually is estimated from the N accumulated in the aerial parts of riceplants grown on a non-N-fertilized plot in the field (sometimes the N brought in withtransplanted seedlings is not deducted). Data pertaining to irrigated rice in differentregions of China ranged from 52 to 107 kg N/ ha. The apparent contributions of soilN to total N uptake of high-yielding varieties ranged from 52 to 83% (estimated fromthe ratio of N at maturity in the aerial parts of rice plants grown on non-N-fertilizedplot to that on N-fertilized plot) (Table 1,2) (Zhu 1985). However, that is only anestimation. Even in non-N-fertilized plots, the N accumulated in rice plants is

152 Zhu ZhaoliangTable 1. Grain yield (Yo) and N in aerial parts of rice plants at maturity (Np) (non-N-fertilizedfield experiment). aCroppingseason aLocationExperiments(no.)Yo (t/ha)MeanSDNP (kg N/ha)MeanSDDCERDCLRSCLRJiangsuZhejiangTai Lake regionHunanGuangxiTai Lake regionGuangdongJiangsuTai Lake region97242912**4110 c13304.3–4.14.54.43.63.64.63.0–5.30.7–1.00.70.61.2–0.6––0.866 1267 b 14 b68 1865 b 14 b65 b 8 b68 1753 -54 b 8 b61 -107 1176 b 16 ba Data compiled from reports of provincial Institutes of Soils and Fertilizers and regional Institutesof Agriculture. See Zhu 1985. DCER = double-cropped early rice, DCLR = doublecroppedlate rice, SCLR = single-cropped late rice. b N brought in with seedlings deducted.c Source: S. L. Zhang and Z. L. Zhu, Institute of Soil Science, Academia Sinica, 1985, unpubl.data.Table 2. Contribution of soil N supply to N requirement (%) for high rice yield(field experiment). aCroppingseasonLocationExperiments(no.)Yield range ofN plot(kg/ha)% contribution ofsoil N supplyMeanSDDCER Jiangsu 51414Shanghai 5Tai Lake region b 12DCLRSCLRJiangsuTai Lake region bJiangsuTai Lake region b 51013276.6-7.35.2-6.7–2.4-5.05.8 (mean)–5.9 (mean)6.6-7.36.6 (mean)5857705264575976671––711417411a Data compiled from reports of provincial Institutes of Soils and Fertilizers andregional Institutes of Agriculture. See Zhu 1985. b Source: S. L. Zhang and Z. L.Zhu, Institute of Soil Science, Academia Sinica, 1985, unpubl. data.derived from various sources. In addition to soil N, sources of nonsoil origin includethe N brought in with seedlings at transplanting, N derived from nonsymbioticdinitrogen fixation (Ndfa) taking place during current rice growth, and the Nbrought in through precipitation and irrigation. In evaluating the contributions ofdifferent N sources to the soil N supply, the most difficult to assess is Ndfa.

Management of rice soil nitrogen 153Calculations to tentatively estimate the contributions of N brought in withseedlings, of Ndfa, and of soil N, for non-N-fertilized plots were laid out in the TaiLake region (Fig. 1).N brought in with seedlingsOn average, N brought in with seedlings was 6, 19, and 7 kg N/ha for doublecroppedearly rice (DCER), doublecropped late rice (DCLR), and single-croppedlate rice (SCLR), respectively, equivalent to 9, 27, and 9% of the total N accumulatedin the plants at maturity (Fig. 1). The higher percentage in DCLR was a result ofolder seedlings used for transplanting.Contribution of nonsymbiotic dinitrogen fixationResults on Ndfa from a pot experiment using 3 15 N-labeled (stabilized) irrigated ricesoils taken from the Tai Lake region are shown in Figure 2. About 21% of the Ntaken up from transplanting to maturity was derived from currently occurringnonsymbiotic dinitrogen fixation. There was no significant difference among the 3soils tested.That makes it possible to estimate the contributions of Ndfa to total N in riceplants, if possible differences among varieties are disregarded. As shown in Figure 2,Ndfa was 13, 11, and 16 kg/ ha, corresponding to 20, 16, and 20% of the total Nuptake, for DCER, DCLR, and SCLR, respectively. Obviously, dinitrogen fixationoccurring during the growth of a current rice crop plays an important role in its Nnutrition.1. Contributions of different N sources to the total N uptake in transplanted rice (field non-N plots in TaiLake region) (Zhu Zhaoliang, Institute of Soil Science, Academia Sinica, unpubl. data).

154 Zhu Zhaoliang2. Contribution of nonsymbiotic nitrogen fixation to the N uptake in rice plants of DCER (%Ndfa) (Zhuet al 1986).Contributions of soil NAfter deducting the Ndfa and N brought in with seedlings at transplanting, the netamount of N derived from soil (disregarding the N brought in through precipitationand irrigation) was 48.8, 42.3, and 58.8 kg/ha, respectively, for the 3 varieties of rice,contributing 72, 58, and 72% of the apparent soil N supply estimated by the total Nuptake in the rice plants grown on non-N plots. The actual contribution of soil Nsupply to the total N uptake of high-yielding rice was 43.7, 34.1, and 45.5%, onaverage, for the 3 varieties in the region. Although the contribution of soil N supplyis not as great as is usually concluded from estimates based on the apparent soil Nsupply, it is still an important N source for high-yielding transplanted and irrigatedrice.N supply in subsoil in ricefields. Microplot experiments in the Tai Lake regionshow that N taken up from the subsoil by rice plants varied from 15 to 38 kg/ha,accounting for 16-49% of the total soil N supply for the 9 ricefields investigated(Table 3) (Chen and Zhu 1986a). The contribution of subsoil N supply to the total(the N in seedlings was deducted) correlated positively with the ratio of the total Ncontent of the soil in the 15- to 30-cm layer to that in the 0- to 30-cm layer ( r = 0.847,n = 9, signifcant at the 1% level). This demonstrates the importance of taking intoaccount the N supply in the subsoil in investigating soil N-supplying capacity.Predicting soil N-supplying capacitySoil N-supplying capacity is not only governed by soil N availability, it also dependson the cropping season of rice. The N mineralized in one rice cropping season is afunction of the soil cumulative effective temperature (CET) (Yoshino and Dei 1977).

Management of rice soil nitrogen 155Table 3. Contributions of subsoil (S): roil total (T) N supply (field microplot experiment)(Chen and Zhu 1986a). aSoil typeTotal N supply(kg/ha)N supply of subsoil(kg/ha)S:T(%)RangeMeanRangeMeanRangeMeanWDC (n = 3)WDNC (n = 3)ID (n = 3)Mean75.1-95.273.5-91.772.5-81.387.679.776.891.415.1-23.114.7-23.229.9-37.820.218.233.323.916.3-29.718.2-31.539.549.423.423.243.430.0a Single-cropped late rice. Field microplots with cylinders, bottomless or with thebottom end covered with nylon net cloth to measure soil N supply in total profileand in plow layer, respectively. Subsoil N supply was calculated by the difference.CET for SCLR (a long-duration rice variety) is much higher than that for eitherDCER or DCLR (short-duration varieties) (Zhu et al 1978). For example, the CET(sum of T-15) for SCLR grown 25 Jun-6 Nov 1981 was about 1,600 °C days; it wasonly 887 °C days for DCER (19 May-31 Jul) and 783 °C days for DCLR (7 Aug-5 Nov) (Z. L. Zhu, Institute of Soil Science, Academia Sinica, 1981, unpubl. data).This is the reason soil N supply and its contribution to SCLR were considerablyhigher than that of either crop in the double-cropped rice systems, as was mentionedearlier. The recommendation of fertilizer N application rate based on soil N supplyshould be made from the individual prediction of soil N-supplying capacity for eachcropping season.Deviations of predictionThe exchangeable ammonium initially present in ricefield soil before fertilizerapplication and transplanting, and the available N released from soil organic N, areconsidered the major compartments of apparent soil N supply. In a rice - wheat(upland crop) cropping system, the initial exchangeable ammonium N is usually10-20 ppm, mostly around 10 ppm. It is about the same as that at rice crop maturity.Consequently, the net contribution of initial exchangeable ammonium to the soil Nsupply in general is low in such cropping systems. Most of the soil N supply shouldbe from soil N mineralization during rice growth. The studies are related primarily toestimation of soil N mineralization capacity, either by incubation or by chemicalextraction. Part of those results are summarized in Table 4. The exchangeableammonium N content after anaerobic incubation (including the initial exchangeableammonium N and that mineralized during incubation), and the ammonia N releasedby NaOH in microdiffusion are the most widely investigated indices for predictingsoil N-supplying capacity. Table 4 shows that both indices have highly significantcorrelations with soil N-supplying capacity in the pot experiments.However, the correlations were not significant or the correlation coefficientswere low in the field experiments (determination coefficients r 2 only around 0.25).This implies that neither the ammonium N content after anaerobic incubation,taking into account the initial ammonium N, nor the N released from microdiffusion

156 Zhu ZhaoliangTable 4. Correlation between soil N supply to rice (Ns) and N availability indices(pot experiment). aCorrelation coefficient (r)Type ofexperimentLocationSoil type(N mineralized+ initialNH 4 -N)vs NsN releasedby NaOHdiffusionvs NsPotFieldFieldZhejiangZhejiangJiangsu &Zhejiang--- (n = 12)--- (n = 24)WDC (n = 8)WDNC (n = 12)PD (n = 9)0.826**0.504*–0.155–0.267–0.5220.893**0.480*0.207–0.4090.569a Data compiled from Zhou et al 1976 and Zhu et al 1984. WDC = well-drainedcalcareous paddy soil; WDNC = well-drained noncalcareous paddy soil; PD =poorly drained paddy soil. * = significant at 5% level; ** = significant at 1% level.with NaOH can quantitatively predict soil N supply in the field. It was suggested thata mean value of a conversion factor derived from the regression of the measuredvalue of N index of anaerobic incubation or from NaOH microdiffusion against thesoil N supply for the particular cropping season of rice and soil type be used to get asemiquantitative estimation of soil N supply (Zhu et al 1984). An example of thedeviations from such estimation is shown in Table 5. The deviations of predictionwere mostly less than 30% (Zhu et al 1984).Factors responsible for the large deviationIt should be emphasized that the so-called soil N supply is estimated by the Naccumulated in the aerial parts of rice plants grown on non-N-fertilized plots in thefield. Thus, not only the N from soil but also that from nonsoil origin were countedas soil N supply. Consequently, the considerable difference in the contribution ofeach N source of nonsoil origin, as well as that of N from subsoil, will inevitablyinduce a large deviation in the prediction of soil N supply by incubation or chemicalextraction of soil samples from the plow layer.Effect of nonsoil N. It is evident that the difference in percentage ofcontribution of nonsymbiotic dinitrogen fixation taking place in the growth ofcurrent rice was not much among different soils (Fig. 2). Thus, it may not be a factorinducing the large deviation in prediction. However, the errors resulted from thepossible difference in the N brought in with seedlings at transplanting, as well as thatin the N brought in through precipitation and irrigation, may be significant. They arenot easy to correct.Effect of soil N. The mineralization of soil N is strongly affected bymanagement practices, such as soil-drying after plowing and before flooding,puddling, etc. In addition, the differences in the contribution of subsoil N supply tothe total were so large, even among fields of the same soil type (Table 3), that it isimpossible to quantitatively predict soil N-supplying capacity, if only a sample of soilfrom the plow layer is taken for prediction.

Management of rice soil nitrogen 157Furthermore, predicting soil N supply by anaerobic incubation is complicatedby the fact that, for a soil capable of fixing ammonium, the ammonium mineralizedfrom soil organic N may be partly fixed by soil clay minerals, as is revealed in Figure3 (Chen and Zhu 1986b). For the soils taken from the Tai Lake region, the incrementof clay mineral-fixed ammonium N in soil accounted, on average, for around 20% ofTable 5. Deviations between soil N supply estimated by plant uptake of early ricefrom non-N-fertilized plot and predicted value (Zhu et al 1984). aSoil typePredictionmethodFrequency (%) of relative deviation (%)50WDC (n = 8) Incubation 12.5 25.0 12.5 0.0 50.0NaOH diffusion 25.0 25.0 37.5 12.5 0.0WDNC (n = 12) Incubation 33.3 16.7 41.7 0.0 8.3NaOH diffusion 41.7 25.0 8.3 16.7 8.3PD (n = 9) Incubation 22.2 22.2 22.2 22.2 11.1NaOH diffusion 44.2 22.2 22.2 0.0 11.1a Soil N supply predicted by incubation (air-dried sample, 30 °C, 2 wk) = (ppm, Nmineralized + initial ammonium-N) × 2.25 × conversion factor, Conversionfactors for well-drained calcareous paddy soil (WDC), well-drained noncalcareouspaddy soil (WDNC), and poorly drained paddy soil (PD) soils were 0.647,0.377,and 0.243, respectively. Soil N supply predicted by NaOH diffusion (N NaOH, 30°C, 32 h) - (ppm, N released by NaOH diffusion) × 2.25 × conversion factor.Conversion factors for WDC, WDNC, and PD soils were 0.385, 0.270, and 0.188,respectively.3. Increments of exchangeable and fixed ammonium after anaerobic incubation (30 °C, 2 wk) (Chen andZhu 1986b).

158 Zhu Zhaoliangthe sum of the increments of fixed and exchangeable ammonium N. The differencewas large among samples of the same soil type. For growing rice, refixation ofmineralized ammonium may be insignificant, because there would not be a greatopportunity of the mineralized ammonium to be accumulated to a high enoughconcentration to enhance its refixation by clay minerals. Furthermore, even if part ofthe mineralized ammonium were fixed by clay minerals, it would become availableto the rice plants at later growth stages. Therefore, refixation of mineralizedammonium by clay minerals will result in a lower estimation of the mineralizationcapacity of the soil. It was recommended that the sum of the increments of bothexchangeable and fixed ammonium after anaerobic incubation be used as themeasure of soil N mineralization capacity (Chen and Zhu 1986b).It may be concluded that it is possible to make only a semiquantitativeprediction of soil N-supplying capacity. Further improvement of the methodology isneeded for prediction.N fertilizer application rateIn some regions of China, the rate of N fertilizer application has increaseddramatically over the last 10 yr. For example, the application rate has reached ashigh as 199 kg N/ha per crop, in 1982 in the Tai Lake region. Optimizing the rate ofN fertilizer application has become the most important approach to improving Nefficiency. Several methods have been proposed so far.Estimating from N balanceThe N fertilizer application rate for rice can be estimated from the difference betweenthe total N needed for a definite yield target and the sum of N provided by soil andorganic manures applied to the current crop (Zhu 1982). In such estimation, thegreatest difficulty is predicting the soil N supply. That can only be done at asemiquantitative level. The yield target is generally set by experience.Estimating from the index of soil N supplyIt has been found that N mineralized after anaerobic incubation or N released bymicrodiffusion with 1.2 N NaOH for 24 h at 50 °C had a significant negativecorrelation with the rate of N application for maximum yield of rice. Maximumyield was calculated from the yield response equationY = a + bX + cX 2for the particular soil type and crop of rice in a given region. It was suggested thatonly a single measurement of N-supplying index, either by incubation ormicrodiffusion, would be enough for recommending the rate of N fertilizerapplication. The deviation of such an estimation was generally acceptable (Gao et al1984a, Zhang et al 1986).Other alternativesCalculating the maximum yield attainable on an irrigated ricefield from the yield of anon-N-fertilized plot and estimating the optimal rate of N fertilizer application were

Management of rice soil nitrogen 159suggested by Zhou (1987). Zhu et al (1986b) suggested that the recommended rate ofNc fertilizer application for a ricefield may be based on the mean value of the optimalrates of application obtained from the network of field experiments conducted for aparticular crop of rice in a given cropping system in a region.Nitrogen-supplying pattern of irrigated rice soilSimulation of soil N mineralization patternThe N-supplying pattern of an irrigated soil is governed primarily by the Nmineralization pattern of the soil. The N mineralization pattern of soil in anaerobicincubation under constant temperature can be simulated by the equationwhere Y = the N mineralized,T = the temperature in incubation,T o = the threshold temperature of 15 °C,D = the no. of days of incubation,(T – T o )D = the cumulative effective temperature (CET), andk and n = the coefficients depending on soil properties and the pretreatment(Yoshino and Dei 1977).In fluctuating temperature regimes and rice-growing conditions, the equationcan be modified towhere X is the sum of T–T o for each day. Although it can be simulated by theequation of first order kinetics (Zhu and Huang 1983, Yamamoto et al 1986), mostpapers published in China simulated it with the equation of CET. From the point ofview of agronomy, it seems satisfactory to use this equation to characterize the Nmineralization pattern of an individual soil.Implication of k and n in N fertilizationEvidently, the k value in the mineralization equation is a capacity factor, whichrelates the amount of N mineralized with the CET. The n value is an indication of thecharacteristics of the N mineralization pattern. For a soil with an n value higher than1, the rate of mineralization will increase with an increase in CET. For a soil with ann value less than 1, the rate of N mineralization will decrease with an increase inCET.The k and n values in the equation may be useful in the recommendation of Nfertilization. For example, as shown in Table 6, the efficiency of N applied at panicleinitiation of early rice seems to be higher on soils with n values of less than 1 than onthose with n values higher than 1. The k value in the equation was correlatedsignificantly ( r = 7.784*, n = 11) with the a value of the yield-N rates responseequation (Y = a + bX + cX 2 )

160 Zhu ZhaoliangTable 6. Efficiency of N topdressed at panicle initiation (PI) in relation to n valuein mineralization equation (field experiment, Gao et al 1984b).Grain yield (t/ha)soil type an value60 kg N/haas basal60 kg N/ha as basal+ 15 kg N/hatopdressed at PIYieldincreaseWDNCWDCWDNCPD0.8210.6520.6620.8520.9230.8000.7660.4760.6611.031.851.342.322.321.545.865.876.085.555.425.225.754.985.346.315.425.265.936.355.486.065.856.005.495.605.426.125.326.006.145.285.135.636.325.68+0.20–0.02–0.08–0.06+0.18+0.20+0.37+0.34*+0.66*–0.17–0.14–0.13–0.30–0.03+0.20a WDNC = well-drained noncalcareous paddy soil, WDC = well-drained calcareoussoil, PD = poorly drained paddy soil. * = significant at 5% level.for well-drained paddy soils in the Tai Lake region (Gao et al 1984b). Cai et al (1981)pointed out (Table 7) that, although efficiency in grain production per kg N appliedhad a significant positive correlation with apparent recovery of urea-N incorporatedas basal for SCLR, ( r = 0.846*, n = 7), which can be expected, the efficiency in grainproduction of each kg fertilizer N absorbed by rice had a significant positivecorrelation with the n value in the CET mineralization equation, ( r = 0.760*, n = 7).That implies that, on soil with a comparatively lower rate of N mineralization atearly growth (indicated by the higher n value in mineralization equation), applying Nfertilizer as basal to improve the N nutrition of rice plants at early growth will give ahigher efficiency than applying on a soil with higher initial N mineralization rate(indicated by a lower n value in the mineralization equation), if the apparentrecoveries of fertilizer N were the same on the soils tested. The relationships betweenparameters a, b, and c in the yield-N rates response equation and the k and n valuesin the CET mineralization equation are worth further investigation.Estimating the n value of irrigated rice soilsThe n value of a soil is a parameter (in addition to the characteristics of the ricevariety) that can be used as an indicator for the recommended timing of N fertilizerapplication. The n value of soils of the same type in a region generally does not differconsiderably (Table 8).For well-drained calcareous soil and bleached soil in the Tai Lake region, nvalues are considerably lower than 1; for poorly drained soil, they are generally

Management of rice soil nitrogen 161Table 7. Efficiency of N incorporated as basal in relation to apparent recovery ofN in rice plants and n value in mineralization equation (pot experiment, Cai et al1981). aN efficiency Apparent recovery (%) n value of soilIncrement, in yield/gN appliedIncrement, in yield/gN assimilated of fertilizer N0.846*––0.760*a Single-cropped late rice. * = correlation coefficient significant at 5% level.Table 8. n values of CET mineralization equation in anaerobic incubation.Soil type a Soil sample Data set(no.)n valueReferenceWDCWDNCWDNC, bleachedPDAir-dried 2 0.57Fresh soil 3 0.78Mean 5 0.70Air-driedFresh soilFresh soilFresh soilMeanAir-driedFresh soilMeanAir-driedFresh soilFresh soilMean532212325433100.861.360.760.720.950.740.700.721.960.831.631.52Gao et al 1984bChen 1985Gao et al 1984bChen 1985Cai et al 1981Cai and Zhu 1979 bGao et al 1984bCai and Zhu 1977 bGao et al 1984bCai and Zhu 1979 bChen 1985a WDC = well-drained calcareous paddy soil, WDNC = well-drained noncalcareouspaddy soil, PD E poorly drained paddy soil. G. X. Cai and Z. L. Zhu, Institute ofSoil Science, Academia Sinica, unpubl. data.higher than 1; for welldrained noncalcareous paddy soil, they are around 1 or less.For convenience, the mean value of the parameter n in the CET mineralizationequation of a particular soil type, instead of the n value of the soil of a particularricefield, was recommended to be used for predicting the N mineralization pattern ofthe soil. Once the mean value of n of a particular soil type has been found, it is notnecessary to measure the n value of a particular ricefield (Cai and Zhu 1983).Cai and Zhu (1983) showed in a pot experiment that the n value calculated fromthe apparent N mineralization pattern of a soil under rice-growing conditions wasalways higher than that in anaerobic incubation under the same fluctuatingtemperature regime (Table 9). This may be attributed to the nonsymbioticdinitrogen fixation which becomes significant at later growth stages. The relationshipbetween anaerobic incubation and the field experiment in this regard is further

162 Zhu ZhaoliangTable 9. Difference between n values obtained in incubation and in ricegrowingconditions (pot experiment, Cai and Zhu 1983).Soil type a Experiment method k (10 -3 ) b n R 2WDNCIncubationDCER pot experimentSCLR pot experiment13.85.706.000.861.041.020.9960.9880.996PDIncubationDCER pot experimentSCLR pot experiment5.75 0.911.30 1.202.31 1.090.9840.9960.996a WDNC = well-drained noncalcareous paddy soil, PD = poorly drained paddy soil.b k = mg N/100g soil per effective temperature (°C day).complicated by the fact that rice plants can absorb considerable amounts of N fromthe subsoil. The contribution of subsoil to total soil N differs from soil to soil (Chenand Zhu 1986a). It is preferable to estimate the n value of the N-supplying pattern ofa particular soil type in the field.Estimating k value by NaOH microdiffusionWang et al (1983) found that for poorly drained soils taken from the Shanghaisuburbs, k value had a significant positive correlation with the N released frommicrodiffusion of soil with 1.2 N NaOH at 30 °C for 15 h ( r = 0.834, n = 14,significant at 1% level). For convenience, n value was calculated from anaerobicincubation with air-dried soil samples. To predict the N mineralization pattern of theTable 10. Deviations between soil N supply estimated from N in plants grown on non-Nfertilizedplot and predicted value (Wang et al 1983). aCroppingseasonSiteAir CET(°C day)MeasuredSoil N supply (kg N/ha)PredictedDeviationDCERSongjiangQingpuQingpuJinshanQingpuQingpuQingpu667.8546.2682.9733.3714.9731.8601.447.059.848.848.291.356.954.751.870.749.632.794.769.252.3+ 4.8+ 10.9+ 0.8– 15.5+ 3.4+ 12.3– 2.4DCLRSongjiangQingpuQingpuJingshanQingpuSongjiangSongjiang589.0560.5514.8518.3505.5665.3604.049.158.265.147.358.963.171.147.748.870.460.668.055.984.1– 1.4– 9.4+ 5.3+ 13.39.1– 7.2+ 13.0a CET = cumulative effective temperature, DCER = double-cropped early rice. DCLR = doublecroppedlate rice.

Management of rice soil nitrogen 163type of soil, ambient temperature, instead of soil temperature, was used in theirdynamic equationfor DCER, andfor DCLRwhere Y = N mineralized,NaOH-N = N released by NaOH microdiffusion, andCET = cumulative effective temperature of air.Table 10 shows the deviations of the prediction made from these equations. Itseems as good as can be expected. The advantage of this technique of prediction overthat discussed earlier is that it takes into account CET, and thus may eliminate theerror resulting from differences in CET among the fields under investigation. Thistechnique also may be used to predict the pattern of soil N supply in a ricefield,although the deviation may be higher.References citedCai G X, Zhang S L, Zhu Z L (1981) Characteristics of nitrogen mineralization of paddy soil and theireffect on the efficiency of nitrogen fertilizer. Pages 793-799 in Proceedings of the symposium onpaddy soil. Institute of Soil Science, Academia Sinica, ed. Science Press, Beijing and Springer-Verlag, Berlin.Cai G X, Zhu Z L (1983) Effect of rice growth on the mineralization of soil nitrogen [in Chinese, Englishsummary]. Acta Pedol. Sin. 20:272-278.Chen D L (1985) Studies on nitrogen supply of paddy fields. MS thesis, Institute of Soil Science,Academia Sinica, Nanjing, China. 51 p.Chen D L, Zhu Z L (1986a) Nitrogen supply of subsoil in flooded rice field [in Chinese]. Soils 18:33-34.Chen D L, Zhu Z L (1986b) Content of nonexchangeable ammonium in paddy soils of Tai-Lake regionand its variation during incubation [in Chinese]. Soils 18:34-35.Gao J H, Zhang Y, Huang D M, Wu J M, Pan Z P (1984a) Investigations on the recommendation ofnitrogen fertilization for early rice by means of the parameters of mineralization [in Chinese, Englishsummary]. Chin. Agric. Sci. 5:67-72.Gao J H, Zhang Y, Huang D M, Wu J M, Pan Z P (1984b) Nitrogen mineralization pattern and nitrogenefficiency in paddy soil [in Chinese, English summary]. Acta Pedol. Sin. 21:341-350.Wang Y H, Jiang S Z, Gu Y M (1983) A study on predicting nitrogen supplying capacity of gleyed paddysoil in the suburbs of Shanghai [in Chinese, English summary]. Acta Pedol. Sin. 20:262-271.Yamamoto T, Kubota T, Manabe H (1986) Estimation of soil nitrogen mineralization during growthperiod of rice plant by kinetic method [in Japanese]. Sci. Soil Manure, Jpn. 57:486-492.Yoshino T, Dei Y (1977) Prediction of nitrogen release in paddy soils by means of the concept of effectivetemperature [in Japanese, English summary]. J. Cent. Agric. Exp. Stn. Jpn. 25:1-62.Zhang Y, Gao J H, Huang D M, Wu J M, Pan Z P (1986) Report of intermediated trial on forecasting theoptimum dressing rate of nitrogen fertilizer for early rice by means of some soil nitrogen parameters[in Chinese]. Soils 18:230-235.Zhou M Z (1987) Soil testing in China [in Chinese]. Chin. J. Soil Sci. 18(1):7-13.Zhou M Z, Yu W T, Fong Z F (1976) Method for estimation of soil available nitrogen [in Chinese]. Soils5-6:3216-3223.Zhu Z L (1982) Parameters for assessing the application rate of nitrogen fertilizer on rice and wheat [inChinese]. Soils 14:136-140.Zhu Z L (1985) Advances in investigations on soil nitrogen supply and fate of fertilizer nitrogen in soils ofChina [in Chinese]. Soils 17:2-9.

164 Zhu ZhaoliangZhu Z L, Cai G X, Xu Y H, Zhang S L (1984) Nitrogen mineralization of paddy soils in Tai-Lake regionand the prediction of soil nitrogen supply [in Chinese, English summary]. Acta Pedol. Sin. 21:29-36.Zhu Z L, Chen D L, Zhang S L, Xu Y H (1986a) Contributions of nonsymbiotic nitrogen fixation to thenitrogen uptake by growing rice under flooded conditions [in Chinese]. Soils 18:225-229.Zhu Z L, Huang D M (1983) Investigations on mineralization potentials of residual fertilizer nitrogen [inChinese]. Jiangsu Agric. Sci. 11:1-7.Zhu Z L, LiaoXL, Cai G X, Yu J Z (1978) Soil nutrition status under “rice-rice-wheat” rotation and theresponse of rice to fertilizers in Suzhou district [in Chinese, English summary]. Acta Pedol. Sin.15:126-137.Zhu Z L, Zhang S L, Xu Y H (1986b) On the implications of mean optimal rate of application of nitrogenfertilizer [in Chinese]. Soils 18:316-317.NotesAddress: Zhu Zhaoliang, Institute of Soil Science, Academia Sinica, P.O. Box 821, Nanjing, China.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Management of farm-grownnutrient sources for riceWEN QIXIAOGreen manure has made large contributions to rice production in thetraditional agriculture of China. Cultivation of leguminous green manurecrops depends on the cropping system, which in turn isgoverned by climaticconditions. In the mid-subtropics, a rice - rice - milk vetch cropping systemprevails. In the northern subtropics and the region south to the Huai River,rice - wheat and rice - milk vetch are the major cropping systems. In the cooltemperate zone, no winter leguminous green manure crop can be cultivated.Extensive research has shown that leguminous green manure-N (more than80% of which is derived from the atmosphere) provides 11.7 kg grain/kg Napplied, comparable to urea and ammonium bicarbonate. The proportion ofgreen manure N retained in the soil is higher than that of chemical fertilizerN. Recently it was found that when green manure and chemical N fertilizerswere combined, the N-supplying pattern to some extent became steady andlong-lasting. Plant recovery of N almost equaled the algebraic sum of the twoapplied separately. However, the results were conflicting and merit furtherinvestigation. With the intensification of agriculture, cultivation of greenmanure crops is decreasing and application of rice straw as an alternativesource of soil organic matter has received more attention. The generalrecommendation is to incorporate 1.5-2.3 t air-dried straw/ha withsupplementary fertilizer N.Green manure crops, in particular legumes grown in rotation or intercropped with rice,have been traditional nutrient sources in rice-based cropping systems in China. Theycan be plowed under before rice is transplanted, or composted with rice straw andhuman and animal wastes and applied as basal fertilizer.Recently, with the tremendous increase in the production of chemical fertilizers,the benefits of green manuring have been questioned. More attention has been paid toutilizing straw in other ways. We discuss here the limitations in exploiting greenmanure crops for crop production, as well as the efficient use of green manures andcrop straw in rice-based cropping systems.Green manure crops in rice-based cropping systemsThe season for cultivating a green manure crop and the varieties cropped are dependenton the cropping system in which the green manure is grown as a catch crop. Thecropping system, in turn, is governed by climatic conditions (Xu 1981). Different

166 Wen Qixiaopatterns of cultivating green manure crops in rice-based cropping systems are found indifferent climatic zones. The high temperatures and rainfall in the southern subtropicsof China provide an opportunity for a rice - rice - rice triple-cropping system or a rice-rice double-cropping system. In a double-rice system, milk vetch, common vetch, etc.,can be grown in the winter, or a green manure crop such as sesbania can beintercropped with early rice. In the mid-subtropics, the time between the harvest ofearly rice and the transplanting of late rice is so short that a sesbania crop will produce alow biomass. In addition, humid weather in Mar-May is unfavorable to wheat andrape. These are the reasons the rice - rice - milk vetch cropping system still prevails inthis region. In the northern subtropics and the region south to the Huai River, withannual mean temperatures around 15 °C, the major cropping systems are rice - wheator rice - milk vetch (or common vetch). In the cool temperate zone, a winter greenmanure crop cannot be cultivated.Although azolla has been cultivated for a long time in China, it can be grown asa green manure crop in almost all the rice-growing areas only after screening forcold- and warm-tolerant cultivars, and after developing practices for survival growththrough the summer and winter. Obviously, different cultivars are adapted todifferent climatic zones (Lu 1986).Nutrient and nitrogen fixationRecycling of nutrients is essential, not only to reduce inputs of high-cost chemicalfertilizers, but also because of environmental protection concerns. It has been foundthat 83% of the K in rice and 79% in wheat was in the straw (X. X. Lin and T. Zhong,1986, unpubl.). The corresponding values for Ca were 83 and 78%; almost all the Siin rice was accumulated in the straw and husk. For the microelements, results showthat Zn accumulated in the straw of early rice and late rice amounted to 58-60% ofthe total assimilated, the corresponding value in rape straw was 83%. Applying strawis important in retarding the depletion of nutrients in the soil, particularly K. The Kdeficit in the nutrient balance in Chinese agriculture has been severe.Investigations show that the proportion of N derived from dinitrogen fixationin milk vetch, common vetch, sickle alfalfa, and broad bean is 85-89% (Table 1).Because these experiments were conducted without N fertilizer application, thevalues mentioned, especially those for broad bean, may be higher than in farm fields.Table 1. Percentage of Ndfa of nitrogen assimilated by leguminous crops. aCropN assimilationPlant top (mg/pot)NdfaRoots (mg/pot)N assimilationNdfa% NdfaAstragalusSickle alfalfaVetchBroad bean937.0 ± 66.71219.2 ± 24.71688.7 ± 166.81557.2 ± 238.5815.3 ± 62.71084.3 ± 19.21537.7 ± 153.61431.9 ± 241.9163.3 ± 33.1139.3 ± 28.0280.0 ± 34.6457.2 ± 34.5105.1 ± 23.798.5 ± 20.2202.7 ± 32.2366.7 ± 41.983.8 ± 0.8687.1 ± 0.5288.4 ± 0.6089.0 ± 1.98a Source: Wen, 1986, unpubl.

Farm-grown nutrient sources for rice 167As to the proportion of azolla N derived from dinitrogen fixation, investigationswith N 15 in soil culture have not yet been conducted (Liu and Zhen 1986).Efficient use of nutrients in green manure cropsNutrient efficiency for grain productionMany investigations have shown that the availability of N in leguminous greenmanures and azolla is usually lower than that in chemical N fertilizers. The higher Nin milk vetch, common vetch, and sesbania than in azolla (Table 2) can be attributedto the difference in chemical composition. Irrespective of the diversity of N contentand C-N ratio of different azolla cultivars, their lignin content is generally higherthan 20%, much higher than that of milk vetch, common vetch, and sesbania (mostly8-13%) (Lin et al 1980).The efficiency of green manure crops for rice production was estimated at 60 ±18 kg grain/ 1,000 kg fresh weight milk vetch and common vetch applied and 43 ± 14kg grain/ 1,000 kg azolla.Efficiency may also vary with soil fertility and rate of green manure application.In general, the optimum rate is 15 t fresh weight green manure/ ha on high-fertilitysoil, around 23 t/ha on moderate-fertility soil, and more than 30 t/ha on welldrainedsoil with very low fertility (Jiangxi Academy of Agricultural Sciences,Institute of Crop Science 1982; Mo and Qian 1983).The time of azolla incorporation is more important than the rate of application.The Zhejiang Academy of Agricultural Sciences Soil and Fertilizer Institute (1975)found that incorporating azolla 20-25 d after inoculation (DAI) increased rice yields634-642 kg/ ha; incorporating it at 10 and 25 DAI gave higher increase—l,040-1,270kg/ ha (Table 3). Presumably, the split incorporation gave a N-supplying patternthat could match the N need of rice plants.In addition, applying green manure results in a higher proportion of N retainedin the soil than with chemical N fertilizers (Table 4). This favors the maintenance andimprovement of soil-N reserve, although the residual effects on succeeding crops areinsignificant.Table 2. Recovery of green manure and fertilizer N in tops of rice by differentmethods. aMethodN recovery (%)Astragalus, vetch Azolla (NH 4 ) 2 SO 4Field experiment 31.1 ± 10.5 28.1 52.6 ± 13.5(n = 13) (n = 39)Pot experiment 46.5 ± 16.6(n = 11)31.4 ± 12.7(n = 12)65.0 ± 7.0(n = 9)aCompiled from Cheng et al 1986, Mo and Qian 1983, Tao and Fen 1982, Zhu etal 1983.

168 Wen QixiaoTable 3. Effects of timing and times of incorporating azolla on rice grain yield. aTreatmentAzolla yield(t/ha)Rice yield(t/ha)Check (no azolla)Azolla died naturallyAzola incorporationAfter 20 dAfter 25 dAfter 10 and 20 dAfter 10 and 25 dAfter 10, 20, and 30 d– 3.7324.604.4021.6525.1521.6528.9830.704.384.384.795.035.05a Source: Zhejiang Academy of Agricultural Sciences Soil and Fertilizer Institute,1975.Table 4. Role of green manure and (NH 4 ) 2 SO 4 in the maintenance of soil N(microplot experiment). aTreatmentSoil N mineralizeddue to priming effectmg N/100 g soilN retainedin soilNet residualN bAstragalus c 0.77 3.59Sesbania c 0.41 3.64Azolla c 1.07 5.74(NH 4 ) 2 SO d41.11 1.522.82 (36.2)3.23 (41.5)4.67 (60.0)0.42 (8.9)a Source: Shi SL, Wen QX, Liao HQ, Xu XQ, Pan SP (1984) unpubl. b Figures inparentheses are in terms of % of applied N. c Application rate: 7.78 mg N/100 gsoil. d Application rate: 4.72 mg N/100 g soil.Utilizing green manureBesides being directly incorporated, green manure is applied basally aftercomposting under waterlogged conditions. In such cases, the possible adverse effectsof toxic substances produced during early decomposition is eliminated and the Nrelease pattern is steady and long-lasting. However, waterlogged compost is laborconsumingand N loss during composting is high (Lin and Ma 1986, Wen and Zhang1986). Feeding green manure to livestock, then fertilizing crops with farmyardmanure may be a profitable way to use green manure that merits furtherinvestigation (Gu 1977).In intensive agriculture, integrated management of green manure and chemicalfertilizer application is essential. For example, because of low temperatures duringearly growth in early rice, the slow release of N from green manure incorporated intosoil cannot match the need of the crop. A high rate of incorporation may have anadverse effect; thus, supplementing with N fertilizer is indispensable. The time andrate of application of N fertilizer are of primary importance. On rice soils derivedfrom red earth in the mid-subtropics and southern subtropics, applying N fertilizerat tillering and panicle initiation stages is preferable. On neutral soils in the northern

Farm-grown nutrient sources for rice 169subtropics, N fertilizer should be applied earlier; applying N at panicle initiation isgenerally unfavorable.Many factors may be responsible for such differences:1. Hydromica and montmorillonite, the dominant clay minerals in neutral ricesoils, can fix the ammonium mineralized early from green manure, thenrelease it for N assimilation by rice plants later. Kaolinite, the dominant claymineral in soil derived from red earth, has no discernible fixation-defixationrate of ammonium released from green manure (Table 5). N from greenmanure in red earth soils will be taken up rapidly at early growth stages.2. The mineralization pattern of N in neutral rice soil differs from that in soilsderived from red earth in that neutral soils are characterized by a high rate ofN mineralization at later stages (Inubushi et al 1985). Delayed application ofN may induce poor spikelet filling.When chemical fertilizer in combination with crotalaria was incorporated asbasal, the N-supplying pattern becomes steady and long-lasting, as was shown by ahigher N supply at mid- and later growth stages. Recovery of N by the rice plants andloss of fertilizer N were lower, and retention of N in the soil after harvest wasincreased (Huang et al 1981). In contrast, the loss of crotalaria N was higher and itsretention was lower. The net result of crotalaria combined with N fertilizer almostequals that of the algebraic sum of the two applied separately (Table 6).In a cropping system with leguminous green manure crop in rotation, applyingP to the legume is more profitable than applying it to rice. Applying P to the legumeenhances dinitrogen fixation and, when the green manure is incorporated, improvesthe N and P for the succeeding rice (Table 7).Table 5. Transformation of fertilizer 15 N in the course of rice growth. a15 Percent of added 15 NN b 8 Jun 2 Jul 23 Jul 16 Aug 29 AugNeutral paddy soilRISCMFBIRISCMFBIRISCMFBI67.156.110.998.977.021.913.51.212.355.935.330.63.820.6 26.8Calcareous paddy soil63.9 33.742.9 10.221.0 23.5Acid paddy soil25.7 24.51.7 0.824.0 23.724.11.622.530.25.824.425.50.824.620.81.219.628.96.322.521.40.421.0a 84 ppm ( 15 NH 2 ) 2 CO-N and 0.13% (wt/wt) of rice straw were added on 28 May,and rice seedlings were transplanted on 30 May. Source: Chen L L, Wen Q X, andLi H 1985, unpubl. b RiS = retained in wil, CMF = clay mineral fixed, BI = biologicallyfixed.

170 Wen QixiaoTable 6.fertilizerEffect of combined use of organic and inorganic fertilizers on the fate ofN.TreatmentPlant recoveryPercent of applied NRetained in soilNot accounted for1/2 (NH 4 ) 2 SO 41/2 (NH 4 ) 2 SO 41/2 crotalariaCrotalaria54.6 ± 2.9(n = 4)45.2 ± 3.4(n = 8)––37.4 ± 4.6(n = 4)18.7 ± 3.0(n = 4)39.0 ± 2.8(n = 4)29.6 ± 6.1(n = 4)46.5 ± 5.6(n = 4)26.7 ± 1.1(n = 4)20.2 ± 2.1(n = 8)––16.3 ± 2.9(n = 4)a Source: Huang et al (1981).Table 7. Effect of methods of P fertilizer application on crop yields in a rotation system. ZAASResearch Group of Soil Reclamation, 1965.Yield (t/ha)TreatmentClayey acid paddy soilLoamy acid paddy soilAstragalusEarlyriceLatericeAstragalusEarlyriceMaizeP applied to astragalus1/2 P applied to astragalusP applied to early riceNo P, with astragalusNo P, no astragalus19.115.80.93––3.06 2.28 24.6 3.452.76 2.32 22.5 3.411.91 2.32 4.7 2.621.24 2.18 – 1.521.22 2.09 – 1.260.860.770.340.320.26Mineral N will be immobilized during straw decomposition. The amount of Nimmobilized is dependent not only on the C:N of the straw but also on the conditionsfor decomposition (Cheng et al 1986). Under submergence, the N factor of rice strawis generally in the range of 0.7-0.9, lower than in upland conditions. Remineralizationof the immobilized N is negligible during growth of the current rice crop (Table 5).Consequently, there is a need to apply more N when straw is incorporated than whenit is not. S. X. Mo and J. F. Qian (1981, unpubl.) indicated that the adverse effect onyield of the current rice crop induced by incorporating 1.5-2.3 t rice straw/ha can beeliminated by supplementing with 75-112 kg ammonium sulfate/ ha. Pot experimentshave shown no adverse effect on yield when rice straw was incorporated at0.45% (wt/wt of soil) when 80 ppm urea-N was applied (Table 8).The general recommendation is to incorporate 1.5-2.3 t/ha air-dried straw,with a lower rate on poorly drained soil.

Farm-grown nutrient sources for rice 171Table 8. Effect of rice straw and inorganic fertilizer N on rice yields (pot experiment).aUrea-NYield (g/pot) at straw level b ofadded(ppm) 0 0.15% 0.30% 0.45%0 13.3 ± 0.7– ––30 24.5 ± 0.8 24.0 ± 1.2 25.4 ± 0.5 25.1 ± 0.6100 27.8 ± 1.1 28.0 ± 1.0 28.6 ± 1.1 29.9 ± 0.8120 29.5 ± 0.2 29.6 ± 1.6 32.6 ± 1.6 32.2 ± 1.2a Source: Cheng L L, We, Q X, Li H, 1984, unpubl. b % of soil (wt/wt).ConclusionLeguminous green manure and crop straws have been important sources ofnutrients in traditional agriculture in China. Recently, with intensification ofagriculture, the relative contribution of these two organic materials to the total inputof nutrients has been greatly reduced.Nonetheless, green manure crops cannot be ignored. Even in 1983, applicationof chemical N fertilizers was only 79 kg N/ha annually, about 50 kg N/ha less thanthe recommended optimum. It can be expected that, although the area planted togreen manure crops has been acutely reduced in some regions of highly intensiveagriculture, it may still be a considerable hectarage in the foreseeable future in areaswhere climatic conditions do not favor growing wheat and rape.Green manure also can provide organic material for replenishing soil organicmatter. However, with intensification of agriculture, the contribution of greenmanures will decrease while that of straw will increase remarkably.References citedCheng L L, Wen Q X, Shi S L (1986) Transformation of organic manure- and chemical fertilizer-Napplied in combination and its effect on soil N supply [in Chinese]. Pages 104-115 in Recent advancesand perspectives of soil nitrogen research in China. Soil Science Society of China, ed. Science Press,Beijing.Gu R S (1977) The profits of green manure crop ( Astragalus sinicus ) under different ways of utilization [inChinese]. Nongye Keji Tongxun 12, 3.Huang D M, Gao H J, Zhu P L (1981) The transformation and distribution of organic and inorganicfertilizer nitrogen in rice-soil system [in Chinese, English summary]. Acta Pedol. Sin. 18:107-121.Jiangxi Academy of Agricultural Sciences, Institute of Crop Science (1982) Cultivation and utilization ofgreen manure crops [in Chinese]. Shanghai Science and Technology Press. 396 p.Inubushi K, Wada H, Takai Y (1985) Easily decomposable organic matter in paddy soil. VI. Kinetics ofnitrogen mineralization in submerged soils. Soil Sci. Plant Nutr. 4:563-572.Lin D F, MaXL (1986) Astragalus sinicus. Pages 291-340 in Green manure in China [in Chinese]. B. Jiao,ed. Agriculture Press, Beijing.Lin X X, Cheng L L, Shi S L, Wen Q X (1980) Characteristics of decomposition of plant residues in soilsof south part of Jiangsu Province [in Chinese, English summary]. Acta Pedol. Sin. 17:319-326.Liu Z Z, Zhen W W (1986) Nitrogen fixation of Azolla and its utilization. Pages 195-202 in Recentadvances and perspectives of soil nitrogen research in China [in Chinese]. Soil Science Society ofChina, ed. Science Press, Beijing.

172 Wen QixiaoLu S Y (1986) Azolla. Pages 560-592 in Green manure in China [in Chinese]. B. Jiao, ed. AgriculturePress, Beijing.Mo S X, Qian J F (1983) Studies on the transformation of nitrogen milk vetch in red earth and itsavailability to rice plant [in Chinese, English summary]. Acta Pedol. Sin. 20:12-22.Research Group of Soil Reclamation, Zhejiang Academy of Agricultural Sciences (1965) Effect ofapplying phosphorus fertilizer directly to rice plant and to milk vetch prior to rice on soil fertility andrice yields [in Chinese]. Zhejiang Agric. Sci. 9.Soil and Fertilizer Institute, Zhejiang Academy of Agricultural Sciences (1975) Propagation andutilization of azolla [in Chinese]. Agriculture Press, Beijing.Tao Q X, Fan Y C (1982) Effect of application of combined green manure and inorganic fertilizer on earlyrice yield [in Chinese]. Jiangxi Agric. Sci. 1:13-15.Wen Q X, Zhang X H (1986) Fixed ammonium in soils. Pages 34-45 in Recent advances and perspectivesof soil nitrogen research in China [in Chinese]. Soil Science Society of China, ed. Science Press,Beijing.Xu Q (1981) Cropping system in relation to fertility of paddy soils in China. Pages 220-230 in Proceedingsof symposium on paddy soil. Academia Sinica, ed. Science Press, Beijing.Zhu Z L, Liao X L, Cai G X, Chen R Y, Wang Z Q (1983) On the improvement of the efficiency ofchemical fertilizers and organic manures in rice production. Soil Sci. 135:35-39.NotesAddress: Wen Qixiao, Institute of Soil Science, Academia Sinica, Beijing, China.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Nutrient kinetics and availabilityin flooded rice soilsH. U. NEUE AND P. R. BLOOMRecent studies on nutrient kinetics and the decomposition of organicsubstrates in flooded rice soils are discussed. In the tropics the turnover oforganic matter in flooded rice soils can be as fast as in aerobic soils. Thiscauses net immobilization of nitrogen in flooded rice soils after rice strawincorporation. Fermentation of organic matter results in low redoxpotential and high partial pressure of CO 2 , which leads to an initialincrease of Fe 2+ and Mn 2+ in the soil solution followed by precipitation ascarbonates. However, the reactions are not determined by simplecarbonate solubility equilibria. Ion concentration in soil solutions offlooded soils can be highly oversaturated with respect to well-known solidphases. In continuously flooded soils, sulfide seems to be controlled bysolubility of amorphous FeS. The only pure phase that could control Zn 2+ isZnS, but the quantity of sulfide sulfur in most soils is insufficient toaccount for the decreased availability of Zn after flooding. Co-precipitationor adsorption in Fe-Mn carbonates or other minerals may also control theavailability of Zn in flooded soils.Flooding an air-dried soil sets in motion a series of chemical changes thatconsiderably affect the soil’s capacity to supply nutrients. Gas exchange between theair and the soil decreases tremendously. The oxygen supplied from the air cannotmeet the demand of aerobic organisms in the soil, so that O 2 is depleted and CO 2 andHCO 3-concentrations increase to very high levels. Consequently, the redoxpotential falls sharply and the soil solution pH of acid soils increases while that ofsodic and calcareous soils decreases. The soil solution pH of a reduced soil maystabilize at a pH between 6.5 and 7.0 (Ponnamperuma 1985).Flooding and puddling render a fertile soil an ideal growth medium for rice, bysupplying abundant water; buffering soil pH at near-neutral, enhancing N fixation;and increasing diffusion rates, mass flow, and availability of most nutrients. In lessfavorable soils, flooding may result in toxicities of Fe 2+ , H 2 S, or organic acids, or inZn or in S deficiencies.The properties of rice soils, their ecology, and the chemical transformationsthat occur after flooding have been reviewed extensively (De Datta 1981; Moormanand Wetering 1985; Patrick et al 1985; Patrick and Reddy 1978; Ponnamperuma1972, 1985; Roger et al 1987; Watanabe and Roger 1985; Yu 1985).

174 Neue and BloomThe first part of this paper discusses current work on organic matterdecomposition, with emphasis on short-term transformations that affect the Eh,PCO 2 , and NH+4 kinetics. The second part discusses factors that controlconcentrations of metallic cations as well as silica and PO3-4 . The role of dissolved-CO 2 and HCO 3 and the importance of carbonate chemistry are emphasized for soilsthat attain a near-neutral pH on flooding. Some aspects of sulfide chemistry also arediscussed.Organic matter decompositionDecomposition patternAlthough the breakdown and humification of organic materials in aerated soils arewell understood (Scharpenseel and Neue 1984), their decomposition in floodedtropical rice soils is not well understood. The processes of decomposition,mineralization, immobilization, and humification, however, are known to bedelayed under anaerobic conditions. The known characteristics of anaerobic carbonturnover are• low energy derived from the fermentation processes, resulting in the synthesisof fewer microbial cells per unit C degraded;• incomplete decomposition; and• less humification than in aerated soils.Recently, the decomposition patterns of 14 C-labeled rice straw in three aerobicand three permanently flooded soils in tropical ricefields (Fig. la, b) have beenestablished (Neue 1985, Neue and Scharpenseel 1987). Submergence retarded initialdecomposition only slightly, compared to upland soils, for the neutral and alkalinesoils, while the decomposition pattern of the upland acid Humult coincided withthat of the three submerged soils. After rapid mineralization in the first year,decomposition curves followed a logarithmic function in all soils, regardless of waterregime. Decomposition of the remaining, more resistant metabolites and residueswas similar, with half lives of about 2 yr in all soils and water regimes. The alternatedrying and wetting in normal field operations may decrease the differences in initialdecomposition between the flooded and upland soils.In experiments at the IRRI farm, returning the straw of 2 rice crops/ yr for 11 yrdid not significantly change carbon contents of the soils, regardless of water regime(Neue and Scharpenseel 1987). This is in line with the rapid decomposition pattern.The decomposition patterns indicate that a ricefield with 3-5 cm standingfloodwater cannot be compared with the pure anaerobic conditions obtained inlaboratory studies. The ecology of the floodwater and the composition and activityof the soil edaphon seem to be more definitive of the actual decomposition pattern inthe field than may be assumed from the redox potential, which remained below -50mV in all submerged soils of our experiment.In ricefields, nutrient recycling is performed by microorganisms, protozoa,zooplankton, and the benthos, which include bottom-dwelling animal and certaininvertebrate fauna such as oligochaetes and chironomid larvae (Roger et al 1987).Soil N mineralization, measured as NH 4+production, was doubled in 7 d bytubificial activities (Grant and Seegers 1985).

Nutrient kinetics in flooded rice soils 1751. Decomposition pattern of 14 C-labeled rice straw in tropical upland soils and flooded tropical lowlandsoils (adapted from Neue and Scharpenseel 1987).The ricefield fauna responsible for the breakdown of organic substratesfrequently are microcrustaceans and gastropods. Snails are known for beingefficient lignin decomposers. Their activity, together with that of Protozoa, Rotifera,and the primary decomposers (bacteria), is very important. The combined activity ofthe ricefield fauna and flora results in much faster decomposition rates than may beassumed from the sum of individual components and activities. Because the extentand degree of all factors affecting decomposition and its interrelation are not wellestablished, there are still major difficulties in clarifying the dynamics ofdecomposition unequivocally.Other factors that enhance decomposition in submerged ricefields in the tropicsare• soil temperature, 25-30 °C• neutral pH• low soil bulk density and a wide soil-water ratio (because of puddling)• shallow floodwater• high and balanced nutrient supply• low siltation rates• permanent but fluctuating supply of energy-rich photosynthetic aquatic andbenthic biomass. The total dry weight of aquatic biomass rarely exceeds1 t/ha at any time. The productivity is similar to eutrophic lakes (Roger1986). The total organic carbon input in rice soil during a 90-d rice crop wasestimated to be 1.7-2.3 t/ha (Watanabe and Roger 1985).• high diversity of micro- and macroorganisms that provide successivefermentation down to products like CO 2 , CH 4 , H 2 , H 2 S, and NH 3• small supply of O 2 into the reduced layer by rice root excretion andoligochaetes population (in experimental fields on the International RiceResearch Institute farm, the population of oligochaetes may be up to

176 Neue and Bloom104/m 2 ) (Grant et al 1983). The diurnal oversaturation of the floodwaterwith O 2 due to photosynthesis by the aquatic biomass enhances the aerationfunction of tubificids.• short-term instabilities and fluctuations by nature and by human activities.The extreme short-term instabilities and fluctuations of the rice-field ecosystemcaused by nature and by human activities establish long-term stability (Watanabeand Roger 1985). Despite the eutrophic nature of the ricefield, the artificialmaintenance and balance of these instabilities and fluctuations prevent theestablishment of a pure anaerobic soil matrix that, when permanently submerged,leads to the development of marshes or peats.Effect on redox potentialThe supply of biodegradable carbon is the key to most of the characteristicbiochemical and chemical processes in flooded rice soils. These processes include soilreduction and associated electrochemical changes, N immobilization and fixation,production of organic acids, and release of CO 2 , CH 4 , and H 2 S. These processesaffect the availability and uptake of nutrients directly and indirectly.The magnitude of reduction is determined by the amount of easily degradableorganic substrates, their rate of decomposition, and the amounts of easily reducibleiron and manganese oxides, nitrate, and sulfate. A rapid initial decrease of Eh afterflooding in most soils is caused by high initial decomposition rates for organic matterand low contents of O 2 , NO 3-, and Mn oxides which could buffer a decrease in Eh. Inmost rice soils, the most important redox buffer systems are Fe(III) oxyhydroxides/Fe 2+ and the organic compounds. Most flooded soils after the initial rapid Ehdecrease are somewhat stabilized at an Eh between +100 and –100 mV. Katyal(1977) demonstrated the acceleration and intensification of Eh and pH changes withthe addition of plant residues. The effect of vetch, which has a relatively narrow C-Nratio, is greater than that of rice straw, which has a wide C-N ratio (Yu 1985), andchanges are more pronounced when organic substrates are added to soils low inorganic matter (Nagarajah et al 1987).Effect on PCO 2Although the increase in pH of acid soils is initially caused by soil reduction, whichreleases OH - from Fe oxyhydroxides, thereafter it is regulated by PCO 2 . The pHvalues of flooded soils are sensitive to changes in PCO 2 . Carbon dioxide thataccumulates in large amounts profoundly influences the chemical equilibria ofalmost all divalent cations (Ca 2+ , Mg 2+ , Fe 2+ , Mn 2+ , Cu 2+ , Zn 2+ ) in ricefield soils.The drastic restriction of gas exchange with the atmosphere leads to theaccumulation of N 2 , CO 2 , CH 4 , and H 2 in flooded rice soil. CO 2 , CH 4 , and H 2 areformed mainly through the fermentation of organic matter. Small amounts of CO 2may be derived from root respiration. Although there is a wide variation in thegaseous composition of flooded soils (Neue and Scharpenseel 1984), the formationof gases always follows a distinct pattern (Fig. 2). Methane production is alwaysdelayed. At higher temperatures, as are found in the tropics, CO 2 and CH 4formation occurs sooner and in larger amounts than in cooler climates (Tsutsuki andPonnamperuma 1987). Moreover, when temperature and pH increase, the ratio of

Nutrient kinetics in flooded rice soils 1772. Changes in the composition of H 2 , CO 2 , and CH 4 gases in an anaerobic incubated soil (Maahas clay)(adapted from Inubushi and Watanabe 1987).CH 4 and CO 2 changes in favor of methane. This effect is enhanced by the addition ofeasil y decomposable substrates (Yamane and Sato 1963, 1967). One to three tonsCO 2 per hectare is produced in the puddled layer during the first week ofsubmergence (Ponnamperuma 1972), but no methane is detectable. After the firstweek, however, the amount of CH 4 found in the soil solution and gas bubbles offlooded soils may be 4 times that of CO 2 . The change in favor of CH 4 is caused eitherby the reduction of CO 2 to CH 4 o r by the assimilation of carbon and precipitation ofcarbonates of Fe II, Mn II, or Ca. The controlling process still needs elucidation.Common patterns of P CO2 in soil solutions are given in Figure 3. According to Takai(1970), the bulk of CH 4 is formed through decarboxylation of acetic acid, whichwould result in a 1:1 ratio of CO 2 and CH 4 .Effect on NH 4+ availabilityBecause of the low N requirement of anaerobic metabolism, N immobilization inflooded soils is generally considered agronomically insignificant. Ponnamperuma(1972) concluded that organic materials with wide C:N, such as rice straw, onlytemporarily depresses N availability to rice, especially in soils low in organic matter.According to Broadbent (1979), N immobilization is short lived and can be avoidedby adding fertilizer N or by delaying planting.In lowland rice, 60-80% of N adsorbed by the crop in N-fertilized fields isderived from the native nitrogen pool (Broadbent 1979). Recent survey results,however, suggest that approximately 60% of rice yields ranging between 2 and 4 t/haare produced without any N fertilization (De Datta 1987). Promoting the use oforganic manures is common. Knowledge of the effects of organic residues oramendments in ricefields on short-term nutrient availabilities and long-term soilfertility, however, is lacking.

178 Neue and Bloom3. Kinetics of P CO 2 in 3 submerged soils treated with 0.15% chopped straw and Glyricidia sepium (IRRI,unpubl. data).Nagarajah et al (1987) compared organic amendments in 5 Philippine rice soilswhose organic carbon content varied from 0.5 to 3.6%. They found that sesbaniaand azolla incorporation increased exchangeable and soil solution NH 4 -N, whereasincorporating rice straw depressed it. At higher application rates, the effects weremore pronounced and persisted throughout the cropping season (Fig. 4a,b). Azollareleased less NH 4 -N than sesbania in all soils, probably because of the higher lignincontents in the azolla.In other straw experiments, late season flushes of NH 4+that may have beenrelated to remineralization were observed. But these flushes always occurred too latein the cropping season to be beneficial. These results agree with mineralizationstudies that showed a clear correlation between the C:N of substrates and thepercentage of N mineralized under flooded conditions (Roger et al 1987).Immediate agronomic benefits of organic amendments is therefore related tothe C:N, the lignin content of the substrate, and the nitrogen equivalent added.

Nutrient kinetics in flooded rice soils 1794. Kinetics of soil solution NH 4+-N in a flooded Maahas clay without and with rice plants as affected byincorporation of organic substrates at equivalents of 58 kg N/ha and 116 kg N/ha (adapted fromNagarajah et al 1987).Because Zn availability may also decline after straw application, this must berecognized as a possible problem.Effects of decrease in Eh and elevated CO 2 on mineral elementsIron and manganeseThe decrease in Eh after flooding results in a reduction of Fe(III) and Mn(IV) oxidesand hydroxides releasing Fe 2+ and Mn 2+ into the solution (Fig. 5, 6). The net

180 Neue and Bloom5. Kinetics of water-soluble Fe +2 (adapted from Aduna et al 1987).reaction is oxidation of readily oxidizable organic carbon to CO 2 and reduction ofFe(III) and Mn(IV) to Mn 2+ and Fe 2+ :1/4 organic C + Fe(OH) 3 " Fe 2+ + 2OH + 1/2 H 2 O + 1/4 CO 2 (I)1/2 organic C + MnO 2 + H 2 O " Mn 2+ + 2OH - + 1/2 CO 2 (II)The production of OH - ions results in an increase in pH of acid soils to near-neutral.Because the reduction of Mn(IV) oxides can occur at a higher Eh than the reductionof Fe(III) oxyhydroxide, the Mn 2+ concentration increases before Fe 2+ (Ponnamperuma1972, Yu 1985).

Nutrient kinetics in flooded rice soils 1816. Kinetics of water-soluble Mn 2+ (adapted from Aduna et al 1987).The rate of decrease in Eh and the rates of reduction of Fe(III) and Mn(IV) aredependent on the quantity of readily oxidizable carbon (Ponnamperuma 1972). Thepatterns in Figures 4 and 5 are for soils without the addition of any source of freshorganic carbon. Other experiments with similar soils have shown that adding ricestraw increases the rate of production of Fe 2+ and Mn 2+ (Patra 1987).The production of CO 2 by the fermentation of organic matter is an importantfactor in determining the pH of most flooded soils (except for acid sulfate soils).Partial CO 2 pressures as high as 0.8 atm have been reported with the addition of highlevels of plant residues, but more typical values range from 0.05 to 0.2 atm (Fig. 3;Kundu 1987, Patra 1987, Ponnamperuma 1972).In calcareous soils where the pH is buffered by the presence of CaCO 3 (calcite),the increase in partial CO 2 pressure decreases pH to near 7 (Ponnamperuma 1972).The pH, however, is not determined by a simple carbonate solubility equilibrium.Rather, the calculated ion activity product for calcite, (Ca 2+ ), (CO 3-), shows that thecalcite solubility of soil solutions can be oversaturated more than 15-fold (Amrhein

182 Neue and Bloomand Suarez 1987; Bloom and Kundu, unpubl.). Similar oversaturation has beenobserved in soils that are wet but not flooded (Bloom and Inskeep 1986, Inskeep andBloom 1986a). The oversaturation, which results in pH values higher than predictedby solubility equilibrium, is caused by blockage of crystal growth sites by adsorptionof very small amounts of soluble polymeric organic matter (Inskeep and Bloom1986b). With sufficient oversaturation, nucleation of new calcite crystallites occurs,but the crystallites cannot grow very large because of the adsorption of organicmatter.In acid soils, the production of OH - results in an increase in pH. The increase inpH, however, is limited by the precipitation of Fe(II) and Mn(II) carbonates whichoccur at about pH 7. The net reactions areSchwab and Lindsay (1983a,b) suggested that at the Eh and ionic concentrationstypically found in flooded soils, siderite (FeCO 3 ) and rhodochrosite (MnCO 3 )control the solubility of Fe 2+ and Mn 2+ . Pure rhodochrosite and siderite, however,are not likely to form because the Mn 2+ and Fe 2+ ions have similar ionic radii (.82and .78 A°, respectively), and can readily substitute for one another. Rhodochrositeand siderite have the same crystal structures and are end members of a continuoussolid solution series of iron-manganese carbonates (Deer et al 1966). Ironmanganesecarbonates also readily incorporate Mg 2+ ( r = .72 A°) and smallerquantities of Ca 2+ ( r = 1.00 A°) and other divalent cations. Manganese and iron alsocan be incorporated into calcite (Deer et al 1966) in calcareous soils.Despite the complex composition of Fe 2+ -Mn 2 + carbonates, it is useful to lookseparately at the ion activity products for Fe 2+ and Mn 2+ carbonates. In the initialstages after flooding, reduction produces Fe 2+ and Mn 2+ faster than carbonateprecipitation removes these ions from solution. This can result in high oversaturationsin the precipitation of rhodochrosite and siderite. For the acid(Luisiana), neutral (Maahas), and calcareous (Pila) soils shown in Figures 5 and 6,siderite oversaturations were 100-fold and rhodochrosite oversaturations 60-fold(Aduna et al 1987). After reaching a peak value, soluble Fe 2+ and Mn 2+ decreased inconcentration, but they remained well oversaturated, with the exception of the Mn 2+in the acid Luisiana soil. Apparently, blocking of crystal growth sites by organicmatter is important for Fe 2+ -Mn 2+ carbonates as well as for calcite.In the Luisiana soils which are high in Fe and low in Mn, the Fe-Mn carbonateformed was high in Fe and low in Mn. Because of the high Fe-Mn ratio in the solidphase, the apparent solubility of MnCO 3 was reduced to less than the solubility ofrhodochrosite (Aduna et al 1987).Soluble Fe 2+ can be toxic to rice growth at the concentrations observed in theLuisiana soil, an Ultisol high in easily reducible Fe (Fig. 5). The relationship betweenthe concentration of soluble Fe 2+ and the appearance of Fe toxicity symptoms,however, is not simple. Symptoms have been observed at concentrations as low as 45ppm, but concentrations for inducing Fe toxicity are reported to be as high as 1,700ppm (Tadano and Yoshida 1978). Iron toxicity apparently is affected by the

Nutrient kinetics in flooded rice soils 183physiological status of the plants. Preflooding potentially iron-toxic acid soils andplanting after the decrease in Fe 2+ due to FeCO 3 precipitation is a strategy that canbe used to avoid the toxic concentrations of iron.In acid sulfate soils, the reduction of Fe(III) in jarosite (KFe 3 (OH) 6 (SO 4 ) 2 andFe(III) oxyhydroxides can readily produce concentrations of Fe 2+ in excess of 3,000ppm (Ponnamperuma 1985). If the pH is not increased enough to result in FeCO 3precipitation, Fe 2+ is controlled by the formation of FeS (Aduna et al 1987). Thequantity of S 2- produced by jarosite reduction is insufficient to remove all of the Fe 2+released. However, if other sources of sulfate are available, as in acid sulfate soils thatcontain gypsum (Van der Kevie 1972), Fe 2+ concentrations will be kept low by theformation of FeS. Sulfate, however, is reduced at a lower Eh than Fe(III), so thatFe 2+ will build to a peak before decreasing due to FeS precipitation (Burabod soil,Fig. 5). The Fe 2+ in Burabod soil decreased to a relatively low level

184 Neue and BloomAfter an initial increase in the concentration of exchangeable cations insolution, the concentration generally decreases. In all but acid sulfate soils, thisdecrease in ionic strength is due to the precipitation of Fe(II) and Mn(II) carbonates.In acid sulfate soils, the decrease in ionic strength is caused by the reduction of SO 4=to S = and the precipitation of Fe 2+ as FeS.The elevated cation concentration is important with respect to increaseddiffusion of exchangeable cations to roots (Ponnamperuma 1972). Anotherimportant factor in increasing diffusion to roots is the effect of the improvement indiffusion caused by the filling of soil pores with water. The increase in the diffusionrate is especially important for K + nutrition because diffusion is the most importantfactor on the uptake of K + (Malavolta 1985).Clay mineralogy can also be a factor in determining the long-term availabilityof potassium and response to K + fertilization. Vermiculite, a 21 layer silicate thatcan fix K + by trapping K + in interlayers, occurs frequently in the tropical lowlands.Greenland (1987) assembled data from studies of 410 ricefield soils of Asia; 40% ofthe soils sampled contain vermiculite. Bajwa and Ponnamperuma (1980) found thatvermiculite was the predominant clay mineral in 60 of 161 surface rice soil samplesfrom the Philippines. In vermiculitic soils, response to continual application of K +fertilizer is minimal in the first few years, but with continued application, theresponse increases as more of the K + fixation capacity is satisfied (Greenland 1987).Micaceous clays in soils are a source for the long-term supply of K + for cropgrowth (Malavolta 1985). The ricefield soils of Asia, however, do not tend to be highin micaceous clays (Greenland 1987).PhosphorusFlooding is generally thought to increase the concentration of soluble phosphate andits availability (Patrick et al 1985; Ponnamperuma 1972, 1985). When ricefield soilsare flooded, the reduction of Fe(III) oxyhydroxides releases adsorbed and occludedP (Khalid et al 1977, Patrick et al 1985, Roy and De Datta 1986). The increase in pHcaused by flooding of acid soils also can result in desorption of P from clays andaluminum oxides (Ponnamperuma 1972), but recent evidence (Sah and Mikkelsen1986) suggests that this effect is small in ricefield soils.Turner and Gilliam (1976) studied soils with a range of soil properties andfound that flooding increased solution P in acid soils, but not in neutral andcalcareous soils. They also found no effect of flooding on the availability of soilreserve P as measured by 35 P exchange in 9 soils. They did, however, find a modestincrease in available P in two calcareous soils.Adding phosphate to soils removes P from the solution by adsorption andprecipitation reactions. Because of the difficulty in distinguishing precipitation fromadsorption, the removal of phosphate ions from solution is generally described as anapparent adsorption.Flooding of soils to achieve an aerobic condition before measuring theapparent adsorption of phosphate can change the extent of adsorption. When Padditions to preflooded soils are of the level comparable to that of fertilizer additionsto ricefield soils, flooding reduces P adsorption (Khalid et al 1977, Roy and DeDatta 1985).

Nutrient kinetics in flooded rice soils 185When higher concentrations of P are added, however, the tendency is foradsorption to be greater under anaerobic conditions (Khalid et al 1977, Roy and DeDatta 1985, Sah and Mikkelsen 1986). At high P additions, the quantity of Padsorbed is correlated to the quantity of oxalate extractable Fe (Sah and Mikkelsen1986, Patrick and Khalid 1974). Patrick and Khalid suggested that the highadsorption at high P concentration results from an increase in the surface area ofFe(III) oxyhydroxides under anaerobic conditions.Prolonged flooding for rice production decreases the availability of P for thefollowing upland crops (Brandon and Mikkelsen 1979). The reduced P availability istemporary and disappears if upland crop cultivation continues. This is likely aneffect of the high surface area of the poorly ordered Fe(III) oxyhydroxides thatinitially form upon soil drying.Adsorption of P following flooding is much less in soils that have not beenpreviously flooded compared to similar soils that have been used for rice production.This is due to the accumulation of poorly ordered Fe(III) oxyhydroxides caused bythe periodic flooding and drying of the rice soils.Plant P uptake is primarily a function of the rate of P diffusion to roots (Turnerand Gilliam 1976). The rate of diffusion is a function of P concentration in soilsolutions and the soil moisture. Turner and Gilliam (1976) showed that the mostimportant effect of waterlogging on plant P uptake is an increase in the diffusivity,not in solution concentrations. Data of Hossner et al (1973) and Roy and De Datta(1986) suggest that the minimum soil solution concentration needed for themaximum production of rice is 0.1 ppm. The data of Turner and Gilliam (1976),however, suggest that because of the importance of the diffusivity, the criticalsolution concentration may vary with soil.SulfurUpon flooding, sulfate sulfur is reduced to sulfide sulfur (Fig. 7). Sulfide sulfur, asH 2 S, can be very toxic to plants (Neue and Mamaril 1985), but in most ricefield soils,H 2 S is maintained at a very low concentration by the precipitation of FeS (Connelland Patrick 1968, Patrick and Reddy 1978, Yu 1985). Measurements of sulfide in aneutral-pH, continuously flooded ricefield soil show that total soluble sulfide was inthe range of 0.05-0.10 ppm. The S 2- concentration was controlled by FeS solubilityat a level about 15 times the solubility of well-crystalline FeS (Troilite) (Aduna et al1987). This appears to be similar to the solubility of amorphous FeS.The pK of the first ionization of H 2 S is 7.0 (Stumm and Morgan 1981). Thus, ina neutral soil, about half of the dissolved sulfide is H 2 S. If Fe 2+ concentrations aretypical of most soils, the solution concentration of H 2 S should remain below thegenerally agreed 0.1 ppm limit for toxicity (Tadano and Yoshida 1978). In someorganic and sandy soils low in iron, however, H 2 S toxicity is possible. Also, when thepH remains low, as it does for most acid sulfate soils, H 2 S toxicity is a potentialproblem.Rice plants assimilate sulfate, not sulfide ions (Patrick and Reddy 1978). Thus,in soils that have been flooded for some period, and the sulfate concentration is nearzero (Fig. 7), sulfate uptake can occur only in zones where the Eh is greater than it isin the bulk of soil. Engler and Patrick (1975) have shown that FeS sulfur can be

186 Neue and Bloom7. Kinetics of water-soluble SO 4- in four soils under moist but well-aerated and flooded conditions(adapted from Kundu 1987).assimilated by rice plants because oxidation of sulfide sulfur occurs in the oxidizedrhizosphere of rice plants. Sulfate in the toxic surface of the soil may also contributeto sulfur uptake. This zone of the soil is thin but rooting density is high in the soilsurface.SilicaSilica tends to increase in ricefield soils after submergence (Patrick and Reddy 1978,Ponnamperuma 1972) due to the release of occluded and adsorbed silica in Fe(III)oxyhydroxides. Flooding of soils not previously flooded, however, results in adecreased soluble Si (Kundu 1987). This is because the solubility of soil silicadecreases when the soil pH of acid or alkaline soils goes to 7 (McKeage and Cline1963). With flooding followed by drying, silica is adsorbed and occluded in poorlyordered Fe(III) oxyhydroxides, which can be released upon reflooding.ZincZinc deficiency is the most common micronutrient problem in flooded rice(Mikkelsen and Kuo 1977). Although many studies have been conducted todetermine the chemical factors that control the availability of Zn in paddy soils,many questions still exist.

Nutrient kinetics in flooded rice soils 187Flooding generally decreases Zn availability compared to well-aerated soils(Fig. 8), and prolonged flooding can increase the potential for Zn deficiencies. Onestrategy suggested to decrease Zn deficiency is periodic soil drying (Ponnamperuma1985).In acid soils, much of the decrease in Zn availability due to flooding (Fig. 8) canbe explained by the pH increase with flooding and the dependence of Zn 2+adsorption on pH (Mikkelsen and Kuo 1977). Control of solubility by silicate,carbonate, phosphate, and sulfide phases which are more soluble at acid pH than atneutral pH has been proposed. Thermodynamic analysis, however, has shown thatthe only pure phase that could be controlling Zn 2+ is ZnS. Aduna et al (1987) showedthat Zn 2+ in a continuously flooded soil was 10,000 times oversaturated in8. Kinetics of water-soluble Zn in three soils under moist but well-aerated and flooded conditions(adapted from Kundu 1987).

188 Neue and Bloomprecipitation of crystalline ZnS, but the quantity of sulfide sulfur in the soil wasinsufficient to account for the precipitation of the added Zn (Bloom, unpubl.).Co-precipitation or adsorption in Fe-Mn carbonate or other minerals may alsocontribute to the low plant available Zn in continuously flooded soils.Zinc deficiencies are frequent in alkaline or calcareous soils (Mikkelsen andKuo 1977). In a study of plant response along a toposequence of calcareous soils,Van Breemen et al (1980) showed that the effect of waterlogging on Zn availabilitywas independent of pH. They suggested that waterlogging reduced Zn uptakebecause of the high solution concentration of Mg 2+ , Ca 2+ , and HCO 3-. Partialcorrelations revealed strong correlations between Zn deficiencies and Mg andHCO 3-. Scharpenseel et al (1983) concluded that Zn may be exchanged against Mginto the trioctahedral clay minerals.Factors such as Mg 2+ , HCO 3-, phosphate, and organic acids which may affectZn uptake and translocation in rice plants have been suggested as causes of Zndeficiency. Forno et al (1975) found that both HCO 3-and acetate inhibit Zn uptake.Tiwari and Pathak (1976) and Pathak et al (1975) found that phosphate inhibits Znuptake. Cayton et al (1985) found that a Zn-efficient variety was better able tomaintain low Fe/Zn, Cu/Zn, Mg/ Zn, and P/Zn. They suggested that the ratios ofthe availabilities of these elements may affect Zn uptake.References citedAduna J B, Bloom P R, Kundu D K, Neue H U, Zarate E B (1987) Evaluation of mineral solubilityrelations in selected flooded soils. Paper presented at the Third Philippine Chemistry Congress,28-31 May 1987, Cagayan de Oro City, Philippines.Amrhein C, Suarez D L (1987) Calcite supersaturation in soils as a result of organic mattermineralization. Soil Sci. Soc. Am. J. 51:932-937.Bajwa M I, Ponnamperuma F N (1980) Clay mineralogies of some Philippine rice soils and theirrelationship to the available phosphorus and exchangeable potassium status. Pages 1-15 inProceedings of the 11th Science Meeting, Leyte. Crop Science Society of the Philippines, Baybay,Leyte.Bloom P R, Inskeep W P (1986) Factors affecting bicarbonate chemistry and iron chlorosis in soils. J.Plant Nutr. 9:125-228.Brandon D M, Mikkelsen D S (1979) Phosphorus transformations in alternately flooded California soils.I. Cause of plant phosphorus deficiency in rice rotation crops and correctional methods. Soil Sci.Soc. Am. J. 43:989-994.Broadbent F E (1979) Mineralization of organic nitrogen in paddy soils. Pages 105-118 in Nitrogen andrice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Cayton M T C, Reyes E D, Neue H U (1985) Effect of zinc fertilization on the mineral nutrition of ricesdiffering to zinc efficiency. Plant Soil 87:319-327.Connell W L, Patrick W H Jr. (1968) Sulfate reduction in soil effects of redox potential and pH. Science159:86-87.De Datta S K (1981) Principles and practices of rice production. John Wiley and Sons, New York.De Datta S K (1987) Nitrogen transformation processes in relation to improved cultural practices forlowland rice. Plant Soil 100:47-69.Deer W A, Howie R A, Zussman J (1966) An introduction to rock forming minerals. Longman, Essex,England.Engler R M, Patrick W H Jr. (1975) Stability of manganese, iron, zinc, copper and mercury in floodedand nonflooded soil. Soil Sci. 119:217-221.Forno D A, Yoshida S, Ash C J (1975) Zinc deficiency in rice. I. Soil factors associated with deficiency.Plant Soil 42:537-550.Grant I F, Seegers R (1985) Tubificid role in soil mineralization and recovery of algal nitrogen by lowlandrice. Soil Biol. Biochem. 17:559-563.

Nutrient kinetics in flooded rice soils 189Grant I F, Tirol A C, Aziz T, Watanabe I (1983) Regulation of invertebrate grazers as a means to enhancebiomass and nitrogen fixation of Cyanophyceae in wetland rice fields. Soil Sci. Soc. Am. J.47:669-675.Greenland D J (1987) Experimental approaches in defining the needs for potassium. Pages 293-306 inPotassium in the agricultural systems of the humid tropics. Proceedings of the 19th Colloquium ofthe International Potash Institute, Bangkok, Thailand, 1985. International Potash Institute, Bern.Hossner L R, Freeout J A, Folsom B L (1973) Solution phosphorus concentration and growth of rice( Oryza sativa L.) in flooded soils. Soil Sci. Soc. Am. Proc. 37:405-408.Inskeep W P, Bloom P R (1986a) Calcium carbonate supersaturation in soil solutions of Calciaquolls.Soil Sci. Soc. Am. J. 50:1431-1437.Inskeep W P, Bloom P R (1986b) Kinetics of calcite precipitation in the presence of water-soluble organicligands. Soil Sci. Soc. Am. J. 50:1167-1172.Inubushi K, Watanabe I (1987) Microbial biomass nitrogen in anaerobic soil as affected by N-immobilization and N 2 -fixation. Soil Sci. Plant Nutr. 33(2):213-224.Katyal J C(1977) Influence of organic matter on chemical and electrochemical properties of some floodedsoils. Soil Biol. Biochem. 9:259-266.Khalid R A, Patrick W H Jr., DeLaune R D (1977) Phosphorus sorption characteristics of flooded soils.Soil Sci. Soc. Am. J. 41:305-310.Kundu D K (1987) Chemical kinetics of aerobic soils and rice growth. Ph D thesis, Indian AgriculturalResearch Institute, New Delhi, India.McKeage J A, Cline M G (1963) Silica in soils. Adv. Agron. 24:29-96.McKenzie R M (1977) Manganese oxides and hydroxides. Minerals in soil environment. Soil Sci. Soc.Am. J. 41(1):181-193.Malavolta E (1985) Potassium status of tropical and subtropical region soils. In Potassium in agriculture.R. D. Munson, ed. American Society of Agronomy, Madison, Wisconsin.Mikkelsen D S, Kuo S (1977) Zinc fertilization and behavior in flooded soils. Spec. Publ. 5,Commonwealth B. Soil, England.Moormann F R, Van de Wetering H T J (1985) Problems in characterizing and classifying wetland soils.Pages 53-68 in Wetland soils: characterization, classification and utilization. International RiceResearch Institute, P.O. Box 933, Manila, Philippines.Nagarajah S, Neue H U, Alberto M C R (1987) Effect of Sesbania, Azolla and rice straw incorporation onthe kinetics of NH 4 , K, Fe, Mn, Zn and P in some flooded rice soils. Plant Soil (accepted forpublication)Neue H U (1985) Organic matter dynamics in wetland soils. Pages 109-122 in Wetland soils:characterization, classification and utilization. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Neue H U, Mamaril C P (1985) Zinc, sulfur and other micronutrients in wetland soils. Pages 307-320 inWetland soils: characterization, classification and utilization. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Neue H U, Scharpenseel H W (1984) Gaseous products of the decomposition of organic matter insubmerged soils. Pages 109-122 in Organic matter and rice. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Neue H U, Scharpenseel H W (1987) Decomposition pattern of 14 C-labeled rice straw in aerobic andsubmerged rice soils of the Philippines. Sci. Total Environ. 62:431-434.Pathak AN, Tiwari K N, Singh K( 1975) Zinc-phosphate interrelationship in rice. J. Indian Soc. Soil Sci.23:477-483.Patra P K (1987) Influence of water regime on the chemical kinetics of soils and rice growth. Ph D thesis,Indian Agricultural Research Institute, New Delhi, India.Patrick W H Jr., Khalid R A (1974) Phosphate release and sorption by soils and sediments: effect ofaerobic and anaerobic conditions. Science 186:53-55.Patrick W H Jr., Mikkelsen D S, Wells B R (1985) Plant nutrient behavior in flooded soil. Pages 197-228in Fertilizer technology and use. 3d ed. Soil Science Society of America, Madison, Wisconsin.Patrick W H Jr., Reddy C N (1978) Chemical changes in rice soils. Pages 361-379 in Soils and rice.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Ponnamperuma F N (1972) The chemistry of submerged soils. Adv. Agron. 24:29-96.Ponnamperuma F N (1985) Chemical kinetics of wetland rice soils relative to soil fertility. Pages 71-89 inWetland soils: characterization, classification and utilization. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Roger P A (1986) Effect of algae and aquatic macrophytes on nitrogen dynamics in wetland rice fields.Congr. Int. Soil Sci. Soc. 13-21.

190 Neue and BloomRoger P A, Grant I F, Reddy P M, Watanabe I (1987) The photosynthetic aquatic biomass in wetlandricefields and its effect on nitrogen dynamics. In Efficiency of N-fertilizers for rice. International RiceResearch Institute, P.O. Box 933, Manila, Philippines.Ross S J Jr., Franzmein D P, Roth B (1976) Mineralogy and chemistry of manganese oxides in someIndiana soils. Soil Sci. Soc. Am. J. 40:137-142.Roy A C, De Datta S K (1985) Phosphate sorption isotherms for evaluating phosphorus requirements ofwetland rice soils. Plant Soil 86:185-196.Sah R N, Mikkelsen D S (1986) Effects of anaerobic decomposition of organic matter on sorption andtransformations of phosphate in drained soils: 1. Effects on phosphate sorption. Soil Sci.142:267-274.Scharpenseel H W, Eichwald E, Haupenthal C, Neue H U (1983) Zinc deficiency in a soil toposequencegrown to rice at Tiaong, Quezon Province, Philippines. Catena 10:115-132.Scharpenseel H W, Neue H U (1984) Use of isotopes in studying the dynamics of organic matter in soils.Pages 273-310 in Organic matter and rice. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Schwab A P, Lindsay W L (1983a) Effect of redox on the solubility and availability of iron. Soil Sci. Soc.Am. J. 47:201-205.Schwab A P, Lindsay W L (1983b) The effect of redox on the solubility and availability of manganese in acalcareous soil. Soil Sci. Soc. Am. J. 47:217-220.Schwertmann W, Carlsom L, Murad E (1987) Properties of iron oxides in two Finnish lakes in relation tothe environment of their formation. Clays Clay Miner. 35:297-304.Stumm W, Morgan J J (1981) Aquatic chemistry. Wiley Interscience, New York. 780 p.Tadano T, Yoshida S (1978) Chemical changes in submerged soils and their effect on rice growth. Pages399-420 in Soils and rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Takai Y (1970) The mechanism of methane fermentation in flooded soils. Soil Sci. Plant Nutr. 16:238.Tiwari K N, Pathak A N (1976) Effect of phosphate fertilization on zinc nutrition of rice crop in andalluvial soil of Uttar Pradesh. Indian J. Agric. Sci. 46:269-273.Tsutsuki K, Ponnamperuma F N (1987) Behavior of anaerobic decomposition products in submergedsoils. Soil Sci. Plant Nutr. 33(1):1-11.Turner F T, Gilliam J W (1976) Increased P diffusion as an explanation of increased P availability inflooded rice soils. Plant Soil 45:365-377.Van Breemen C, Quijano C, Le Ngoc Sen (1980) Zinc deficiency in wetland rice along a toposequence ofhydromorphic soils in the Philippines. I. Soil conditions and hydrology. Plant Soil 57:203-214.Vanderberghe R E, DeGrave E, DeGeyter G, Landuydt C (1986) Characterization of goethite andhematite in a Tunisian soil profile by Mossbauer spectroscopy. Clays Clay Miner. 34:275-280.Van der Kevie W (1972) Acid sulfate soils in central Thailand. In Proceedings of the first ASEAN soilsconference. Bangkok, Thailand.Watanabe I, Roger P A (1985) Ecology of flooded ricefields. Pages 229-243 in Wetland soils:characterization, classification, and utilization. International Rice Research Institute, P.O. BOX 933,Manila, Philippines.Yamane I, Sato K (1963) Decomposition of organic matter and gas formation in flooded soils. Soil Sci.Plant Nutr. 9:32-36.Yamane I, Sato K (1967) Effect of temperature on the decomposition of organic substances in floodedsoil. Soil Sci. Plant Nutr. 13:94-100.Yu T (1985) Physical chemistry of paddy soils. Springer-Verlag, Berlin.NotesAddresses: H. U. Neue, Department of Soils, International Rice Research Institute, P.O. Box 933, Manila, Philippines;P. R. Bloom, Department of Soil Science, University of Minnesota, St. Paul, Minnesota, 55108, USA.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. BOX 933,Manila, Philippines.

Abstracts 191ABSTRACTS: NUTRIENT MANAGEMENTIntegrated nitrogen managementin irrigated riceS. K. DE DATTA AND R. J. BURESHUse of inorganic N fertilizers has increased dramatically during the past 20yr, while use of organic fertilizers and green manure has declined. Urea isnow the major N fertilizer for rice in Asia. Extensive research hasdemonstrated that normally only 20-40% of applied N fertilizer is utilizedby irrigated rice. Direct field measurements of ammonia loss confirmedthe importance of ammonia volatilization in N fertilizer loss. Recentindirect estimates of denitrification by the difference betweenunaccounted-for 15 N in 15 N balancesand directly measured ammonia losssuggest that denitrification might be as important as, or more importantthan, ammonia volatilization. The goal of integrated N management is tosupply sufficient N to match the N uptake demand of rice while minimizingN loss from the soil/plant system. Nitrogen losses can be reduced, but noteliminated, by incorporating urea before transplanting with no standingfloodwater rather than by incorporating with standing floodwater or bybroadcasting into floodwater. Coatings to control urea release and ureadeep placement frequently have been more successful in reducing N lossthan has incorporating prilled urea with no standing water. Ureaseinhibitors offer an alternate strategy for reducing N loss, but the ureaseinhibitors evaluated usually have not matched deep placement of urea orsulfur-coated urea in ability to increase grain yield. Some recent studieshave shown that the proportion of N loss from urea can be reduced byusing lower N application rates. Research is needed to determine whetherfarmers can reduce N loss and increase crop utilization of N by using morefrequent, smaller fertilizer doses or by substituting organic sources of N forsome of the inorganic fertilizer used.S. K. De Datta, Department of Agronomy, International Rice Research Institute (IRRI), P.O. Box933, Manila, Philippines; R. J. Buresh, International Fertilizer Development Center, P.O. Box2040, Muscle Shoals, Alabama 35662. USA (visiting scientist at IRRI).

192 AbstractsManagement of acid sulfate rice soilsin South ChinaLI JINPEI AND HUANG YUNIANSouth China has more than 20,000 ha of salt-affected swamp soil andmore than 67,000 cultivated ha of acid sulfate soil. Mangrove swamp soilis muddy, high in nutrients, and essentially anaerobic, with 3.6-4.0%organic matter content, pH 7.3, and 0.6-2.3% total salt content. The majorchemical characteristics of acid sulfate soil are low pH, available P and Ca,and excessive sulfur. Management practices for rice cultivation includeconstructing separate irrigation and drainage ditches, leaching with freshwater, and maintaining continuous submergence after transplanting.Phosphorus fertilizer and acid-tolerant rice varieties are effective forincreasing yields. For dryland crops, drainage ditches should be deepenough to effectively drain the toxicant. Adding mud to raise the surface,mulching with fresh straw and sugarcane leaves, and applying N and Parenecessary.Li Jinpei and Huang Yunian, South China Agricultural University, Guangzhou, China.Nutrient management in saline, acid sulfate,and other problem soils of VietnamVO-TONGXUANThe fertility status of Vietnamese soils is rather low. Problem soils includeacidic alluvial soils, acid sulfate soils, saline soils, degraded graysoils, andpeat soils. Acidic alluvial soils need well-balanced N-P nutrient management.Nitrogen should be split into 3 or more doses; N topdressed at 18 dbefore heading is better than at panicle initiation. A zero tillage techniqueto overcome acidity and techniques for green manure application duringflood fallow are described. Acid sulfate soils (occupying about 1.7 millionha) require integrated management: (a) cultural techniques such as earlyplowing, dry seeding rice or mungbean, or submergence seeding; (b) watermanagement such as empoldering; (c) chemical management, such as Pfertilizer, organic material ash, and liming; (d) appropriate farming systemsfor natural nutrient balance. Saline soils (occupying less than 0.8 millionha) can be managed for double-cropping under rainfed conditions. Thefirst crop, a modern variety rice or mungbean, is dry seeded to withstandirregular rains and to better utilize added nutrients; the second crop, a talltraditional rice, is transplanted in a previously harvested field with allstraw removed. In saline soils affected by acidic alluvial soils, onemanagement technique uses a shallow drainage System. Empoldering isalso a good traditional method to use in saline soils; it allows integratedsystem, such as rice - fish - fruit tree, rice - cash crop, or rice - shrimp,without disrupting the environment balance.Vo-Tong Xuan, University of Cantho, Haugiang, Vietnam.

Irrigation system principlesand practices for reliableand efficient water supplyto rice farmsS. M. MIRANDAThe adoption of high-yielding rice varieties has been largely confined toirrigated areas, but the benefits expected from investment in irrigationdevelopment remain to be fully realized. This situation is at least partly dueto the relatively unreliable and inefficient delivery of water to rice farms inmost irrigation schemes. This paper presents emerging principles andpractices required to make irrigation water supply more reliable andefficient at the main-system level, thereby bringing about an improvementin on-farm water management. irrigation system types are reviewed andthe gap between desired and actual practices identified. An interventionapproach and its usefulness in closing that gap, via the introduction ofirrigation management innovations, are discussed.The enthusiasm that accompanied the initial release of high-yielding rice varieties ledmany to assume that the new technology would quickly spread to all parts of therice-growing world. Instead, adoption has been confined primarily to irrigatedareas, particularly in tropical Asia. This limited adoption can be explained byexamining the yield response of rice to nitrogen under different physical regimes.The yield response of rice to nitrogen is lower, and highly erratic, in wet season thanin dry-season irrigated conditions when there is more solar energy. Under rainfedconditions, the uncertainty of adequate moisture and of flooding in many areasdiscourages adoption of modern rice technology (Barker and Herdt 1985).That has led to the rapid expansion of irrigation as a primary component ofagricultural development in the major rice-growing countries during the last 15-20 yr. Now, there is growing evidence that various technical, economic, and socioinstitutionalproblems impede the realization of the benefits expected by farmersfrom investments in irrigation. The relatively unreliable and inefficient supply ofwater to rice farmers in most irrigation schemes is often blamed for this benefit gap.Irrigation system typesAn understanding of the different types of irrigation systems currently used for ricecultivation is helpful in analyzing the associated principles and practices of irrigationmanagement.

194 S.M. MirandaHistorical systemRice irrigation has been practiced in Asia for centuries. In China, rice cultivation inthe upper reaches of the Yellow River reportedly began to spread thousands of yearsago partly as a result of improvements in water control. The origin of largecooperative water projects frequently is attributed to Yu, founder of the first ChineseDynasty, in the floodplain of the Yellow River (Chang 1977). In Sri Lanka,development of a system of large tank reservoirs to irrigate rice in the dry zone beganabout 505 B.C. (Perera 1987). Other ancient irrigation systems are found throughoutAsia, such as the tanks in South India and the irrigation canals in the Indus Valley.Levine (1981) characterized irrigation systems as going through three stages,hydrologic-hydraulic, agriculture-based, and farmer-oriented. The emphasis inhydrologic-hydraulic stage is on capture, conveyance, and equity in allocation ofwater. At this stage, management capability is scarce. In the agriculture-based stage,management capability improves and land becomes the scarce production factor. Inthe third stage, the farmer is an active participant in designing, constructing, andoperating a system. At this stage, water is the most scarce resource.Except for the system of tanks in Sri Lanka and South India, early irrigationsystems in Asia were little more than simple diversion structures in flowing streams.Water management and distribution were also simple; they were limited to thetimely repair of temporary barrage structures and rudimentary delivery channels.Equity in dividing the water diverted was by simple proportional structures (stillused by the Subaks in Bali) (Horst 1984).Modern systemsGiven the economic incentives to develop a year-round water supply, especially thebenefits derived from dry-season cropping, in recent years major investments havebeen made in storage and tubewell systems. That development has resulted inincreased cropping intensity as well as increased management.In Indonesia, irrigation systems are classified into three types on the basis ofwater control and the measurement capacity required to manage the water.Technical irrigation: irrigation flow can be measured and controlled, allstructures are permanent.Semitechnical irrigation: irrigation flow can be measured, but either the flowcannot be controlled or it can be controlled but not measured, all structures aresemipermanent.Simple irrigation: irrigation flow cannot be measured and controlled, allstructures are semipermanent or temporary.In the Philippines, irrigation systems are classified into two types, based on whooperates and maintains them.National systems: constructed, operated, and maintained by the governmentthrough the National Irrigation Administration.Communal systems: operated and maintained by farmers, but not necessarilyconstructed only by them.In most countries, national systems are similar to publicly managed schemesand communals to village- or community-managed schemes (in some South Asian

Irrigation systems for rice farms 195countries) and to peoples’ systems (in Thailand). Somewhat similar to the peoplemanagedsystems, but distinct in many ways, are the irrigation association-managedsystems in Taiwan. These are relatively larger in command area and are capable ofemploying their own staff to attend to day-today operations.Size of service area is another criterion used to classify irrigation systems. In SriLanka, minor systems serve less than 80 ha, medium systems less than 600 ha, andmajor systems more than 600 ha (Jayawardene 1986).Irrigation systems used for rice usually are gravity-delivered open canals;pressurized pipe systems also are used. They can be upstream, downstream, orcontrolled automatically. They can be fed with flowing river water, stored water,groundwater, or even recycled water. They can be single purpose or multipurpose.Other typologies could be cited, but primarily the need is to recognize that eachclassification has a bearing on how an irrigation system can be managed.Principles for reliable and efficient water supplyWhen deciding whether or not to invest in modern rice technologies, farmerslogically expect to have dependable and reliable water supply at the inlets to theirfields. Efficiency of water supply seems to be of more interest to the irrigation serviceagency than to the farmers, unless the farmer is also the owner or otherwiseintimately involved with system management. From a purely technical point of view,the basic principle involved in meeting both requirements is simply to match asclosely as possible water supply with water demand or crop requirements. Theplanning to do this can be as simple or as complex as is needed to manipulate supplyto meet demand. It can be simply informing farmers about water availability and thetimes it will be distributed. In relatively large canal systems, planning can meancomplex matching of estimated future water supply and the water demand of theexpected cropping pattern.Estimating future water supply depends on several factors, includinganticipated rainfall distribution during the wet and dry seasons, type of waterdiversion and storage systems used, and reliability of hydrologic and climatic data.An estimation is complicated in cases where future water supply is variable andunpredictable.Water demand is primarily determined by estimating expected croppingpattern and irrigation efficiencies at the on-farm and main-system levels. Toaccurately calculate water requirement for the system, information is needed notonly on the expected cropping pattern, but also on the actual water requirements ofdifferent crops under different soil conditions (which vary with type of field or farmoperation, stage of crop growth, etc.). Tentative assumptions are made regarding thestart of cropping season, such as crops to be grown, time span of land preparation,start of normal irrigation, and end of season.Once the calculations about supply and demand are complete, decisions on theappropriate distribution practices or other measures are made. Those determine thetarget flows at various levels of an irrigation system. The final choice of distributionmethod depends on the capacity of the canal network, flow regulation available, and

196 S.M. Mirandathe managerial capacity of the irrigation water distributors and water users.Planning the delivery schedule is tempered by experience gained through monitoringthe results of previous crop seasons.Once a plan is operationalized, it is important that its implementation bemonitored and any change or deviation be communicated to all concerned,especially the farmers. Monitoring information can be used for further fine-tuningand to improve planning during the current and succeeding seasons. For planadjustment, periodic consultation at various levels in the management system areneeded for timely presentation, discussion, and resolution of crucial issues that arise.Irrigation practicesBefore the start of any cultivation season, it is useful for irrigation and associatedgovernment officials to meet with farmers and their representatives to formallydecide the start of the season; areas and types of crops to be cultivated; length of landpreparation period; start of normal irrigation; end of season; distribution method(continuous or intermittent); and maintenance schedules and responsibilities.At this meeting the irrigation staff presents the plan for the season, based oninformation at hand and the experience accumulated in operating the system. Theplan is usually discussed before the decision is finally made. Farmers’ suggestionsmay or may not be entertained in the process. This type of meeting is legally requiredin some countries (e.g., Sri Lanka) and is becoming institutionalized in many otherSoutheast and South Asian countries.In implementing the plan for the main season or wet season in which the crop isbasically rice, the starting date and choice of distribution method for landpreparation are dictated by the availability of water at the start of the season. Inrun-of-the-river direct diversion systems, water flow normally increases with therelative activity of the monsoon. In this situation, a staggered delivery scheduleusually is chosen to serve a gradually increasing hectarage, according to flow andrainfall pattern. Diverted flow is concentrated or rotated among sections of the canalservice area. The staggered rotation schedule is an attempt to provide reliable andequitable supply during peak demand (Pasandaran 1985).In a storage facility system with adequate stored water, the water is deliveredcontinuously to the whole service area simultaneously for about 30 d for landpreparation. After planting, normal irrigation starts. This system has the flexibilityto deliver water continuously or intermittently, depending on the canal networkconfiguration and flow regulation. In a direct diversion type, continuous watersupply is adopted for as long as the diverted flow can meet the requirement of thearea command. However, when water becomes short (such as because of failure ofthe monsoon), the limited flow is rotated among sections of the system.The level of rotation may be below or at the tertiary, at the secondary, or alongsections of the primary canal, depending on the severity of the water shortage.Another alternative is to tap a supplementary water source upstream. At the fieldlevel, enterprising farmers often install their own tubewells to augment the systemsupply. In some systems, large capacity tubewells for supplementary and conjunctiveuse feed directly to the canal network. In severe cases of water shortage, agreement is

lrrigation systems for rice farms 197sometimes reached to deliver limited water according to crop growth stage; the morecritical the stage, the higher the priority of receiving water. Sometimes a decision ismade to deliver water to areas easy to irrigate, or to areas that have superior waterrights (Siy and Early 1982).In a storage system, interruption of water flow to the canal network is normallypracticed whenever sufficient rainfall falls in the service area. In a direct diversionsystem, the flow is interrupted only if rainfall is so heavy as to cause flooding in partsof the service area when combined with the irrigation supply. Another reason forclosure at the headworks is to avoid breaching and silting of the canal network.Drainage of excess water flow is practiced extensively, although drainage facilitiesgenerally are inadequate or are not properly maintained.During the second or third cropping season, when water supply becomesrelatively scarce, irrigation and cultivation practices vary across locations andsituations. In the Philippines, which has only two cropping seasons, the service areais often reduced to about one-third the area served during the wet season. The area isrotated every year, with the area served in year one receiving water again in year four.Rice is normally grown in the irrigated area and nonrice crops in the unirrigatedportions, except in the northwest part of the country. There, attempts are made tocultivate the whole service area with a combination of less water-consuming nonricecrops in the well-drained higher land and rice in the lower lands with highgroundwater tables.In Java during the second season, if water, although limited, is still adequateand assured, farmers tend to prefer to cultivate rice. This is also true in many parts ofTaiwan, where farmers are able to grow three irrigated crops a year.In most countries where only two crops or less are possible, other variations arefound. During the dry season in Sri Lanka, only the reduced upper portion of theservice area is scheduled for cultivation. Farmers from the lower portion share in thecultivation of the irrigated upper portion. While rice used to be the only crop, withincreasing self-sufficiency in rice in the country, nonrice crop cultivation is nowpromoted during the dry season to optimize use of the limited water supply,particularly on the better drained, lighter textured soils in the higher portion of thesoil catena.A similar drive in the Philippines involves targeting cultivation of nonrice cropson diversified and dual land class soils with high percolation and seepage rates (thecoarse-textured soils along river levees). Crops with import substitution potential,such as maize and soybean for livestock feed, are promoted. The same crops arebeing emphasized in Indonesia. Even Thailand, which has been a traditional riceexportingcountry, is now looking for alternative crops to grow in its irrigated areasduring the drier part of the year, because of the shrinking international rice market.This shift in policy of several governments to grow nonrice crops during the dryseason in areas served by irrigation systems designed and constructed for riceproduction presents an opportunity to optimize the use of limited water resources.However, it is becoming clear that because nonrice crops are more sensitive to bothinadequate moisture and oversupply of moisture (especially), improved precision indelivering a reduced flow of water on an intermittent basis is necessary. This requiresa higher degree of water control. New and additional demands are thus placed not

198 S.M. Mirandaonly on the physical system, but also on the irrigation staff and farmers in managingand sharing the reduced amount of water and in cultivating relatively unfamiliarcrops.The key seems to lie in providing a reliable water supply at the main system tobring about an improvement in on-farm water management. Early experimentsfocused at the farm level in attempts to ensure that water was used by farmers in themost efficient way to meet basic crop water requirements. It became apparent that inmany systems, farmers’ attempts to use water more efficiently were constrainedbecause the main system was not delivering water in a timely, reliable, and adequatemanner.The focus then moved to the secondary and primary parts of irrigation systems.Studies at the International Rice Research Institute showed that maldistribution ofwater in the secondary and primary parts of a system resulted in major differences inwater availability from one tertiary canal to another. In general, it was found that thetail-end portions had serious water deficiencies while the head or upper portion hadexcess water.This led to implementation in the Peñaranda River Irrigation System in thePhilippines of scheduled checking of flows along the length of secondary canals witha regular schedule of water deliveries specified by day of the week. Substantialproduction increases were reported in all sections of the scheme, although theincrease rose sharply at the tail end (Valera and Wickham 1976). For the four mainsections, top to tail, the percentage increases from the 1973 dry season to the 1975 dryseason were 23, 69, 154, and 1,494.On the nearby Lower Talavera River Irrigation System, secondary canals weremonitored at the top, middle, and tail sections. A comparison of 1976 wet seasonyield (before management intervention) and 1977 wet season yield (afterintervention) showed yield increases of 94 and 62% for 2 top-end secondary canals,16 and 10% for the 2 middle canals, and an average of 104% for the 3 tailend canals.Yields evened out at the top end and tail end, after having been highest in the middle(Early 1980).The obvious implication is that farmers were able to use and share water moreeffectively, if not more efficiently, once the water supply became reliable at the headof the tertiary canals.To further attain reliability in the main-system water supply in relatively largeschemes, intermediate water storage at the head of secondary canals is beingproposed. This is already a common practice in China. Some of the ancient tanksystems in Sri Lanka incorporate certain aspects of this practice. This was possiblebecause of the ideal physiography and hydrological characteristics of the landscapesin which the systems were located.The Alexander Gusmao project in Brazil illustrates an extreme case.Intermediate storage equivalent to 2-3 d irrigation is provided on each 10-ha farm.Each storage is supplied by a continuous flow. Essentially no communication isrequired except in emergencies, and each farmer can utilize the irrigation water as hedesires. A variation may be found in the Gezira Scheme in Sudan. There, primarycanals are enlarged to temporarily hold water accumulated during the night by

Irrigation systems for rice farms 199closing all the headgates to secondary canals. The water is released during the day.Tubewells that tap stored groundwater are another means of providing additionalwater in short-supply situations.Gap between desired and actual practicesIn managing an irrigation system, even in its simplest form, the mechanism forapplying water to farmers’ fields can be considered to consist of three parts: a set ofphysical works that move the water from its source to the crop; a plan that definesthe activities to be undertaken; and the people, individually and in groups, whoimplement the plan. Using the new computer lingo, the physical infrastructure canbe referred to as hardware and the nonphysical managerial inputs as software.Levine (1980) says that up to a certain point, there is some degree of substitutabilitybetween the hardware and software elements in each of the basic functions—waterdelivery, maintenance, and conflict management—of irrigation systems. The choicecan influence the actual irrigation management practices existing in a system. Thegap between the irrigation practice that is desired and that which exists may becaused by any, a combination, or all of the following:• Incomplete or inappropriately designed and constructed physical works;• Poorly maintained and deteriorated physical system (often a result ofinadequate funding for operation and maintenance);• Lack of accountability of irrigation staff due to incompetence, politicalinterference, management system weakness, and/or corruption; and• Lack of cooperation of farmers, caused by their noninvolvement and lack ofappreciation of system management.The result of a deficient hardware-software mix is an inefficient and unstablewater supply to various parts of the irrigation system, causing conflicts betweenfarmers and irrigation staff and among farmers. The ultimate outcome is pooradoption of modern rice technology by the farmers and low agricultural production.An approach to bridge the gapIn bridging the gap between desired irrigation practice and that which exists, anapproach to rapidly appraise or diagnose the specific condition of a given system isnecessary. One approach that has been used in a limited way involves asking pointedquestions about hydrology, engineering, agronomy, economics, and communitylevelsociology pertinent to the scheme (Chambers 1980).• What water (quantity, timing, probability) is available?• How (quantity, timing, place) is it distributed?• Using the criteria of productivity, equity, stability, and utility of irrigation,how can water be redistributed so that all concerned—top-enders, tailenders,and irrigation agency staff—will gain?• What steps can be taken to achieve the changes needed?• What changes in institutions and procedures will make it rational for thosewho will lose water to accept their loss?

200 S.M. MirandaThese questions are suggested as a framework for identifying technical andmanagerial deficiencies and for determining appropriate interventions to improvethe performance of an irrigation system.Some key steps in doing operational interventions in irrigation managementare (Early et al 1982)• Explaining the results of the appraisal conducted to the irrigation staff andfarmers, discussing the problems found and possible solutions, to achieveagreement on the intervention measures to be tried;• Working with all concerned on the seasonal calendar and schedule of waterdeliveries;• Measuring flows at the headworks, selected pilot secondary canals, andturnouts to tertiary channels from pilot secondary canals; measuring rainfall,evapotranspiration, seepage, and percolation; and keeping tabs on specificfarming activities;• Controlling, including calculating, target discharge allocations to eachsecondary and tertiary channel, based on water measurement and farmingactivities;• Monitoring target flow achievement, water adequacy, and field performancein the system; obtaining feedback on farmers’ satisfaction and farmers’positive and negative behavior; and• Evaluating the intervention, including assessing farmers’ responses, theirrigation staff accountability to farmers’ needs, and the feasibility ofimplementing the methodology by an irrigation agency in other areas.The International Irrigation Management Institute (IIMI) is using a similarapproach to carry out intervention research of dry season irrigation management inrice-based farming systems. IIMI has found this innovative approach to irrigationmanagement research feasible and promising for improving the reliability and equityof water distribution during the water-short dry season in the Kalankuttiya Block ofthe Mahaweli H system in Sri Lanka.Highlights of a report presented by the IIMI group during its recent meetingwith senior Mahaweli agency staff on the intervention research for the 1987 dryseason follow.• When faced with an entirely new situation at the beginning of the seasonwhere only the well-drained portions of turnout areas were to be permittedfor shared cultivation, the delivery schedule and the supply to each turnouthad to be modified considerably from those of the previous season.• The flow data of the last three seasons were used to propose an appropriaterotational schedule to fit into the new situation, where only parts of turnoutswere to be cultivated. The rationale of this new delivery schedule from theintermediate storage sluice to the distributary (secondary) canals and field(tertiary) channels was explained to the irrigation staff. Before the end of theseason, the new schedule could be implemented by the irrigation staff on therest of the 20 distributaries served by the branch canal.• A major change from the previous season’s delivery pattern was in lieu of asimultaneous flow in all field channel turnouts served by a distributaryduring the usual four days of flow. A rational approach ensured a steady

Irrigation systems for rice farms 201stream for 1-3 d for each turnout, depending on the number of allotmentsserved.• The measured water delivery for each rotational issue at the individualturnouts was fed back to the irrigation block staff prior to the subsequentrotational issue. This enabled the staff to estimate either undersupply oroversupply of water at the turnout for the duration of each delivery.• Farmers readily accepted the new delivery schedule, with their ownmodifications within a turnout. In a majority of instances, farmers preferredto utilize the full stream, rather than the half stream for each two farmersenvisioned when the on-farm facilities were designed and constructed.• Based on their experience during the 1987 dry season, farmers say they prefertotal nonrice crop cultivation for the dry season and that they couldeffectively manage deliveries for the nonrice crops on well-drained andimperfectly drained soils, leaving out the poorly drained soils.• Farmers were able to suggest a reasonable and workable calendar for futuredry seasons with respect to the first water delivery and frequency of rotationaldeliveries.Some lessons gleaned from this operational action research are• Flow measurement is a useful tool for management decisionmaking andimplementation as well as for improving farmer-agency cooperation.• Regular scheduled rotation of turnouts enhances the capacity of farmers totake over management functions below the distributary channel gates.• Regular meetings of farmer leaders and irrigation officials after each waterdelivery are an effective way to improve communication and to identifyspecific water problems and possible solutions at the secondary and tertiarylevels.Some implications emerging from this approach to irrigation managementinclude the following:• The physical condition of the irrigation system could be made moremanageable by pragmatic rehabilitation to make it functional in capturing,conveying, controlling, and distributing water from the source to the farm,and also in removing excess water.• Depending on the hardware available, there is a need to improve waterallocation and distribution procedures (software) in the main system toincrease reliability and equity of farmers’ access to water and to enhance theefficiency of their water use.• There is a need to upgrade the management and technical capacity ofirrigation agency staff in operating and maintaining the system to make itmore responsive to farmers’ needs.• Increased farmer cooperation could occur through increased farmerparticipation in planning, implementation, monitoring, and evaluating theoperation and maintenance of the system.• Resource mobilization for sustained system operation and maintenanceshould be enhanced.• Appropriate irrigation design features will improve management of thesystem.

202 S.M. MirandaOther implications could be cited, as can be expected, given the organic natureof irrigation systems. They are evolving and living human enterprises that thrive andchange in accordance with attractions or incentives and disciplinary actions (Kellerand Peterson 1986). Irrigation systems can be made to respond to managementinnovations designed to provide reliable and efficient water supply to farmers,thereby increasing agricultural production through opportunities to the use ofmodern and improved rice technologies.References citedBarker R, Herdt R W (1985) The rice economy of Asia. Resources for the Future, Inc., Washington, D.C.324 p.Chambers R (1980) In search of a water revolution: questions for managing canal irrigation in the 1980s.Pages 23-37 in Report of a planning workshop on irrigation water management. International RiceResearch Institute, P.O. Box 933, Manila, Philippines.Chang T (1977) The rice cultures. In The early history of agriculture. Oxford University Press, London.Early A (1980) An approach to solving irrigation system management problems. Pages 83-113 in Reportof a planning workshop on irrigation water management. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Early A, Moya T B, Cablayan D M (1982) Collaborative irrigation system management research resultsfrom the Upper Pampanga integrated irrigation systems. Paper presented at a Saturday seminar.International Rice Research Institute, Los Baños, Laguna, Philippines.Horst L (1984) Irrigation water management in Indonesia Int. J. Dev. Technol. 2:211-221.Jayawardene J (1986) Evolution of irrigation of management systems in Sri Lanka. Mahaweli Manage.41-15.Keller J, Peterson D F (1986) Exploration of canal systems: structure, management and evolution. Paperpresented at a Symposium on Irrigation in International Development - Benefits and Problems,Philadelphia.Levine G (1980) Hardware and software; an engineering perspective on the mix for irrigationmanagement. Pages 5-21 in Report of a planning workshop on irrigation water management.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Levine G (1981) Perspectives on integrating findings from research on irrigation systems in SoutheastAsia. Paper presented at a Workshop on Investment Decisions to Further Develop and Make Use ofSoutheast Asia’s Irrigation Resources, Agricultural Development Council, Bangkok, Thailand.Pasandaran E (1985) The status of irrigation research in Indonesia. Paper presented at a Workshop onResearch Priorities for Irrigation Management, International Irrigation Management Institute,Digana Viage, Sri Lanka.Perera K D P (1987) Irrigation in Sri Lanka. Paper presented at the Asian Regional Symposium onIrrigation Design for Management, Kandy, Sri Lanka.Siy R, Early A (1982) Community irrigation: indigenous solutions to management of water resources.Paper presented at a Saturday seminar, International Rice Research Institute, Los Baños, Laguna,Philippines.Valera A, Wickham T (1976) Management of traditional and improved irrigation systems: some findingsin the Philippines. Paper presented at a Workshop on Choice on Irrigation Management, OverseasDevelopment Institute, Canterbury, London.NotesAddress: S. M. Miranda, International Irrigation Management Institute, Digana Vi Via Kandy, Sri LankaCitation information: International Rice Rice Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstracts 203ABSTRACTS: WATER MANAGEMENTIncreasing water-use efficiencyon irrigated rice farmsS.I. BHUlYAN AND K. PALANlSAMlEfficiency of water use on the farm in irrigated rice culture can beincreased by reducing field losses and by applying only the amounts ofwater needed. Field water losses are caused by deep percolation, seepage,and surface runoff. Deep percolation loss can be minimized by puddlingthe soil and allowing formation of plow pans and by reducing the depth ofirrigation water in the field. Seepage losses can be reduced by landleveling; maintaining uniform, and low water depths; keeping ricefielddikes free of cracks and holes; and, in light-textured soils, applying morefrequent irrigations with less water. Surface runoff losses can beminimized by avoiding overirrigation and properly maintaining boundaryareas. Three efficiency concepts—technical, production, and allocation—can be applied to determine the optimal level of water applied under givenwater supply conditions. Data from tank irrigation systems of Tamil Nadu,India, and deep tubewells of Guimba, Nueva Ecija, Philippines, were usedto evaluate these concepts. In Tamil Nadu, the number of irrigationsneeded to reach production, allocation, and technical efficiencies were10.2, 10.0, and 7.4, respectively. In Guimba, due to fixed water charges,the number of irrigations needed to reach production and allocationefficiencies was 4.9. This suggests that technical efficiency is important inirrigation decisions when water supply is inadequate for the entire farm,but allocation efficiency is more important when water supply is adequatebut water has a realistic price. Using improved technology to convey waterto farms achieved higher water-use efficiency and gave greater benefits tofarmers.S.I. Bhuiyan and K. Palanisami, International Rice Research Institute. P.O. Box 933, Manila,Philippines.Relationship of drainage practices to rice yieldZHANG WEI AND SITU SONGMeteorology and topography are the decisive factors in cultivation andwater management practices for different areas of China. Drainage andirrigation practices are equally important in controlling the water balance ofa ricefield. With advances in irrigation and drainage techniques since1949, the importance of water management in rice technology has beenemphasized.Zhang Wei and Situ Song, China National Rice Research Institute, Hangzhou, China.

Integrating women's concernsinto farming systems researchPUDJWINATl SAJOGYO AND T. PARISWomen in Asia play important roles in farming systems. Although they arevisibly integrated intovarious production and income-earning activities asfarm managers and wage laborers, consideration of their roles has not yetbeen integrated into research and into technology development. Projectsto increase food production and income and to promote farm householdwelfare do not take sufficient account of women's current and potentialcontributions. Studies in Indonesia, Philippines, and other Asian countriesshow that women provide more than one-third to one-half the total laborin agriculture. Awareness among agricultural researchers about women'sroles as users and beneficiaries of technology is growing. Involvingwomen in designing, testing, and transferring existing and emergingtechnologies remains a major challenge. Coordinated efforts in internationaland national research programs are needed to integrate women'sconcerns into the agricultural and extension programs dealing with ricefarming systems. Active involvement of biological scientists, socialscientists, engineers, and trainers is essential if work in the Women InRice Farming Systems (WIRFS) network is to lead to the desired goal:increasing women's income, and thereby the welfare of the entire family.Farming systems is becoming an increasingly important approach to research, asscientists attempt to raise agricultural production and income even further throughefficient use of production resources. The farming systems approach focuses on theinterdependencies of the components under the control of the men and women whoare members of farm households, and examines how those components interact withphysical, biological, and socioeconomic factors beyond the household's control.It is the household that makes the management decisions, provides the labor,markets the products, and performs many other functions within a farm. But thehousehold is not a homogeneous decisionmaking unit. Within any given household,there are degrees of gender-specific specialization among tasks and decisiondomains. Those specializations affect the adoption of innovations. Lack of attentionto gender-specific activities in farming systems research has resulted in the inefficientdevelopment and transfer of the technologies that will be principally used by women.The needs, constraints, and potentials of technology users vary. The adoptionof a systems approach and adequate understanding of different farming systems will

206 Pudjiwati and Parisbe incomplete unless women’s multiple roles in farm, nonfarm, and domesticactivities are considered.Here we identify some important issues in understanding the role of women inagriculture and describe how consideration of the roles of farming women is beingintegrated into farming systems research activities.Women‘s issues in agricultureMany studies have documented the significant contributions women make in Asianagriculture (IRRI 1985). Women provide more than one-third the total labor inputin most parts of Asia; in Nepal, South India, Sri Lanka, and Indonesia, they providemore than half. Their labor contributions are particularly significant in jobsinvolving considerable drudgery, such as transplanting, weeding, harvesting,threshing, and winnowing. They also have important roles in most aspects ofpostharvest handling and marketing.Macrostudies in rural West Java show that, on the average, farm women’sincome-earning work involves 2-4 h a day and covers a wide variety of tasks(farming, working as farm labor and as nonfarm labor, trading, making handicrafts,etc.) (Pudjiwati 1983). The average workload of women in home maintenanceinvolves 5-6 h a day. Women spend 7-10 h a day working, men only 6-8 h. In manyhouseholds, women are key decisionmakers, directly or indirectly. As land useintensities, their participation grows. With agricultural development, their contributionscan be expected to increase further.Microstudies in rural Indonesia analyzed the time allocation and decisionmakingpatterns of men and women in housekeeping and income-generatingactivities of household members (White 1976). Those studies provide an empiricalbase for defining issues related to women in agriculture and for sensitizingagricultural researchers to the important roles women play which have beenundervalued or unperceived. In many instances, it is fair to say that women workingin agriculture are physically visible, but conceptually or culturally invisible.The invisibility of women’s work in agriculture is obvious when we examine themacrolevel data on women in the labor force in Indonesia (Central Bureau ofStatistics 1981). The data are incomplete, because they do not touch on themultiplicity of women’s roles as providers of household income and on the doubleroles they play in housekeeping and in income-generating activities.Recent studies in rural Java indicated that poorer households were moredependent on the earnings of women, whereas richer households were moredependent on the social status of the work of the women (Pudjiwati 1977, 1983;Stoler 1977). In 1971, 19% of the households among the rural poor in Java wereheaded by women. In 1976, approximately 4.11 million households in Indonesiawere headed by females. The 1980 population census recorded 4.34 millionhouseholds headed by women, 80.3% of them in rural areas.Modernization of agriculture in developing countries has provided women insome areas with better income-earning opportunities, but in others it has displacedthem from their traditional roles. The displacement is particularly serious when job

Women’s concerns in rice farming systems 207destruction is not accompanied by alternative job creation, either within a diversifiedagricultural sector or in nonfarm employment. In Indonesia, for example, changingrice processing technology had an impact on agricultural labor. Traditionally,women hand-pounded unhusked rice. Today, much of this processing is done bymechanized hullers. It has been women, especially those from poorer householdswho have little or no access to land, who are the main victims of the lost incomeearningopportunities.Female labor in Javanese rice production declined from about 65% of the totallabor in the 1920s to 53% in the 1960s and 37% in the 1970s (Collier 1980), in part dueto the introduction of the sickle and the rice mill.Microstudies in rural Indonesia (Pudjiwati 1984) indicate that analysis of roledifferences, especially those within the family and the household that are based ongender, provides an opportunity to analyze the role of women in relation to men,particularly in relationships that stem not only from biological differences but alsofrom social differences.Farming systems research, while introducing a user perspective into technologydevelopment, still assumes that the farm household is a homogeneous unit that canbe adequately represented by the male farmer as the culturally defined head. Manyextension programs also ignore women agricultural workers and decisionmakers.Consequently, the traditional user-beneficiaries of technology, agricultural information,extension services, training, credit, and organizational efforts tend to be malefarmers.It seems that the problems of the invisibility of women in farming systems stillstem from the fact that male leaders in national agricultural research systems sufferfrom a gender-issue-resistance syndrome (Castillo 1986, Pudjiwati 1983). Fortunately,visibility is improving. The research that we do must go beyond sensitizingto being operationally significant. It must provide those responsible for policy andprogram development and implementation with a more precise definition of theproblem, so that more feasible solutions can be sought. Analysis of poor farmhouseholds on the basis of gender specificity in labor activities, production andconsumption, decisionmaking, and general well-being should be explicitly consideredin technology design and diffusion, as well as in the development of relatedpolicies and institutional changes. Ignoring gender specificity leads to technologiesand policies inappropriate for growth and equity.Integrating women’s concerns into farming systemsThe International Rice Research Institute (IRRI) is involved in generatingtechnologies for rice-based production systems. Its explicit attention to women’sconcerns was focused in September 1983 at a conference of biological scientists andagricultural policymakers to discuss women’s roles in farming. Participantsexamined whether women had benefited from the introduction of new ricetechnology, how women benefit from emerging technologies, and how women’sroles in technology development and transfer might be enhanced. The conferencewas followed by a project design workshop during which Asian participants

208 Pudjiwati and Parisrecommended that IRRI initiate collaborative efforts to institutionalize concernsabout women’s roles in agricultural research and extension programs on ricefarming systems (IRRI 1987).One strategy to achieve that goal is to integrate Women in Rice FarmingSystems (WIRFS) research into the established Asian Rice Farming SystemsNetwork (ARFSN), the International Rice Testing Program (IRTP), and theInternational Network on Soil Fertility and Sustainable Rice Farming (INSURF).These networks are crucial in the development, testing, and extension of improvedtechnologies, methods, and germplasm for rice-based agriculture. The basicapproach is to work with national programs to identify, develop, test, anddisseminate technologies that match the needs of rice farming women.Additional attention will focus on identifying mechanisms that increasesensitivity to women’s needs and encourage the involvement of greater numbers ofwomen in agricultural research and extension; evaluating the extent to whichresearchers’concerns promote women’s interests and contribute to the positive effectof technical change on the welfare of women and rural households; identifying theinstitutional and policy framework necessary to enable farm women and womenlaborers to participate actively in technology development and to derive benefit fromtechnological innovations; and promoting the development of appropriate researchand training programs for women. The farming systems methodology developed forARFSN is being used to integrate WIRFS activities into network research at keysites in the Philippines, Indonesia, and Thailand. WIRFS activities also will beexpanded in India, Bangladesh, and Nepal (IRRI 1987).WIRFS in the PhilippinesWomen’s concerns were examined in a crop-livestock project involving two villages(rainfed and irrigated areas) in Santa Barbara, Pangasinan, Philippines. Processingand marketing glutinous rice were identified as important traditional incomegeneratingactivities for women. By processing glutinous rice, women contributed14% of total household income (Table 1). Production and processing constraintsalso were identifed. IR65, a high-yielding, early-maturing glutinous variety, andDiket, a commonly grown local glutinous variety, were compared in farmers’ fieldtrials. IR65, with substantially higher yield (Table 2), had cooking and eatingqualities acceptable to women. Glutinous rice preparation requires considerable fueland cooking time. IRRI agricultural engineers developed and tested several simplemechanical devices to reduce drudgery, cooking time, and energy requirements.As an additional source of household income, women were given hands-ontraining in growing mushrooms on rice straw and other plant residues as substrates.To complement these technologies, programs to spread technical knowledge and toprovide training in appropriate skills were introduced for both men and women.Data on decisionmaking and intrahousehold allocations of resources are beingcollected to quantify the effects of changing technology on family members,particularly women.WIRFS activities are now being extended to other farming systems researchsites in the Philippines: Guimba, Nueva Ecija (partially irrigated); Claveria,Mindanao (acid upland); and Trece Martirez, Cavite (upland).

Women's concerns in rice farming systems 209Table 1. Income of farm households by source and by location, Santa Barbara,Pangasinan, Jan-Dec 1986.Income sourceIncome (P) aMalanayCarosucan(irrigated)(rainfed)(n = 18) (n = 171On-farmCrops 5,451 (40.4) 3,057 (19.0)Livestock 2,404 (17.8) 2,293 (21.7)Others 618 ( 4.6) 353 ( 3.3)Subtotal 8,473 5,703Off-farmMale wages 871 ( 6.4) 240 ( 2.2)Female wages 281 ( 2.2) 124 ( 1.2)Both 149 ( 1.1)–Subtotal 1,301 364NonfarmRemittances 716 ( 5.3) 1,804 (17.1)Other business/lottery 1,530 (11.3) 388 ( 3.7)Male (nonfarm) 1,248 ( 9.3) 873 ( 8.3)Female (nonfarm) 213 ( 1.6) 1,424 (13.5)Total 13,481 100.0 10,556 100.0a Figures in parentheses are percentages. From Ministry of Agriculture, Crop -Livestock Project, Santa Barbara, Pangasinan, Jul-Dec 1986.Table 2. Cost and returns (P/ha) of glutinous rice varieties. Carosucan, SantaBarbara (rainfed rite), Pangasinan. 1986. aItem IR65 Diket bYield (kg/ha) fresh wt 5,420 4,680Price (P/kg) 2.92 2.92Gross returns (A) 15,826 13,666Labor and power costs (B) 4,949 4,372Land preparation 1,161 1,023Crop establishment 575 569Weed control 1 6Fertilizer application 14 11Insecticide application 2 2Other care 31 28Harvesting 3,165 2,733Meterial costs (C) 797 607Seeds 343 119Fertilizer 425 419Insecticides 29 63Others – 6Total variable costs 5,746 4,979Returns above variable costs (A/D) 10,080 8,687Returns to labor end power costs (A-C/B) 3.04 2.59Returns to material costs (A-B/C) 13.65 15.31No. of plots 22 22Av plot size (m 2 ) 429.79 646.56a From Ministry of Agriculture, Crop - Livestock Project, Santa Barbara, Pangasi-nan, Jul-Dec 1986. b Local variety.

210 Pudjiwati and ParisFarming systems research in IndonesiaFarming systems research started in Indonesia with the IRRI-Indonesia rice-basedcropping systems collaboration and evolved into an important component of theresearch programs of the food crops research institutes of the Agency forAgricultural Research and Development (Pusat Penelitian dan PengembanganPertanian [PUSLITBANG]) (Kasryno et al 1985).Multiple cropping experiments began at the Central Research Institute forAgriculture, Bogor, in 1970. In 1973, the Bogor Research Institute for Food Crops(BORIF) began cropping systems research in cooperation with IRRI. Agriculturaleconomists at BORIF have conducted baseline surveys, farm recordkeeping studies,economic analyses, and adoption and impact analyses. Later, cropping systems wereexpanded to include livestock, perennial crops, and fishery.Inclusion of these other enterprises established the farming systems approach,particularly when the research was specifically designed to increase farmerparticipation. As more research institutions became involved, farming systemsresearch emerged as a specific mission of the project. The process developed intospecializations (Nataatmadja 1985), such as food crop-based farming system,perennial crop-based farming system, livestock-based farming system, fishery-basedfarming system, and forestry-based farming system.Early research made agriculturists aware that improvements in totalagricultural production cannot be achieved through a single innovation. Even whenmany factors (biological, socioeconomic, etc.) are considered, efforts may still fail.This has been especially true in changing traditional agriculture in developingcountries. The use of farm machinery, fertilizer, pesticides, high-yielding varieties,farm credit, and extension does not necessarily result in sustained increased output.There is a big gap between experimental results and farmers’ yields. To reduce thisgap, a holistic or systems approach is now being considered in farming systemsresearch.In a systems approach, the interrelationships among the activities andcomponents involved in agricultural production are considered. That givesresearchers and farmers tools to understand and to manipulate the subsystems.Understanding the entire system helps those who work with different components tounderstand the importance of their contribution in relation to other inputs.Farming systems-related research has been carried out through many farmmanagement case studies and area surveys. The most recent examples of farmingsystems-related research are the studies conducted by the Agro-EconomicSurvey/Rurd Dynamics Study, in which all household enterprises, includingnonagricultural income sources, are analyzed. The present PATANAS (NationalPanel of Farmers Research Program of the Center for Agro-Economic Research[CAER]) can also be considered an adaptation of farming systems-related research.Integrating women’s concerns into farming systems research. Production andcredit programs (BIMAS, INMAS, INSUS, and OPUS) have been implemented inIndonesia for 17 yr, to increase food production, farm productivity, and farmerincomes; expand employment opportunities; improve equity in employment andincome; and conserve agricultural resources and the environment. These goals

Women’s concerns in rice farming systems 211require an integrated program balancing appropriate technological change,economic inputs, support services, and, most importantly, human resourcedevelopment. Because Indonesian agriculture is predominantly rice production,where the majority of rural women play a significant role, women should be includedin the programs.Several collaborating institutions are involved in promoting the role of womenin farming systems: CAER Central Research Institute for Food Crops (CRIFC);Agency for Agricultural Education, Training and Extension (AATE); and theInstitut Pertanian Bogor (IPB) Center of Development Studies of BogorAgricultural University. CAER and IRRI are collaborating on studying thedifferential impact of rice technologies in favorable and unfavorable areas. Thatresearch will also include analyzing the impact of new rice technologies on men,women, and children. The National Panel of Farmers Study of CAER on the impactof agricultural development programs for labor absorption and raising incomes ofrural communities will provide data on the roles of women in agriculture and theirposition in the rural labor market. Farming systems research is being conducted byinterdisciplinary teams in CRIFC at some 40 cropping/farming systems researchsites. IRRI has been involved in collaborative programs with CRIFC since 1975,particularly through the ARFSN. There is a wide scope for introducing a women’scomponent into one or more sites; two are beginning to integrate a women’scomponent into the research projects—the crop-livestock project in the BatumartaTransmigration Area, South Sumatra (rainfed upland environment), and theSukamandi irrigated site. A women’s component will be added to activities in thesesites soon. In all sites, women’s roles will be identified and technologies suited to theirneeds will be developed, tested, and disseminated.Research on the role of rural women in development was conducted in 1977-78by the Rural Dynamics Study-Agro-Economic Survey of Indonesia at Bogor andthe Centre for Rural Sociological Research-Bogor Agricultural University in ruralWest Java. Based on that experience, the Bogor Agricultural University extendedthe study throughout the country in 1981 by setting up a network of 14 universities inJava and the outer islands (Sumatra, Kalimantan, Sulawesi, Bali, Ambon, and NusaTenggara Timur). Faculty from agriculture, animal husbandry, economics,sociology, law, and education are involved. The study will provide data on men’s andwomen’s time allocations, income and expenditure, decisionmaking, familynutritional status, and fuel energy problems in Java and the outer islands (Sajogyo1984). The broad database will enable us to identify women’s roles and technology,credit, and extension needs in agriculture and in home production activities. Withthe coordinated efforts of CAER, CRIFC, AATE, IPB, and IRRI, the objective ofinstitutionalizing women’s concerns into agricultural research and extension onfarming systems in Indonesia can be achieved.Research findings. The overall objective of the study “The Role of Women inRural Development” (1981-87) coordinated by Bogor Agricultural University is toprovide some baseline data which will assist policymakers in improving theeffectiveness of all human resources, men and women. The field studies wereconducted not only to understand women’s problems or women’s roles in

212 Pudjiwati and Parisagriculture (production, distribution, and marketing) but also to evaluate andacknowledge women’s labor, managerial, and entrepreneurial contribution tofarming systems, and their contribution to food (primary and secondary foods)production (Table 3).Analysis of gender issues covers three aspects:a. quantification of labor input by gender;b. quantification of men’s and women’s work in different areas of production andgainful employment;c. gender division in decisionmaking.The most important policy implication from findings of this study is that in allareas, poor families depend on women’s earnings to survive. They are seriously hurtby the displacement of women from traditional earning opportunities whenalternative income opportunities are not available. Development policies had a morenegative effect on poorer women than on women in more affluent households.Decisionmaking in the households. The same study investigated familydecisionmaking in production and trading. In two villages, men and women withdifferent average household incomes showed some differences in decisionmaking. Inthe poorer village, decisions commonly were made by husband and wife together. Atthe highest income level within the poor village, decisions on the purchase ofequipment and use of capital frequently tended to be dominated more by the wives.Hiring of labor was more the husband’s decision. Decisions on whether to sell theproduce were influenced more by husbands, but method of sale was more frequentlydecided by wives, perhaps because wives did more of the selling.In the more affluent village, production decisions seldom were made equally byhusbands and wives. Polarization of decisionmaking was characterized by adominant role for husbands, except in decisions concerning the marketing of farmproducts, where women played a very important role.Households in the more affluent village tended to adopt new rice productiontechnologies which included a method of harvesting that usually excludes femalelabor. Use of high-yielding rice varieties, chemical inputs, and official creditincorporated households into the nexus of BIMAS programs that provided servicesonly to male farmers. When examining intrahousehold decisionmaking patterns, itis often difficult to separate “who decides” from “who negotiates.” Even ifgovernment programs consider husband’s economic authority as head of thehousehold de facto as well as de jure, there is evidence that under traditionalagricultural production and trading activities, women share equally in decisionmaking.In the poorer village, there was a greater tendency for men to seek off-farmand nonfarm work by commuting to the towns. It is possible that this male seasonalmigration increased women’s managerial roles, not only in the household but also infarming activities.This study highlights the unrealistic nature of many government agriculturalprograms that explicitly or implicitly direct activities, technologies, extension, andcredit toward male farmers.Farming systems in a transmigration area. In agricultural production inBatumarta, South Sumatra, there is a fairly well-defined division of labor. Data of

Table 3. Average hours worked per year by men and women in three household income classes in two villages in West Java. aVillage P b Village S cMale Female Male Female Male Female Male Female Male Female Male Femalea Housework must be added to these hours. Source: Pudjiwati Sajogyo et el 1980, pages III-14, III-15. b Poor village. c Rich village.694261649545273381538521618084831091,0634902161125158482240027723832802210ActivityLow-income Middle-income High-income Low-income Middle-income High-incomeRice cropDryland cropHome gardenServicesTradeHome industryCollecting firewood,vegetables, grasses, etc.Other191742150938888139200432701405381620184230840513076605214914180802130101845132547742603160357131306454099023617771924725190455573

214 Pudjiwati and Parishousehold cooperators showed that women and men contribute 32.5 and 67.5%,respectively, to total labor use in production agricultural activities. For all activities,including household, women contribute 25.0% in agriculture and 22.7% inhousehold activities. Men contribute 37.5% in agriculture and 45% in householdactivities.While men undertake tillage and most transporting of produce, women areengaged in planting, weeding, manuring, harvesting, transporting, and processingthe product. Weeding and manuring are important in ensuring maximumagricultural yields, and women’s labor is essential in these activities. Harvesting andpostharvest activities such as hand-harvesting rice ( ani-ani method), threshing,winnowing, clearing, drying, and storing are predominantly done by women.Tending goats and poultry is also predominantly women’s responsibilities. Forwomen, allocating time between housework and farming is crucial. With an averagefemale work burden of 11.5 h/d (compared to 10 for men), rural women have littleleisure time. The workloads of women, the seasonal cycle of their farmingworkloads, and their daily household activities should be considered in developingtechnologies that will affect their labor.These women also perform their traditional roles as wives and mothers. Theywork around the homestead and on their farm; men work the homestead outside,where they have more opportunities to earn cash and more time for social activities.Opportunities for women to participate in income-earning activities are limited byinadequate education, knowledge, and skills.Women do help generate income by processing “soybean cake” from soybeans,selling mungbean sprouts, processing cassava chips, and selling poultry and goats.They start working early, leaving the house (usually after preparing breakfast for thefamily) before the children are awake. Sometimes, the older children take care of theyounger ones and do part of the housekeeping tasks.By contributing to agricultural production, women have to pay the possiblesocial cost of inadequate child care (the most common result is home accidentsamong children, such as burns and scalds).Initial findings show that, because women in this transmigration area have avery heavy work and reproduction burden, labor-saving technologies-particularlyin food processing which adds value to food crops-are needed to lighten women’sworkloads. Labor-saving devices would help reduce time use and drudgery andwould enhance women’s productivity. Since women are involved in poultry and goatproduction where new technologies are being introduced, extension and trainingprograms should include them. This has become part of the activities planned for theBatumarta site.References citedCentral Bureau of Statistics (1981) The population of Indonesia by province: the result of completeenumeration of the 1980 population census. Series L-3.1, Jakarta, IndonesiaCollier W L (1980) Declining labor absorption (1978 to 1980) in Javanese rice production. Agro-Economic Rural Dynamic Survey 02, 1979.IRRI—International Rice Research Institute (1987) Women in rice farming systems action research andtraining program. Report submitted to Ford Foundation, August, 1987.

Women’s concerns in rice farming systems 215Kasryno F, Nataatmadja H, Pasandaran E, Rosahan C A, Swenson C G (1985) Development of anintegrated farming systems research network in Indonesia. Center for Agro-Economic Research,Bogor.Mayrowani H (1987) Women in transmigration area: a case study in Batumarta, South Sumatra. BogorResearch Institute for Crops, Bogor, Indonesia.Nataatmadja H (1985) Farming systems research in transmigration areas: an ideological prescription.Center for Agro-Economic Research, Bogor, Indonesia.Palmers, Weeks-Vagliani W (1987) Gender issues in food policy research the case of Java. DevelopmentCentre of the Organization for Economic Cooperative and Development, Paris.Paris T R (1987) Integrating women’s concerns in a crop-livestock farming systems project in Sta.Barbara, Pangasinan, Philippines. Ext. Bull. 264, ASPAC Food and Fertilizer Technology Center,Taiwan, China.Pudjiwati Sajogyo (1977) Golongan Miskin dan Patisipasinya dalam Pembangunan Desa DalamPrisma No. 3, Tahun ke-4, LP3ES, JakartaPudjiwati Sajogyo (1983) Peranan Wanita Dalam Keluarga Rumahtangga dan Masyarakat yang lebihluas di Pedesaan Jawa Ph D dissertation, University of Indonesia, Jakarta.Pudjiwati Sajogyo (1984) Report on studies about the role of rural women in Indonesia. BogorAgricultural University, Bogor.Pudjiwati Sajogyo, Hastuti E L, Wigna W, Surkati S, White B, Suryanata K (1980) The role of women indifferent perspectives. Rural Dynamic Study, Agro-Economic Survey and CRSR. BogorAgricultural University, Bogor.Pudjiwati Sajogyo, Wiradi G (1987) Rural poverty and efforts for its alleviation in Indonesia Food andAgriculture Organization, Rome, Italy.Rumawas F (1985) Farming systems research a conceptual framework. Institut Pertanian Bogor (BogorAgricultural University), Bogor.Stoler A (1977) Class structure and female autonomy in rural Java. In Women and national development.University of Chicago Press, USA.White B (1976) Problems in estimating the value of work in peasant household economies: an examplefrom rural Java. Prepared for the ESCAP Expert Group Meeting on Rural Institution ServingSmall Farmers, 13-17 Dec 1976, Bangkok.NotesAddresses: Pudjiwati Sajogyo, Bogor Center of Development Studies, Bogor Agricultural University, Bogor, Indonesia;T. R. Paris, Agricultural Economics Department, International Rice Research Institute, P.O. Box 933, Manila,Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

216 AbstractsABSTRACTS: FARMING SYSTEMSCollaborative research on cropping patternstesting in irrigated rice areas of AsiaV. R. CARANGALOne important activity of the Asian Rice Farming Systems Network istesting cropping patterns in irrigated, partially irrigated upland, deepwater,and rainfed lowland rice environments. Cropping patterns testing is underway in 10 Asian countries. Classifying irrigated rice environments bywater duration is recommended—4 mo, 6 mo, 8 mo, and 10 mo of water.The methodology used is developed at IRRl and further refined by nationalprogram scientists. The steps are selection of target areas, selection anddescription of research site, design of cropping pattern and componenttechnology research, multilocation testing and pilot production, andproduction. Experimental cropping patterns in irrigated areas have beencompared with farmers’ existing cropping patterns. On the basis ofproduction and net returns, several promising cropping patterns havebeen identified in 4 sites in Bangladesh, 4 in Burma, 5 in mainland China,3 in Taiwan, 6 in India, 3 in Nepal, 22 in the Philippines, 3 in South Korea, 2in Sri Lanka, and 2 in Thailand. The more important problems encounteredin increasing cropping intensity, production, and net returns are watersupply in, the command areas not uniform and assured; poor watermanagement for upland crops; low yields of upland crops grown beforeand after rice; disease and insect infestation; poor upland crop establishmentafter rice; low and inadequate adoption of improved croppingpatterns; fertilizer recommendations for each crop, not for the croppingpattern; yield losses due to intensive cropping; and short turnaround timebetween crops.V. R. Carangal, Asian Rice Farming Systems Network, International Rice Research Institute,P.O. Box 933, Manila, Philippines.

Abstracts 217Rice - wheat rotation: constraintsand future directionsD. SAUNDERSRice - wheat rotation is estimated to occupy some 28% of the wheat area inAsia. Constraints to increased yields are seeding of wheat after theoptimum date, due to late harvest of rice or to time consumed in preparingthe wheat seedbed in heavy puddled soils; weed infestations; andsuboptimal fertilizer and irrigation water applications. It is suggested thatzero or minimum tillage may be appropriate over much of the region, thatintegrated weed control should be undertaken, and that more emphasis beplaced on establishing fertilizer recommendations on the basis of researchin farmers' fields. Yield declines reported for rice -wheat cropping systemsare noted. While other factors are also implicated, a large portion of thecause may be nutrient depletion. Additional problems involved in wheatproduction at tropical latitudes are the lack of current resistance todiseases caused by Helminthosporium spp., Fusarium spp., andSclerotium rolfsii; lack of effective chemicals for disease control; and poorfertilizer efficiency.D. Saunders, International Maize and Wheat Improvement Center (CIMMYT), P.O. Box 9-188,Bangkok 10900, Thailand.Rice - azolla - fish cropping systemLIU CHUNGCHUThe rice - azolla -fish cropping system is a combination of two traditionalChinese practices—raising fish in ricefields and growing azolla inricefields. Experiments have shown that azolla can both fix nitrogen fromthe air and carry on photosynthesis. The abundant nutrients in azolla canbe fed to grass-feeding and omnivorous fish. About 60% of the azolla N isdigested by Tilapia nilotica. Using 15 N tracing, we found that azolla N isabsorbed and distributed to the fish internal organs, then graduallytransported to the muscle and skeleton. In addition to slightly increasedrice yields, fish yields may reach 1 t/ha. This system has the potential toincrease farm income by U.S.$525/ha. In rice, the system increases filledgrain, 1.000-grain weight, and panicle numbers; controls pests, diseases,and weeds; and increases soil fertility. Some basic management practicesinvolve field construction, fish species arrangements, fodder supplements,water management, and fertilizer and pesticide application.Liu Chungchu, Azolla Research Center, Fujian Academy of Agricultural Sciences, Fuzhou,Fujian, China.

Hybrid rice: achievementsand outlookYUAN LONGPING, S. S. VIRMANI, AND MAO CHANGXIONGExtensive research on and development of hybrid rice in China haveclearly demonstrated its usefulness in significantly increasing rice yieldsbeyond the levels of improved semidwarf varieties. Hybrid rice is currentlyplanted on 9 million ha in China. Several International Rice ResearchInstitute (IRRI)-bred cultivars are used as male parents of commercialvarieties. Research at IRRl and in several collaborating countries showsthat hybrids have yields 15-20% higher than those of the best semidwarfvarieties. Hybrid varieties suitable for other countries are still in thepipeline. In addition to higher yield, heterotic rice hybrids show higherproductivity per day, adaptability to certain stress environments, and betterutilization of applied nitrogen fertilizers. Hybrid rice seed productiontechnology has been well developed in China, and prospects for itsadoption outside China appear promising. A number of the cytoplasmicmale sterile (CMS) lines developed and used in China are not adaptableoutside China for lack of adequate disease and insect resistance andacceptable grain quality. Several CMS lines developed at IRRl are nowbeing evaluated in collaborating countries. Both China and IRRl areinvolved in research to diversify CMS sources, to prevent geneticvulnerability problems in hybrid varieties. Sufficient numbers of restorerlines are available among indica rice cultivars, but restorer numbers arenegligible in japonica rices. By selecting appropriate CMS and restorerlines, hybrids possessing multiple disease and insect resistance anddesired grain quality can be developed. Constraints and the outlook forhybrid rice technology also are discussed.Development during the 1960s and 1970s of semidwarf rice varieties possessingmultiple resistance and/or tolerance for biological and physicochemical stresseshelped national programs achieve high and stable rice yields, particularly underirrigated and favorable rainfed lowland environments. On the basis of availabletechnology and projections of infrastructural development for rice production,Barker et al (1985) predict that world rice production will increase more than 3% ayear, against a projected rice demand of 3.5% a year, at least to the end of thecentury.That shortfall prediction makes it logical to look at the prospects for thosetechnologies that can help increase rice yields per unit area per unit time.

220 Yuan et alExperiences in China over the last 10 yr indicate that hybrid rice is a technology thatcould help rice producers meet that goal. China’s success in developing hybrid rice isnot only a major breakthrough, but also a technological innovation in rice breeding.China is the first country in the world to put hybrid rice into commercial use.Research on hybrid rice in China began in 1964. The cytoplasmic male sterile(CMS), maintainer, and restorer lines essential for producing F 1 hybrids weredeveloped by 1973; hybrid seed production techniques were essentially developed by1975. By 1976, hybrid rice had been released commercially and was planted on140,000 ha. In 1986, hybrid rice was grown on 9 million ha (Fig. 1), yielding about20% more than improved rice varieties. To cover such a vast area with hybrid rices,thousands of technicians and farmers were trained.Encouraged by the developments in China, the International Rice ResearchInstitute (IRRI) took initiatives in 1979 to explore the potentials and problems ofdeveloping hybrid rice for countries outside China. In collaboration with theChinese Academy of Agricultural Sciences, IRRI organized courses on hybrid ricetechnology at Changsha, Hunan, China, during 1980 and 1981, to train ricescientists from several Asian countries. Those scientists initiated hybrid rice researchin their home countries. In 1980, China transferred hybrid rice technology throughprivate seed companies to the U.S. and some other countries.This paper highlights the achievements and outlook for hybrid rice technologyin increasing rice yields beyond the levels possible with improved semidwarf ricevarieties.Grain production, yield potential, and yield stabilityof F 1 rice hybridsThe maximum yield from a single crop of an indica rice hybrid has been recorded at14.4 t/ha, in Jiangsu Province, China. That compares to 10.4 t/ha from an improvedvariety. In Jiangsu, average yield of hybrid rices in 1986 was 8 t/ha (from 0.77 millionha). In Hunan Province, a 15 t/ha average yield was obtained from 2 crops of hybrid1. Area planted to hybrid rice in China, 1976-86.

Hybrid rice 221rices (0.14 million ha). Among the japonica hybrids, Li-You 57 yielded the highest(13.7 t/ha in Liaoning Province). Japonica hybrid variety Xiu-You 57 yielded anaverage 28% more than improved japonica variety Jingying 39 in Ninxia Province(Table 1). Average yield of hybrid rice in China 1983-86 was 6.5 t/ha (Table 2). In1985, the hybrid rice-growing area was 26.4% of the total rice area; it contributed32.7% of total rice production. The cumulative production increase due tocultivation of hybrid rice in China 1976-85 has been estimated at 94 million t.Outside China, hybrid rice is still in the experimental stage. In general, hybridsdeveloped in China are not adaptable in the tropics, primarily because they aresusceptible to major diseases and insects. A number of experimental rice hybrids,mostly developed at IRRI from China- or IRRI-bred CMS lines and IRRI-bredrestorers, were compared with the best available improved rice varieties. The besthybrids yielded an average 16% more than the best improved varieties (Table 3).Growth durations of heterotic hybrids ranged from 104 to 133 d, indicating thathigher yielding rice hybrids can be developed in different varietal maturity groups.Table 1. Yields of hybrid rice and conventional rice, 1982-86, Ninxia, China.YearHybrid rice Xiu-You 57Growing area Yield (t/ha)(ha)ConventionalJingying 39Yield (t/ha)Yield advantageof hybrid(%)1982 3.5 10.4 8.2 26.81983 420.0 10.5 7.8 34.61984 3,597.1 10.2 7.6 34.21985 4,665.8 9.6 7.7 24.71986 10,097.9 9.4 7.7 22.1Table 2. Total growing area, yield, and average yield/ha of hybrid rice in China1983-86.YearTotal area Total yield Average yield(million ha) (million t) (t/ha)1983 6.741984 8.841985 8.271986 9.1342.9756.6253.5360.246.46.46.56.6Table 3. Yield of the best experimental F 1 rice hybrids and the best check varieties.IRRI, 1981-86.SeasonTrials(no.)Hybridsevaluated(no.)Yield (t/ha)Percent of checkRange Mean Range MeanDry 14 207 5.4-9.6 7.8 86-141 116Wet 16 202 2.6-5.6 4.2 100-140 116

222 Yuan et alDuring 1986-87, IRRI also evaluated some promising experimental ricehybrids, along with more than 370 elite breeding lines and varieties developedthrough conventional rice breeding programs at IRRI. The highest yieldingexperimental hybrid was only 0.3 t/ha higher than the best breeding lines and0.7 t/ ha higher than the best commercial variety, IR64 (Table 4). The hybrid wasstrikingly superior to all other lines in productivity per day.The best experimental rice hybrids identified in the hybrid rice breedingprogram at IRRI are being evaluated with the best improved lines developedthrough the conventional breeding program, to identify hybrids qualified for onfarmmultilocation testing outside IRRI.A number of experimental rice hybrids also were evaluated in replicated yieldtrials in collaboration with the national programs of the Philippines, Indonesia,Korea, India, Malaysia, and Vietnam. On average, the highest yielding hybridsyielded 16% higher than the best improved varieties (Table 5).Commercial rice hybrid Wei-You 64 developed jointly by Chinese and IRRIscientists (Yuan et al 1985) was evaluated in the 1986 International Rice YieldNursery-Very Early, coordinated by the International Rice Testing Program (IRRI1987). It yielded the highest (5.4 t/ha) among 24 entries evaluated at 25 locations,with a CV less than 25%. The second ranking line yielded 5.3 t/ha. The hybridranked first among the 24 entries at 5 locations (4 in China—Guangzhou, Fuzhou,Luzhou, and Lian Tang—and 1 in Bangladesh—Comilla). The hybrid was amongthe top five entries in Chainat, Thailand; Sakha, Egypt; Amol, Iran; and Menemen,Turkey. Wei-You 64 is not suitable for tropical countries because it does not possessadequate disease and insect resistance.At certain locations (Namyang and Milyang, Korea, and Bangalore,Aduthurai, and Cuttack, India), none of the IRRI-bred hybrids tested so far haveperformed better than the checks. For such situations, hybrids derived from locallyadaptable CMS and restorer lines that possess acceptable grain quality are needed.Such lines are being developed at IRRI and in national programs.Table 4. Performance of an F1 rice hybrid, best elite lines, and best commercial variety. Replicatedyield trials, IRRI, 1986-87.Hybrid/VarietyProductivity (kg/dayYield (t/ha) Percent of IR36 per he) Meangrowth1986 1987 Mean 1986 1987 Mean 1986 1987 Mean durationDSDS DS (d)DS WSDS WS DS WSlR46830 A/lR9761-19-1lR35366-90-3-2-1-3IR64 (Ck)lR44707-31-1-3-2lR44668-85-1-2-2-37.7 4.26.5 4.56.3 4.27.5 3.5– 3.76.9 6.37.06.36.97.26.05.66.05.5108 125 111 115 86 51 75 71 10990 157 122 123 65 48 71 61 11893 135 107 112 66 41 64 57 120132 113 144 130 68 32 62 54 131– 98 118 108 – 42 78 60 111

Hybrid rice 223Table 5. Yield performance of best experimental F1varieties in international trials, 1980-86.rice hybrids and best checkCountryTrials(no.)Yield of besthybrids (t/ha)RangeMeanPercent of checkRangeMeanIndonesia 15Korea 11India 21Malaysia 2Philippines 8Vietnam 4Overall 614.1- 8.9 6.28.1-11.5 9.13.3- 9.8 6.24.2- 5.0 4.74.8- 7.4 5.45.3- 6.6 6.03.3-11.5 6.6102-143 11797-142 11391-143 11689-127 10892-133 11491-122 10889-143 116These results indicate that F 1 hybrids that have helped increase rice varietalproductivity in China beyond the levels of improved semidwarf varieties also canhelp increase varietal yields 15-20% in countries outside China. Suitable hybridsadapted to these countries are in the pipeline and should be available within a year ortwo.Hybrids show a general tendency to possess higher productivity per day thanparents and commercial check varieties (Virmani 1986). Higher yield potentialcombined with higher per day productivity should make hybrid rice technology oneway to meet the challenge of producing more rice on less land and provideopportunities for crop diversification without risking reduction in rice production.Adaptability of rice hybrids in stress environmentsHybrid rices have been adapted to various climatic (tropical, subtropical, andtemperate), topographical (plain, coastal area, and hilly regions), and cultural(irrigated, drought-prone, and upland) conditions in China. Hybrids are cultivatedin single-crop, double-crop, and ratooned fields. They have been adapted to semidryirrigated areas in north and northeast China, including Liaoning, Hunan, Beijing,and Tainjing Provinces, where average yields of 5-6 t/ ha are obtained from 67,000ha. Rice hybrids have been grown with 50% less water (4,500 m 3 compared to 9,000m 3 ) in irrigated fields. In northern China, growing hybrid rice has become moreprofitable than growing maize (Table 6).IRRI results also indicate F 1 superiority for root number and root diameter (R.Peiris, G. Loresto, and T. T. Ch ang, 1982, unpubl.) and root-pulling resistance (theforce required to pull a plant from the soil) (Ekanayake et al 1986). Root-pullingresistance and tolerance for moisture stress during vegetative growth have beenfound to be correlated (O’Toole and Soemartono 1981). We assume the F 1 hybridswould have better adaptation than their parents in drought-prone rainfed area.In Liaoning Province, China, hybrid rices showed tolerance for soil alkalinity(Table 7) and are being grown in coastal areas. At IRRI, we also observed bettersurvival of hybrids than parents under saline conditions (EC = 7 dS/ m) (Senadhiraand Virmani 1987).

224 Yuan et alTable 6. Benefit of hybrid rice over maize under semidry irrigated conditions.mode county, Tainjing, China, 1984.SiteHybrid riceYield Input Net income(t/ha) ($/ha) ($/ha)MaizeYield Input Net income(t/ha) ($/ha) ($/ha)Benefitfor rice($/ha)1 4.88 266 518 4.20 59 2772412 5.25 266 574 4.50 54 3052693 4.86 248 534 3.00 46 194 3404 5.52 268 615 5.25 85 335 280Av 5.13 262 562 4.24 61 278 284Table 7. Alkali-tolerant abilities of different rices. Liaoning, China, 1986.Rice type Productive panicles/plantRelative alkalitolerance(%)Conventional riceHybrid riceAlkali-tolerant rice6.83 ± 1.477.66 ± 0.908.31 ± 1.018292100Kaw and Khush (1985) report heterosis for various traits related to lowtemperature tolerance. We also observed better performance of certain F 1 hybridsunder high-altitude irrigated conditions at Banaue, Philippines (Table 8).These results indicate the usefulness of F 1 rice hybrids, not only under favorableconditions but also under certain stress environments.Hybrid performance under different fertility levelsChinese scientists report that hybrid rices utilize applied fertilizer more efficientlythan improved varieties. Korea-IRRI collaborative studies show yield advantages ofthe F 1 of V20 A/Milyang 46 at different N fertilizer levels (Fig. 2). IRRI evaluated anumber of experimental rice hybrids, their parents, and check varieties under threeN levels. Selected hybrids showed significant superiority over parents, but onlynumerical superiority over the check variety (Table 9). The hybrid from IR54752B/IR19392-211-1 yielded the highest (7.3 t/ha) in the trial at 75 kg N; best checkvariety IR64 yielded the highest (6.6 t/ha) at 150 kg N. These results indicate that notevery hybrid will utilize applied N better than its parents. Perhaps only heteroticcombinations will possess such capability.Advances in hybrid seed production technologyIn the 1970s, hybrid seed yields in China were very low. Yields have improvedtremendously (Fig. 3). It is not uncommon to get 2-2.5 t hybrid seeds/ ha. The highest

Hybrid rice 225Table 8. Yield and growth duration of some promising experimental rice hybrids.elite breeding lines, and commercial varieties at high altitude location. Banaue,Philippines, 1986 wet season.Hybrid/lineObservational Yield TrialIR54752 A/IR14753-120-3 F1lR54752 A/IR19392-211-1 F1V20 A/Milyang 46 RIR40094-4-5-5Barkat (early check)Pinidwa (local check)Replicated Yield TrialWei-You 64 F1IR40094-1-5-2lR9202-5-2-2-2Barkat (early check)Pinidwa (local check)LSD (0.5%)Yield (t/ha)7.47.47.37.23.14.46.67.34.54.04.10.91Growthduration(d)1681601451 60140180140159148140180–2. Grain yields of F 1 rice hybrid V20 A/ Milyang 46 and commercial variety Suweon 294 under differentN levels at Suweon and Iri, Republic of Korea, 1984.hybrid seed yield in China was 6.1 t/ ha for hybrid Wei-You 64 in Xu-Pu county,Hunan Province, during summer 1986.With increasing seed yields, the field area ratio between A line multiplication,hybrid seed production, and commercial production of hybrid rice has changed,from 1:30:1000/ ha in the 1970s to 1:50:3,000-5,000/ ha today. Increased seed yieldshave been primarily responsible for the expansion of the rice area planted to hybrids.

226 Yuan et alTable 9. Yield of rice hybrids, their parents, and check vorieties at 3 N levels.IRRI, 1986 dry season.Parents and hybrid aGrain yield (t/ha)0 kg N 75 kg N 150 kg N MeanlR54752 B 4.9 4.8 4.7 4.8F 1 4.1 5.7 4.0 4.6IR54 5.1 5.9 6.3 5.7lR54752 B 4.9 4.8 4.7 4.8F 1 5.1 6.1 6.3 5.8IR29512-81-2-1 4.4 5.4 4.7 4.8lR54752 B 4.9 4.8 4.7 4.8F 1 5.2 7.3 7.0 6.5lR19392-211-1 4.3 5.9 4.9 5.0lR54752 B 4.9 4.8 4.7 4.8F 1lR20933-68-21-1-24.13.45.73.95.03.34.93.5lR54752 B 4.9 4.8 4.7 4.8F 1lR4422-480-2-3-34.94.15.44.93.94.44.74.4lR46830 B 2.4 4.3 5.0 3.9F 1IR503.34.45.35.25.55.44.75.0V20 B 0.9 1.2 1.3 1.1F 1lR9761-19-12.03.53.55.53.25.92.95.0IR64 (Ck) 3.8 6.0 6.6 5.5LSD 1.05) 0.9 0.9 0.9a In a group, line 1 = female parent; line 2 = hybrid; line 3 = male parent.3. Average hybrid rice seed yield in China, 1973-86.

Hybrid rice 227The increased yields reduced seed prices and farmer investments in hybrid ricecultivation.The increase in hybrid rice seed yield and quality in China has been attributed tothe following factors:1. Shifting seed production from autumn to summer.2. Planting two CMS line seedling per hill instead of the one seedling per hillplanted previously. This increased the number of total effective panicles of aCMS line per unit area.3. Increasing the row ratio of A:R lines. Currently, row ratios of 1:8-10 or2:14-16 are used for indica rice and 1:6 or 2:8 for japonica rice.4. Increasing the gibberellic acid (GA 3 ) dosage to enhance spikelet and panicleexsertion.5. Discontinuing or reducing flag leaf clipping to increase seed weight andquality.6. Developing CMS lines that show higher outcrossing rates (up to 50%)-11-32 A, Chang Hui 22 A, Xu Qing Zao A, and L301 A.7. Increasing the efficiency of the organization of hybrid seed production,certification, and distribution. The provincial-, prefectural-, and countylevelmanagement system for hybrid rice seed production has been veryeffective. Under this system, the provincial seed company is in charge ofpurification and foundation-seed production; the prefectural seed companyis responsible for large-scale CMS seed multiplication; and the county seedcompany does commercial seed production. Earlier CMS multiplicationcarried out mostly by county seed companies resulted in some problems withseed purity. Also, in recent years, provincial governments have enacted somelaws regulating seed production and seed quality.At IRRI, we have attempted to adapt the basic seed production techniquesdeveloped in China. In experimental seed production plots (size 10-1, 250 m 2 ), seedset on CMS lines ranged from 0.1 to 43% and seed yield ranged from 5 to 1,510kg/ha. Outcrossing on a line was generally lower in the wet season than in the dry,because of unfavorable weather (heavy rains and typhoons) and higher incidence ofdiseases and insects during the wet season. Outcrossing rate and seed yield dependon synchronization of flowering in the male and female parents and the agronomicand floral traits of the parental lines.Indonesian and Korean scientists also have tested the adaptability of the hybridseed production techniques developed in China, in collaboration with IRRI. Theyhave obtained seed yields of 60-1,800 kg/ ha in Indonesia and 750-1,530 kg/ ha inKorea.We recognize that hybrid rice technology will not succeed outside China unlessappropriate and economical packages of practices for hybrid seed production, alongwith suitable F 1 rice hybrids, can be developed. IRRI, in cooperation with Chinaand other collaborating countries, is actively involved in developing such packagesof practices and suitable CMS and restorer lines.

228 Yuan et alDiversification of usable CMS systemsChinese scientists have identified seven different CMS systems among the CMS linesused to develop commercial hybrids. Five are sporophytic—WA, Gam, IndonesianPaddy (IP), Dissi (Di), and dwarf wild rice (DW). The two others are gametophyticBT (CMS-boro) and Hong-Lien (HL).Two or three years ago, more than 95% of the CMS lines used in developingcommercial hybrids in indica rice were of the WA CMS system. This situation madehybrid rice in China potentially vulnerable to an outbreak of a disease or insect thatmight be genetically associated with this CMS system. Recently, new CMS lineswith different CMS sources—II-32 A (IP), Xiu Qing Zao A (DW), DZS97 (Di)—have been released, which should help diversify the CMS sources in China.Outside China, mostly the WA cytosterility system has been transferred to elitemaintainer lines to develop new CMS lines. During the last 8 yr, 29 new CMS lineshave been developed at IRRI (Table 10). Some of them have been found suitable forthe development of rice hybrids for the tropics.Table 10. CMS lines developed at IRRl to 1987.CMS lineElite breedingline used asmaintainerOrigin ofmaintainerVarietalgroup aGrowthduration(d)lR46826 AlR46827 AlR46828 AIR46829 AIR46830 AIR46831 AlR48483 AlR54752 AlR54753 AlR54754 AlR54756 AlR54757 AlR54758 AIR58019 AIR58020 AlR58021 AlR58022 AlR58023 AIR58024 AlR58025 AlR58026 AlR58027 AlR58052 AIR58053 AIR58054 AlR58055 AlR58056 AIR58057 AlR58058 AIR10154-23-3-3lR10176-24-6-2lRl0179-2-3-1lR19792-15-2-3-3lR19807-21-2-2Jikkoku/Seranai 52-37MR365lR21845-90-3lR19657-34-2-2-3-3lR19657-87-3-3Iri 356Suweon 310PAU269-1-8-4-1-1-1lR19809-12-3-2-1lR17525-278-1-1-2IR19805-12-1-3-1-2lR19774-23-2-2-1-3PY2Suweon 161Pusa 167-120-3-2lR31787-24-3-2-2lR15795-151-2-3-2-2lR4763-73-3-11IR19746-27-3-3-1-3lR22103-26-6-2IR19728-9-3-2-3-3lR25474-41-2-3-2lR19661-283-1-3-2IR12979-24-1IRRlIRRlIRRlIRRlIRRlIndiaIndiaIRRlIRRlIRRlKoreaKoreaIndiaIRRlIRRIIRRlIRRlIndiaKoreaIndiaIRRlIRRlIRRIIRRIIRRlIRRIIRRlIRRlIRRlIIIIII/JJIIII/JI/JIIIIIIJIIIIIIIIII105105110110110115110135135135125130125105130110100110110120110120115115117120130140130a I = indica, J =japonica.

Hybrid rice 229Concurrently, attempts have been made to identify new sources of CMS.Interspecific, intraspecific, and intervarietal crosses have been made. We havedeveloped a stable CMS line (IR54755 A) that possesses the CMS source of Oryzasativa cultivar ARC13829-16 introduced from Assam, India. Preliminary resultsindicate that the CMS system of IR54755 A is different from WA (Virmani andDalmacio 1987).Although no evidence so far associates any disease or insect susceptibility in ricewith the WA or any other cytosterility system, hybrid rice breeders in and outsideChina cannot afford to be complacent. Cytoplasmic and genetic diversity must beassured when parents are chosen to develop commercial hybrids. Also, therelationship between the available CMS sources and resistance or susceptibility tomajor diseases and insects found in the tropics must be monitored.Lu and Wang (1988) reported a genetic male sterility system in rice that isphotoperiod sensitive. It showed complete male sterility under long daylengths butreverted to fertility under short daylengths. Jin et al (1988) proposed using thissystem in hybrid rice breeding, If effective, it would simplify hybrid seed production.The CMS line can be multiplied by selfing and growing under short daylengthconditions. Moreover, the choice of male parents is not restricted to restorers; anyfertile cultivar can be used as the male parent. Hybrid development would involveonly two lines, the male sterile and a fertile male parent, instead of the three linesrequired in the CMS system.Development of restorer lines and the geneticsof fertility restorationChinese and IRRI scientists have used a large number of restorer lines from amongcultivated rice varieties and elite breeding lines for WA, Gam, BT, and newlyidentified CMS systems. The restorer lines widely used in developing commercialrice hybrids in China were mostly introduced from IRRI.Restorer lines are more often found among rice cultivars originating at lowerlatitudes than among cultivars from higher latitudes. The frequency of restorer linesfound among japonica rices is negligible. Consequently, japonica F 1 hybrids inChina have been developed from restorer lines bred by transferring restorer genesfrom indica rices.Work at IRRI also has indicated that several commercial rice varieties (IR24,IR26, IR28, IR36, IR42, IR46, IR50, IR54, IR56, IR58, IR60, and IR64) areeffective restorers. In fact, of about 3,000 elite lines and varieties screened at IRRI todate, 20% are effective restorers for the WA CMS system. Therefore, IRRI haslinked hybrid rice breeding programs with the line breeding program so that the bestavailable conventional lines can be used as parental lines to develop heterotichybrids. IRRI is constantly supplying elite restorer lines possessing multiple diseaseand insect resistance and early maturity to China to develop heterotic rice hybrids.A number of Tong-il (indica/japonica derivatives) rice varieties from SouthKorea (Suweon 287, Suweon 294, Milyang 46, and Milyang 54) also have beenfound to be effective restorers. Their fertility restoration ability may be due to therestorer genes inherited from indica parents.

230 Yuan et alWe have found that the restorer lines identified are usually a mixture ofrestorer, partial restorer, and nonrestorer genotypes. The test F 1 progenies derivedfrom single plant selection of restorer lines showed differential behavior in fertilityrestoration (Table 11). Purification of restorer lines is essential for breeding F 1hybrids.Results obtained in China (Wang 1980, Yang and Hao Ran 1984, Zhou 1983)and at IRRI (Govinda Raj and Virmani, unpubl.; Virmani et al 1986; Young andVirmani 1984) indicate that the restoration ability of the WA CMS system isgoverned by two dominant genes, one of which appears to be stronger than theother. The mode of action of the two genes varies with different CMS/restorercombinations (Govinda Raj and Virmani, unpubl.). Four groups of restorerspossessing different pairs of restorer genes have been identified at IRRI.It appears that a number of restorer genes are present in rice. That results in awidespread occurrence of restorer lines among elite breeding lines. Hybrid ricebreeders have the opportunity to choose genetically diverse restorer parents todevelop heterotic rice hybrids. Govinda Raj and Virmani (unpubl.) also found thatcertain CMS lines possess inhibitory genes that affect fertility restoration.Disease and insect resistance in rice hybridsThe genes in rice that control resistance to major diseases and insects in rice aremostly dominant or partially dominant (Khush 1977, Khush and Virmani 1985). Ifone of the parents has dominant resistance genes, the F 1 hybrid is also resistant. Thehybrid breeding approach facilitates expeditious pyramiding of dominant majorgenes or minor polygenes. The hybrid Shan-You 63 released in China is resistant toblast, bacterial blight, and brown planthopper. The resistance genes are contributedby both parents. In studies at IRRI, certain F 1 rice hybrids showed a wider spectrumof blast resistance than their parents (IRRI 1983). The vigor of hybrids also maycontribute to their field tolerance for diseases and insects. This aspect of rice hybridsneeds to be studied.Grain quality of rice hybridsThe economic product of rice hybrids is the grain borne on F 1 plants. Although F 1plants are uniform, the grains they produce represent the F 2 generation and areexpected to segregate on some important grain characteristics. We must consider theeffect of this segregation on grain quality, because consumer acceptance of the grainof F 1 rice hybrids will have an important bearing on adoption of this technology.There are three major determinants of grain quality in hybrid rice: milling andhead rice recovery; size, shape, and appearance; and cooking and eating qualitycompared to parents. Khush et al (1988) studied the effect of genetic differences forgrain characteristics of the parents on the quality of grain borne on the F 1 ricehybrids derived from them. They drew the following conclusions:1. Physical properties (differences in length, breadth, shape, and weight ofgrains of parents) do not pose any problem because the seeds borne on

Hybrid rice 231Table 11. Fertility restoration behavior of single plant selections of restorers in purificationnursery.RestorerTesterSingleBehavior of testcross F 1 progenies aplants(no.) F F/PF F/PS F/PS/S FS SIR54 lR465831 A 32 15 14 3lR9761-19-1 lR46830 A 56 43 7 1 1 3 1IR64 lR54752 A 56 23 23 10IR13419-113-1 lR54752 A 78 39 21 13 4 1a F = fertile, PF = partially fertile, PS = partially sterile, S = sterile.hybrid plants do not vary from each other. F 1 hybrids with desired millingand head rice recovery can be obtained.2. Crosses among parents of different endosperm appearance result in hybridplant grains with different types of endosperm. Such variation in grainappearance would affect market acceptability. Using a waxy- or dullendospermparent with parents possessing translucent grains should beavoided in hybrid rice breeding programs.3 . When parents differ widely in amylose content, F 2 single grains are clearlyclassifiable into 2-4 categories. However, segregation for amylose contentdoes not have any adverse effect on cooking and eating quality.4. Parents possessing grain with different gelatinization temperatures (low,intermediate, or high) do not result in any detectable difference in cookingquality of grain borne on their F 1 hybrids.We concluded that rice hybrids with desired physical, chemical, and cookingcharacteristics can be developed with appropriate selection of parents.The first set of hybrids developed in China (Wei-You 2, Wei-You 6, Shan-You2, Shan-You 6, etc.) possessed bold, chalky grains that are not acceptable in severalcountries outside China. The grain quality of these hybrids was inherited from thefemale parent developed in China. Chinese scientists are now evaluating the parentallines used to develop new rice hybrids. Some CMS lines (L301 A, U-1 A, Qiu GuangA) and restorer lines (R29, IR9761-19-1-64) possessing good grain quality have beendeveloped. The hybrid L301 A/R29 has been found to possess excellent grainquality acceptable in the U.S. market, where Wei-You 6 and some other firstgenerationhybrids were rejected.ConstraintsDespite the tremendous success of hybrid rice in China, some constraints need to beovercome.1. The indica hybrids now used in China are mainly of medium and longduration. They cannot be cultivated as the first crop in the double ricecropping system in the Yangtze Valley, the major rice production region inChina (7 million ha). Very few short-duration hybrids suitable for this region

232 Yuan et alare available so far. Development of short- to very short-duration hybridspossessing high yield potential is extremely important if the hybrid rice areais to be expanded to 13 million ha by the end of 1990, as is called for inChina’s national plan.2. The commercial F 1 hybrids currently grown in China have very littlecytoplasmic diversity; that makes rice production potentially vulnerable to adisease or insect outbreak. New hybrids with diverse CMS systems areneeded. Development of CMS lines with diverse CMS sources is a highpriorityresearch area. For japonica hybrids, the available CMS lines are notstable for complete sterility under high temperature. That causes impurityproblems. Stable CMS lines are needed for japonica hybrids.3. Effective restorer lines to develop heterotic japonica rice hybrids are lackingin japonica rice.4. The high cost of hybrid rice seed is a major constraint to further expansion ofhybrid rice. The best way to improve hybrid seed yield and to reduce seedproduction costs is to develop CMS lines possessing high outcrossing rates.5. Most of the available commercial rice hybrids do not possess good grainquality. To improve grain quality, both male and female parents must havegood grain quality and be uniform in certain grain characteristics. Breedingfor grain quality is an important objective of the hybrid rice breedingprogram in China.6. The leading rice hybrids in China are becoming susceptible to diseases andinsects in certain regions, due to changes in physiological races and biotypes.For example, about 7,000 ha in Sichuan Province were seriously damagedby blast disease in 1985. Breeding hybrids that possess multiple disease andinsect resistance is a continuous objective of hybrid rice breeders.7. Rice hybrids derived using chemical emasculation techniques have shownhigher yield potential than those derived from a CMS system. But chemicalemasculants have not been used extensively to develop commercial ricehybrids because of the lack of effective and safe gametocides. Research toidentify suitable chemical male gametocides needs to be intensified.The major constraints to hybrid rice research and development in countriesoutside China are1. inadequate numbers of trained scientists and lack of infrastructure andgovernment support for hybrid rice research and development;2. an attitude among research managers and policymakers that hybrid ricetechnology cannot be adopted in developing countries with marketeconomies, and that efforts should be directed toward improving riceproduction in unfavorable rice environments rather than toward increasingproduction in favorable environments;3. lack of outstanding and stable male sterile lines, especially in the tropics;4. lack of strikingly superior and stable hybrids for commercial use;5. low yields in hybrid seed production plots, resulting in high costs for hybridseed; and

Hybrid rice 2336. inadequate information on the economics of hybrid rice cultivation andhybrid seed production in China and its applicability in countries outsideChina.The technical constraints could be overcome with additional research at IRRIin collaboration with national rice improvement programs interested in exploringthe potentials and problems of this technology. The national programs need toestablish multidisciplinary teams to work full time on hybrid rice research if they areto participate effectively in this collaboration. Those teams should work closely withongoing programs on improved variety development.Outlook for the futureIn China, research and utilization of heterosis in rice have made tremendousadvances during the last 20 yr. Preliminary results at IRRI and in some national riceimprovement programs indicate that hybrid rice technology can help increase ricevarietal yields 15-20% beyond the levels obtained with semidwarf improved ricevarieties. However, packages of technology suitable for rice farming in countriesoutside China have yet to be developed.The classical, three-line breeding method used to develop heterotic rice hybrids,involving CMS, maintainer, and restorer lines, is expected to remain effective for thenext decade. But it is more complicated than is necessary and may in the long run bereplaced by two-line or one-line systems. Two-line systems may involve photoperiodsensitivegenetic male steriles or chemical emasculation. The one-line methodinvolving apomixis is considered the most worthwhile goal. It will make possibletrue-breeding hybrids with permanently fixed heterosis. Development of apomicticrice will require biotechnology processes.To increase heterosis levels beyond the level currently obtained, emphasis mayhave to be shifted from intervarietal hybrids to intraspecific hybrids (involvingindica and japonica cultivars) which exhibit very strong heterosis in spikelet number(Table 12). However, spikelet sterility in such hybrids gets in the way of exploitingthis heterosis commercially. The recent discovery of a wide-compatibility gene(Araki et al 1988, Ikehashi and Araki 1986) should make it possible to get indicajaponicahybrids to set normal seed. To make this approach practical, widecompatibilitygenes will have to be transferred to various CMS and restorer lines.Using hybrid vigor from wide crosses is hard to imagine today. But with thehelp of genetic engineering tools, it may be possible to develop elite lines frominterspecific crosses with unique gene blocks, resulting in greater heterosis in F 1hybrids.To develop appropriate hybrid rice technology for countries outside China, thefollowing research needs to be undertaken:1. Develop suitable CMS and restorer lines for F 1 rice hybrids that will yield15-20% (0.75-1 t/ ha) more than the best improved lines developed throughconventional breeding. The hybrids must possess multiple disease and insectresistance and acceptable grain quality.

234 Yuan et alTable 12. Yield potential of indica-japonica and indica-indica hybrid rices. Hunan Hybrid RiceResearch Center, 1986.PlantSeedType height Spikelets/panicle Spikelets/plant set(cm) (%)Yield(t/ha)Indica/japonicaChengte 232/26 Zhai zaoIndica/indicaV20 A/26 Zhai zao (Ck)% increase or decrease1208936269.6 1779.4 54 8.2102.6163800.312293 8.6–42 –42. Develop and adapt economical seed production techniques to producegoodquality hybrid seed.3. Develop optimum management practices for maximum economic yieldsand adaptability of hybrids.4. Assess the economic feasibility of hybrid rice.5. Use growth regulators to modify floral characters and select CMS lines thatpossess large exserted stigma and multiple pistil to influence outcrossing.6. Study the effect of hybrid vigor in imparting field tolerance for diseases,insects, and other stresses.7. Explore prospects of somatic embryogenesis for hybrid seed or seedlingproduction, as an alternative to large-scale seed production in the field.Critics of the hybrid breeding approach contend that heterozygosity is not aprerequisite to high performance, uniformity, and stability of performance of hybridvarieties (Jinks 1983). They say that heterosis is primarily due to the bringingtogether of unidirectionally dominant alleles dispersed between the parental linesshowing linkage disequilibrium. Therefore, it is contended that conventionally bredlines with performance equal to or better than F 1 hybrids can be developed,especially in self-pollinated crops.However, there are no critical data in rice to show that conventionally bred linesthat perform as well as a heterotic F 1 hybrid have been developed from such a cross.We believe that repulsion phase genetic linkages in parental lines would not allow allthe useful genes from the parents to combine in the F 2 and subsequent generationsthrough pedigree breeding methods. The hybrid breeding approach would enablethe effects of repulsion phase linkages in the F 1 generation to be overcome.IRRI is exploring the possibility of working collaboratively with the Universityof Birmingham to study whether or not, and how, pedigree lines with as high a yieldpotential as F 1 hybrids can be developed.Hybrid rice has already revolutionized rice production in China, and willcontinue to do so during the remaining years of this century. Outside China, the fateof this technology is still uncertain. Its future will depend on the resourcesinternational and national rice improvement programs provide to develop and usethe technology and on the availability of alternative conventional breedingmethodologies to increase rice yields per unit area per unit time.

Hybrid rice 235References citedAraki H, Toya K, Ikehashi H (1988) Role of wide-compatibility genes in hybrid rice breeding. Pages79-83 in Hybrid rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Barker R, Herdt R W, Rose B (1985) The rice economy of Asia. The Johns Hopkins University Press,Washington, D.C.Ekanayake I J, Ganity D P, Virmani S S (1986) Heterosis for root pulling resistance in F 1 rice hybrids.Int. Rice Res. Newsl. 11(3):6.Ikehashi H, Araki H (1986) Genetics of F 1 sterility in remote crosses of rice. Pages 119-130 in Ricegenetics. International Rice Research Institute, P.O. Box 933, Manila, Philippines.IRRI—International Rice Research Institute (1983) Annual report for 1982. P.O. Box 933, Manila,Philippines. p. 125.IRRI—International Rice Research Institute (1987) Preliminary report of 1986 IRTP nurseries results.P.O. Box 933, Manila, Philippines. p. 2-5.Jin D M, Li Z B, Wan J M (1988) Use of photoperiod-sensitive genic male sterility in rice breeding. Pages267-268 in Hybrid rice. International Rice Research Institute. P.O. Box 933, Manila, Philippines.Jinks J L (1983) Biometrical genetics of heterosis. Pages 1-46 in Heterosis, reappraisal of theory andpractice. R. Frankel, ed. Springer-Verlag, Berlin.Kaw R N, Khush G S (1985) Heterosis in traits related to low temperature tolerance in rice. Philipp. J.Crop Sci. 10:93-105.Khush G S (1977) Disease and insect resistance in rice. Adv. Agron. 29:265-341.Khush G S, Kumar I, Virmani S S (1988) Grain quality of hybrid rice. Pages 201-215 in Hybrid rice.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Khush G S, Virmani S S (1985) Breeding rice for disease resistance. Page 239 in Progress in plantbreeding. G. E. Russel, ed. Butterworth, London.Lu X G, Wang J L (1988) Fertility transformation and genetic behavior of Hubei photoperiod-sensitivegenic male sterile rice. Pages 129-138 in Hybrid rice. International Rice Research Institute, P.O. Box933, Manila, Philippines.O'Toole J C, Soemartono (1981) Evaluation of a simple technique for characterizing rice root systems inrelation to drought resistance. Euphytica 30:283-290.Senadhira D, Virmani S S (1987) Survival of some F 1 rice hybrids and their parents in saline soil. Int. RiceRes. Newsl. 12(1):14-15.Virmani S S (1986) Prospects of hybrid rice in developing countries. Rice: progress assessment andorientation in the 1980s. Int. Rice Comm. Newsl. 34(2):143-152.Virmani S S, Dalmacio R D (1987) Cytogenic relationship between two cytoplasmic male sterile lines ofrice. Int. Rice Res. Newsl. 12(1):14.Virmani S S, Govinda Raj K, Casal C, Dalmacio R D, Aurin P A (1986) Current knowledge of andoutlook on cytoplasmic- genetic male sterility and fertility restoration in rice. Pages 633-647 in Ricegenetics. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Wang S L (1980) Inheritance of R genes in rice and methods of selection of new ‘R’ lines. Agric. Sci.Technol. (Hunan) 4:1-4.Yang R C, Hao Ran L (1984) Preliminary analysis of R genes in IR24. Acta Agron, Sin. 10(2):81-86.Young J B, Virmani S S (1984) Inheritance of fertility restoration in a rice cross. Rice Genet. Newsl.1:102-103.Yuan L P, Virmani S S, Khush G S (1985) Wei You 64 - an early duration hybrid for China. Int. Rice Res.Newsl. 19(5):11-12.Zhou T L (1983) Analysis of R genes in hybrid indica rice of ‘WA’ type. Acta Agron. Sin. 9(4):241-247.NotesAddresses: Yuan Longping and Mao Changxiong, Hunan Hybrid Rice Research Center, Changsha, Hunan, China; S.S. Virmani, International Rice Research Institute, P.O. Box 933, Manila, Philippines.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Using chemical male gametocidesin hybrid rice breeding in ChinaTU ZENGPING AND HU DAWENResearch on chemically emasculated hybrid rice (CEHR) in Guangdong,China, started in 1970 with screening for effective chemical malegametocides. Some CEHR combinations developed in Guangdong andJiangxi consistently gave the highest yields for 4 yr in multilocation yieldtests and high-yielding fields. Seed production of CEHR also increased,from 0.4 t/ha with 40-60% seed purity to 1.5 t/ha with 80-90% seedpurity. The advantages of CEHR are 1) it does not need a special sterile line,greatly increasing the range of combinations with desirable parents; 2) itgives a stable distant hybridization F 1 combination with stronger hybridvigor, faster and easier; 3) it can interact with conventional breeding, usingoutstanding conventional rice varieties as parents; and 4) with somecombinations, the F 2 can be used in rice production. The difficulties inutilizing CEHR are 1 )the level of CEHR seed production is lower than withMS lines; 2) it is still impossible to produce CEHR seed on a large scale; and3) the current sprayers, male gametocides, and CEHR seed productionorganization need improvement.Hybrid vigor has made important contributions to the development of cropproduction, in the U.S. with hybrid maize (Burton 1983) and in China with rice(Yuan 1985, 1986). Success in producing hybrid rice seeds using three lines (malesterile, maintainer, and restorer) greatly increased utilization of hybrid vigor inlarge-scale grain production, from cross-pollinated plant to self-pollinated plant.But the potential of hybrid vigor in rice is still far from being fully exploited.The use of chemical male gametocide to induce an artificial, nongenetical, malesterile parent for producing hybrid rice seeds, in what is called a two-line method, isanother approach with great promise in the utilization of hybrid vigor in rice (Huand Tu 1987, IRRI 1987). In addition to its scientific significance, it has specialeconomic significance. Burton (1983) pointed out that achemical treatment capableof temporarily making a bisexual plant male sterile would have great potential in thecommercial production of hybrid seed.Research on chemically emasculated hybrid rice (CEHR) started in China in1970, with the screening of about 150 chemicals for effective chemical malegametocides (Guangdong Collaborative Investigation Group for Utilization ofHeterosis in Crops [GCIGUHC] 1978). In the 1970s, selecting hybrid combinationsby chemical emasculation was primarily carried out in Guangdong Province

238 Tu Zengping and Hu Dawen(GCIGUHC 1981, Hu 1981, Zhou et al 1982) and Jiangxi Province (Jiang et al1980). Zinc methyl arsenate (CH 3 As O 3 Zn • H 2O) and sodium methyl arsenate(CH 3 AsO 3 Na 2 • 5-6 H 2 O) were selected as the main ingredients of male gametocideduring that period. They are still the most effective and practical male gametocides inChina.Some CEHR combinations developed by the Rice Research Institute ofGuangdong Academy of Agricultural Sciences (Qing-Hua-Fu-Gui, Gang-Hua-Qing-Lan, Gang-Er-Hua-Shuang-Gui, Gang-Hua-Qing-Hua-Ai 6) gave thehighest grain yields for 4 yr in multilocation yield tests on hybrid rice (Table 1). In1984, CEHR combination Gang-Hua 2, developed by Jiangxi AgriculturalUniversity, reached a maximum yield of 13.5 t/ha as single-cropped rice in NorthJiangsu.The success of CEHR in Guangdong and Jiangsu has greatly stimulatedresearch in other rice-growing provinces, such as Hunan, Zhejiang, and Sichuan. Anetwork on CEHR research and utilization has been established for the exchange ofresearch information.History of CEHRAlthough it is an attractive area, research on CEHR is difficult. A review of thetortuous path to develop CEHR is helpful.Table 1. Performance of chemically emasculated hybrid rim (CEHR) in Guangdongmultilocation yield tests. 1982-86.CEHR combination aGrainyield(t/ha)RankYield increase overcheck bt/ha %1982Late Gang-Hua-Qing-Lan1983Early Qing-Hua-Gui-GhaoLate Gang-Hua-Qing-Lan1984Early Qing-Hua-Fu-GulLate Gang-Er-Hua-Shuang-Gui1985Early Qing-Hua-Fu-GuiLate Gang-Hua-Qing-Hue-Ai 61986Late Gang-Hua-Qing-Hue-Ai 66.67.65.87.46.77.15.65.9121111120.6**0.4*0.4**1.0**1.0**0.6**0.7**0.5**105816188.7169a Nomenclature of CEHR combinations: first character represents name of femaleparent; Hue means chemical emasculation; the last two characters represent nameof male parent, b Check combination was Shan-You 2, a three-line hybrid rice. **= significant at 1% level, * = significant at 5% level.

Chemical male gametocides for hybrid rice breeding 239Finding effective, practical chemical male gametocidesThe Guangdong Collaborative Investigation Group for Utilization of Heterosis inCrops (GCIGUHC) began its work on chemical male gametocides in the winter of1970 (GCIGUHC 1978). Researchers found that Dao-Jiao-Qing fungicide (usedagainst rice sheath blight) at above-standard rates could induce male sterility in riceplants. Dao-Jiao-Qing was confirmed as the best chemical male gametocide for riceamong 150 chemicals examined (GCIGUHC 1978, 1981).In June 1971, Jiangxi Agricultural University began using the critical ingredientof Dao-Jiao-Qing, zinc methyl arsenate, as male gametocide 73010.By 1975, GCIGUHC, using zinc methyl arsenate with other components, haddeveloped Male Gametocide No. 1. The amount of spray per unit area was reducedto 5% of the original amount of zinc methyl arsenate. Improved Male GametocideNo. 2 was developed by the Guangzhou Institute of Chemistry, in cooperation withGCIGUHC, in 1977. It was widely used in CEHR seed production by the RiceResearch Institute of Guangdong Academy of Agricultural Sciences and now is themale gametocide used in producing CEHR seeds in Guangdong Province.The discovery and improvement of an effective and practical male gametocidelaid an important base for the utilization of CEHR in rice production. The areaplanted to CEHR reached 7,000 ha in Guangdong Province in 1978. The secondgeneration of CEHR was planted on nearly 50,000 ha (GCIGUHC 1981). In 1978CEHR covered about 140 ha in Jiangxi Province (GCIGUHC 1981).Decline in planting area of CEHRAlthough research on male gametocides and selection of CEHR combinations hadsome early success, there were still two problems:1. Hybrid seed production, at about 400 kg/ ha, was too low to be commercial.Sometimes hybrid seed production by chemical emasculation also failed forother reasons.2. The yield-increasing effect of CEHR was unstable, and Gang-Hua-Da-Zhawas susceptible to bacterial leaf blight.These factors contributed to a gradual decrease in the area planted to CEHR,and GCIGUHC played no role in later CEHR research and production.New research on utilizing CEHRAlthough large-scale utilization of CEHR had met some difficulties, the RiceResearch Institute of Guangdong Academy of Agricultural Sciences and somecooperative units continued research on CEHR, primarily on new combinationsand techniques of hybrid seed production by chemical emasculation. Remarkableprogress was made in the 1980s. New combinations, such as Gang-Hua-Qing-Lanand Qing-Hua-Fu-Gui, gave the highest grain yield for 4 yr (Table l), causing manyagronomists and breeders to reevaluate the potential of CEHR in rice production.Techniques of hybrid seed production by chemical emasculation also improved.In 1984 and 1985, hybrid seed production of the new combinations was 1.60-1.76 t/ha, maximum yield reached 2.24 t/ha. The purity of CEHR seeds producedfrom 9 basic units was 80-87%, meeting the standards for commercial CEHR seed

240 Tu Zengping and Hu Dawen(the purity standard for CEHR is 80% in Guangdong Province). In 1986, a basic unitof CEHR seed production in Lunjiao district, Shunde county, successfully producedCEHR on 9.2 ha, with an average yield of 1.8 t/ha at 84% purity.Advantages of chemical emasculation for hybrid riceRecently, with a decrease in the area available for rice, an increase in population,concern for environmental pollution, and the need to raise people’s standard ofliving, the goal of rice breeding has become more difficult, demanding not only highyield but also good quality; not only multiple resistance, but also low cost and highbenefits. Some practical approaches to meeting an integrated breeding goal include• Three-line approach: develop and select new MS lines to create newcombinations;• Distant hybridization approach, especially indica-japonica hybridization;• Pedigree approach, through further improvement of plant type andphysiological characters, especially photosynthetic efficiency; and• Chemically emasculated hybrid rice approach.We consider the primary advantage of the CEHR approach to be that it cantake advantage of the strong points of other approaches while avoiding theirweaknesses.Compared with three-line hybrid rice. With CEHR, a special sterile line is notneeded. It is free of the unfavorable characteristics of a particular sterile line, such assusceptibility to disease or poor grain quality. In theory, with CEHR, any desirablerice variety can be used as the female parent to cross with any male parent. Thatgreatly increases the possibility of the appearance of ideal combinations with goodgrain quality, high yield, and multiresistance. Some promising combinations havebeen selected at our institute.Compared with distant hybridization. CEHR can greatly shorten breedingtime, taking advantage of the stronger hybrid vigor of this approach while avoidingthe shortage of strong separation in the offspring. Because there is no separation inthe F 1 , as soon as distant hybridization is successful with an ideal F 1 , it can be used inrice production.Compared with pedigree breeding. CEHR can take excellent conventionalvarieties as parents and add hybrid vigor to new combinations. Most of the currentlyavailable CEHR are combinations from the best improved varieties: Qing-Hua-Gui-Chao, Qing-Hua-Fu-Gui, and Gang-Hua-Qing-Hua-Ai 6 are developed from thehigh-yielding varieties Gui-Chao, Fu-Gui, and Qing-Hua-Ai 6.Using the F 2 in riceproduction. If the parents of a CEHR F 1 combination arevery similar in plant height and growth period, seeds from the F 1 plants show a levelof hybrid vigor in yield (Table 2).Difficulties and problemsThe primary difficulty with CEHR is in seed production. We have obtained hybridseed yields of 1.5-1.8 t/ha with some combinations of CEHR, at an economic valueabout the price of 15-18 t of common variety yield. Producers of CEHR seed could

Chemical male gametocides for hybrid rice breeding 241Table 2. Yields of Gang-Hua-Qing-Lan F 1 and F 2 and Shan-You 30.1984 1985CombinationYield increase at/ha %Yield increaset/ha %Gang-Hua-Qing-Lan F 1 8.4 +17** 8.1 +16**Gang-Hua-Qing-Lan F 2 7.9 +10* 7.7 10*Shan-You 30 (Ck) 7.2 7.0a ** = significant at 1% level, * = significant at 5% level.obtain higher benefits than from growing common rice varieties. But there are stillsome problems.• Compared with the seed yield by MS lines, the seed yield by chemicalemasculation is still not high enough for commercial seed production.Sometimes failure to obtain qualified hybrid seeds occurs because ofunfavorable weather or uncontrollable factors.• It is still not possible to produce as much hybrid seed by chemicalemasculation for any combination as is produced for some particularcombinations. The mechanism of chemical emasculation is dependent on thedifference between the pistil and the stamen in tolerance of male gametocidespray. The proportion of As distribution among pistil, stamen, and lodiculeis about 2:1:1 (GCIGUHC 1978). That means the pistil also suffers damageby the male gametocide. But under a certain rate, the pistil is more tolerant ofmale gametocide than the stamen. With a lower rate of male gametocide, thepistil can still live but the stamen will be severely damaged and lose itsactivity. If the rate of male gametocide is too high, the pistil will also beseverely damaged, resulting in remarkable reductions in outcrossing rate andhybrid seed yield. If the rate of male gametocide is too low, the stamen will betolerant of the damage and keep its activity, resulting in self-pollination andfailure of hybrid seed production. The critical range of male gametocideapplication rate differs with variety, developmental stage, nutrient status,ecological conditions, etc. It is not easy to treat a rice community in whichplants are at different developmental stages with a suitable rate of malegametocide at a suitable time.• A third problem is organization of large-scale CEHR seed production.Because the techniques for chemical emasculation are different from andstricter than those for the MS line method (determination of effectiveemasculation period, determination of suitable rate of chemical malegametocide, spraying techniques, etc.), if even one step is done incorrectly,the whole seed production process will fail. In our experience, we cannotapply the organization system and rules and regulations for hybrid seedproduction by MS lines to seed production by chemical male gametocides.So far we have some experience in organizing hybrid seed production bychemical male gametocide on about a 10 ha scale, by individual peasantfamilies. But as we look at future development of CEHR, we must design an

242 Tu Zengping and Hu Daweneffective and safe organization system as well as special regulations forCEHR seed production.• The chemical male gametocide itself is a problem. The residual arsenic inseeds from the F 1 CEHR is only 1.214-0.214 mg/ kg (GCIGUHC 1978), veryclose to the natural content of grain, But if a new, toxicity-free malegametocide with high emasculating efficiency could be found, it would bebetter.Research prioritiesTechniques of hybrid seed production by chemical emasculation and selection ofcombinations with super hybrid vigor are two research priorities for the developmentof CEHR. Excellent combinations of CEHR will inspire researchers to improve thetechniques of hybrid seed production. Highly efficient seed production techniqueswill promote the adoption and spread of the new combinations. Some main researchgoals are1. To improve and perfect the emasculating technique, investigating thegeneral rules of chemical emasculation to develop generalized emasculatingtechniques for all desired female parents.2. To design an automatic sprayer especially for chemical emasculation, toguarantee efficient, even, stable spraying.3. To screen for new chemical male gametocides that are toxicity-free and lowcost, with high emasculation effect but light damage on pistil.4. To develop new combinations with high yield, good quality, and single ormultiple resistances, as well as higher yield potential.ProspectsCEHR seed production has increased from 0.38-0.45 t/ ha in the 1970s to more than1.5 t/ ha in the 1980s, and seed purity has increased from 40-60% to more than 80%.Guangdong Province already has 4 basic units for CEHR seed production. Theyhave been producing high-yielding, good-purity CEHR seed for 3-4 yr. There were24 ha of CEHR seed production in Guangdong in 1986, the area increased to 36 ha in1987.Research on improved techniques for CEHR seed production and selection ofnew combinations with super hybrid vigor are going on in our institute. In all ofChina, research units and projects on CEHR have increased rapidly in recent years,and some success has been obtained. We are confident that if significant process onthe 4 research priorities is made in the next 5 yr, CEHR will have a major place in riceproduction in the second 5 yr.References citedBurton G W (1983) Utilization of hybrid vigor. Pages 89-107 in Crop. D. R. Wood, K. M. Rawal, and M.N. Wood, eds. American Society of Agronomy and Crop Science Society of America, Madison,Wisconsin.

Chemical male gametocides for hybrid rice breeding 243GCIGUHC—Guangdong Cooperative Investigation Group for the Utilization of Heterosis in Crops,Laboratory of Ecological Genetics, Agronomy Department, South China Agricultural College andLaboratory of Biophysics, South China Agricultural College (1978) Studies on male-sterility of riceinduced by “Male-Gametocide No. 1”. Acta Bot. Sin. 20(4):305-313.GCIGUHC—Guangdong Collaborative Investigation Group for Utilization of Heterosis in Crops (1981)Chemical emasculation and utilization of hybrid vigor in rice. Guangdong Science and TechnologyPublishing House, China 102 p.Hu Dawen, Liang Bingshu, Huang Fengyi, Hu Yongcheng, Ye Kongchu (1981) Summary on techniquesof hybrid seed production by chemical emasculation. J. Guangdong Agric. Sci. 5:5-8.Hu Dawen, Tu Zengping (1987) Chemically emasculating hybrid rice: another approach in utilization ofhybrid vigor in rice. Bull. Agric. Sci. Technol. 5:2-3.IRRI—International Rice Research Institute (1987) International symposium on hybrid rice. HybridRice Newsl. 1(1):1.Jiang Yongcheng, Shao Haoxing, Zong Yunhua (1980) Hybrid rice by chemical emasculation. TheJiangxi People’s Publishing House, Nanchang, China. 82 p.Yuan Longping (1985) A concise course in hybrid rice. Hunan Provincial Science and TechnologyPublishing House, China. 168 p.Yuan Longping (1986) Hybrid rice in China. Chin. J. Rice Sci. 1(1):8-18.Zhou Tianli, Lou Yonghai, Hu Dawen(1982) Breeding hybrid rice by chemical emasculation. Bull. Agric.Sci. Technol. 2:1-4.NotesAddress: Tu Zengping and Hu Dawen, Rice Research Institute, Guangdong Academy of Agricultural Sciences,Guangzhou, ChinaCitation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

DNA-mediated transformationin rice protoplastsH. UCHIMIYAProtoplasts isolated from rice suspension-cultured cells were treated withbacterial plasmid DNA possessing a chimeric gene of nopaline synthasepromoter, structural gene of aminoglycoside phosphotransferase II[APH(3’)11] from bacterial transposon Tn5, and terminator region fromcauliflower mosaic virus DNA. Colonies that proliferated in a mediumcontaining kanamycin (100 µg/ml) were selected. Transformationfrequency was 2-3% in several experiments. Enzyme APH(3’)ll was alsodetected in kanamycin-resistant callus that survived after repeatedselection. Other vectors containing cauliflower mosaic virus DNApromoter had similar transformation frequencies. Genes introduced intothe transformed clones were maintained for 1 yr in selective and/ornonselective conditions.Progress in the genetic modification of higher plants has made it possible to transferforeign genetic materials directly into plant cells (Krens et al 1982). Recently,transformation by bacterial plasmids has been demonstrated in several monocotyledonousspecies (Lörz et al 1985, Potrykus et al 1985, Uchimiya et al 1986a) anddicotyledonous species (Deshayes et al 1985, Hain et al 1985, Paszkowski et al 1984).Transformation experiments of this kind may be applicable to molecular andbiochemical genetics in higher plants.We constructed vectors containing two markers, a chimeric gene possessingaminoglycoside phosphotransferase [APH(3’)II] from bacterial transposon Tn5 andan entire nopaline synthase gene. The effects on the molecular and generalcharacteristics of the transformants of rice protoplasts obtained by these vectors aredescribed here.Materials and methodsCell cultureA cell line derived from roots of rice seedlings, Oryza sativa L. C5924 (indica type)Oc line, was maintained in a liquid suspension medium containing Murashige andSkoog (1962) formulation supplemented with 1 mg 2,4-D/liter and 3% sucrose(Medium A). The culture was kept on a gyratory shaker (120 rpm) at 25 °C underdim light. Serial subculture was done once a week by mixing the old culture andfresh medium (1:10).

246 H. UchimiyaProtoplastsFive-day-old cells were incubated in a solution containing 1% Cellulase OnozukaRS, 0.1% Pectolyase Y-23, 2% Driselase, 0.55 M mannitol, and 8 mM calciumchloride. Osmolarity of enzyme solution was 790 mOsmol/kg H 2 O. After 2 hincubation at 25 °C with gentle agitation (50 rpm), protoplasts were sieved through a25-µm nylon mesh and collected by centrifugation (100 xg). Protoplasts werewashed with a 0.6 M mannitol solution by centrifuging at least twice.DNA transferThe method used for DNA transformation was basically a modifcation of Krens etal (1982) and Paszkowski et al (1984). Briefly, 0.9 ml protoplasts (about 5 × 10 6 )suspended in 0.6 M mannitol were mixed with 0.25 ml DNA solution containing 10µg of the bacterial plasmid (circular form); pCT2T3 (Fig. 1), consisting of the1. The plasmid, pCT2T3, used in this investigation. Nos = nopaline synthase gene. NosKm R = a chimericgene consisting of nopaline synthase promoter, structural gene of APH (3’) II from Tn5 and terminatorof cauliflower mosaic virus DNA. Km R = kanamycin-resistant gene from Tn5. Sm R = streptomycinresistantgene. t3-ARS = 1.2 kbp autonomously replicating sequences in yeast isolated from tobaccochromosomal DNA. Restriction endonuclease cleavage sites = BamHI (B), BglII (Bg), EcoRI (E), andHindIII (H).

DNA-mediated transformation in rice protoplasts 247derivative of pGV1122 (Leemans et al 1982) and a chimeric gene of nopalinesynthase promoter (Herrera-Estrella et al 1983); a structural gene of aminoglycosidephosphotransferase II [APH(3’)II] from transposon Tn5 (Beck et al 1982); and aterminator region from cauliflower mosaic virus DNA (Gardner et al 1981). Thisvector also contained an intact gene of nopaline synthase (Depicker et al 1980) andautonomously replicating sequences of yeast (ars) cloned from tobacco nuclear,DNA (Uchimiya et al 1983). The plasmid was prepared without RNase treatment bythe method of Birnboim and Doly (1979).After 5 min, 0.5 ml of 40% (W/V) polyethylene glycol 6000 dissolved in Fmedium (Krens et al 1982) was added to the protoplast-DNA mixture. After 30 min,the incubation mixture was diluted with an equal volume of an F medium whoseosmotic value had been adjusted to 790 mOsmol/ kg H 2O with additional glucose.This stepwise dilution was performed every 10 min, 3 times.Protoplast culture and selection of transformantsProtoplasts (1.2 × 10 6 ) were cultured in 3 ml Medium B (same as Medium A, exceptthat 5 mM ammonium nitrate was used) containing 0.46 M mannitol. After 2 wk,the medium was solidified by an equal volume of Medium A supplemented with 0.25M mannitol and 1.2% agarose (low melting point agarose, Bethesda Res. Lab., MD,USA). The agarose beads obtained were kept in Medium A containing 0.36 Mmannitol for 1 wk. Then Medium A was replaced by a liquid culture medium with0.26 M mannitol. After 1 more week, cells dividing in agarose beads were subjectedto the first selection, using Medium A with 0.16 M mannitol and kanamycin sulfate(100 µg/ml, Meiji Seika Co., Tokyo, Japan).After 1 mo, colonies sustaining cell divisions were transferred for secondselection in Medium A containing 1% Bacto agar and kanamycin sulfate (100µg/ml).APH(3’)ll assayAnalysis of APH(3’)II was conducted by the method of Schreier et al (1985).DNADNA was prepared from callus by the method of Paszkowski et al (1984) andpurified by CsCl density gradient centrifugation. Fifteen µg DNA digested withrestriction enzyme(s) was separated by agarose gel electrophoresis, blotted to anitrocellulose filter, and hybridized with nick-translated probe DNA (Southern1975).Results and discussionIn our experience, colony formation from rice protoplasts has not been significantlyhigh. In a series of experiments, we were able to induce about 3 × 10 3 colonies fromapproximately 10 6 protoplasts. Plating efficiency was on the order of 10 -3 . This valuewas consistently achieved by reducing ammonium nitrate to 5 mM for the initialculture medium.

248 H. UchimiyaIn 2 independent experiments, we obtained 414 colonies larger than 1 mm fromDNA-treated protoplasts in the first selection (1 mo in culture). When those colonieswere transferred to the second kanamycin medium, 102 colonies survived; their sizeincreased to more than 5 mm after 1 mo in culture (Table 1, Fig. 2).Analysis of the APH(3')II in 34 such clones indicated that 31 (about 90%)possessed the same enzyme (Fig. 3). The transformation rate can be calculated as1.5% of the colonies surviving in the initial kanamycin-free medium.In other transformation experiments using different vector constructs, such aspCT1T2 (Uchimiya et al 1986b), similar transformation frequencies were obtained.Lörz et al (1985), using Triticum monococcum protoplasts, reported a 0.02%transformation frequency with 25% plating efficiency.Despite the low frequency of colony formation from rice protoplasts, thereproducible rate of transformation is encouraging for the genetic manipulation ofrice plants. We selected one clone for further investigation.The cell line was cultured for more than a year in selective and nonselectivemedia. The results obtained by DNA hybridization indicated stable maintenance offoreign DNA (Fig. 4). The vector pCT2T3 also contained nopaline synthase geneand ars from tobacco chromosomal DNA. We also detected the presence ofnopaline synthase gene in both cell lines.Table 1. Colony formation from rice protoplasts in DNA transformation experiments.Treatmentlnitial Colonies obtained Colonies a Colonies aprotoplasts by nonselective after 1st after 2d(no.) condition selection selectionNo DNA 7 x 10 5 8 x 10 2 14 0DNA added 8 x 10 5 3 x 10 3 158 41DNA added 2.4 x 10 6 3 x 10 3 256 61a Kenemycin sulfate added at 100 µg/ml, then cultured 1 mo.2. Protoplasts freshly isolated from rice suspension cultures (a); cultures derived from DNA-treatedprotoplasts after the first selection (b), and clones resistant to kanamycin after the second selection (c).Kanamycin sulfate at 100 µg/ml was added in the selective medium.

DNA-mediated transformation in rice protoplasts 2493. The presence or absence of APH(3’) II in the callus of 16 independent kanamycin-resistant clonesobtained in the second selection. Arrow indicates the position of APH (3’) II.4. An autoradiogram of Southern blot hybridization of DNA prepared from callus of a transformedclone which had been cultured more than 1 yr in medium containing kanamycin (+KM) or mediumwithout kanamycin (–KM). Ten microgram DNA digested with EcoRI and BGlII was applied to eachtrack. The presence of 2 kbp fragments indicates that an intact foreign gene was maintained in thetransformed clone.

250 H. Uchimiya5. Diagram illustrating the possible manner foreign DNA is integrated into host chromosomal DNA.Parenthetically, attempts to detect nopaline synthase, whose gene was located1.2 kbp away from the kanamycin-resistant gene, have been unsuccessful so far,because of the presence of unknown substances that disturb the visual identificationof nopaline after electrophoresis.Efforts are being made to investigate the possible role of the homologous regionof chromosomal DNA for the site-specific insertion of foreign DNA (Fig. 5).Systematic evaluation is needed to develop vectors possessing replication origin. Itwould be worthwhile to establish conditions that will facilitate regeneration of wholeplants from transformed callus.References citedBeck E, Ludwig G, Auerswald E A, Reiss B, Schaller H (1982) Nucleotide sequence and exact localizationof the neomycin phosphotransferase gene from transposon Tn5. Gene 19:327-336.Birnboim H C, Doly J (1979) A rapid alkaline extraction procedure for screening recombinant plasmidDNA. Nucleic Acids Res. 7:1513-1523.Depicker A, De Wilde M, De Vos G, De Vos R, Van Montague M, Schell J (1980) Molecular cloning ofoverlapping segments of the nopaline Ti-plasmid pTiC58 as a means to restriction endonucleasemapping. Plasmid 3:193-211.Deshayes A, Herrera-Estrella L, Caboche M (1985) Liposome-mediated transformation of tobaccomesophyll protoplasts by an Escherichia coli plasmid. EMBO J. 4:2731-2737.Gardner R C, Howarth A J, Hahn P, Brown-Luedi M, Shepherd R J, Messing J (1981) The completenucleotide sequence of an infectious clone of cauliflower mosaic virus by M13mp7 shotgunsequencing. Nucleic Acids Res. 9:2871-2888.Hain R, Stabel P, Czernilofsky A P, Steinbib H H, Herrera-Estrella L, Schell J (1985) Uptake,integration, expression and genetic transmission of a selectable chimeric gene by plant protoplasts.Mol. Gen. Genet. 199:161-168.Hemra-Estrella L, De Block M, Messens E, Hernalsteens J P, Van Montague M, Schell J (1983)Chimeric genes as dominant selectable markers in plant cells. EMBO J. 2:987-995.

DNA-mediated transformation in rice protoplasts 251Krens F A, Molendijk L, Wullems G J, Schilperoort R A (1982) In vitro transformation of plantprotoplasts with Ti-plasmid DNA. Nature 296:72-74.Leemans J, Langenakens J, De Greve I I, Deblaere R, Van Montague M, Schell J (1982) Broad-hostrangecloning vectors derived from W-plasmid Sa. Gene 19:361-364.Lörz H, Baker B, Schell J (1985) Gene transfer to cereal cells mediated by protoplast transformation.Mol. Gen. Genet. 199:178-182.Murashige T, Skoog F (1962) A revised medium for rapid growth and bioassays with tobacco tissuecultures. Physiol. Plant. 15:473-497.Paszkowski J, Shillito R D, Saul M, Mandak V, Hohn T, Hohn B, Potrykus I (1984) Direct gene transferto plants. EMBO J. 3:2717-2722.Potrykus I, Saul M W, Petruska J, Paszkowski J, Shillito R D (1985) Direct gene transfer to cells of agraminaceous monocot. Mol. Gen. Genet. 199:183-188.Schreier P H, Seftor E A, Schell J, Bohnert H J (1985) The use of nuclear-encoded sequences to direct thelight-regulated synthesis and transport of a foreign protein into plant chloroplasts. EMBO J.4:25-32.Southern E (1975) Detection of specific sequences among DNA fragments separated by gelelectrophoresis. J. Mol. Biol. 98:503-517.Uchimiya H, Fushimi T, Hashimoto H, Harada H, Syono K, Sugawara Y (1986a) Expression of aforeign gene in callus derived from DNA-treated protoplasts of rice ( Oryza sativa L.). Mol. Gen.Genet. 204:204-207.Uchimiya H, Hirochika H, Hashimoto H, Hara A, Masuda T, Kasumimoto T, Harada H, Ikeda J E,Yoshioka M (1986b) Co-expression and inheritance of foreign genes in transformants obtained bydirect DNA transformation of tobacco protoplasts. Mol. Gen. Genet. 205:1-8.Uchimiya H, Ohtani T, Ohgawara T, Harada H, Sugita M, Sigiura M (1983) Molecular cloning oftobacco chromosomal and chloroplast DNA segments capable of replication in yeast. Mol. Gen.Genet. 192:1-4.NotesAcknowledgments: I am grateful to T. Fushimi, Y. Sugawara, and H. Morota for their collaborative work. This researchwas supported by Grants-in-Aid for Science Research from the Ministry of Education, Science, and Culture, Japan.Address: H. Uchimiya, Institute of Biological Sciences, University of Tsukuba, Ibaraki 305, Japan.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Using rapid generation advancewith single seed descentin rice breedingK. MARUYAMARapid generation advance (RGA) with single seed descent is an effectivetool for rice breeders. It speeds up the breeding cycle, increases thenumber of favorable genotypes, and reduces breeding costs. Althoughselection through RGA has limited applicability, because of the miniatureplants produced, it does increase the ratio of favorable genotypes in abreeding population. During RGA, it is possible to screen for resistance topests and diseases, physiological characters such as low temperaturetolerance, grain characters that are stable under miniature culture,morphological characters like hairlessness, and characters linked tomarker genes.Population genetics in self-pollinating plants gave rise to the bulk method ofgrowing breeding populations, in which early generations are treated as apopulation. Raising seeds for the next generation is based on single seed descent(SSD), which gives the maximum chance for recombination within a givenpopulation size. The bulk method was combined with three times a year culture ofminiature rice plants using short-day treatment in the greenhouse to create a methodof rapid generation advance (RGA) with SSD.In the temperate zone of northern Asia, only one crop/ yr is possible because oflow winter temperatures. This means that, from first crossing to release, it takesalmost 10 yr to develop a rice variety by the standard bulk method. That breedingduration is often too long to meet the original breeding objectives.A Japanese rice breeder first tried RGA in the 1930s. He grew F 1 seeds in a20-28 °C greenhouse from late October to late January, then treated them with 8-hdaylength for 40 d. He was able to sow the F 2 generation in late March. The long-daytreatment in the early growth stage encouraged vegetative growth.Double cropping early-generation nurseries also has been tried in Kyushu(32 °N). However, only early genotypes could be safely double-cropped; first cropphotoperiod-sensitive genotypes headed too late for a second crop to be sown.Fujiminori, released in 1958, was the first variety developed by the bulkmethod. Nippon-bare, released in 1963, was the first variety bred by RGA with SSD.These cultivars once shared the largest cropping area of rice in Japan.This report discusses the advantages of using RGA with SSD and of selectionduring RGA.

254 K. MaruyamaAdvantagesThe benefits of RGA with SSD in rice breeding can be summed up in three points.Speeding up the breeding cycle. Shortening the breeding cycle is important insystematic breeding. By using RGA in heated greenhouses with short-day treatment,three crops a year have been possible. By the preliminary yield trial, most breederscan judge whether or not a breeding plant or a cross combination was successful.That takes at least 5 yr with only 1 crop a year. Using RGA, the first yield trial isplanted 34 yr after crossing.The reduction of total growth duration is caused primarily by high temperaturesand short-day conditions. The minimum temperature in the greenhouse is 20-25 °C.Short-day treatment somewhat accelerates the heading time of most cultivars(Fig. 1). Typical photoperiod-sensitive cultivars, however, respond dramatically.They head very early under short days, but do not head under long days or undercontinuous weak illumination.A typical RGA greenhouse consists of a glassroom and a darkroom, connectedby railways on which nursery beds can be moved. An economical facility uses a thickblack curtain wall hung from a track that can be opened and closed in the morningand evening. Usually a 9- to 10-h daylength is used as the short-day treatment.Anther culture, also proposed as a method to fix alleles and speed up thebreeding cycle, shortens breeding duration by only 1 yr, and selection cannot bepracticed.Increasing the number of favorable genotypes. Many agronomically usefulgenes are recessive. In early generations, heterozygosis veils useful characters and theratio of favorable genotypes in a population is extremely low. For example, if 10useful recessive genes are not common to both parents, we can find only 1 favorableplant in a million F 2 individuals. But we can expect 1,000 after enough fixation.Moreover, even if a dominant gene is favorable, it will segregate in the nextgeneration and we will have to select again.The concept of SSD in connection with RGA was proposed by Goulden (1939).Since then, theoretical improvement of SSD has been investigated.Harvesting all seeds from a population may cause random drift, with a largeprobability of losing favorable individuals. This means that a large population mustbe maintained. SSD gives a minimum population size. In practice, several SSD sets,including those for short- and long-term reserves, are harvested from a population.Breaking dormancy, uniform germination, appropriate spacing, etc., are alsoimportant in minimizing genetic drift. Cultivation should be precise to grow allplants to harvest. In crosses that involve a tall parent, leaf pruning will checkexcessive vegetative growth. If unchecked, excessive growth will selectively eliminateshort plants from the population (HilleRisLambers and Romena 1987).The focus of breeding is recombination. Without recombination, only 2 12 (i.e.,4,096 cultivars) will occur in rice (which has a genome of 12 chromosomes).The effect of recombination becomes particularly apparent in later generations.Recombination occurring only on the heterozygous chromosome fraction is useful.

Rapid generation advance in rice breeding 2551. Relationship between basic vegetative growth (d to heading) under 9-h days and photoperiodsensitivity (difference between 15-h days and 9-h days) in rice (Heterosis Breeding Laboratory, NationalAgricultural Research Center, Japan, unpubl. data).Heterozygosity is maximum in the F 1 generation, then drops with each generation.Therefore, the number of recombinants or of favorable individuals increases witheach generation. An example of this relationship, analyzed using computersimulation (Ikehashi 1977b), is illustrated in Figure 2. The adverse correlation of–0.430 in the F 2 improved to –0.224 in the F 4 .Fujimaki (1979) has proposed recurrent selection using a recessive male sterilegene to raise the chance of recombination. A cross between a cultivar with the geneand a special gene source segregates on sterility in the F 2 . The population for the nextgeneration is established via SSD from seeds harvested from the male sterile plants.Total heterozygosity, which decides the frequency of recombination occurring in thepopulation, becomes high. Repeating this procedure will produce recombinants inwhich previously closely bounded genes are recombined.This method would be useful for wide crosses, such as indica-japonica. Thepopulation obtained would be a good genetic resource. Combining this method withRGA may be advantageous, because the problem of late heading is almost resolvedusing shortday treatment.Reducing breeding costs. Ikehashi (1977a) discussed the merits of RGA:“Besides its genetic advantages, SSD requires little field space, allows shortcuts inrecord ...” Using RGA with SSD reduces labor and field space. It does need agreenhouse and facilities for shortday treatment.

256 K. Maruyama2. Examples of simulated two-dimensional discrete distribution. The dynamic shift of correlationcoefficients from F 2 to F 4 reflects the recombination of linked loci in the simulated distribution. Theadvance of recombination increase the number of individuals relieved of linkage bonding, and those thatfall above the defined fraction could be the good recombinations (well-recombined fraction). Cumulativebar charts are for columns (top) and rows (righthand side) (Ikehashi 1977b).Selection during rapid generation advanceRGA with SSD has many advantages. One is an increase through homozygosis inthe number of favorable individuals in a breeding population. But this process isautomatic and somewhat passive. Selection during RGA is an active alternative.Plant type is an important agronomic trait. But a breeder cannot visualize planttype accurately from miniature plants. Therefore, the characters that may be selectedduring RGA are those with high heritability that are easy to identify at the seedlingstage (D. HilleRisLambers, pers. comm.). These include resistance to pests anddiseases, physiological characters, grain characters, morphological characters, andcharacters linked to marker genes. Some agronomic characters that may be selectedare given in Table 1.Many resistances to pests and diseases are controlled by a single gene and areexpressed at the seedling stage. If gene action is strong, plants without the resistancegene are easy to eliminate from an inoculated population. If resistance expression issomewhat obscure, selection at the individual level is not possible. However, byeliminating severely infected plants, the frequency of the resistance gene among thenext generation will increase significantly. Repeated mass selection for severalgenerations will be effective.Some physiological characters also are easy to select for during RGA. Theyinclude leaf discoloration or wilting due to low temperature, tolerance for salinity,tolerance for submergence, etc. Plant responses to most physiological stresses arenot clear. Selection, therefore, will be based not on the individual plant, but on massselection.

Rapid generation advance in rice breeding 257Table 1. Some agronomic traits that may be selected during rapid generationadvance.Agronomic character aResistance to pests and diseasesBrown planthopperGreen leafhopperSmaller brown planthopperLeaf blastBacterial leaf blightPhysiological charactersLow temperature toleranceSalinity toleranceSubmergence tolerancePreharvest sprouting toleranceGrain charactersGrain size and shapeGrain colorGlutinous or nonglutinousMorphological charactersHairlessness (grain and leaf)AwnStigma extrusionCharacters linked to marker geneWide compatibility ( C and Wx )Blast field tolerance ( Ph )Selection criteriaIndividualMass selectionMass selectionIndividualindividualMass selectionMass selectionMass selectionMass selectionIndividualIndividuallndividualIndividualMass selectionIndividualIndividualIndividuala Tentative.Hot humid weather in the summer or early fall in some parts of Japan causespreharvest sprouting. The relatively weak dormancy of Japanese cultivars isexhibited in polygenic segregation. We tried mass selection for this trait in two ways,using cross combinations of tolerant and susceptible parents for the tests.The F 3 SSD seeds of 400 individuals were classified into fast, moderate, andslow germinating groups of 133 individuals each. All F 4 and F 5 seeds were harvestedand soaked in water the same day. We selected the fastest germinating 133 seedsfrom the fast group, the moderate 133 seeds from the moderate group, and theslowest 133 seeds from the slowest group.Indirect selection used the correlation between dormancy and injury of seed byheat treatment. F 3 , F 4 , and F 5 seeds were incubated 5 or 4 d at 70 °C and the seedsthat survived were sown. The F 6 population of each treatment was raised by SSDand cultivated in the field. Tolerance for preharvest sprouting improved significantly(Fig. 3) and did not affect such agronomic traits as heading date, culm length, etc.Although dense seeding decreases total grain number drastically, graincharacters are rather stable. Size and shape, color of apiculus and hull, glutinous ornonglutinous, etc., are all stable characters and easy to select at the individual level.During RGA, it is also possible to select some morphological charactersimportant for production, such as hairlessness of grain and leaf, awn, stigmaextrusion, etc. Culm length and panicle length are important characters, but it is noteasy to screen for semidwarf or long panicles on miniature plants.

268 K. Maruyama3. Preharvest sprouting of F 6 rice plant populations selected by germination speed and seed tolerance forhigh temperature. Treatment from F 3 to F 5 in the greenhouse (Mamyama 1980). Hokuriku 93:susceptible parent. Koshihikari: tolerant parent. Control: population derived by SSD up to F 6 . SG F 3 -F 5 :slowest germinating seeds selected at F 3 , F 4 , and F 5 . MG F 3 -F 5 : moderate germinating seeds selected at F 3 ,F 4 , and F 5 . FG F 3 -F 5 : fastest germinating seeds selected at F 3 , F 4 , and F 5 . HT F 3 -F 5 : F 3 , F 4 , and F 5 seedstreated at 70 °C; surviving seeds sown. HT F 3 -F 4 : F 3 and F 4 seeds treated at 70 °C, surviving seeds sown.HT F 3 : F 3 seeds treated at 70 °C; surviving seeds sown.Selection using the linkage between a common marker gene and a useful genealso increases the ratio of favorable individuals in a breeding population. Forexample, the wide-compatibility gene S-5 n is useful in an indica-japonica cross. Butwhether or not a selected line possesses it must be decided through a crossexperiment. Fortunately, it links with the C (Chromogen) gene (Ikehashi and Araki1986). Selecting a plant with pigmented apiculus will raise the probability of selectingS-5 n .

Rapid generation advance in rice breeding 259ConclusionRGA with SSD can be an effective tool for a rice breeder. The advantages are inspeeding up the breeding cycle, increasing the number of favorable genotypes, andreducing breeding costs. Although RGA does have limited applicability, because ofthe miniature plants grown, it enhances the ratio of favorable genotypes in thebreeding population. During RGA, it is possible to screen for resistance to pests anddiseases, physiological characters like cold tolerance, grain characters which arestable under miniature culture, morphological characters like hairlessness, andcharacters linked to marker genes.References citedFujimaki H (1979) Recurrent selection by using genetic male sterility for rice improvement. Jpn. Agric.Res. Q. 13:153-156.Goulden C H (1939) Problems in plant selection. Pages 132-133 in Proceedings of the 7th InternationalCongress of Genetics. Organizing Committee of the 7th International Congress of Genetics,Edinburgh.HilleRisLambers D, Romena B U (1987) Rapid generation advance. Lecture notes for the GEU trainingprogram, 1987 Apr, International Rice Research Institute, Los Baños, Laguna, Philippines.Ikehashi H (1977a) New procedure for breeding photoperiod-sensitive deep-water rice with rapidgeneration advance. Pages 45-54 in Proceedings of the 1976 deepwater rice workshop, 8-10November, Bangkok, Thailand. International Rice Research Institute, P.O. Box 933, Manila,Philippines.Ikehashi H (1977b) Simulation of single seed descent in self-pollinating population. I. Advance ofpolygenic recombination through generations. Jpn. J. Breed. 27:367-377.Ikehashi H, Araki H (1986) Genetics of F 1 sterility in remote crosses of rice. Pages 119-130 in Ricegenetics. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Maruyama K (1980) Methods of selection against pre-harvest sprouting of rice during rapid generationadvance [in Japanese, English summary]. Jpn. J. Breed. 30:344-350.NotesAddress: K. Maruyama, National Agriculture Research Center, Kannonndai 3-1-1, Yatabe, Tsukuba, Ibaraki 305,Japan.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Genetic variation in rice/sorghumhybrids and their applicationin rice breedingCHEN SHANBAO, DUAN XIAOLAN, AND FU JUNLUANew rice breeding methods and genetic variations in distant hybridizationwere explored through repeated experiments. We found it possible tocross rice with sorghum. Relationships and genetic variations in hybridswere analyzed in the context of the following: 1) Genetic variations ofcharacters—abnormal development and low fertility in early generations,wide character segregation across many generations, and distinct anddiverse forms of variations; 2) Cytological variation—abnormal meiosis ofpollen mother cells and changes in chromosome Giemsa bandingpatterns; 3) Phenotypic variation of molecular levels in progeny—anenzyme band presented in sorghum, but not in rice, occurred in esteraseisoenzyme zymogram and variations of protein compositions in chloroplastthylakoid membrane occurred. A group of germplasm and geneticresources with wide variations and diversity and elite economic characterswas obtained. New varieties were developed by backcrossing with hybridprogeny that had elite characters. Some new varieties tolerant of droughtand saline-alkali soils and resistant to diseases, with high quality grain,high yields, and different growth durations, have been developed.Distant hybridization can introduce beneficial genes from paternal plants, improveeconomic characters, bring in diversity and new plant types rare in intervarietycrosses, and expand the genetic basis for varietal improvement, especially in pest anddisease resistance (Chen 1986). Many researchers and farmer-technicians throughoutChina have been using plants from a dozen genera ( Sorghum, Zea, Coix, Zizania,Phragmites, Typha, Echinochloa, Triticum, Setaria, Bambusa, and Spartinaangelica ) as paternal parents in crosses with Oryza sativa since the 1950s. Progenieswith significant variations have been obtained, and new rice varieties with eliteeconomic characters have been selected and released for production.We began our studies of intergeneric hybridization between Oryza sativa andSorghum bicolor in 1960, to explore new rice breeding methods and geneticvariations in distant hybridization. The ability to cross rice with sorghum has beenproven through repeated hybridization.We have obtained hybrid types and germplasm resources with a broad range ofvery diverse variations. Genetic variations have been comprehensively analyzed fortheir morphology, cytology, biochemistry, and molecular biology (Duan et al 1985;Fu et al 1986; Zhu et al 1983; Zu et al 1979, 1985). Rice breeding work has beencarried out at the same time.

262 Chen et alGenetic variation in Oryza sativa/Sorghum bicolor crossesTo produce intergeneric hybrids, hot water and glume cutting were used toemasculate rice spikelets. Fresh sorghum pollen was dusted onto the rice. Seed setwas only a few per thousand.Agronomic charactersSegregation and variation in the progeny of distant crosses were large, and differentfrom that in the progeny of intervarietal crosses. Characters and forms rare inmaternal parents often occurred.Abnormal development in early generations. F 1 plants from rice varietyYinfang crossed with sorghum variety Hegari were tall and strong, but they grewslowly, headed 44 d later than the maternal parent, and had large panicles with sterileflowers. Those plants were overwintered in the greenhouse. Seeds from the manypanicles that headed from the same plant the following year were few and shriveled.Most did not germinate; of those that did germinate, most plants died at the seedlingstage. Seed set in the few F 2 plants that develop was very low. This continued forseveral generations, because of sterile pollen.The F 1 plants from rice variety Jingza 1/sorghum variety Yuanza 10 were taller,headed 29 d later, and had many more tillers and floscules than the maternal parents.Seeds were small and shriveled, seed set was 25.4%.In composite hybrids from sorghum-rice A7505/sorghum Hegari, F 1 plantswere leafy and tall. They headed late and were not uniform. Seed set was 16.7%.Seeds were large and fell off easily.Complex segregation for characters. Segregation of characters in hybridsbegan in the first generation and intensified from the F 2 . The difference among linesand individual plants was very wide. For example, in 26 F 2 plants fromYinfang/ Hegari, dates from first to last heading differed by 80 d. Differences in plantheight, leaf length and width, panicle size, number of floscules and % seed set,panicle shape, seed set density, grain shape and size, awn length, and glume colorwere great. The segregation range in the F 2 of rice Jingying l/sorghum Yuanza 10was similar; days to heading varied across 54 d.Wide segregation in distant hybrids was manifest not only in the plant lines, butalso in the F 2 and later generations with characters the maternal parents never had,such as violet glume tips, violet awns, and violet glumes. Another example is in thecross O. sativa Jingying 1/ Zea mays Huanong 2. Violet plants segregated from 4 ofthe 24 plant lines in the F 3 . The segregation range was 6.7-10.4%. Characters variedwidely among individual plants.The number of generations that segregated was higher in distant hybrids than inintervarietal hybrids. Characters were not stable, even after five generations.Segregations of the first five generations from rice Hua 30/sorghum-sugarcane werethe same as with the other hybrid combinations.In the F 6 , characters in most of the lines tended to be stable, but new variationsstill occurred in a few lines, including two very dwarf types. One had a plant height of

Genetic variation in rice/sorghum hybrids 263about 25 cm and bushy tillering with wide, short, vertical leaves. The panicle wasclub shaped, less than 10 cm in length, with short branches, dense seed set, and smallgrains. The other type had a plant height of about 45 cm and short, narrow leaveswith a 45 degree angle toward the stem. The panicle was 11 cm long with small grain.Seed set of both types was less than 3%, the progeny segregated.A few lines of some hybrid combinations continued to segregate widely to theF 10 .Distinct character variations. The F 1 plants from the composite hybridsorghum-rice A7505/sorghum Hegari were obviously different from the maternalparent. Great variation among individual plants also occurred in the F 2 . Segregationcontinued for several generations. Some new characters and forms, such as violetglume tips and welldeveloped bracteal leaves, appeared in the F 2 plants. Someabnormal forms also were observed, such as two panicles growing on the same nodeof the flag leaf or second panicle growing from the neck of a normal panicle. Grainsize from the two panicles differed greatly.New variations appeared in the F 3 : tillers growing on the first node above theground that headed normally and panicle-less tillers produced after the developmentof the apical cone of the primary stem, but with productive secondary tillers thatheaded normally.In the F 4 , large difference in grain size occurred between the two extremepanicles on the same plant. Average 1,000-grain weight was 45.5 g for large-grainpanicles and 36.7 g for small-grain panicles. In some special cases, 1,000-grain weightfrom 2 panicles on the same plant were 54.4 g and 37.0 g. Usually the larger panicledid not have a main panicle axis, but had double flag leaves. In addition, 20-50% ofthe seeds in a panicle were inembryonate.These variations do not appear separately, and they disappear suddenly, butthey do appear on the same plant of the same line at the same time. The charactersare heritable and their occurrence increases across generations. The geneticvariations indicate that the maternal rice received genetic material from plants of aforeign genus.Cytological variations in hybridsAbnormal meiosis of the pollen mother cells. Chromosome number, morpha, andbehavior in F 1 plants are disordered. Many F 1 plants had 10, 11, 13, or morechromosomes. Abnormal cytological phenomena in the F 2 were expressed asfollows:a) One pair more satellite chromosomes than in the maternal plant, tending towardthe number of sorghum.b) Disordered numbers of chromosomes at diakinesis, with number of bivalents 13,14, 15, or higher.c) Chromosome size differing greatly.d) Chromosome fragments and chromatic granule appearing in various numbersand different sizes and shapes at diakinesis.e) Some chromosomes lagging in metaphase I and anaphase I.

264 Chen et alf) Nonsynchronized meiosis of the pollen mother cells in the same floscule, withpachynema-metaphase I, diakinesis-metaphase II, anaphase I-microspore, andeven diakinesis-tetrad observed.The range of abnormality in the F 3 was wider and more complicated than in theF 2 . The major traits were as follows:a) Satellite chromosomes varying from 1 to 4 pairs in different pollen mother cells ofthe same anther; almost all the chromosomes connected to the nucleoli.b) Various numbers, sizes, and shapes of chromosome fragments and chromaticgranule, similar to those of F 2 ; bivalents usually 13 or 14 (the highest was 18), butsome lower than the normal number; chromosome nondisjunction alsoappearing.c) Chromosome bridges usually lagging in metaphase I, II, and anaphase I, II.d) At metaphase I, II, bivalent secondary pairing to form six groups andchromosome grouping of various numbers.e) Double spindles arranged vertically often found.f) Tripolar, multipolar, and unequal divisions observed in most cells during thetetrad phase.g) At anaphase of cell division, multinuclear cells with 5 to 8 nuclei, some with 13.h) Unsynchronized tetrad formation, quarter with multinuclei, unequal size, andabnormal arrangement of quarter, etc., at the tetrad phase.Progeny from Oryza sativa/ Zea mays had even more abnormal phenomenaand traits.Changes in chromosome Giemsa’s banding pattern. During late prophase ofmitosis, nuclear types and Giemsa’s banding pattern in stabilized hybrids of lategenerations of Yinfang/Hegari and their parents were analyzed. The nuclear typesof maternal parent Yinfang, paternal parent Hegari, and their hybrid 77125 are 2n =24 = 14M + 6SM = 4ST, 2n = 20 = 14M + 4SM = 2ST, and 2n = 24 = 8M + 8SM= 8ST, respectively. The nuclear types in the hybrids were obviously further fromthe centermost loci of the chromosomes than in maternal parents; the arm ratioincreased. The Giemsa’s banding patterns of maternal parent Yinfang, paternalparent Hegari, and their hybrid 77125 are 2n = 24 = 14C/C + 2C/CI + 4W/C +2WN/C + 2W/W, 2n = 20 = 8C/CI = 4C/C + 4W/C + 2WN/C, and 2n = 24 =4C/CI + 4C/C + 4CI/C + 6W/C + 2W/CI + 2W/W, respectively. Hybrids hadcomplicated banding patterns and obviously had four more intercalary bands thanthe maternal parents. The relative quantity of heterochromatin was 38.2-48.096 forYinfang (maternal parent), 36.2-451% for Hegari (paternal parent), and 30.0-30.2%for their hybrids. Obviously, the ratio of heterochromatin in total quantity ofchromatin is smaller in hybrids than in the parents.The variations in cytology described are the result of hybridization of twodistantly related species whose allochromosomes are difficult to pair normally. Thechromosome structure changed, consistent with segregation in morphologicalcharacters.Phenotypic variations in molecular levelsEsterase isoenzyme analysis. The zymogram bases of hybrids and their maternalparents are those of japonica rice. An enzyme band (Band 11) located in the same

Genetic variation in rice/sorghum hybrids 265locus as in the male sorghum parent, which is absent in the maternal rice parent,appeared in young roots, gemmule, flag leaves, anthers, and seed embryos of thehybrids. Zymogram segregation, occurring mostly in the F 2 and F 3 , was discoveredafter analyzing the occurrence of enzyme Band II in the F 2 , F 3 , F 4 , and F 5 .Segregation after the F 4 decreased significantly. Lines and individual plants withBand II decreased by generation. Band II still occurred in more than 50% of theplants in the F 5 , but was stabilizing. Enzyme band segregation appeared primarily inplants with Band II. The majority were individuals with Band II in the segregatedpopulation. Plants without Band II in the F 2 rarely segregated. Isoenzyme analysisindicated that the hybrids did accept genetic materials from sorghum. Theoccurrence of enzyme Band II is a phenotypic variation of molecular level.Protein composition of chloroplast thylakoid membrane. More than 30polypeptide bands were isolated in the maternal parent Yinfang and its hybridprogeny. Most of the hybrids showed 3 polypeptide bands with molecular weights of13.5 kb, 18 kb, and 64 kb. The band with 18 kb belongs to the male parent sorghum.The two others belong not to the male or female parent, but to their hybrids. Thisindicates the significant function of pollen from the male parent during hybridizationand of the formation of thylakoid membrane polypeptide in hybrid progeny.Fertilization and embryogenesisNot only pollen from gramineous plants, such as Sorghum, Zea mays, Coix,Zizania, etc., but also pollen from dicotyledonous plants, such as Ricinus communisand Nicotiana tabacum, can be germinated on rice stigma. Fertilization between riceand sorghum is different from fertilization in self-pollinated rice. The fertilizationprocess is slow and varies greatly. Usually germination begins 20 min afterpollination. A pollen tube takes 2-10 h to reach the embryo sac. Then two sperm arereleased. Embryo sacs containing sperm from sorghum were 11.57% of the total sacs2 d after pollination. Sperm-egg fusion took place 5 h to 3 d after pollination. Only afew sperm nuclei were observed moving toward the egg nuclei and tending to fuse inslides prepared 8 and 12 h after pollination. Only 0.44% of the sorghum sperm fusedwith rice eggs and developed into embryonic tissue.DNA molecular hybridizationZhou Guanggu and others (Shen and Zhou 1983; Zhou et al 1979, 1980) analyzedthe repeated DNA sequence of rice, sorghum, and their hybrids, emphasizingdifferences in repeated sequences between hybrids and their parents. Liquid phasehybridization was used to study the kinetics of reassociation. The discovery of adistinct DNA sequence of sorghum Hegari in genes of stabilized lines 77125 and4437 from progeny of Yinfang/Hegari shows that sorghum DNA sequences hadreassociated into the maternal rice parent.The film solid phase hybridizing technique was used to intercross DNAmolecules from hybrids and their parents. The number of copies of the repeatedsequences in line 77125 was obviously reduced. Analysis of genes from parents andhybrids indicated that the repeated sequence in hybrid 77125 changed greatly; 77125had more repeated sequences than its maternal parent, which is homologous tosorghum. The middle repeated sequence was obviously different from that of the

266 Chen et almaternal parent and is related to genetic expression, therefore causing phenotypicvariations.Comprehensive studies of multiple principles showed that the chromosomegenomes in rice have associated genetic material from the foreign genus Sorghumthrough the sexual process; the hybrid progeny obtained are true distant hybrids.Character variations from directly introduced DNATo avoid some of the difficulties in distant sexual hybridization, we exploredtechniques for introducing foreign DNA directly into rice plants (Duan and Chen1985). Direct microinjection and pollen tube techniques were used to introduceforeign DNA into self-pollinated rice embryo sacs, transforming fertilized eggs orcells. Some mutated offspring have been obtained.Rice variety Xiabei recepted DNA from sorghum variety Pingluowawatou.The single plant in the F 1 had no obvious variation, but there was significantvariation in the F 2 . F 2 plants had a 15.6% seed set and poor seed filling. Only sixplants developed in the F 3 ; their traits were completely different from Xiabei rice andfrom each other. Those plants were only 18-53 cm tall and heading differed acrossmore than 30 d. No seed set the first year.DNA from violet rice was introduced into rice Jingying 1 using the pollen tubepath. Violet traits occurred in the progeny. Another example is the introduction ofDNA from Spartina angelica into rice Xiabei. Their protein and 16 amino acidcontents were higher than in the receptor rice.Molecular testing has verified that a foreign DNA sequence may reassociate ina rice receptor. Through this direct DNA introduction technique, progeny mayprovide germplasm resources or may be selected to be utilized directly. An exampleis early ripening rice line 829042 released for testing and production, obtained byintroducing DNA from early-ripening violet maize into rice Jingying 47.Applying rice/sorghum hybrids in rice improvementThe current hybrid breeding program relies on intraspecific crossing, but theopportunity to select good material is limited because of the narrow genetic basesand the segregation range. Intervarietal crossing is not helpful when usefulcharacters from another species are needed. Distant hybridization is considered animportant new breeding method.Significant variations in segregation occurred in progeny from rice hybridizedwith sorghum and other plants. Hybrid vigor, variations in morphologicalcharacteristics, and beneficial economic characters, as well as specific plant types,such as compact plants, well-developed root systems, thick and strong stems, largepanicles, and large grain size, appear in progeny. A wide range of variation in growthcharacteristics, such as sensitivity to daylength, sensitivity to temperature, and stressresistances, also occurred.Differences in response to light and temperature were obvious. For example,stabilized lines 3277 and 5216 from progeny of Yinfang/Hegari had growthdurations in the Beijing area of 130 and 160 d, respectively. Line 5216 had only 105 dduration when planted in Guangdong, earlier than line 3277. In the photorespiration

Genetic variation in rice/sorghum hybrids 267test, photosynthetic efficiency of line 5216 and others was higher than that of thematernal parent.One characteristic of a sorghum/rice hybrid is its drought and saline-alkalitolerances. In repeated testing, drought and saline-alkali tolerance in hybrids andbackcross progeny was higher than is usual in rice. Some hybrids also had higherresistance to bacterial leaf blight and blast. Sorghum/rice hybrids also had higherrestoration of rice fertility.With the wide-ranging variations and segregations occurring in progeny ofdistant hybrids, many new characters and forms come out, giving greateropportunity for selection. Variations and types, even some progeny with individualelite characters, should be retained as breeding material, even though abnormalgrowth and development occurs in early stages. Seed set percentage and seed weightmay be gradually improved with generation advance. We have obtained a group ofstabilized progeny and specific types with several elite economic characters or traits.It usually is impossible to select new varieties with integrated characters, such ashigh yield, good grain quality, and stress resistances, directly from widelysegregating progeny of distant hybrids. The progeny have some undesirablecharacters as well as some elite ones. Backcrossing with rice, then selection, is thebest procedure. Some types that have excellent traits and integrated characters alongwith certain bad traits may be used in composite crosses with rice varieties that haveelite characters to cancel out the bad ones.Some distant hybrid progeny or lines with narrow variation ranges that growand develop almost normally and stabilize quickly can have some practical value indeveloping new varieties in a short time. Anther culture in combination withscreening and backcrossing can be used to speed stabilization as well as selection(Song et al 1983).We have been using these breeding methods since the early 1970s to develop ricevarieties. In northern China, rice production is limited by water shortages. In rainfedfields without irrigation in the hilly areas of the south, rice production and yieldcannot be guaranteed. To maintain and expand rice hectarage and rice productionin those areas, cultural practices for dry seeded rice are needed and new varietiestolerant of drought are required. By exploiting drought tolerance and othercharacters in progeny of rice/sorghum hybrids, we have developed rice varietiessuitable for upland planting.Some new varieties (lines) of japonica rice suitable for both lowland and uplandplanting have been developed, tested, and released. A7929 (Chen et al 1985), fromthe progeny of rice-sorghum A7505/rice Jingying 83, has a welldeveloped rootsystem, grows vigorously, and is highly tolerant of drought and saline-alkali soils.Directly sown in dry fields, it is tolerant of soil pH 8.5 and salt content 0.3% or moreduring the seedling stage. Growth resumes quickly after irrigation. It yields about5.2 t/ ha. It is resistant to rice blast, has wide adaptability, and shows no prematuresenescence during late growth. The 1,000-seed weight is about 30 g. Its growthduration in the Beijing area is 125 d. It has been grown as a single rice crop in thespring or in a double-crop system in the summer, either direct seeded or transplantedafter wheat. Shandong, Henan, and northern Anhui are the major production areas.A7929 now is grown inside and outside the Great Wall, south and north of theYangtze River, and in hilly areas. Yields are more than 7.5 t/ha.

268 Chen et alSome lines of different growth durations and sowing seasons are adapted toother areas. A8315, a sibling of A7929, has a growth duration of 125 d in the Beijingarea. Its drought and saline-alkali tolerances, blast resistance, and grain quality arehigher than those of A7929. Seedling response to osmotic stress and its relationshipto osmotic regulation show that A8315’s drought tolerance is better than that ofupland variety Qin-ai planted in the north. Parameters such as water potential (ow),osmotic potential (0), turgor potential (Op), and relative water content in the leavesdecrease slowly and the range of decrease is small.Another example is line 837003 from sorghum/rice D7846/Nan 81. It has agrowth duration of 145 d in the Beijing area; plants are thick and strong with darkgreen leaves. The leaf blades roll to the inside. It is resistant to lodging and diseases,tolerant of drought, and has good grain quality with large panicles and large grains.It has been released for Beijing, Tienjing, and Hebei as a single crop in the spring oras a transplanted crop following wheat in the summer. Its yield is higher than that ofhybrid rice Li-You 57, which has the same duration.It is possible to create new germplasm resources through distant hybridizationand to use those materials as hybrid parents or in composite crosses to improvevarieties, especially to develop new varieties specifically tolerant of drought or otherinjurious factors.References citedChen Shanbao (1986) Breeding effects of distant hybridization in rice. Pages 316-328 in Rice science inChina. Agricultural Press, Beijing.Chen Shanbao, Duan Xiaolan, Fu Junlua (1985) New dry seeded rice variety A7927. Crops 4:25.Duan Xiaolan, Chen Shanbao (1985) Variation of the characters in rice (Oryza sativa) induced by foreignDNA uptake. Sci. Agric. Sin. 3:6-10.Duan Xiaolan, Chen Shanbao, Zu Deming (1985) Genetic study on the esterase isoenzyme in hybridbetween rice and sorghum. Acta Agric. Sin. 3:173-180.Fu Junlua, Li Liancheng, Chen Shanbao (1986) Abnormal meiosis in the early generations of the hybridbetween rice and sorghum. J. Wahan Bot. Res. 1:7-11.Shen Jianlua, Zhou Guangyu (1983) The reassociation kinetic analyses of the repeated sequence DNA ofrice, sorghum and their hybrid. Acta Genet. Sin. 10:28-35.Song Xianbin, Duan Xiaolan, Chen Shanbao (1983) Preliminary report of application of anther culturein distant hybrid breeding. Page 207 in Studies on anther-cultured breeding in rice. AgriculturalPress, Beijing. (abstr.)Zhou Guangyu, Gong Zhenzhen, Wang Zien (1979) The molecular basis of remote hybridization-anevidence of the hypothesis that DNA segments of distantly related plants may be hybridized. ActaGenet. Sin. 6(4):405-413.Zhou Guangyu, Zeng Yishen, Yang Wanxia (1980) Molecular basis of remote hybridization-therecombination of sorghum DNA sequences with rice genome during remote hybridization. ActaGenet. Sin. 7:119-122.Zhu Fengsui, Fu Junlua, Li Liancheng, Chen Shanbao (1983) A cytological study on the intergenerichybrid between rice and sorghum. Sci. Agric. Sin. 4:26-29.Zu Deming, Chen Shanbao, Duan Xiaolan, Fu Junhua (1985) Genetic variations in the hybrids of rice(Oryza sativa) and sorghum (Sorghum vulgare). Theor. Appl. Genet. 70:542-547.Zu Deming, Dai Lanfang, Chen Shanbao, Song Xianbin, Duan Xiaolan (1979) Diversity and Specificperformance of progenies from distant hybridization between rice and sorghum. Acta Genet. Sin.6(4):414-420.NotesAddress: Chen Shanbao, Duan Xiaolan, and Fu Junlua, Institute of Crop Breeding and Cultivation, Chinese Academyof Agricultural Sciences, Beijing, China.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstracts 269ABSTRACTS: INNOVATIVE BREEDINGBiotechnology for rice varietal improvementA. A. APP, G. H. TOENNIESSEN, AND R. W. HERDTThe exploitation of biotechnology—tissue culture, diagnostic techniques,chromosome mapping, genetic transformation, and the genetics andmolecular biology of agronomic traits—can enhance the speed andprecision of rice varietal improvement work. Certain aspects of biotechnology,such as anther culture, somaclonal variation, diagnostictechniques, embryo rescue for wide cross hybridization, and chromosomemapping, have immediate applications. The possibility of duplicating inrice biotechnology applications that recently have been successful withother plants suggests a potential for developing new types of pest andpathogen resistances. Transformation of protease inhibitors and viralproteins, not to mention herbicide resistance, with genes controllingBacillus thuringiensis toxins exists. Altering rhizospheric bacteria populationswith Bacillus thuringiensis toxin genes also may be possible.Agreements between the public sector in developing countries and theprivate sector in certain developed countries could facilitate this process.Potential applications of genetic transformation to varietal improvementinclude raising the yield potential ceiling through enhanced biomassproduction; altering or including new plant characteristics, such as graincomposition, apomixis, and nitrogen fixation; developing novel and morestable forms of pathogen and pest tolerance; and developing greatertolerance for such environmental stresses as flooding, drought, nutrientdeficiencies, soil toxicities, salinity, and low temperature. Althoughtransient transformation of rice has been demonstrated and a successfulprotocol developed for regenerating rice plants from protoplasts, additionalresearch will be needed before the enormous potential from the insertionand expression of alien genes will be realized in rice breeding. In Asia, ricebiotechnology efforts are under way in mainland China and Taiwan, India,Japan, Korea, and the USSR and at the International Rice ResearchInstitute. The private sector in Japan is particularly active in applyingbiotechnology research to rice. If biotechnology research is to be ofpractical value to rice breeding programs, it must be supported byagronomy, plant pathology, plant physiology, biochemistry, entomology,microbiology, economics, and seed technology. Several donors, particularlythe Rockefeller Foundation, are funding international research onrice biotechnology in recognition of the importance of rice as a staple foodcrop in the developing world, the lack of basic research on rice, and theprojected need for a dramatic increase in rice production by the year 2000.Development of biotechnological techniques is proceeding rapidly, butlack of knowledge about the genetics and molecular biology of genes inrice that control important commercial characteristics may soon slow itsapplication. With limited resources, national rice improvement programsmust set priorities for the development and application of rice biotechnologyresearch in relation to its potential impact on the economy,environment, and social policies of the particular country.A. A. App. G. H. Toenniessen, and R. W. Herdt, Rockefeller Foundation, 1133 Avenue of theAmericas, New York, N.Y. 10036, USA.

270 AbstractsEconomic efficiency of hybridand conventional rice productionin Jiangsu Province, ChinaHE GUITING AND J. C. FLINNHybrid rice, first released in China in 1976, is now grown on nearly9 million hectares of China’s ricelands. This study compares resource useand productivity of hybrid and conventional japonica and indica ricevarieties. The data set was based on interviews with 90 conventional ricefarmers in Jiangsu Province, China. In the south, hybrids (7.8 t/ha)outyielded japonicas (6.8 t/ha) by about 15%. In the north, hybrids(7.1 t/ha) also outyielded indicas (6.2 t/ha) by 15%. Labor use for hybrids(273 d/ha) was less than for japonicas (298 d/ha) in the north. Fertilizeruse in the north and in the south did not differ significantly betweenvarieties, although pesticide use was higher in the south than in the north,and higher on hybrids and japonicas. The analysis of resource use showsthat the higher yields of hybrids are overwhelmingly due to technicalchange, as opposed to differences in management. The profitability ofhybrid and japonica rices were similar; although hybrids were higheryielding, japonicas were higher priced. Returns to labor were higher forhybrids, but returns to total costs did not differ significantly. Hybrids wereclearly more profitable than indicas in northern Jiangsu Province, andgenerated higher returns to both labor and nonlabor inputs.He Guiting, Agro-Economic Research Institute, Chinese Academy of Agricultural Sciences,Beijing, China; J. C. Flinn, Agricultural Economics Department, International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Application of photoperiod-sensitive genic malesterility in hybrid rice breedingLU XINGGUI, ZHOU JIXIAN, WANG JILIN, FANG GUOCHEN,ZHOU WENHUA, AND YANG SHIYUANPhotoperiod-sensitive genic male sterility (PGMS) was transferred intorice varieties with different genetic backgrounds, and different types ofindica and japonica PGMS lines have been bred. Fertility and results ofcross-combination are reported. Possibilities for breeding male-sterilelines adapted to different geographic areas and of using two-line hybridrice in place of three-line hybrid rice are discussed.Lu Xinggui, Zhou Jixian, Wang Jilin, Fang Guochen, Zhou Wenhua, and Yang Shiyuan, FoodCrop Institute, Hubei Academy of Agricultural Science, Hubei, China.

Abstracts 271Diversification of cytoplasmic male sterilityin hybrid riceWAN BANGHUICytoplasmic male sterility (CMS) results from the interaction between thesterile gene in the cytoplasm and the corresponding recessive sterilegenes in the nucleus. Diversification of CMS in hybrid rice is closelyassociated with high and stable yields. At present, the CMS belonginggenetically to sporophyte or gametophyte possesses different properties.The CMS developed so far can be divided into 7 restoration-maintenancetypes, according to the relationship between its restorers and maintainers,which are controlled by the male sterile (ms) cytogene. Although hybridrice yield is determined principally by nuclear background, trial resultsshowed that yield was influenced directly or indirectly by ms cytoplasm.The cytoplasm and the nucleus affect outcrossing rates and agronomictraits of CMS lines. Hybrid indica rice with WA (wild rice with abortivepollen) cytoplasm and hybrid japonica rice with BT (Chinsurah Boro II)cytoplasm are suited to China: these cytoplasms satisfy the primarydemand for developing commercial hybrid rices. But the vulnerability of asingle ms cytoplasm cannot be neglected in production. Since a number ofms cytoplasm having uniform specificity with WA, BT cytoplasm havebeen developed, it should be easy to alter the status of a single mscytoplasm if identification of CMS is speeded up.Wan Banghui, South China Agricultural University, Guangzhou, China.Tissue culture in rice improvementF. J. ZAPATA AND L. B. TORRIZOConventional breeding techniques in rice have enabled production to keeppace with growing populations and increasing food demands. However,the rate of productivity increases may slow in the coming years, making itnecessary to find other means to increase production. The use of tissueculture techniques such as haploidy, particularly anther culture, somaticcell culture, embryo rescue, and in vitro fertilization and protoplast cultureand fusion, to complement conventional breeding techniques is discussed.F. J. Zapata and L. E. Torrizo, International Rice Research Institute, P.O. Box 933, Manila,Philippines.

272 AbstractsSomaclonal variation in rice improvementXIONG ZHENMIN AND ZHENG KANGLEIn vitro-regenerated rice plants vary widely. But not all the variations areheritable; some are physiological. The correlation between regeneratedplants and their selfed progeny was r = 0.365** for seed fertility. Highsterility might be used as a marker for selection from regenerated plants.Somaclonal variation was particularly apparent in the progeny T 2 lines ofthe primary regenerant. There were high frequencies and wide spectra ofvariations in agronomic characters. In some T 2 lines, only one charactervaried; in others, several characters varied simultaneously. Certaincharacters had obvious tendencies toward variation. Reduced plantheight, earlier maturity, and decreased fertility prevailed in T 2 lines. Mostvariations were stable. Grain length in T 2 lines decreased significantly, andvariations in grain characters of four varieties with different grain typeswere consistent. Gel consistency increased in T 2 lines. Variability wasincreased by combining tissue culture and low dosage radiation. Somerice blast-resistant lines were isolated from the T 2 lines of a susceptiblevariety. The quantitative changes occurring because of repeated DNAsequences, mainly during the dedifferentiation process, might be onemechanism of somaclonal variation. The enhanced genetic variability hasbeen useful in rice improvement. Several promising lines isolated havebeen accepted for extension. Problems and application of somaclonalvariation are discussed.Xiong Zhenmin, Plant Genetics and Breeding Department; Zheng Kangle, BiotechnologyDepartment, China National Rice Research Institute, Hangzhou, China.Shuttle breeding for rice improvementMIN SHAOKAI, LU ZITONG, AND G. S. KHUSHShuttle breeding uses diverse ecological environments to developimproved varieties with higher adaptability. Alternate generations of earlybreeding materials are grown under different environments. The basis ofshuttle breeding is cooperative research among nations and institutions.The benefit is increased breeding efficiency. Currently the shuttle breedingapproach is being used to develop improved varieties of wheat, maize, andrice. In 1974, the International Center for Maize and Wheat Improvement(CIMMYT) and the Government of Brazil began shuttle breeding to developwheat varieties tolerant of aluminum toxicity. In 1982, ClMMYT and Chinastarted a shuttle breeding program to develop wheat varieties resistant towheat scab, with high yield potential and wider adaptability. In 1983, theChina National Rice Research Institute (CNRRI) and the International RiceResearch Institute (IRRI) initiated a shuttle breeding project to developearly-maturing rice varieties with high yield, good grain quality, multipleresistance, and wide adaptability. This paper focuses on the shuttlebreeding procedures followed in that project, the progress made, and theeffect of selecting breeding material under different ecologicalenvironments.Min Shaokai and Lu Zitong. China National Rice Research Institute, Hangzhou, Zhejiang, China;G. S. Khush, lnternational Rice Research Institute, P.O. Box 933, Manila, Philippines.

Abstracts 273Trends in breeding rice for high yieldYANG SHOUREN AND CHEN WINFUChinese rice scientists increased rice yields during the 1950s and 1960sby improving the plant type and since the 1970s. by exploiting thephenomenon of heterosis in developing F 1 hybrid cultivars. Bothapproaches seem to have reached a plateau, with yields of 8-9 t/ha. If stillhigher yields are to be achieved, total biomass yield has to be increasedwhile maintaining a reasonablegrain-straw ratio. Research efforts shouldaim at increasing leaf area and photosynthetic efficiency per unit leaf areaand at improving fertilizer responsiveness and lodging resistance. This willrequire combining ideal plant morphology with favorable vigor. Indica/japonica hybridization should meet the following objectives: the highstomata frequency in indicas combined the compact plant type, higherspecific leaf weight, higher chlorophyll content per unit leaf area, andhigher nitrogen and RUBPC content in japonicas. These characteristicsare advantageous for close planting and for increasing photosyntheticefficiency of leaves and total biomass yield. Indica/japonica crossesshould also have increased growth vigor. More than 30 yr of research oncrossing indicas and japonicas at Shenyang Agricultural University haveresulted in the development of rice strains that yield more than 10 t/ha.Exploiting the nucleus-cytoplasm interaction of indica/japonica crosses toincrease yield potential is also proposed.Yang Shouren and Chen Winfu, Shenyang Agricultural University, China.Role of indica/japonica hybridizationin rice improvementM. S. BALALIndica and japonica groups of Oryza sativa L. differ morphologically andchemically. Crosses between varieties of the two groups show a widerange of F 1 fertility, from 6 to 98% for pollen and from 1 to 92% forspikelets. Unique sources of economically significant genes have beenidentified among both indica and japonica accessions in the InternationalRice Germplasm Center. Genetic analysis of short stature, earliness, andblast resistance in indica/japonica crosses showed that each trait iscontrolled by one to three genes; in general, those in one group are allelicto those in the other. Several improved high-yielding varieties with shortstature and/or blast resistance (Mahsuri, ADT27, Malinja, Toride 1 ,Toride2, Tong-il, and Giza 175) have been obtained from indica/japonicahybridization. Some indica/japonica varieties with wide adaptability andbroad resistance to blast have been released for farmer cultivation.M. S. Balal, Rice Research Section, Field Crops Research Institute, Agricultural ResearchCenter, Giza, Egypt.

274 AbstractsWide hybridization for rice improvementK. K. JENA AND G. S. KHUSHWild relatives of crop species possess several traits of economicimportance, such as resistance to diseases and insects and tolerance foradverse soils. Genes for resistance to diseases and insects and tolerancefor salinity have been successfully transferred from wild species intocultivated wheat, oat, maize, barley, and tomato. Genes for resistance tograssy stunt virus, brown planthopper, and whitebacked planthopper havebeen transferred from wild species of Oryza into several rice cultivars.Pre- and postfertilization barriers to wide hybridization have been overcometo some extent by the application of growth regulators and by embryorescue techniques. Synthetic amphiploids, alien addition lines, aliensubstitution lines, and induced translocations have been used to overcomebarriers to recombination. Recently developed biotechnology techniques,such as tissue culture, protoplast fusion, and recombinant DNA, provideopportunities for transferring useful genes from distantly related speciesor genera into cultivated species.K. K. Jena, collaborative research scientist, and G. S. Khush. principal plant breeder and head,Plant Breeding Department, International Rice Research Institute, P.O. Box 933, Manila,Philippines.Gene transfer in rice using protoplast fusionand recombinant DNA technologyE. C. COCKINGThe second Shouichi Yoshida Memorial Lecture highlights a landmark inour ability to manipulate rice protoplasts and to regenerate fertile plants: arecently developed system for the efficient regeneration of plants from riceprotoplasts through somatic embryogenesis. This system—which combinesheat shock, protoplast culture in agarose, and direct rapid plantregeneration from protoplast-derived callus through somatic embryogenesis—haswide applicability for efficient plant regeneration fromjaponica rice protoplasts isolated from cell suspensions of a wide range ofexplants. Protoplast fusion to transfer both nuclear and cytoplasmicencoded genes is now being undertaken in rice. Opportunities exist forproducing somatic hybrids from crosses of cultivated rice and wild ricespecies that have such useful traits as salinity tolerance and resistance toa range of plant diseases and insects. The transfer of cytoplasmic malesterility leading to the formation of cybrids of use in the production ofhybrid rice is possible. Protoplast fusion also may enable the transfer ofapomictic genes into rice and the generation of novel heterosis. Now thattechniques exist for the transformation of rice protoplasts using recombinantDNA technology and the regeneration of plants from protoplasts,the remaining challenge is to have “genes-in-hand.” Transfer of singlegene traits, such as those for herbicide resistance—already accomplishedin certain dicotyledonous species—is now technically feasible with rice.The major challenge remaining is to achieve those agronomically desiredimprovements in yield, pest and pathogen resistance, and stress tolerancethat involve many genes of unknown identity.The Second Shouichi Yoshida Memorial Lecture, International Rice Research Conference, 24Sep 1987, Hangzhou, China. (Published by IRRI, P.O. Box 933, Manila, Philippines.)E. C. Cocking, Department of Botany, University of Nottingham, Nottingham Park, NottinghamNG7 2RD, U.K.

Physicochemicaland economic aspectsof rice grain qualityB. O. JULIANO AND L. A. GONZALESVariety, environment, and processing affect rice grain quality. In additionto the grain properties readily discerned by consumers, physicochemicalfactors are important. Varietal differences in moisture adsorption stresstolerance (fissuring resistance) contribute to stable high head rice yieldseven when the grain is overripe. Relevant starch properties are the majorfactor: amylose (linear starch fraction) content screened by iodinecolorimetry and starch final gelatinization temperature (GT) screened byalkali digestibility value and gel consistency (or viscosity). Amylose contentis correlated positively with water absorption and volume expansionduring cooking and with cooked rice hardness, and negatively with cookedrice stickiness. Nutritional value is indexed by protein content. Studies onconsumer demand for rice indicate that domestic consumers in SoutheastAsia are willing to pay an implicit premium for grain quality characteristics.Consumers significantly prefer better milled (low percentage of brokens)rice, aroma, and intermediate amylose content. The thinness of the worldrice market and the variability of consumer domestic demand for ricequality from one country to another make it difficult to establish aninternational consumer demand for grain quality. lRRl is currentlyundertaking research on domestic and international demand for ricequality.Rice grain quality consists of raw rice, or physical, quality; cooking and eating, orphysicochemical, quality; and nutritional quality. Rice quality is influenced byvariety, environmental conditions during ripening and harvesting, and postharvestoperations. Some physical properties are readily discernible to the consumer, otherphysicochemical properties need chemical analysis to measure (IRRI 1979, Juliano1985b). Physical properties such as length, width, length-width ratio, brokens,degree of milling and whiteness, translucency, discoloration, and aroma are easilyperceived (Khush et al 1979, Khush and Juliano 1985).Physicochemical propertiesThe rice grain consists of 16-28% hull and brown rice. Brown rice consists of branlayers of pericarp, seed coat, nucellus (maternal tissue) and aleurone layer(endosperm), and embryo and starchy endosperm. Low hull content contributes

276 Juliano and Gonzalesdirectly to high total milled rice yield, since essentially about 10% by weight of brownrice is removed during milling.Milled rice is composed of about 90% starch and about 8% protein dry basis.Starch occurs as polyhedral compound granules 3-9 µm in size, and protein occursmainly as spherical and crystalline protein bodies 0.54 µm in size (Harris andJuliano 1977, Bechtel and Juliano 1980). Starch consists of a branched fraction,amylopectin, and a linear less branched fraction, amylose. Apparent amylosecontent of milled rice is classified as waxy and nonwaxy (Juliano 1979a,b) (Table 1).Amylose content is determined by iodine colorimetry (Juliano 1971, Perez andJuliano 1978, Juliano et al 1981b).Another starch granule property is final gelatinization temperature (GT), thetemperature at which starch granules start to swell irreversibly in hot water, with lossof crystallinity. GT is indexed in a breeding program by the alkali digestibility valuein 1.7% KOH after 23 h at 30 °C (Little et al 1958, Juliano et al 1982).A third property is gel consistency representing the gel length of 100 mg flourdispersed in 2 ml 0.2 N KOH in 13- × 100-mm tubes held horizontally for 1 h(Cagampang et al 1973, Juliano et al 1980). Gel viscosity may be measured on 1 ml ofthe gel with a Wells-Brookfield Model RVT-CP 1.565° cone-plate microviscometer(Juliano and Perdon 1975). It relates to cooked rice hardness. These starchproperties have little effect on grain yield, except for the slightly lower grain weightof waxy rice.The relationship between grain size and shape, low temperature tolerance, andstarch properties has become more complicated with the development ofindica/japonica hybrids such as long-grain Mahsuri and the short-grain Koreanvarieties Tong-il and Milyang 23. In addition, long-grain California and Portuguesevarieties have been developed to compete in the world markets with US. long-grainindica rices.Recent cooperative studies at Kagoshima University indicate that highamylosetropical rices have true amylose content similar to low-amylose JapaneseTable 1. Apparent amylose content, gelatinization temperature, and gel consistencyof milled rices at IRRI.Property Type ValueApparent amylose content Waxy 0-2(% milled rice dry basis) NonwaxyLow 10-20Intermediate 20-25High 25-33Gelatinization temperature Low 6-7 (

Rice grain quality 277rices (Takeda et al 1987). Apparently, differences in apparent amylose content aredue to the high iodine affinity of amylopectins of high-amylose rices (Reyes et al1965, Takeda et al 1987). Because amylose content is overestimated, particularly inhigh-amylose rices, we propose that the term “apparent amylose content” be used foramylose determined by iodine colorimetry.Environmental and processing effectsDelayed harvest or overripening results in overdrying and shattering of overriperough rice and in fissured brown rice, which yields only brokens on milling.Immature grains result in chalky milled rices. Delayed threshing and drying ofharvested panicles may cause rotting or stack burning due to microbial respiration inthe wet straw surrounding the panicles; this contributes to grain discoloration.Discolored or yellow grains reflect poor handling and have slightly lower proteinvalue than white grains (Eggum et al 1984). Sprouting or germination occurs onlyoccasionally, since most tropical varieties have some degree of dormancy.Degree of milling also affects milled rice whiteness. Chalkiness, such as whitecore, also may be induced by environmental factors such as high night temperature(Ebata and Nagato 1967).Market qualityConsumers buy milled rice on the basis of physical appearance and varietydesignation made by retailers. Consumer demand models used to assess marketquality are discussed in the section on economic aspects. A consumer demand studyhas an advantage over consumer preference tests (Del Mundo and Juliano 1981),since it relates preference in terms of price differentials. The assumption is that pricedifferences are mainly due to quality.Potential sources of improvement in market quality are variety, preharvestmanagement, postharvest handling, and processing/ milling. Chalky portions in thenonwaxy grain contribute to grain breakage during milling. However, waxy riceswith opaque endosperm have high head rice yields (Khush and Juliano 1985).Evidently, uniformly chalky nonwaxy endosperm also has high head rice yield,suggesting that heterogeneity of endosperm translucency or chalkiness contributesto grain stress and breakage during milling (Srinivas and Bhashyam 1985).Stable high head rice yields are screened by subjecting harvested grain tomoisture adsorption stress (IRRI 1986, 1987). In Muda Agricultural DevelopmentAuthority, Malaysia, in 1985, IR42 had extremely poor head rice yields (38%) whenharvested late. IR42 gives excellent head rice yields when harvested at optimummaturity, but readily fissures when overdried or subjected to moisture adsorptionstress (IRRI 1986, 1987). IR20 is susceptible to fissuring (Srinivas and Bhashyam1985).We have developed methods to stress grain, by overdrying with an infraredlamp or a mechanical convection oven at 45-48 °C, but sensitivity is variable. We areadapting the use of shadedried grains at 14% moisture soaked in water (Srinivas andBhashyam 1985). All rough rices resist cracking at 18% moisture, but only resistantvarieties tolerate soaking in water for 3 h at 14% moisture. Hopefully, more

278 Juliano and Gonzalesreproducible results will be obtained by this method than by drying to below 12%moisture, when all rices are susceptible to cracking.Cooking and eating qualityCooking properties of importance include water absorption, volume expansion,dissolved solids in cooking water, cooking time, grain elongation, and aroma.Aroma was shown to be mainly due to 2-acetyl-1-pyrroline (Buttery et al 1983).Screening by gas chromatography allows only two analyses daily (Buttery et al1986). Water absorption and volume expansion at 100 °C are correlated positivelywith amylose content, but are affected by GT at 77-82 °C. Dissolved solids also arecorrelated negatively with amylose content.Cooking time, the period required for the grain core to be gelatinized (absenceof opaque center) in boiling water, is affected directly by GT and protein content(Juliano et al 1965, Juliano and Perez 1986). Grain elongation of presoaked milledrice (Juliano and Perez 1984) seems greater with intermediate-amylose, low-GT, andmedium gel-consistency samples, but not all samples with this combination of starchproperties are good elongators (Juliano 1979b). Basmati and Sadri rices and D254(Nga Kywee) from Burma possess this extreme elongation property. Although thebest quality Basmati rices traditionally have been grown in Punjab, Thailand is nowgrowing Basmati rices for export.Volume expansion and water absorption during cooking are correlatedpositively with amylose content (Juliano et al 1965), and are measured in somebreeding programs (Juliano 1982). Degree of cooking affects these properties.Cooking method can be the excess-water method, wherein cooking is terminatedwhen the grain core is gelatinized, or the optimum-water method, wherein milledrice is cooked to dryness in the amount it will absorb to obtain a soft texture (Julianoand Perez 1983). Water content is about 73% wet basis for all samples in theexcess-water method; it is lower in the optimum-water method (55-67%). Watercontent of cooked rice is correlated directly with amylose content, particularly in theoptimum-water method. Hot water-soluble solids are correlated negatively withamylose content and are lowest for high-amylose rices with hard gel consistency(Maniñgat and Juliano 1978).Cooked rice texture, particularly with the optimum-water method, is correlatedwith amylose content. Stickiness, gloss, softness, and color of cooked rice arecorrelated negatively with amylose content, even with the water-rice ratio adjusted(Juliano et al 1965, 1972) (Table 2). Instrument methods for measuring cooked ricetexture are significantly correlated with sensory evaluation and are morereproducible (Juliano et al 1981a, 1984).We measure cooked rice hardness using a 10-cm 2 Ottawa Texture MeasuringSystem cell in an Instron Model 1140 unit; the value is affected not only by amylosecontent, but also by gel consistency and protein content. Rice (15 g) is cooked for 20min in a double boiler with 19.5-31.5 ml water, depending on amylose content (Perezand Juliano 1979, Perez et a 1979). We no longer routinely measure cooked ricestickiness because it is correlated mainly (and negatively) with amylose content. Weare now trying to develop methods that discriminate among rices with similaramylose content and starch GT.

Rice grain quality 279Table 2. Properties of raw and cooked low-amylose and high-amylose pairs fromthree crosses, using identical and adjusted water-rice ratio (Juliano et al 1972).PropertyIdentical water-rice Adjusted water-riceratioratioLow High Low Highamylose amylose amylose amyloseAmylose (% dry basis) 14.2 25.3 14.2 25.3Crude protein (% wet basis) 10.4 10.4 10.410.4Final GT (°C) 62 61 62 61Water-rice ratio for cooking 1.8 1.8 1.6 1.8Taste panel scores a for cooked riceTenderness 7.6 4.0 6.7 4.1Cohesiveness 7.1 3.4 6.6 3.5Color 2.7 1.6 1.7 1.6Gloss 8.3 4.4 6.9 4.2a Meen of duplicate assessment by a taste panel of four judges. Numerical scores of1 to 9 assigned: “1” = least expression of the property in question; “9” = highestexpression, All differences significant except for color.Amylose content is the most important index of eating quality. However,within each amylose type, soft to medium gel consistency is preferred over hard gelconsistency, particularly among high-amylose samples, because of the preference forsoft cooked rice texture (Perez and Juliano 1979). For intermediate- and highamylosesamples, intermediate GT seems to be related to softer texture, such as inC4-63G vs BPI 121-407 and their derived IR varieties IR64 vs IR48, and inhigh-amylose IR5 vs IR8, IR32, IR36, IR62, and IR66 vs IR42 and IR58.Differences in texture seem to be related to varietal differences in the amylopectinfraction (Takeda et al 1987) rather than the amylose fraction (Takeda et al 1986).Among waxy rices, low-GT rices gave better rice products than high-GT rices(Perdon and Juliano 1975, Perezet al 1979). The objective of the IRRI program fornonwaxy rice is for long translucent grain, intermediate amylose, and intermediateGT with soft gel consistency (Khush and Juliano 1985).Aging and parboilingAging or storing rough rice for 3-4 mo after harvest also affects grain quality. Highertotal and head rice yields are obtained from aged rice (Perez and Juliano 1981,1982;Villareal et al 1976). In addition, aged milled rice has higher volume expansion andwater absorption and less dissolved solids on cooking, and the cooked grain is moreflaky (Villareal et al 1976). Aroma, however, decreases during storage in opencontainers. Thus, aged rices are preferred in testing for milling and cookingproperties. Aged rice is preferred over freshly harvested rice by consumers in tropicalAsia, but disliked in countries where japonica rice is consumed.Parboiling is practiced in India, Pakistan, Bangladesh, and Sri Lanka toaccelerate aging and to improve milling recovery. It consists of steeping rough rice inwater, steaming to fully gelatinized endosperm starch, followed by sun-drying(Bhattacharya 1985, Raghavendra Rao and Juliano 1970). The rate of steaming orparboiling is affected by the GT of the starch (Biswas 1987). Tests for parboiled rice

280 Juliano and Gonzalesquality are usually performed on laboratory parboiled rice samples. Rice scientistsbelieve that raw rice quality can predict parboiled rice quality (IRRI 1979). Studieson rices differing widely in amylose content and GT suggest that raw rice quality,particularly amylose content, predicts parboiled rice equilibrium water content andcooked rice Instron hardness and stickiness (Biswas 1987).Processed rice productsSpecific variety types are preferred for each processed rice product. Processingprobably magnifies small textural differences not apparent in boiled rice. We havebeen studying processed rice products to better understand indexes of grain quality(Juliano 1986). Products studied include rice noodles, rice wines, waxy riceproducts, breads, cakes, and extruded and puffed rices.Nutritional qualityRice protein. Milled rice has about 7% protein. It is the principal source of dietaryenergy (50%) and protein (35-40%) in tropical Asia (FAO 1984). For example,milled rice contributed 56% of the energy, 43% of the protein, 10% of the fat, 67% ofthe carbohydrate, 30% of the iron, 19% of the calcium, 45% of the thiamine, 29% ofthe riboflavin, and 49% of the niacin in the daily Filipino diet in 1982 (FNRI 1984).Thus, Asian diets are more deficient in energy than in protein. The energy content ofrice may be improved through increased fat content, but that may adversely affectthe keeping quality of milled rice through greater fat hydrolytic and oxidativerancidity.Nutritional value may be increased by improving the essential amino acidpattern or the protein content. Lysine is the first limiting essential amino acid in riceprotein, as it is in other cereal proteins. High lysine mutants which are at least 1%higher than the 4% lysine in milled rice protein have not been confirmed (Juliano1985a). Besides, rice-based diets are not limiting in lysine content, due to the nonriceprotein sources which are rich in lysine. A cooked rice-legume diet had a betteramino acid score (Juliano et al 1987) and net protein utilization (NPU) than cookedrice alone in growing rats (Eggum et al 1987).Protein content has poor heritability and is significantly affected byenvironmental factors such as season, spacing, N fertilizer level, and growthduration. Efforts at IRRI to improve protein content have not been successful(Khush and Juliano 1984). Yield and protein content tend to be negativelycorrelated. Growth duration and brown rice protein consistently are negativelycorrelated in the IRRI replicated yield trials (Juliano 1985b). This trend is beinginvestigated in farmers’ fields. All promising selections at IRRI are routinelyscreened for protein content to ensure that nutritional value is maintained.Protein content indexes the nutritional value of milled rice (Eggum and Juliano1973, Hegsted and Juliano 1974). Brown rice protein of advanced lines is monitoredin the breeding program because of the high correlation of brown rice and milled riceprotein content (Juliano et al 1973). The difficulty is in obtaining uniform milling insmall samples. Very little endosperm fraction is removed during 10%-by-weightbran removal in friction and abrasive laboratory mills (Ellis et al 1986).

Rice grain quality 281High-protein rice. Increased protein content is nutritionally available, as isshown by the increase in lysine content of milled rice (Juliano et al 1973), by animalfeeding trials (Bressani et al 1971; Eggum and Juliano 1973, 1975; Hegsted andJuliano 1974; Murata et al 1978), and in nitrogen balance studies with preschoolchildren (MacLean et al 1978, Roxas et al 1979). Replacement of average-proteinrice by high-protein rice also improved the nitrogen balance of adults on a rice diet(Clark et al 1971). Replacement of average-protein rice by high-protein rice inchildren's diets improved the nitrogen balance of rice-fish and rice-mungbean diets(Roxas et al 1975, 1976), in long-term trials on the South Indian diet (Pereira et al1981), and in a rice-based diet (Roxas et al 1980). High-protein rice improvesgrowth, provided that other nutritional factors, such as zinc, do not become limiting(Pereira et al 1981, Roxas et al 1980).Processing effects. Compared with milled rice, brown rice has higher protein,minerals and vitamins, and lysine content in its protein (Eggum et al 1982,Resurreccion et al 1979). However, it also has higher phytin, antinutrition factors,and neutral detergent fiber (Table 3). Balance studies in rats showed slightly lowertrue digestibility (TD) of brown rice protein, but similar biological value (BV) andNPU in brown rice and milled rices (Table 3). Digestibility energy is slightly lower inbrown rice. Similar results were obtained with preschool children fed rice-casein orrice-milk (2:1 N ratio) diets (Santiago et al 1984) (Table 3). However, purplepericarpedPerurutong had lower NPU in rats than nonpigmented and redpericarpedH4 brown rices because of the extremely reduced TD (Eggum et al 1981).Table 3. Composition and nutritional value of milling fractions of IR32 brownrice at 14% moisture (Eggurn et al 1982, Santiago et al 1984).Property aBrown riceUndermilledriceMilled riceCrude protein (% N × 6.25)Neutral detergent fiber (%)Crude fat (%)Crude ash (%)Total P (%)Energy value (kJ/g)Lysine (g/16 g N)Balance date in five growing rats bDigestible energy (% of total)True digestibility (% of N intake)Biological value (% of digested N)Net protein utilization (% of N intake)Balance data in five preschool children cApparent N absorbed (% of intake)Apparent N retained (% of Intake)Apparent energy absorbed (% of intake)Apparent fat absorbed (% of intake)8.5 a2.5 82.3 a0.8 a0.14 a15.9 a3.8 a94.3 b96.9 b68.9 ab66.7 a63 a28 a90 b93 b8.3 b1.8 b1.5 b0.6 ab0.14 a15.7 a3.6 b95.5 ab97.3 ab69.7 a67.8 a63 a26 a90 b96 ab8.1 c0.8 c0.7 c0.4 b0.08 b15.5 a3.6 b96.6 a98.4 a67.5 b66.4 a62 a27 a93 a98 aa In a row, means followed by a common letter are not significantly different atthe 5% level by Duncan’s (1955) multiple range test. b Data from Eggum et al(1982). c Data from Santiago et al (1984). Intake of 200 mg N/kg body wt daily.First rice-casein diet (2:1 N ratio) had 77%b mean N absorbed, 33%a N absorbed,91% ab energy absorbed, and 94%b fat absorbed.

282 Juliano and GonzalesHeat processing treatments can affect protein properties. Boiling and parboilingreduce TD but increase BV correspondingly, without any adverse effect on NPU(Eggum et al 1977, 1984). Roasting also decomposes amino acids such as lysine(Chopra and Hira 1986). Extrusion cooking lowers lysine and cysteine levels andreduces NPU of milled rice protein (Eggum et al 1986). Gun puffing decreases thecysteine content of rice protein (IRRI 1987), and subsequent toasting decreaseslysine content (Chopra and Hira 1986).Vitamins and minerals. Vitamin A deficiency (xerophthalmia) is an importantnutritional problem in tropical Asia, despite the abundance of green leafy vegetables(Chong 1979). Some researchers are looking into the feasibility of improving thecarotene (provitamin A) content of rice grain. The distribution of vitamin A in thesenew rices needs to be established. Because it is a fat-soluble vitamin, it may belocalized in the bran layer. A yellow rice also may not be acceptable to consumers.The vitamin B 1 (thiamine) and B 2 (riboflavin) contents of IR varieties are beingscreened to determine their range and variation with season.Mineral content of milled rice is influenced by the soil on which the rice cropwas grown.Economic aspects of grain qualityThe focus here is on the relationship between price and grain quality characteristicsand the international demand for rice as it relates to quality. The linkage betweenprice and quality characteristics of goods generally falls within the domain ofconsumer demand theory. The theory begins with the premise that, given personaltastes and preferences, a limited budget, and the utility or satisfaction that acommodity offers, the rational consumer maximizes the utility obtainable from thegood, subject to personal budget constraints. This theory is well expounded in basiceconomic texts, including the operational procedure of using the Lagrangeanmultiplier to maximize utility subject to budget constraint.Several types of economic models empirically estimate the consumer demandfunction. The basic economic relationships of a consumer demand function can beexpressed aswhere: Q di = quantity demanded of commodity i,P i = price of commodity i,P j = price of commodity j substitutable or complementary to commodity i,I = income, andT = taste or preference of the consumer.Hedonic demand modelsA variant of the consumer demand model relative to characteristics of the good is theHedonic demand model. This type of economic model is extensively discussed inDhrymes (1967), Cowling and Rayner (1970), Rosen (1974), Lucas (1979), Ladd andMartin (1976), and Ladd and Suvannunt (1976). The Hedonic, or the implicit pricedemand model, hypothesizes that the consumer demand function for goods is

Rice grain quality 283affected by the characteristics of the goods. The Hedonic model was used by Laddand Martin (1976) to estimate input demand characteristics, Dhrymes (1967) toexplain the quality demand for the automobile industry, and Ladd and Suvannunt(1976) to analyze the implicit prices of the nutritional elements in 31 food items.Petzel and Monke (1979) and, more recently, Unnevehr et al (1985a,b) andUnnevehr (1986) used the Hedonic model to analyze the demand for grain qualitycharacteristics.In their study of the linkages between price and quality characteristics of theThai-U.S. rice markets, Petzel and Monke (1979) found consistent premiums forcertain rice characteristics between 1967-72 and 1973-78. That study, which focusedon characteristics such as grain length, percent brokens, and raw vs parboiled rice,also showed that parboiled rice prices failed to maintain a consistent relationship toprices of indica varieties. The implicit price model used by Petzel and Monke (1979)wasP = f (X 1 , X 2 , X 3 , X 4 )where: P = price of rice,X 1 = country of origin (1 if U.S., and 0 if Thailand),X 2 = grain length (1 if long, and 0 if medium),X 3 = percent brokens (1 if less than 5% brokens, 0 if greater than 5%brokens), andX 4 = raw or parboiled (1 if raw, and 0 if parboiled).A recent study by Unnevehr et al (1985b) extended the model developed byLadd and Suvannunt (1976) to look at the implicit values that consumers in threeSoutheast Asian countries are willing to pay for rice grain quality. Since the utility ofa good can be viewed as the sum of the utility obtained from its differentcharacteristics, Unnevehr et al (1985b) estimated the implicit price of rice grainquality using the following economic model [for a complete mathematicalderivation of the consumer demand model used by Unnevehr et al (1985b), see Laddand Suvannunt (1976)]:mP R = X Rj P Rjj = 1where: P R = market price of rice,X Rj = quantity of characteristic j per unit of rice, andP Rj = implicit value of characteristic j.If the characteristics that define grain quality can be quantified, then theimplicit value of these characteristics can be statistically estimated by adding therandom error term U to the economic model. The market price of rice will vary,given the different quality characteristics of rice. The independent variables XRJshould explain variance in rice price. The parameter estimates in the statistical modelalso will provide the implicit values of grain characteristics.In the Unnevehr et al (1985b) study, the implicit price of eight characteristics ofgrain quality (whiteness, brokens, shape, chalkiness, amylose, gel consistency, alkali

284 Juliano and Gonzalesspreading value, and aroma) were measured. The results indicate that consumers inThailand, Indonesia, and the Philippines prefer milling quality (fewer brokens) andaroma (Table 4). Preferences for shape and chemical properties varied, butconsumers generally preferred intermediate amylose.The results of the Unnevehr et al (1985b) study incorporating some physicochemicalcharacteristics of rice grain quality are very revealing. But do these resultsreflect world rice demand for grain quality? Before answering this question, oneshould take at least a cursory look at the world rice market.World rice market and grain qualityThe world rice market is very thin and unreliable (Siamwalla and Haykin 1983). Incontrast to the 22% of total wheat production and 17% of maize production that areinternationally traded, only 4% of total world rice production is internationallytraded. In addition, rice is not just rice; varietal differences are notable.Six basic types of rice are traded in the world market, with quality varyingmarkedly within each basic type (Efferson 1985). The six types are 1) predominantlyindica, high-quality, long-grain, raw milled rice; 2) predominantly indica, mediumquality,long-grain, raw milled rice; 3) japonica short- or medium-grain, raw milledrice; 4) parboiled rice with any grain length; and two specialty types: 5) aromatic(fragrant) rice and 6) glutinous (waxy) rice. Consumer quality preferences varywidely, from country to country and even within a country.The structure of world trade in rice also shows that the world rice market isdistinguished by different qualities within the broad headings of grain length (e.g.,long, medium, and short) and percent brokens (Table 5). Differences in qualitiesgenerally relate to moisture content, degree of chalkiness, percentage of red rice, pestinfestation, degree of milling, and the proportion of brokens to head rice. In theinternational rice market, proportion of brokens is used as the general criterion todistinguish between qualities (FAO 1987).International rice quality price differentials also are reflected in grain length andpercent brokens (Table 6). The price differentials are higher for high-quality, longgrainrice (e.g., USA No. 2 4% vs Thai 100% 2nd grade) than for medium-grain rice.An increasing trend in price differentials in high-quality rice traded in Europe (andto some extent parboiled rice vs raw rice) is also observed. This quality priceTable 4. Implicit prices of grain quality characteristics (USc/kg per unit of change)(Unnevehr et al 1985b).Milled rice characteristic Thailand Indonesia PhilippinesWhiteness (%) 0.30*Brokens (%) 0.15*Chalkiness score –0.15Shape (length-width ratio) 2.47*Amylose (%) -0.02Gel consistency (mm) 0.02Alkali spreading value -0.04Aroma 5.89**Significant at 10% level or better.1.14*-0.18*0.00-4.68*0.140.051.92*9.07*0.34*-0.12*–0.38*2.85*-1.12*-0.011.94*–

Rice grain quality 285Table 5. Structure of world trade in rice selected years (FAO 1987).Grain classificationTotal rice export shipments (million tons)1975-77 1979-81 1983-85Grain lengthLong grain (>6 mm)(%)Medium/short grain (

Item 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985Table 6. Price differentials in selected major types of rice (US$/ton) (FAO 1987).Long grainHigh qualityUSA No. 2 4% a 358 434 529 531 593 634 480 512 514 487Thai 100% 2nd grade a – 320 340 439 402 514 623 363 341 311 245Price difference (USA-Thai) – 38 94 90 129 79 11 117 171 203 242Low qualityBurma Emata 30-35% b 200 185 216 ... ... 335 325 246 193 200 174Pakistan IRRl 40-45% b 175 180 205 245 248 316 328 227 198 208 172Price difference (Burma-Pakistan) 25 5 11 – – 19 -3 19 -5 -8 2China long shaped 30-35% b 360 ... 222 366 240 332 337 ... ... 216 172High and low qualityThai 100% 2nd grade b380 269 286 382 354 449 489 300 290 262 227Thai AI super b 244 177 183 224 198 252 250 198 194 212 172Price difference (Thai 100% - Thai AI) 136 92 103 158 156 197 239 102 96 50 55Parboiled and milled white riceParboiled c 365 277 303 405 394 475 528 404 373 361 323White rice d 413 302 301 404 387 442 495 327 326 306 272Price difference (parboiled whige rice) -48 -25 2 1 7 33 33 77 47 55 51Medium grainUSA e 385 242 274 297 292 348 448 364 355 333 328Australia b 324 299 262 331 329 372 498 388 440 382 299Price difference (USA-Australia) 61 –57 12 –34 –37 –24 –50 –24 –85 –49 29a Refers to C&F prices in Rotterdam.b Refers to F.O.B. prices. cWeighted average prices of parboiled rice from Thailand and the United Statesd Weighted average prices of comparable grades of Thai and United States white rice. e Refers to F. A. S. prices.

Rice grain quality 287Table 7. Selected physicochemical properties of high- end medium-quality ricer,by source country (Khush and Juliano 1985).CountryAmylose content a(% dry basis)Final gelatinizationtemperature a (°C)Gelconsistency a(mm)Long-grain ricePakistan (Basmati) Intermediate Low - Intermediate MediumThailand Intermediate - High Low - Intermediate Hard - SoftU. S. Intermediate Intermediate SoftAustralia Low - Intermediate Intermediate SoftMedium-grain riceU. S. Low Low SoftAustralia Low Low Softa See Table 1 for clarification IeveIs.determinant of domestic and international demand for grain quality. This isfollowed by physicochemical characteristics which, although not visually observable,are implied by the choice of variety made by customers in domestic trade and by thechoice of country that exports the quality grain made by importers in internationaltrade. Nutritional content appears to be the last consideration in domestic andinternational demand for quality.This hypothesis needs to be tested by measuring the actual magnitude andsignificance of the structural relationship between international market price and thephysicochemical-nutritional characteristics of rice. The world market for rice couldbe subdivided into several market types (Efferson 1985), each with distinctdifferences as to consumer preferences. Research along these lines is beingundertaken by IRRI (Duff 1987a,b; Wedgewood et al 1987).References citedAndrianilana F, Rasolo F, Rakotonjanahary R, Flinn J C, Shahi B B, Perez C M (1987) Rice quality andprices in Madagascar. National Center for Applied Research in Rural Development, Ministry ofAgriculture and Rural Development, Madagascar, and International Rice Research Institute, P.O.Box 933, Manila, Philippines.Bechtel D B, Juliano B O (1980) Formation of protein bodies in the starchy endosperm of rice (Oryzasativa L.): a reinvestigation. Ann. Bot. 45:503-509.Bhattacharya K R (1985) Parboiling of rice. Pages 289-348 in Rice: chemistry and technology. 2d ed. B.O. Juliano, ed. American Association of Cereal Chemists, St. Paul, Minnesota.Bhattacharya K R (1989) Screening for quality of parboiled rice. Page 291 in Progress in irrigated riceresearch. International Rice Research Institute, P.O. Box 933, Manila, Philippines. (abstr.)Biswas S K (1987) Effect of starch properties on parboiling process and some physicochemical propertiesof parboiled rice. MS thesis, University of the Philippines, Los Baños, Laguna, Philippines.Bressani R, Elias L G, Juliano B O (1971) Evaluation of the protein quality of milled rices differing inprotein content. J. Agric. Food Chem. 19:1028-1034.Buttery R G, Ling L C, Juliano B O, Turnbaugh J G (1983) Cooked rice aroma and 2-acetyl-1-pyrroline.J. Agric. Food Chem. 31:823-826.Buttery R G, Ling L C, Mon T R (1986) Quantitative analysis of 2-acetyl-1-pyrroline in rice. J. Agric.Food Chem. 34:112-114.Cagampang G B, Perez C M, Juliano B O (1973) A gel consistency test for eating quality of rice. J. Sci.Food Agric. 24:1589-1594.

288 Juliano and GonzalesChong Y H (1979) Malnutrition, food patterns, and nutritional requirements in Southeast Asia. Pages1-17 in Proceedings of a 1977 workshop on the interfaces between agriculture, nutrition, and foodscience. The United Nations University, Tokyo, and International Rice Research Institute, P.O. Box933, Manila, Philippines.Chopra N, Hira C K (1986) Effect of roasting on protein quality of cereals. J. Food Sci. Technol.23:233-235.Clark H E, Howe J M, Lee C J (1971) Nitrogen retention of adult human subjects fed a high protein rice.Am. J. Clin. Nutr. 24:324-328.Cowling K, Rayner A J (1970) Price, quality, and market share. J. Political Econ. 78:1292-1309.del Mundo A M, Juliano B O (1981) Consumer preference and properties of raw and cooked rice. J.Texture Stud. 12:107-120.Dhrymes P J (1967) On the measurement of price and quality changes in some consumer capital goods.Am. Econ. Rev. 57(2):501-521.Duff B (1987a) Assessing grain quality characteristics in domestic rice markets, a proposal. InternationalRice Research Institute, Los Baños, Laguna. International Development Research Centre Project3-P-87-00001. National Grain Quality Economics (Asia).Duff B (1987b) Assessing grain quality characteristics in international rice markets, a proposal.International Rice Research Institute, Los Baños, Laguna. International Development ResearchCentre Project 3-P-86-0340. National Grain Quality Economics (Asia).Ebata M, Nagato K (1967) Ripening conditions and grain characteristics. Int. Rice Comm. Newsl.(special issue):10-17.Efferson J N (1985) Rice quality in world markets. Pages 1-13 in Rice grain quality and marketing.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Eggum B O, Alabata E P, Juliano B O (1981) Protein utilization of pigmented and nonpigmented brownand milled rices by rats. Qual. Plant. Plant Food Hum. Nutr. 31:175-179.Eggum B O, Juliano B O (1973) Nitrogen balance in rats fed rices differing in protein content. J. Sci. FoodAgric. 24:921-927.Eggum B O, Juliano B O (1975) Higher protein content from nitrogen fertilizer application and nutritivevalue of milled-rice protein. J. Sci. Food Agric. 26:425-427.Eggum B O, Resurreccion A P, Juliano B O (1977) Effect of cooking on nutritional value of milled rice inrats. Nutr. Rep. Int. 16:649-655.Eggum B O, Juliano B O, Ibabao M G B, Perez C M (1986) Effect of extrusion cooking on nutritionalvalue of rice flour. Food Chem. 19:235-240.Eggum B O, Juliano B O, Ibabao M G B, Perez C M, Carangal V R (1987) Protein and energy utilizationof boiled rice-legume diets and boiled cereals in growing rats. Qual. Plant. Plant Foods Hum. Nutr.37(3):237-244.Eggum B O, Juliano B O, Maniñgat C C (1982) Protein and energy utilization of rice milling fractions byrats. Qual. Plant. Plant Foods Hum. Nutr. 31:371-376.Eggum B O, Juliano B O, Viareal C P, Perez C M (1984) Effect of treatment on composition and proteinand energy utilization of rice and mungbean by rats. Qual. Plant. Plant Foods Hum. Nutr.34:261-272Ellis J R. Viareal C P. Juliano B O (1986) Protein content. distribution and retention during milling ofbrown rice. Qual. Plant. Plant Foods Hum. Nutr. 36:17-26.FAO—Food and Agriculture Organization of the United Nations (1984) Data bank. FAO, Rome. [Citedin Technical Advisory Committee, 1986 Review of CGIAR Priorities and Future Strategies, editedversion. Consultative Group on International Agricultural Research. Washington, D.C.]FAO—Food and Agriculture Organization of the United Nations (1987) Rice export prices: majordevelopment and issues. Committee on Commodity Problems Intergovernment Group on RiceDocument CCP:RI 87/2. Rome. 19 p.FNRI—Food and Nutrition Research Institute (1984) Second nationwide nutrition survey Philippines.1982. National Science and Technology Authority, Manila. 228 p.Harris N, Juliano B O (1977) Ultrastructure of endosperm protein bodies in developing rice grainsdiffering in protein content. Ann. Bot. 41:l-5.Hegsted D M, Juliano B O (1974) Difficulties in assessing the nutritional quality of rice protein. J. Nutr.104:772-781.IRRI—International Rice Research Institute (1979) Proceedings of the workshop on chemical aspects ofrice grain quality. P.O. Box 933, Manila, Philippines. 390 p.IRRI—International Rice Research Institute (1986) Annual report for 1985. P.O. Box 933, Manila,Philippines. p. 23.IRRI—International Rice Research Institute (1987) Annual report for 1986. P.O. Box 933, Manila,Philippines.Juliano B O (1971) A simplified assay for milled-rice amylose. Cereal Sci. Today 16:334-338, 340, 360.

Rice grain quality 289Juliano B O (1979a) Amylose content in rice - a review. Pages 251-260 in Proceedings of the workshop inchemical aspects of rice grain quality. International Rice Research Institute, P.O. Box 933, Manila,Philippines.Juliano B O (1979b) The chemical basis of rice grain quality. Pages 69-90 in Proceedings of the workshopon chemical aspects of rice grain quality. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Juliano B O (1982) An international survey of methods used for evaluation of cooking and eating qualitiesof milled rice. IRRI Res. Pap. Ser. 77.Juliano B O (1985a) Factors affecting nutritional properties of rice protein. Trans. Natl. Acad. Sci.Technol. (Philipp.) 7:205-216.Juliano B O (1985b) Rice: chemistry and technology. 2d ed. American Association of Cereal Chemists,St. Paul, Minnesota. 774 p.Juliano B O (1986) Rice properties and processing. Food Rev. Int. 1:423-445.Juliano B O, Antonio A A, Esmama B V (1973) Effects of protein content on the distribution andproperties of rice protein. J. Sci. Food Agric. 24:295-306.Juliano B O, Blakeney A B, Butta I, Castillo D T, Choudhury N H, Iwasaki T, Shibuya N, Kongseree N,Lapis ET, Murty V V S, Paule C M, Perez C M, Webb B D (1982) International cooperative testingon the alkali digestibility values for milled rice. Starch 34:21-26.Juliano B O, Ibabao M G B, Perez C M, Carangal V R (1987) Nutritional properties of nonrice crops inthe Asian Rice Farming Systems Network. Qual. Plant. Plant Foods Hum. Nutr. 36:273-278.Juliano B O, Oñate L U, del Mundo A M (1965) Relation of starch composition, protein content, andgelatinization temperature to cooking and eating qualities of milled rice. Food Technol.19:1006-1011.Juliano B O, Oñate L U, del Mundo A M (1972) Note: Amylose and protein contents of milled rice aseating quality factors. Philipp. Agric. 56:44-47.Juliano B O, Perdon A A (1975) Gel and molecular properties of nonwaxy rice starch. Starch 27:115-120.Juliano B O, Perez C M (1983) Major factors affecting cooked milled rice hardness and cooking time. J.Texture Stud. 14:235-243.Juliano B O, Perez C M (1984) Results of a collaborative test on the measurement of grain elongation ofmilled rice during cooking. J. Cereal Sci. 2:281-292.Juliano B O, Perez C M (1986) Kinetic studies on cooking of tropical milled rice. Food Chem. 20:97-105.Juliano B O, Perez C M, Alyoshin E P, Romanov V B, Blakeney A B, Welsh L A, Choudhury N H,Delgado L L, Iwasaki T, Shibuya N, Mossman A P, Siwi B, Damardjati D S, Suzuki H, Kimura H(1984) International cooperative test on texture of cooked rice. J. Texture Stud. 15:357-376.Juliano B O, Perez C M, Barber S, Blakeney A B, Iwasaki T, Shibuya N, Keneaster K K, Chung S,Laignelet B, Launay B, del Mundo A M, Suzuki H, Shiki J, Tsuji S, Tokoyama J, Tatsumi K, WebbB D (1981a) International cooperative comparison of instrument methods for cooked rice texture. J.Texture Stud. 12:17-38.Juliano B O, Perez C M, Blakeney A B, Breckenridge C, Castillo D T, Choudhury N H, Kongseree N,Laignelet B, Merca F E, Paule C M, Webb B D (1980) Report of the international cooperativetesting on the gel consistency of milled rice. Riso 29:233-237.Juliano B O, Perez C M, Blakeney A B, Castillo D T, Kongseree N, Laignelet B, Lapis E T, Murty V V S,Paule C M, Webb B D (1981b) International cooperative testing on the amylose content of milledrice. Starch 33:157-162.Khush G S, Juliano B O (1984) Rice varietal improvement for protein content at the International RiceResearch Institute. Pages 199-202 in Cereal grain protein improvement. International AtomicEnergy Agency, Vienna.Khush G S, Juliano B O (1985) Breeding for high-yielding rices of excellent cooking and eating qualities.Pages 61-69 in Rice grain quality and marketing. International Rice Research Institute, P.O. Box933, Manila, Philippines.Khush G S, Paule C M, de la Cruz N M (1979) Rice grain quality evaluation and improvement at IRRI.Pages 21-31 in Proceedings of the workshop on chemical aspects of rice grain quality. InternationalRice Research Institute, P.O. Box 933, Manila, Philippines.Ladd E W, Martin M B (1976) Price and demand for input characteristics. Am. J. Agric. Econ. 58:21-30.Ladd E W, Suvannunt V (1976) A model of consumer demand for goods characteristics. Am. J. Agric.Econ. 58:504-510.Little R R, Hilder G B, Dawson E H (1958) Differential effect of dilute alkali on 25 varieties of milledwhite rice. Cereal Chem. 35:111-126.Lucas E B (1975) Hedonic price functions. Econ. Inquiry 8:157-175.MacLcan W C Jr., Klein G L, Lopez de Romaña G, Massa E, Graham G G (1978) Protein quality ofconventional and high-protein rice and digestibility of glutinous and non-glutinous rice by preschoolchildren. J. Nutr. 103:1740-1747.

290 Juliano and GonzalesManiñgat C C, Juliano B O (1978) Alkali digestibility pattern, apparent solubility and gel consistency ofmilled rice. Starch 30:125-127.Murata K, Kitagawa T, Juliano B O (1978) Protein quality of a high protein rice in rats. Agric. Biol.Chem. 42:565-570.Perdon A A, Juliano B O (1975) Gel and molecular properties of waxy rice starch. Starch 27:69-71.Pereira S M, Begum A, Juliano B O (1981) Effect of high protein rice on nitrogen retention and growth ofpreschool children on rice-based diets. Qual. Plant. Plant Foods Hum. Nutr. 31:97-108.Perez C M, Juliano B O (1978) Modifcation of the simplified amylose test for milled rice. Starch30:424-426.Perez C M, Juliano B O (1979) Indicators of eating quality for non-waxy rices. Food Chem. 4:185-195.Perez C M, Juliano B O (1981) Texture changes and storage of rice. J. Texture Stud. 12:321-333.Perez C M, Juliano B O (1982) Physicochemical changes of the rice grain in storage: a brief review. Pages180-190 in Paddy deterioration in the humid tropics. German Agency for Technical Cooperation(GTZ), Eschborn, Germany.Perez C M, Pascual C G, Juliano B O (1979) Eating quality indicators for waxy rices. Food Chem.4:179-184.Petzel T E, Monke E A (1979) The integration of international rice market. Food Res. Inst. Stud.17:307-326.Raghavendra Rao S N, Juliano B O (19701 Effect of parboiling on some physicochemical properties ofrice. J. Agric. Food Chem. 18:289-294.Resurreccion A P, Juliano B O, Tanaka Y (1979) Nutrient content and distribution in milling fractions ofrice grain. J. Sci. Food Agric. 30:475-481.Reyes A C, Albano E L, Briones V P, Juliano B O (1965) Varietal differences in physicochemicalproperties of rice starch and its fractions. J. Agric. Food Chem. 13:438-442.Rosen S (1974) Hedonic prices and implicit markets: product differentiation in pure competition, J.Political Econ. 83:34-55.Roxas B V, Intengan C Ll, Juliano B O (1975) Protein content of milled rice and nitrogen retention ofpreschool children fed rice-mung bean diets. Nutr. Rep. Int. 14:203-207.Roxas B V, Intengan C Ll, Juliano B O (1979) Protein quality of high-protein and low-protein milled ricesin preschool children. J. Nutr. 109:832-839.Roxas B V, Intengan C Ll, Juliano B O (1980) Effect of zinc supplementation and high-protein rice on thegrowth of preschool children on a rice-based diet. Qual. Plant. Plant Foods Hum. Nutr. 30:213-222.Santiago M I C, Roxas B V, Intengan C L1, Juliano B O (1984) Protein and energy utilization of brown,undermilled and milled rices by preschool children. Qual. Plant. Plant Foods Hum. Nutr. 34:15-25.Siamwalla A, Haykin S (1983) The world rice market: structure and performance. Int. Food Policy Res.Inst. Res. Rep. 39. Washington, D.C. 79 p.Srinivas T, Bhashyam M K (1985) Effect of variety and environment on milling quality of rice. Pages49-59 in Rice grain quality and marketing. International Rice Research Institute, P.O. Box 933,Manila, Philippines.Takeda Y, Hizuruki S, Juliano B O (1986) Purification and structure of amylose from rice starch.Carbohyd. Res. 148:399-308.Takeda Y, Hizuruki S, Juliano B O (1987) Structures of rice amylopectins with low and high iodineaffinities. Carbohyd. Res. 168:79-88.Unnevehr L J (1986) Consumer demand for grain quality and returns to research for quality improvementin Southeast Asia Am. J. Agric. Econ. 68:635-641.Unnevehr L J, Juliano B O, Perez C M (1985a) Consumer demand for rice grain quality in SoutheastAsia. Pages 15-23 in Rice grain quality and marketing. International Rice Research Institute, P.O.Box 933, Manila, Philippines.Unnevehr L J, Juliano B O, Perez C M, Marciano E B (1985b) Consumer demand for rice grain quality inThailand, Indonesia, and the Philippines. IRRI Res. Pap. Ser. 116. 19 p.Villareal R M, Resurreccion A P, Suzuki L B, Juliano B O (1976) Changes in physicochemical propertiesof rice during storage. Starch 28:88-94.Wedgewood H B, Maranan C L, Bonifacio E P, Duff B (1987) Considerations in implementing thePhilippine rice grain quality and market study. Paper presented at the Workshop on Grain Qualityon Domestic and International Markets, 22-23 Jun 1987, International Rice Research Institute, LosBaños, Laguna.NotesAddresses: B. O. Juliano, International Rice Research Institute, P.O. Box 933, Manila, Philippines, and L. A. Gonzales,International Food Policy Research Institute, Washington, D.C. (mailing address is IRRI)Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstract 291ABSTRACT: GRAIN QUALITYScreening for quality of parboiled riceK. R. BHATTACHARYAParboiled rice is raw rice that is precooked before milling. The changes thatoccur during the process (such as gelatinization of starch, followed by itspartial reassociation) profoundly affect grain properties that are the basisfor a number of tests used to screen for quality. The most important areratio of water uptake at 55-60 °C to that at boiling temperature,equilibrium moisture content attained by rice soaked in water at roomtemperature, digestion of rice grains immersed in very dilute alkali, andviscosity and sediment volume of a rice-flour slurry. Each test valueincreases, from raw rice to mildly parboiled to severely parboiled.However, the tests apply most specifically to conventional parboiling,involving full soaking followed by steaming. Discriminating tests for dryheat-parboiled rice (soaked grains heated by conduction) and for pressureparboiledrice (incompletely soaked grains steamed under pressure) areyet to be developed. Differential tests for gelatinization, retrogradation,and thermal degradation of starch in parboiled rice also are needed.Varietal differences in grain properties are maintained, even afterparboiling.K. R. Bhattacharya, Discipline of Grain Science and Technology, Central Food TechnologicalResearch Institute, Mysore 570013, India.

Increasing rice production efficiencythrough mechanizationZHANG BAOZHAO, I. MANALILI, AND E. BAUTISTAThe demand for rice production machinery is determined by the degree towhich it can substitute for labor and other energy inputs. Agriculturalmachines that result in increased efficiency, lower cost, and less energyconsumption have been designed to be adaptable to local conditions indeveloping countries. Lightweight power tillers can match the desirableland preparation and buying capacity of small farmer. The floating andminipower tillers for plowing have been shown to have better mobility andmore than 20% higher capacity in soft irrigated fields. Their maneuverabilityon the road needs improvement. The cono puddler displaces the soilmore effectively, with 36% less pushing force than the traditional combtoothharrow. A cono weeder based on a similar concept was developed forlowland crop weeding. Reduced tillage is essential to prevent loss of thenatural vegetative stratum and to save energy input. It has produced goodresults on upland crops in rice-based cropping systems. Progress has beenmade in growing seedlings on mats in low-latitude regions and indeveloping a transplanter for both mat-grown and root-washed seedlings.A low-cost drum seeder was developed to enable farmers to direct seed inwetland fields at optimum seeding rate. The deep-placement machineseems to increase fertilizer-use efficiency in flooded fields compared withbroadcasting by hand. The combine harvester can be used in places thatare economically and technologically advanced. During labor shortages,the reaper can be used.About 92% of the world’s rice is produced in the Asia-Pacific Region. Recentdramatic increases in production are attributed to increased adoption of modernvarieties, increased application of fertilizer, and expansion of irrigated areas (IRC1985). However, rice production in several countries within the region and in otherregions of the world must be accelerated if it is to meet fast growing local demand.Intensity and efficiency of inputs to increase production also can be improved.Mechanization can help improve rice production efficiency in two ways: byincreasing land utilization and by increasing input efficiency. With increasedmechanization, China doubled its grain output and increased its farm laborutilization 164% between 1957 and 1984, with almost the same hectarage cultivated(Table 1). Farm machinery and equipment use also has increased rapidly in otherrice-growing countries during the last two decades. Mechanization in Japan reached100 power tillers/ 1,000 ha in 1961; Taiwan reached that figure in 1978.

Table 1. A comparison of Chinese farming practices, 1957-84 (Wu 1985). aYearAreaTotal Output Marketable Commercial Machinery FertilizerLabor Laborcultivatedoutput(million d) ($/ha) per grain ratepower consumption(million ha) (million t) labor day (million t) (%)(hp/kW) (million t)1957 111.83 193.10 1.727 195.05 1.010 45.97 23.61975 99.70 294.60 2.955 284.52 0.965 52.61 18.51980 99.30 302.11 3.042 320.56 1.061 61.29 19.1 197.95(144.49)1984 97.27 316.85 3.192 407.30 1.285 117.24 28.7 265.00(193.43)a Statistics from 27 provinces: 61% of power tiller (12-hp) was used for transportation.12.6917.39Table 2. Commercial energy inputs for rice production per hectare per growing season.173107.5 kg 1612.5ItemU.S. (highly mechanized) China Philippines (transitional) Philippines (traditional)unit/ha J × 10 6 /ha unit/ha J × 10 6 /ha unit/ha J × 10 6 /ha unit/ha J ×10 6 /haFarm equipment - 42001556.6 a - 335 -Fossil 224.71 8988 27.1 kg b 1218.2 40.1 1600Nitrogen 134.4 kg 10752 99.4 kg c 9142.0 31.5 kg 2520Phosphate- - - - -Potassium 67.2 kg 605 7.5 kg d67.5- -Seeds112.0 kg 1680 112.5 kg e 1687.5 110.5 kg 1650 Irrigation 683.41 27336 125.3 kW-h f 1565.6- -Pesticides 5.6 kg 560 2.6 kg g 257.6 1.5 kg 150Weed killer 5.6 kg 560 - -1.0 kg 100Drying - 4000- - - -Electricity - 3200 60.6 kW-h 757.3- -Transportation - 724 3.3 kg 149.4 - 31Total 40770 2.37 a Steel is accounted for on the basis of 209.3 X 10 6 J/kg. b Diesel fuel: 45 X 10 6 J/kg. c Nitrogen: 92 X 10 6 J/kg. d Potassium: 8.99 X 10 6 J/kg. e Seeds:15 X 10 6 J/kg. f Electricity: 12.50 X 10 6 J/kW-h, Nation's Standard Bureau. g Pesticides: 100.46 X 10 6 J/kg. Sources: Pimentel et el 1973, FAO estimate,6260516401.7 6386 1785.5Labor 31.1 39 1814 h 2278 814.4 h 1022.7Yield (kg/ha) 5800 87588 5700 85500 2700 1250 18750Energy used (J X 10 6 /kg) 11.192.891.43Output/input 1.38 4.485.50 10.50Dei end Shen 1980.

Mechanization for rice production 295Most mechanization efforts in developing countries have concentrated onincreasing land utilization through increased power application. Few efforts haveconcentrated on using mechanization to improve input efficiency.Power and energy in land preparationRaising output and increasing productivity have been achieved primarily byplanting new varieties and by using more inputs. Inputs use energy. In the U.S.,energy used for agriculture is 3% of all that used by the nation (Stout 1984). Othercountries (Japan, France, Italy, and Australia) use less. Fossil fuel, fertilizer, andfarm equipment are the inputs most used (Table 2). Energy used for each kg riceproduced was 11.19 MJ in the U.S., 2.89 MJ in China, and 2.37 MJ in thePhilippines. The energy output:input applied ratios were 1.38 in the U.S., 4.48 inChina, and 5.55 in the Philippines. In other words, energy per kg rice produced was3.87 times higher in the U.S. than in China, and 4.72 times higher than in thetransitional system of the Philippines.Mechanization has had very little impact on output per laborer in developingcountries, due to higher population growth rates. Labor hours applied are 31.1/ha inthe U.S., 1184.4/ha in China, and 814.4/ha in the Philippines. Food production inthe U.S. doubled in the 20 yr 1960-80, while energy use tripled. By 1975, Japan hadraised its food production 52.6%, with energy use increasing 3.6 times. AlthoughChina has applied high amounts of energy to crop production (Fig. 1), the laborrequirement per hectare is still very high because of meticulous land preparation andcareful crop management. Between 1957 and 1984, grain output doubled and farmlabor increased 164% on almost the same hectarage.1. Energy production and use in China, 1984.

296 Zhang et alKuether and Duff (1979) calculated that about 23.8% of the total energy inputin rice production is used for land preparation. (Total energy includes the energyequivalents of human, animal, machine, oil, and other material inputs.) If only theenergy convertible to mechanical power is considered, the requirement for landpreparation would be about 66% of the total.Humans, animals, and machines are the three sources of power used inagriculture. Their field capacities are shown in Table 3. Humans, although a versatilepower source that can be hired when needed, have very limited power. It would takea person 80-90 d to completely till a hectare of land with a hand hoe. With animalpower and traditional implements, the working time can be reduced to about 20 d.Where timeliness is important, as in multiple cropping to intensify production,the time (days) needed for land preparation becomes critical. This is particularly truewhere rainfed double cropping is practiced: a field needs to be prepared quickly afterharvest of the first crop to take advantage of residual rainfall for the second crop.Using mechanical power would substantially reduce time for tillage.The size of power unit required for land preparation depends on the size of theimplement used and the working depth needed. Often, tillage depth is unnecessary inwetland preparation. Kuether (1977) studied the depth of hardpan in floodedMaahas clay fields. He used four methods of land preparation for eight consecutivecropping seasons. His study indicated that, in continuous cropping, floodedricefields were being tilled 65-189% deeper than the minimum depth needed (Fig. 2).The most excessive tillage depth was caused by the heaviest machine used, the4-wheel tractor, followed by the heavy-duty 10-hp power tiller. Even with traditionalanimal-drawn implements, tillage depth was still much deeper than the minimumneeded.If excessive tillage depth could be avoided, substantial savings in energy andtime would be realized. One approach is to use a small power tiller, such as IRRIPT5, for plowing and puddling. In wetland tillage, a small machine can match thecapacity of a larger unit. Yet a small machine is more mobile and less susceptible tobogging down.China has developed a minipower tiller that has the same horsepower rating asthe traditional tiller. With the operator riding on it, it has excellent mobility andTable 3. Effective field capecity of humans, animals, and machines.ImplementHumans (with hand hoe)AnimalPlowing-1 passHarrowing and leveling-9 to 12 passesPower tiller (6- to 8-hp)Plowing-1 passHarrowing end leveling-3 to 4 passesRotary tiller (10-hp)Tractor (60-hp)Plowing and harrowingCapacity (h/ha)520128-13432-4010-121-3

Mechanization for rice production 2972. Mean depth of hardpan to support 24.1 N/cm 2 penetrometer load after tillage with different equipmentover 8 cropping seasons. Maahas clay, IRRI.maneuverability in a ricefield. It uses 12.7% less energy per hour, is 8.5% lighter thanthe traditional tiller, 13.6% cheaper than animal power, and has been shown to be20% more efficient. Capacity is increased 35-62%, while energy use drops 12.7%(Table 4). It is easy and convenient to manufacture and repair, and otherattachments, such as a harrow, can be used.Zero or reduced tillage field preparation has been tested for upland ricefields. Inrice-based multiple cropping cultivation, it is common to sow wheat or transplant asecond crop of rice immediately after harvesting the first crop. Preliminaryexperiments indicate that reduced tillage has these advantages:• It can save 74.4% of input costs if wheat is seeded directly into the softest layerafter shallow tillage (3-5 cm), saving 78-82% of the energy used and 94% ofthe labor (Table 5).• Wheat production can be increased 3-10% and rice production 12-14%.• Soil-bearing capacity is increased 2% (Table 6), decreasing the rollingresistance of machinery and energy input.In soft, waterlogged areas, a skid-supported tiller or floating tiller developed bya private firm in Iloilo, Philippines, has been found to outperform all other tillagesystems (Calilung and Stickney 1985). For very soft soil, the floating tiller has thehighest capacity; the power tiller with cage wheel and comb-tooth harrow the secondhighest (Table 7).

Table 4. Comparison of land preparation by animal and power tiller (Wu et al 1986).PreparationmethodPower(kW/hp)Working Capacity (ha/h) Energy used Capacity Weightoperation depthper kW-h(cm) Plowing Harrowing Tillage Kg/ha J × 10 6 (kg)/ha (ha/kW-h)Water buffalo -- Plowing .013-.02 -- -- 535.5b .021-.034--Plowing machine 2.9/4 Plowing 12-16 .1 -.13 .2 -.3 -- 7.20 301.4 .034-.046 128Power tiller 2.9/4 Tillage 12-17 -- -- .08 8.25 345.4 .027 140-160Power tiller a 3.6/10 Plowing .05 -.08 .13-.2 -- 9.75 408.1 .022--Power tiller 8.8/12 Tillage 14-17 -- -- .157 10.13 423.8 .018 590a From Lu 1987. b From Kiamco and McMennamy 1987 (as cited in Kuether and Duff 1987).Table 5. Labor and energy inputs for wheat production in rice-based croppingpattern with no-tillage cultivation.TillageLabor input a(h/ha)Energy consumptionKg/ha J × 10 6 /haProduction cost(US$/ha)Traditional 163.8 30.30 1268.35 32.48Shallow tillage 10.5 5.25- 219.8- 8.206.75 282.6a Primary and secondary tillage, ridging, breaking, covering, and seeding.

Mechanization for rice production 299Table 6. Yields with different tillage methods in a rice - wheat pattern (Zhou 1985).TillageSoil moisture content Soil-bearing capacity Rice yield (t/ha)0-5 cm 5-10 cm 0-5 cm 5-10 cm 1983 1984Wheat yield(t/ha)1985Traditional 30.29 32.30No tillage 27.51 30.99One tilling/2 yr 25.96 35.17One tilling/yr 28.30 33.1715-1620-2125-3518-258-16 6.015-21 6.420-35 6.314-25 6.37.68.28.48.43.43.83.83.5Table 7. Performance of alternative tillage technologies for first pass on very soft soil. aImplement (n = parses)Capacity(ha/h)Fuel Tillage Volume Volume tilledconsumption depth tilled per liter fuel(liters/h) (cm) (m 3 /h) (m 3 /liter)Hand tractor/Moldboard plow 0.085 2.45 8.4 71.4 29.1(n = 1)Hand tractor/Disc plow b – – – ––Hand tractor/Spiral plow b– – – – –Hand tractor/Cage wheels and 0.116 2.62 10.0 116.0 44.3harrow (n = 2)Floating tiller (n = 2) 0.268 3.26 8.0 c 214.4 65.8a Soils with cone penetrometer depths greater than 31 cm at 2.5 kg/cm 2 . b lmplement not applicablefor very soft soil because of excessive bogging down. c Approximate minimum depth.The International Rice Research Institute (IRRI) modified the floating tiller byreplacing the skid with a pair of pontoons connected by a hollow plate to support theengine and transmission casing. This improved the stability of the machine andeliminated the tendency of the original skid to create ridges on the puddled soil,which required additional leveling operations. This improvement in the design madethe machine effective for incorporating green manure crops, such as sesbania, intopuddled soil.Although deepening of hardpan is primarily caused by heavy-power units, thetype of implement used also greatly influences depth of tillage, field efficiency, andenergy consumption. A comb-tooth harrow is the most commonly used implementin puddling operations. Depending on the condition of the soil, this implementrequires 9-12 passes (80-100 labor hours/ha), and it is not very effective in breakingup soil clods. Maintaining the minimum desired depth is difficult. The result isinefficient use of power.IRRI developed a conical puddler designed to be either animal-drawn or powertiller-drawn (Bautista et al 1987) for operations in soft, wetland soil. The implementconsists of conical rotors with several blades fixed on the surface of the rotor. Therotors are independently mounted on shafts attached on a common frame. Theconcept is based on the principle that, when a bladed cone is rolled along a straightpath on the soil surface, the blades displace the soil differentially at points along theaxis of the curve. The differential soil movement caused by each blade on the cone is

300 Zhang et alutilized to create more aggressive tillage action. Field tests indicate its puddlingcapacity is 2-3 times higher than the traditional comb-tooth harrow.Labor in crop establishmentBy 1980, about 40% of the rice area in South and Southeast Asia was planted tohigh-yielding varieties (IRC 1985). The most common crop establishment methodwas transplanting in puddled fields. The main constraint to this operation was laborshortage during peak transplanting times. This problem prompted China, Japan,and IRRI to develop mechanical transplanters.Different mechanisms for transplanters and pullers for root-washed seedlingshave been studied. In 1970, the indoor soil-bearing seedling technique becamepopular in Japan. Adaptability studies of different transplanting methods underdifferent local conditions in China indicated that 50-70% of the seed is saved; about10-12% of the seedling bed is needed, compared with the traditional seedlingtechniques; and total labor hours are decreased 67.9% (Table 8). Direct costs oftransplanting are decreased with mechanization. However, there is an increase inindirect expenses related to equipment depreciation (Zhang et al 1985).China and IRRI have made progress in cutting transplanting costs/ ha and insimplifying transplanter requirements. Some of the methods are• Trayless seedlings are used in low-latitude regions. Simple wooden guides(IRRI method) or a movable chassis (China method) with plastic sheet liningare used to raise seedlings (Fig. 3). Both the wooden guide and chassis can beremoved and reinstalled repeatedly. This method has dramatically loweredcosts (Table 9).• The design and construction of the manual and power transplanter have beenimproved. A single-wheel drive transmission was adopted in China.It is lightweight and easy to operate, moves satisfactorily, and has a smallturning radius and low power consumption (Gou and Shen 1985). Its pricehas been cut to one-third that of the Japanese transplanter.• Agronomic measures required by the transplanter have been adapted formultiple cropping and diversified crops.• Seedling facilities have been diversified for higher utilization. Greenhousesare used to grow vegetables, edible fungi, turf, and chickens, and for dryingfoodstuff.Table 8. Labor required to grow seedlings per unit main field hectare.SiteCropTrays per hectareLabor required to growseedlings (d)Indoor soil-stick Seedling bedWuxie 1st cropping 495 24.5 46.5Jiangxi 2d cropping 345 7.5 19.5Shanghai Single cropping 10.5 60.0Zhejiang 2d cropping 825 21.0 19.5-31.51st cropping 600 22.5 25.5-31.5

Mechanization for rice production 3013. Modified seedling preparation.Table 9. Changes using only one equipment input with different methods of growingseedlings.SiteMachine used andInput/ha Decreaseseedling methods (US$) (%)Jilin “KUBOTA” indoor soil-bearing 1000 0seedling methodJilin Calcium plastic soft lining 670 33Zhejiang used for 80% of all treyJiangsu Simplified method with 620 38traditional equipmentShanghai Simplified method of growing 400-496 50.5-60seedlingsJiangsu Trayless method of growing 172-239 76.1-82.8seedlingsThe Chinese Academy of Agricultural Mechanization and Sciences (CAAMS)and IRRI have joined in developing a manual rice transplanter for root-washedseedlings. IRRI has developed a manually operated transplanter for soil-bearingseedlings that is becoming popular in Sri Lanka through efforts of the FarmMachinery Research Center. However, most Asian farmers still prefer to transplanttraditionally prepared, root-washed seedlings; this limits wide acceptance of theIRRI transplanter for soil-bearing seedlings.

302 Zhang et alAlthough most irrigated fields in Asia are transplanted, an increasing numberof farmers are shifting to direct seeding or to broadcasting pregerminated seeds inwetland and dryland fields to reduce planting costs. Yields of direct seeded andtransplanted fields have been found to be similar (Cia et al 1984, Moody andCordova 1983). Malaysian farmers use only 25-50 kg seed/ha (De Datta 1985),below the recommended optimum 50-100 kg/ha (Xuan and Ross 1976).Direct seeded fields are often weed infested. Agronomists recommend usingherbicides, but farmers often rely on other methods of weed control. Filipinofarmers broadcast 150-400 kg seed/ha (Cia et al 1984, Cordova et al 1984, Kiamcoand Khan 1985) to minimize weed infestation. Yields can be maximized whenseeding, especially of high-yielding varieties, is at the optimum rate.IRRI has developed a low-cost drum seeder to enable farmers to direct seed inrows in puddled fields at the optimum seeding rate. This facilitates the use ofmechanical weeders. In an initial adoption study, use of the seeder enabled farmersto increase yields 1.2 t/ha using 63 kg seed/ha less than their normal broadcastseeding rate (UPLB 1987).Chemicals and crop careFertilizerAsia is the largest and fastest growing N consumer in the world, accounting for 69%of the urea consumed in 1981, excluding China (Stangel and De Datta 1985). Chinaalso has been applying high amounts of inorganic fertilizer to raise productivity(Table 1). The most common method of applying N is broadcasting into floodwater2-4 wk after crop establishment. Under such conditions, N recovery is only 15-35%of the total applied (De Datta et al 1968, as cited in Stangel and De Datta 1985).Even with the recommended split applications, recovery is low. With increasing useof N fertilizer in rice production, any improvement in plant recovery would have asignificant impact on world N consumption.So far, deep placement seems to be the most feasible way of increasingfertilizer-use efficiency in wetland fields. IRRI and China have developed machinesthat facilitate mechanical placement of fertilizer at 3-5 cm depths (Fig. 4). Althoughthe IRRI machines have been shown to be effective at low N application rates,improvements are still being made to improve performance. Deep placement ofammonium carbonate and potassium chloride using Chinese machines gave higheryields than broadcast application (Table 10).Many studies are seeking substitutes for N fertilizers. IRRI is trying to identifysuitable green manure crops for lowland ricefields. Incorporating these cropsfacilitates N release. Mechanical incorporators are being developed for such greenmanure crops as crotalaria and sesbania. The hydrotiller, which facilitates landpreparation on wet fields without plowing, also has been found efficient inincorporating both standing straw and tall green manure crops (Ventura et al 1987).A knife attachment for the power tiller cage wheel combined with the moldboardplow used in plowing was also found suitable for cutting and incorporating greenmanure crops.

Mechanization for rice production 3034. Chinese deep-placement fertilizer applicator.Table 10. Yields (t/ha) with different fertilizers deep-placed and broadcast (ChengMing 1985).FertilizerDeepplacementBroadcastGrowth rate(%)Ammonium carbonate67% ammonium carbonate and33% potassium chloride5.25.14.84.67.811.3The stems and roots of rice and wheat can be used as organic fertilizers, up to1.4-2.0 t/ha. N content in the stem is 1.06-1.12% in rice and 0.53% in wheat;phosphate content is 1.4-2.6% in rice and 1.86% in wheat. At present, organicfertilizers provide only 35-45% of the total fertilizer needed for improved ricevarieties to reach their yield potential. Rice - rice - green manure or rice - wheatcropping patterns are recommended because they gave an output-input ratio of N of0.67 and 0.69, respectively (Table 11).PesticidesThe introduction of high production technology involving high-tillering ricevarieties, closer plant spacing, and high fertilizer application seems to have increasedTabla 11. Output-input ratio for different cropping patterns.Cropping patternBiomass Application rate (kg/ha) Output/inputmaterial(t/ha) N P K N P KRice - rice -wheat 2.8 667.50 282.00 371.25 0.58 0.59 1.00Rice - rice - rape 2.6 762.00 534.00 378.75 0.46 0.18 0.54Rice - rice - green manure 1.8 461.25 189.75 206.25 0.67 0.47 0.75Rice - wheat 2.7 488.25 312.75 362.25 0.69 0.39 0.77Rice - rape 2.0 619.50 332.25 361.50 0.76 0.34 0.65

304 Zhang et althe incidence of rice insect pests (Ishikura 1983). More intensive use of pesticides, aswell as the development of new chemicals, has occurred.Litsinger and Sanchez (1983) defined efficient use of insecticides in rice as theapplication of the minimum quantities of chemicals that are safe to use and that willcause minimal ecological perturbations while obtaining optimum profit. Mostfarmers, however, apply chemicals below the recommended rates, using knapsacksprayers that are unsafe to operate. Studies have shown that the effect of thechemicals, particularly granular formulations, could be improved through root zoneapplication (Heinrichs et al 1977). A few farmers have used the IRRI deepplacementfertilizer applicators with mixed insecticide and fertilizer. In addition toincreased effectivity, the advantages of such placement include encouraging theactivity of natural enemies of pests, safety from the hazards of chemical use for theoperators, and reduced contamination of the ecosystem. Mechanization could notonly provide effective ways of applying chemicals, but also reduce the amount ofchemicals applied. Research in this area, especially in farmers’ fields, is stillinconclusive.WeedingFarmers often weed their fields with a combination of chemical and manualmethods. Herbicides, however, are becoming costly for small farmers. Because ofthe high labor requirement for hand weeding, many farmers do not weed at all.Some use Japanese-type rotary weeders.But rotary weeders require a large amount of force to operate and take about80-90 labor hours/ ha. The weeders are moved back and forth to uproot and buryweeds. A conical rotor weeder similar to the conical puddler was developed thatworks in the top 2-3 cm soil layer where most weeds grow. The IRRI cono weederrequires less pushing force to operate (Table 12) and is twice as fast as theconventional weeder. It satisfactorily weeds in a single pass (Khan et al 1987).Harvesting and threshingHarvesting is one of the most labor-intensive operations in rice production,requiring about 120 h with a traditional sickle and up to 200 h with a panicle knife.Many areas have labor shortages during the harvest season. In double-croppedsystems, harvesting the first crop often overlaps land preparation for the succeedingcrop and competes for available labor and power resources.Timely harvesting, particularly of high-yielding varieties that have a tendencyto shatter, is extremely important. Samson and Duff (1973) have shown that a fewdays’ delay in harvesting can result in significant grain losses. For example, if a fieldof IR8 is harvested 7 d after maturity, as much as 35% of the grain may be lost. Themagnitude of this problem is illustrated in Figure 5 (Esmay et al 1979). Where laborshortages exist during harvest, mechanization appears to be the only alternative toprevent excessive losses.A number of factors need to be considered in selecting harvest machinery forthe small rice farms in the tropics (Manalili et al 1981). Size and weight of the

Mechanization for rice production 305Table 12. Pushing form using conventional weeders and coro weeders with 20 -60° cone angler, IRRI, 1985.Unit machine dascriptionAveragepushing force a(N)Weight ofmachine(kg)Standard conventional weeder 116.0 5.50with 2 spiked wheals and 1 flutedroller, single row 130 mmCono weeder with 60° closed rotor 67.4 4.5020 mm nonserrated lugs X 145 mmsingle rowCono weeder with 45° closed rotors 43.3 3.7028 mm serrated lugs X 140 mmsingle rowCono weeder with 40° closed rotors 50.5 3.8520 mm nonserrated lugs X 140 mmsingle rowCono weeder with 20° closed rotors 50.1 4.2520 mm nonserrated lugs X 140 mmsingle rowa Av of 12 trials conducted on 3 sites in Laguna area. Site 1: Barangay Wawa,Laguna hard soil. Newly irrigated clay loam. 10-12 cm hardpan, 1-2 cm waterdepth. Site 2: Hi-way, Calauan, Laguna; very soft soil, Antipolo clay loam. 0-10cm hardpan, 1-2 cm water depth. Site 3: Barangay Labuin, Santa Cruz, Laguna;medium soft, sandy loam soil. 8-10 an hardpan, 1-2.5 cm water depth.5. Grain losses of three rice varieties harvested at different stages of maturity.

306 Zhang et almachine affect its maneuverability and mobility in soft irrigated fields. Machineharvesting should not cause grain shattering losses higher than losses with manualharvesting (2-3%). Costs should be within the economic capacity of the averagesmall farmer. Any harvesting method should consider labor resources, the dailywage of the workers, and the level of technology. In general, using a hand sickle isbetter if the daily wage is low and labor supply is sufficient. Where the economicaland technical environment is favorable, a combine can meet the demand. It is oftenbetter to hire labor or to employ a reaper during times of labor shortages. A study inChina compared different harvesting methods for rice grown as first and secondcrops (Table 13) with the following results:• The small combine decreased labor hours 1.7-2.5 times that of work done bysickles and 1.4-2.1 times that done with a reaper. Its capacity was 4.7-5.8times higher than the other methods, although production costs increased2.2-3.2 times.• Reaper capacity is 18.7-32.2 times that of the sickle and 3.9-5.5 times thecombine. Production costs are the same as with a sickle.• Production expenses are lowest with the sickle, although labor costs arehighest.• The three methods have similar energy consumption per unit area.In 1980, CAAMS and IRRI collaborated to adapt the 1.6-m vertical reaper ofCAAMS to the IRRI power tiller. The machine generated a lot of interest,particularly from national institutions. The Regional Network of AgriculturalMachinery, which was then evaluating the field performance of different makes ofharvesters, obtained favorable test results with the CAAMS-IRRI machine.The unique features of the vertical reaper are the gathering starwheel andholding springs. They enable the machine to gather and hold the crop vertically aftercutting, deliver it sideways, and gently lay it down, leaving behind a neatly formedwindrow. The CAAMS 1.6-m prototype was a sophisticated design suitable only forcapital-intensive production. A more simple, smaller 1.0-m version was developedfor mounting on the IRRI 5-hp power tiller. This much lighter unit can work on softirrigated ricefields. Field tests showed it can completely harvest 2-3 ha/d with lessthan 1% shattering losses.Recently, further modifications were made: the blade register was reduced from76 mm to 50 mm, to reduce vibration and stresses in the cutterbar; the flat-beltconveyor was replaced with roller chain; and the working width was increased from1.0 m to 1.2 m. These changes were patterned on the Kubota vertical reaperintroduced earlier. Unlike the CAAMS-IRRI reaper, the Japanese machine was notan attachment to a power unit, but an integral unit only for harvesting. Its chiefadvantage is that it is lightweight and easy to maneuver on small fields.Threshing can be carried out either by the traditional methods of hand-beatingand animal trampling or by mechanical threshing. The traditional method is laborintensive, requiring as much as 100-150 labor hours/ ha. Mechanical threshing canreduce overall labor requirements 70% (Toquero et al 1977).Of all the field operations in rice production, threshing is the most suitable tomechanization. A survey in the Philippines in 1973 showed that 60-64% of the

Source: data from Yue-xi county, Jiengsu Province, 1980. a Total labor hours from harvesting to storage. b Wage rate: 1980, US$0.25.Table 13. Characteristics of different harvesting and threshing methods.CropFirst cropSecond cropThreshing/ MachineEnergy consumption Production Cost of Laborharvesting efficiencyCapacity Yieldcost b machine usedmethod (ha/h) (ha/h) a (kg/ha) (kg/ha) (J X 10 6 /ha) (US$/ha) (US$) (h/ha)18.3 kW/25-hp 34.923312 145.412.23565 209.310.73181 235.034.073312 132.816.36565 289.815.10181 0.167 0.0765680 18.30766.04head-feedingcombine8.8 kW/12-hp 0.362 0.3005680 16.80703.48reaper + thresherHand sickle +thresher18.3 kW/25-hp 0.195 0.0160.0885680 4240 15.0017.70627.90740.92head-feedingcombine8.8 kW/12-hp 0.580 0.4844240 20.40853.94reaper +thresherHand sickle 0.0154240 18.30766.04338.9+thresher

308 Zhang et al6. Grain losses incurred in harvest and postharvest operations.farmers used mechanical threshers (Toquero and Duff 1974). In those days, the mostcommonly used machine was the McCormick-type thresher. This large and costlymachine requires 30-60 hp to operate. Because of its size and weight, transporting itthrough fields where levees had to be crossed was a problem. This often resulted inmore handling operations between harvesting and threshing, increasing field losses.Figure 6 shows the extent of losses during and between operations (Esmay et al1979).Small and less expensive threshers working on the axial-flow principle weredeveloped at IRRI. These machines work even with wet and freshly harvested rice,keeping unthreshed losses below 2%. Because they are lightweight, they can be easilytransported to where harvesting is taking place, minimizing handling. Thesethreshers are now commonly used in Southeast Asia and other rice-producingregions.In some countries, straw is a valuable product and is gathered and bundledalmost as carefully as grain (Stout 1966). Straw is used for making ropes and mats orfor other industrial purposes. For this reason, threshing is either manual or donewith head-feeding threshers, such as the pedal-operated thresher. The capacity ofthat thresher is much lower than that of the axial-flow thresher.Summary and conclusionAppropriate mechanization can increase the productivity and profitability of a ricefarming system. Reducing turnaround time through mechanization is essential inthe multiple cropping that intensifies land use and productivity. With rising costs offarming inputs, mechanization is becoming an important factor in increasing theefficiency of those inputs. During times of peak labor demand, mechanization isimportant in preventing harvest and threshing losses.References citedBautista R, Calilung E, Mazaredo A, Khan A (1987) Cono puddlers: new approach for energy efficientrotary puddling. Paper presented at the 37th Annual Convention of the Philippine Society ofAgricultural Engineers, Bureau of Plant Industry, Malate, Manila.Calilung E, Stickney R (1985) Comparison of land preparation equipment used on small rice farms in thePhilippines. Paper presented at the IRRI Saturday Seminar, 16 Mar, International Rice ResearchInstitute, Los Baños, Philippines.

Mechanization for rice production 309Cheng Ming (1985) An investigation of deep fertilizer placement applicator model 2DS-2 for lowland.Agricultural Machinery. Information 6. Chinese Academy of Agricultural Mechanization Sciences,China.Cia B, Bernasor P, De Datta S K (1984) Development and spread of modem technology for direct-seededflooded rice in tropical Asia. Paper presented at the 15th CSSP Scientific Meeting, 16-18 May,Batac, Ilocos Norte, Philippines.Cordova V C, Maranan C, David C C (1984) Adoption of wet seeding in selected rice areas in thePhilippines. Paper presented at the 15th CSSP Scientific Meeting, 16-18 May, Batac, Ilocos Norte,Philippines.Dai Zilin, Shen Laifu (1980) Economic analysis of farm mechanization on rice-based multiple croppingsystem. Report No. 6. Study on comprehensive scientific experimental base of farm mechanizationin Tai Lake region, Mar 1980. Jiangsu Academy of Agricultural Sciences and Suzhou Institute ofAgricultural Machinery, China.De Datta S K (1985) Technology development and spread of direct-seeded flooded rice in Southeast Asia.Paper presented at the International Rice Research Conference, 1-5 Jun, International RiceResearch Institute, Los Baños, Laguna, Philippines.Esmay E, Soemangat Eriyatno, Phillips A (1979) Rice post production technology in the tropics.East-West Center, University Press of Hawaii, Honolulu.FAO—Food and Agriculture Organization (1972) Production yearbook. Rome.Gou Fenghua, Shen Runzhai (1985) Principles of equipment design: examples from China. Paperpresented at the International conference on Wetland Utilization for Rice Production inSubSaharan Africa, 4-8 Nov, Ibadan, Nigeria.Heinrichs E A, Aquino G B, McMennamy J A, Arboleda J, Navasero N, Arce R (1977) Increasinginsecticide efficiency in lowland rice. Pages 41-47 in Agricultural mechanization in Asia. Summered.Farm Machinery Industrial Research Corp., Tokyo, Japan.IRC—International Rice Commission (1985) Report of the International Rice Commission, 6th session.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Ishikura H (1984) Projected trend in the use of insecticides in rice insect pest control. Pages 57-66 inJudicious and efficient use of insecticides on rice. International Rice Research Institute, P.O. Box933, Manila, Philippines.Khan A U, Diestro M, Bautista R, Calilung E, Vasallo A (1987) Use of conical rotors for multipurposewetland farming machines. International Rice Research Institute, P.O. Box 933, Manila,Philippines.Kiamco L, Khan A U (1985) Direct row seeder for paddy. Paper presented at the International RiceResearch Conference, 1-5 Jun, International Rice Research Institute, Los Baños, Laguna,Philippines.Kuether D (1977) Soil compaction and wetland rice tillage systems. Paper presented at the SummerMeeting of the American Society of Agricultural Engineers, 26-29 Jun, Raleigh, North Carolina.Kuether D, Duff B (1979) Energy requirements for alternative rice production systems in the tropics.Paper presented at the Annual Meeting of the Society of Automotive Engineers, Sep, Milwaukee,Wisconsin.Kuether D, Duff B (1987) Energy requirements for alternative rice production systems in the tropics.IRRI Res. Pap. Ser. 59. 14 p.Litsinger J A, Sanchez F F (1984) Formulation, dosage, and application techniques related to crop stages.Pages 171-172 in Judicious and efficient use of insecticides on rice. International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Lu Suyu (1987) Mini power tiller for plowing. Luo yang Tractor Institute, China.Manalili I, Ma Ji, Duff B (1981) Technical and economic factors in adopting mechanical reapers to smallrice farms. Paper presented at the Regional Grains Post Harvest Workshop, 20-22 Jan, Philippines,and Regional Seminar on Appropriate Mechanization for Rural Development with SpecialReference to Small Farming in the Asian Countries, 26-31 Jan, Jakarta, Indonesia.Moody K, Cordova V G (1985) Wet-seeded rice. Pages 467-480 in Women in rice farming. InternationalRice Research Institute, P.O. Box 933, Manila, Philippines.Pimentel D, Hurd L E, Bellotti A C, Forster M J, Oka I N, Sholes O D, Whitman R J (1973) Foodproduction and the energy crisis. Science 183(2):443-449.Samson B, Duff B (1973) The pattern and magnitude of field losses in paddy production. Paper presentedat the IRRI Saturday Seminar, 7 Jul, International Rice Research Institute, Los Baños, Laguna,Philippines.

310 Zhang et alStangel P J, De Datta S K (1985) Availability of inorganic fertilizers and their management: a focus onAsia. Paper presented at the International Rice Research Conference, 1-5 Jun, International RiceResearch Institute, Los Baños, Laguna, Philippines.Stout B A (1966) Equipment for rice production. Food and Agriculture Organization of the UnitedNations, Rome.Stout B A (1984) Energy use and management in agriculture. Britton Publishing Co., California.Toquero Z, Duff B (1974) Survey of post production practices among rice farmers in Central Luzon.Paper presented at the IRRI Saturday Seminar, 7 Sep, International Rice Research Institute, LosBaños, Laguna, Philippines.Toquero Z, Maranan C, Ebron L, Duff B (1977) Assessing quantitative and qualitative losses in ricepost-production systems. Paper presented at the FAO Workshop on Post-Harvest Rice Losses,Mar, Alorstar, Malaysia.UPLB—University of the Philippines at Los Baños (1987) Socio-conomic evaluation of eight-row ricedrum seeder in Naujan, Oriental Mindoro. Agricultural Mechanization Development Program,College of Engineering and Ago-industrial Technology, College, Laguna, Philippines.Ventura W, Mascariña G B, Furoc R F, Watanabe I (1987) Azolla and Sesbania as biofertilizers forlowland rice. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Wu Keqiang (1985) The cause, effect and the ways to solve problems on surplus farm labor in China.Selection of agricultural economy 6. Agricultural Sciences Publishing, Beijing.Wu Qiyao, Meng Xianyuan, Lu Jianping (1986) An aspect of development of mini power tiller forplowing. Paper presented at the 1986 Meeting of the Zhejiang Society of Agricultural Machinery,Oct, China.Xuan V T, Ross V E (1976) Training manual for rice production. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Zhang Baozhao, Gou Fenghua, Ying Hudong (1985) Development and prospect of China’s ricemechanical transplanting techniques and implement. Paper presented at the InternationalConference on Agricultural Equipment for Developing Countries, 2-6 Sep, International RiceResearch Institute, Los Baños, Laguna, Philippines.Zhou Yanxiang (1985) Report on investigation of rice - wheat production mechanization with no-tillagesystem in South China. Nanjiang Institute of Farm Mechanization, China.NotesAddresses: Zhang Baozhao, Agricultural Engineering Department, China National Rice Research Institute, Hangzhou,Zhejiang, China; I. Manalili and E. Bautista, Agricultural Engineering Department, International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Citation information: International Rice Research Institute (1987) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstracts 311ABSTRACTS: MACHINERY AND POSTHARVESTSmall farm modernization policy:the efficiency-equity trade-offP. L. PINGALI AND B. DUFFMost Asian countries have experienced rapid increases in their level ofagricultural mechanization during the last two decades. However, growthin the agricultural labor force of these countries has been equally rapid.Concurrent growth of labor force and labor-saving technology presentspolicymakers with a crucial trade-off: Agricultural mechanization couldincrease the efficiency of food grain (rice) production and lead to a declinein food prices. On the other hand, increases in the level of mechanizationcould lead to the displacement of agricultural labor and tenant farmers.That trade-off is severe in labor-abundant, land-scarce economies withoutnonfarm employment opportunities. Mechanization of land preparationand threshing will almost always result in displacement of labor andtenant farmers. Mechanization of milling could have positive welfareeffects, even in labor-abundant areas, because most rural small-scalemills replace the hand labor of female family members rather than hiredlabor. Where alternative employment opportunities are available, such asurban employment, the trade-off is smaller. Shortages of agricultural laborfor land preparation, weeding, and harvesting-threshing operations can beobserved even in densely populated areas. The efficiency-equity trade-offcan be further exacerbated by such government policies as subsidies formachinery imports, support prices, minimum wage laws, and overvaluedexchange rates.P. L. Pingali and B. Duff, Department of Agricultural Economics, International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Innovations in grain drying technologiesYONG WOON JEON, L. S. HALOS, AND A. R. ELEPAÑODespite the many types of mechanical dryers that have been introduced inSouth and Southeast Asia, none has been widely adopted. Sun-drying isstill the prevalent technology in most parts of Asia. In developingappropriate drying technologies, IRRl emphasizes the critical environmentsthat must be considered with practical options for drying unhulledrice and other grains. The criteria for dryer design address not only dryingrequirements, but also the farming household capabilities. An acceptabledryer should be multipurpose, utilize nonconventional energy sources andindigenous construction materials, be simple to operate and maintain, andbe economically affordable to farmers. Some practical options for dryinggrain in developing countries are the IRRl natural convection typewarehouse dryer and the conduction type continuous flow rotary dryer.Yong Woon Jeon, L. S. Halos, and A. R. Elepaño, International Rice Research Institute, P.O. Box933, Manila, Philippines.

312 AbstractsMechanization of small rice farmsin developing countriesA. G. RIJKThe mechanization needs of small farmers deserve attention. Somecommon views or propositions are examined here, including issuesrelated to economies of scale, credit, type of mechanization technology,ownership, training, and extension. Important conclusions include1) mechanization of the small farm requires rethinking the means andways of delivering the benefits associated with mechanization; 2) moreattention must be paid to hand tool and draft animal technology, trainingand extension, efficient hire-services for machinery, and credit policies forfinancing machinery or custom-hire services; 3) ownership of machinerythat also could generate off-farm income should be promoted among smallfarmers; 4) scaling down equipment to suit the needs of small farmers isnot always economically attractive or technically feasible; 5) highlymechanized farming systems may require substantial investments in landdevelopment, including water control, field layout, and access roads; and6) adverse effects of mechanization can be prevented if the operation sthatneed to be mechanized are carefully identified and the mechanizationtechnology selected, priced, and supported by effective policies.A. G. Rijk, Asian Development Bank, P.O. Box 789, Manila, Philippines.Mechanization of rice farming in ChinaFENG BINGYUANIn China, primary and secondary tillage are done with plows, harrows,rotary tillers, and multipurpose tillers using 3- to 5-hp engines, especiallywith the boat-type tractor. Sowing and planting can be done withmechanical transplanters for root-washed and soil-bearing seedlings andwith direct sowing equipment. Recently, a factory nursery system and asimplified tray nursery for the field, with related machines and implements,have been developed. Agrotechniques and machinery for indirect anddirect harvesting and a minicomposite head-feeding rice combine havebeen developed.Feng Bingyuan, Chinese Academy of Agricultural Mechanization Sciences, No. 1 Beishatan,Deshengmen Wai, Beijing, China.

Abstracts 313Small farm machinery requirementsfor irrigated rice in East AfricaG. C. MREMAAgricultural machinery and implement requirements for smallholderirrigated rice farms in East Africa can be divided into those for clearingmain irrigation and drainage canals of reeds and weeds; for landpreparation, planting, weeding, and harvesting; and for postharvestprocessing. The tough and fibrous Typha reeds in the irrigation anddrainage canal systems are difficult to clear. If smallholder irrigation is tosucceed, appropriate machinery for clearing these reeds is needed. Giventhe prevailing technological level of farmers, appropriate hand tools wouldbe more efficient and less arduous than the machete currently used. Mostsmallholder irrigation schemes are in tsetse fly-infested areas, making itdifficult to keep draft animals. Mechanical sources of power for tillage areneeded for land preparation and improved hand tools for sowing andweeding. In view of the small areas being cultivated by most farmers,harvesting and postharvest equipment will be viable only when preharvestphysical constraints have been removed and yields significantly increased.Efforts to increase smallholder rice cultivation in East Africa shouldconcentrate on removing the physical constraints in growing localvarieties rather than on introducing high-yielding varieties which demandmore intensive management.G. C. Mrema, Department of Agricultural Engineering and Land Planning, Sokoine University ofAgriculture, P.O. Box 3003, Morogoro, Tanzania.Experience on mechanizationtechnology transferCHAK CHAKKAPHAK AND B. COCHRANExperiences in strategies to transfer mechanization technology haveshown that no prescribed program can meet the needs of all interestedgroups. However, some common techniques to extend appropriatetechnology to emerging agricultural mechanization industries can beidentified. Improved technology is needed to increase the profitability ofsmall farms in developing countries so that rural workers may have astandard of living comparable to that of urban dwellers. The agriculturalextension services of most countries are not oriented toward disseminatingfarm mechanization technology because they lack personnel.Each country should develop its own national mechanization policy andstrategy for implementation. In Thailand, the system includes an interestedand responsive private sector. Increased attention is being paid todeveloping machines that reduce the drudgery of farm work, particularlyfor women. Adaptation of technology to satisfy local conditions is a keyelement in machine acceptability. Mechanization technology must be

314 Abstractsdirected both to the farmers who will purchase and use the machines andto the manufacturers who will produce the machines. Consideration hasbeen given to transferring technology to manufacturers according to thelevel of production—village artisan, small workshop, small manufacturingplant, and advanced manufacturer. Some constraints to adoption includeinadequate institutional coordination, inadequate market research, loweducational level, and limited financial resources. Training is an importantcomponent of technology transfer and should include programs forfarmers, manufacturers, mechanization-related government project staff,and financial institution staff. Developing countries should cooperate withregional programs to develop, exchange, and implement the transfer ofagricultural mechanization technology. Without intercountry cooperation,research efforts could be duplicated. Current regional programs are notsufficient to develop and transfer agricultural mechanization technology.Chak Chakkaphak, Agricultural Engineering Division Department of Agriculture, Bangkhen,Bangkok, Thailand 10909; B. Cochran, Louisiana State University, P.O. Box 80441, BatonRouge, Louisiana, 70898 USA.

The need for a globalrice research systemH. M. BEACHELLWorld population has increased from 2 billion in 1930 to 5 billion in 1987,and is likely to reach 6 billion by 2000. This population increase has beendue to such modern medical discoveries as vaccines, anesthesiology,antibiotics, and malaria control, and to increased agricultural production.Agricultural advances have been possible through application of thetheory of soil fertility and the laws of genetics, hybrid vigor, and DNA andrelated cellular and nuclear genetics. The outstanding increases in riceproduction in Asia-where more than 90% of the world rice crop isproduced and consumed-were made possible by global internationalcooperation and collaboration. That involved strong national support ofrice research and willingness to utilize assistance from the manydeveloped country agencies and international research institutes thatwork together as a global rice research system. The International RiceResearch Institute (IRRI) has played a major role in this system, cooperatingand collaborating with national programs through a network of research,training, and extension activities. Rice research in Africa and some LatinAmerican countries has lagged behind that in Asia. By applying the sameprinciples, rice research in those continents could be strengthened rapidly.IRRl is taking the lead in applying the new biology by tapping findings fromadvanced research agencies around the world and making them availableto national research programs. The impact of private corporations workingin cooperation with public agencies in hybrid rice research in the U.S. andother countries is discussed. If those efforts are successful, they willbenefit all rice-producing areas. This approach may be applicable to otherareas of rice research as well.An adequate supply of rice to provide food for a rapidly expanding worldpopulation through the balance of the 20th century and into the 21st century is aparamount need, particularly in Asia where more than 90% of the world rice crop isplanted (UN 1986) and where an even higher proportion of the rice produced isconsumed. Through a global international research system, delivering practical,production-oriented research findings to farmers and utilizing both public andprivate agencies, the rice needs of Asia and the world can be met.As is shown in Table 1, 1984 rice yields in East Asia, South Asia, and SoutheastAsia varied widely (5.4, 2.1, and 2.8 t/ha, respectively). Yields in South andSoutheast Asia must be increased drastically if rice production is to keep pace withprojected world population increases (Table 2).

Table 1. Rice production and yields for the world and for major regions (IRRI 1986).RegionProduction (thousand t) Area (thousand ha) Yield (t/ha)1950 1975 1984 1950 1975 1984 1950 1975 1984World 2.54 3.273.87 5.401.88 2.142.08 2.781.81 2.133.92 4.411.811.715.13 5.184.13 3.89163,186 359,693 469,959 103,062 147,519 1.58 2.52 3.19Asia a 151,324 328,018 433,19796,217 142,668 128,955 132,572 1.57East b 75,615 159,219 212,184 32,202 42,192 39,3092.35 South c 45,207 100,615 123,005 41,445 53,48957,5961.15 Southeast d 32,578 69,406 99,273 23,278 33,316 35,690 1.40 South America 4,142 11,687 14,5422,407 6,459 6,815 1.72 North America 2,3977,907 8,5211,071 2,016 1,934 2.24 Africa 3,7397,729 8,582 2,899 4,2755,008 1.29 Europe 1,288 1,9251,959 299 375 378 4.31 Others 2962,427 3,158 169 588 812 1.75 a Countries in East, South, and Southeast Asia, and Iran, Iraq, Turkey, and others.b China including Taiwan, Japan, Korea DPR, and Korea Rep.c Afghanistan, Bangladesh, India, Nepal, Pakistan, and Sri Lanka.d Burma, Indonesia, Kampuchea, Laos, Malaysia, Philippines, Thailand, and Vietnam.Totals may not add up due to use of USDA data.

A global rice research system 317Tabla 2. World rice production and yield projections. a1950 1975 1984 2000 2025World population (billions) 2.51 4.08 4.87 6.00 8.00Asian population (billions) 1.38 2.35 2.83 3.70 5.00World rice production 163 360 470 601 800.00Asia rice production 151.3 328.0 433.2 553.7 737.4World yield 1.58 2.52 3.19 4.07 5.42a Projections for the years 2000 and 2025 were on 1984 planted areas and popula-tions.Human population growth and agricultural developmentBefore discussing research systems, let us look at human population growth from1850 to 1987, review some of the dynamic interrelationships responsible for the rapidgrowth, and project what might be expected in the next 25-30 yr.In 1850, world population was one billion people (Fig. 1). It increased to 2billion by 1930 (80 yr), to 4 billion by 1975 (45 yr), and to 5 billion by 1987 (12 yr). Atpresent rates of growth, world population should reach 6 billion by 2000, or sooner,1. World population growth.

318 H.M. Beachelland 8 billion by 2025 to 2030. (It took 1,650 yr, from 1 A.D. to 1650 A.D., for thepopulation to reach 500 million, and 200 yr, from 1650 to 1850, to reach the firstbillion.)Population growth has been influenced by advances in modern medicine(vaccines, anesthesiology, antibiotics, and malaria control) and by the ability ofagriculture to produce the food needed by the expanding population.Agriculture has been able to produce the food and fiber required by applyinghighly sophisticated research findings, such as• Ludwig’s theory of soil fertility,• Mendel’s laws of genetics,• hybrid vigor,• development of modern fertilizers at prices farmers can afford,• land development (irrigation and land shaping), and• DNA and related cellular and nuclear genetics.In 1860, Asia made up about 60% of the world population; today, Asia stillmakes up close to two-thirds of the world population (USDA 1986).National rice research programsAmazing increases in rice production were made during the last 25 yr (Fig. 2), andper capita availability of rice has actually increased recently. The increased riceproduction achieved in Asia can be attributed to many forces. The demand for morerice by rice-producing countries was the driving force. Strong national rice researchprograms were essential for the advancement of national rice production. Nationalgovernments met this challenge by providing facilities and trained manpower to dothe job. They set goals that considered both the rural and urban segments of theirpopulations and, as the records show, they achieved those goals.They did this in many ways. In some instances, nationalism was set aside asnational leaders looked elsewhere for technology and financial support in thedevelopment of their domestic rice research programs. Why spend research funds,which are usually in short supply, for something already available?The development of new varieties is an excellent example. In Indonesia, asdisease and insect epidemics occurred, varieties developed at the International RiceResearch Institute (IRRI) were introduced to close the gap. Farming practices areanother example. Many nations looked to IRRI and elsewhere for new technologyin order to grow the new high-yielding varieties.International cooperation and collaborationInternational cooperation began to take hold about 1950, when rice shortagesbecame more acute and rice-producing countries saw the need for immediate action.The following developments played important roles in cementing internationalcooperation:• The early program of the International Rice Commission, sponsored by theFood and Agriculture Organization of the United Nations.

A global rice research system 3192. Rice yield—history and projected needs.• Assistance of universities in developed countries in degree training, professorexchange programs with universities in developing countries, and collaborativeresearch programs that brought trained research scientists to Asiato work cooperatively in developing-country rice research programs.• Grant and loan funds from many sources including the World Bank andmany developed nations.• In-country research programs sponsored by governments of developedcountries such as Japan.• IRRI, through cooperative and collaborative research, as well as many otherways.The IRRl programsIRRI has had a profound influence on the development of national rice researchprograms, particularly in Asia. IRRI programs have been carried out through a freeand open interaction between IRRI and national administrators and scientists,followed by a vast network of training and research programs organized by IRRIand national programs. They include• Production-oriented practical training and advanced degree training (incooperation with universities).• The International Rice Production Training program.• The International Rice Germplasm Center, which contains more than 77,000rice accessions. Seeds are available to all agencies requesting them.

320 H.M. Beachell• The Genetic Evaluation and Utilization research and training programs.• The International Rice Testing Program, which is global in scope.• The International Network on Soil Fertility and Fertilizer Evaluation forRice.• The Asian Rice Farming Systems Network.• Cooperative country projects organized at the request of national programs.• A communication and publications program that prepares and publishesreports on international conferences, workshops, monitoring tours, specialscientific reports, books, and other information concerning rice.• Technology sharing with advanced universities and other agencies, throughwhich IRRI is able to tap the scientific expertise and equipment of advancedscientific institutions.Global cooperation and collaborationIt is essential that rice production keep pace with world population growth duringthe next 25 yr and beyond. National research programs must be linked through acontinuously improved international research system that is global in scope. Itshould include many country-to-country interactions. More emphasis needs to beplaced on site-specific production situations that take into account not only precisedelivery systems to the farmer, but also the socioeconomic factors of the country andthe location within the country. All types of rice production should be confronted—lowland irrigated, rainfed, deepwater, tidal swamp, high elevation, and dryland.Both highly intensified and near subsistence farming practices must be addressed,whether in Asia, Africa, Latin America, or elsewhere. Production for both incountryconsumption and export must be considered.We can improve on the present systems through more interaction andcommunication among the many agencies (both public and private) involved ininternational cooperation. When I was stationed in Indonesia (1972-82), six or moreagencies were cooperating with the Indonesian Government on rice-related research,teaching, and extension. Little interaction among the agencies existed, except forstrictly informal communication among the Indonesian and expatriate scientistsinvolved.For the future, the availability of grant and loan funds for rice research likelywill be considerably reduced. With production problems much better understoodnow than in 1960, there is every reason for national and international agencies tointeract and communicate more freely. This would avoid unnecessary duplication ofeffort and would lead to a more direct approach to international cooperation.National leaders should take the initiative in developing and establishingsound, long-term rice production policies that will meet the current and continuingneeds of a particular country. The site-specific nature of rice production and itsinterrelationships with social and economic considerations within a country meansthat more domestic research needs to be undertaken. Strong national leadership willbe needed to carry out the programs. Assistance, collaboration, and cooperationwith other countries and international agencies will be essential. National leadershipmust take the lead in establishing and maintaining cooperation.

A global rice research system 321African and Latin American programsMost Asian rice research programs have made more rapid progress than manyprograms in Africa, Latin America, and adjoining areas. How can these programsbe accelerated? In some instances, too much stress has been given to Asiantechnology (varieties and farming practices). The same situation existed in Asia inthe 1950s, when too much attention was being given the application of technologyfrom developed countries. On the other hand, a lot of information proved to behighly useful and was responsible in part for the rapid advances made. The same willbe true in Africa.Are we paying enough attention to African germplasm? Combining theimproved plant characteristics widely used in Asia into African backgrounds mightbe a favorable move. More detailed studies on African varieties might be considered;this should include the collection of more African cultivars.African national programs must take a leading role in strengthening riceresearch, as the Asian programs did in the 1960s. The international researchinstitutes in Africa and Latin America that are deeply involved in agriculturalresearch in their respective areas are proving to be highly beneficial to the riceresearch programs in Africa and Latin America. As national rice research programsin these areas continue to develop, they will be able to make more efficient use of allof the international research institutes, including IRRI (a global interaction).International cooperation should be initiated by national programs and bebased on a country’s specific needs. The South Korean japonica/indica breedingprogram that led to the Tong-il-type varieties is an example of country-initiatedcooperation and collaboration. Blast-resistant Tong-il-type varieties were needed, aswell as more cold-tolerant types. The cooperative project with IRRI that wasorganized (one of the first such projects) still exists, with extension into otherresearch areas. Blast-resistant varieties were developed. Cold tolerance in the Tongil-typeshas progressed, but is still a problem. The National Research Center of Japanis conducting research in this area. The extra-high yield project that will involvejaponica/ indica hybridization is an example. A better understanding of the nature ofcold tolerance that can be expected from the Japanese project should haveapplication in South Korea and other countries.Applying the new biotechnologyNew research techniques resulting from biotechnology can be expected to develop atan ever increasing rate. We must take a close look at those developments for possiblebreakthroughs, but we must at the same time make sure that a guaranteed minimumflow of adapted and economic production-oriented research reaches farmers’fields.In many instances, it is not necessarily new technology that we need so much as fullutilization of present-day technology. More irrigated hectares and land improvementthrough the reshaping of fields and appropriate farming systems that best fit aCountry’s needs for rice, whether for in-country consumption or for export, shouldbe part of the global research system.

322 H.M. BeachellPrivate corporation inputI would like to discuss the possible impact that large corporations can have onagricultural research, specifically on rice research. For many years, chemicalcompanies have been developing crop protection chemicals. The impact ofmachinery manufacture on mechanized agriculture and the production of presentdayfertilizers in the developed world are other examples (Fig. 3). Large private seedcompanies have been conducting research in the development of varieties ofvegetables, maize, grain sorghum, wheat, sugar beets, and other crops, and havebeen selling seed (e.g., Pioneer, De Kalb). Large chemical and pharmaceuticalcompanies are becoming increasingly active in biotechnology and seed businesses.They see the new plant sciences as a good investment for the future and are becomingincreasingly responsible for rapid developments in biotechnology. In addition, wehave seen biotechnology venture companies moving into the seed business(Bio Technica, United Agri Seeds). Also, we have companies (such as DNA PlantTechnology Corporation) working with the food industry.We need to recognize that private industry has a role to play in agriculturaldevelopment. All of these companies recognize that seed is the delivery vehicle forbiotechnology and plant science developments in agriculture.In the U.S., Europe, and elsewhere, private companies are developing,producing, and marketing seeds of many of our food crops. Rice has been anexception. There is a need to strengthen rice seed programs in most countries. Justhow this might be done is difficult to project. Perhaps we can learn from the3. World fertilizer consumption. 1906-40 (Food and Agriculture Organization), 1950-83 (IRRI statistics).

A global rice research system 323examples of the commercial development of other crops in using both public andprivate agency resources in future rice research.The first large corporate venture on rice research in the U.S. was in 1980, whenRing Around Seed Corporation and the China National Seed Corporation began ajoint venture to evaluate and develop hybrid rice varieties outside China.They produced seed and tested several Chinese hybrid varieties in the U.S. anddeveloped new hybrids. The hybrids produced very high yields, but initially lackedthe grain quality characteristics required by U.S. markets. Seed production was alsoa constraint in adapting the Chinese techniques to the mechanized farming practicesused in the U.S.The venture was expanded in 1986 when Farms of Texas Co., Alvin, Texas—alarge corporate farm (20,000 ha)—was brought into the venture to help researchhybrid rice seed production techniques under mechanized farming practices,develop production practices for hybrid rice, and develop new hybrid varieties. Thisis a multidisciplinary approach involving breeders, cellular and nuclear geneticists,agronomists, soil scientists, pathologists, seed technologists, and economists. Thecorporate members who set up the venture anticipate a profit from the sale of hybridrice seed and standard varieties in the U.S.Rice farmers and seed-conditioning companies from Arkansas, Louisiana,Mississippi, and Texas were selected as associate growers to produce the seed of bothhybrid and standard varieties. The program will be expanding into California.Under a 3-way agreement, the American corporation Hybrid Rice, Inc. wasorganized; all hybrid rice seed sold in the U.S. will be produced and marketedthrough it.In addition to the evaluation studies of the corporations, the agriculturaluniversities—Texas A&M, Louisiana State, Mississippi State, and ArkansasUniversity—are evaluating the hybrid varieties.The business venture has research contracts with the University of Nottingham(England) and DNA Plant Technology Corporation (USA) to bring together thelatest developments in biotechnology. In other words, both plant and graincharacteristics as well as machinery are being utilized to develop the componentVarieties of hybrid rice and to mechanically produce the seed at economic levels.The China National Seed Corporation and Ring Around Seed Corporationhave a similar venture with Mitsui Corporation in Japan to develop japonica hybridvarieties.These projects involve all phases of hybrid rice development, production, andmarketing. Through this collaboration, we can expect a thorough and completeassessment of the use of hybrid varieties throughout the world. Both privatecompanies and public agencies are cooperating in projects covering a wide range ofdisciplines and production conditions, each with specific objectives in mind.The success of this venture will set the stage for other global projects on otherphases of rice and other crop research, such as the types of developments needed tolocate and utilize apomixis in rice, some of the more difficult disease controlsituations (such as those involving sheath blight), a better understanding of coldtolerance, and the further advancement of the new biotechnology.

324 H.M. BeachellConclusionRemarkable advances in rice research in the last 25 yr have been applied to riceproduction in farmers’ fields. This was made possible through strong national riceresearch agencies that cooperated and collaborated freely with many agencies fromdeveloped countries and with international research institutes. IRRI has made ahighly significant contribution through its many network programs coveringresearch, training, and communication.For the future, closer interaction among the international agencies assistingnational programs should be stressed. Further cooperation with African and LatinAmerican countries should be developed.The impact of private corporations on furthering rice research should beconsidered. The present world monetary situation indicates that funds for riceresearch are apt to be reduced considerably compared to those available in 1960-86.If this proves to be the case, every effort should be made to avoid unnecessaryduplication of effort.References citedIRRI—International Rice Research Institute (1985) Research highlights 1985. P.O. Box 933, Manila,Philippines.IRRI—International Rice Research Institute (1986) World rice statistics 1985. P.O. Box 933, Manila,Philippines.UN—United Nations (1986) United Nation’s bulletin of statistics. New York.USDA—United States Department of Agriculture (1986) Grains-world grain situation and outlook.Foreign Agriculture Circular FG8-86. Foreign Agriculture Service, Washington, D.C.NotesAddress: H. M. Beachell, Farms of Texas, Alvin, Texas, USA.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

International collaborationon conservation, sharing,and use of rice germplasmT.T. CHANG. Y. S. DONG, R. S. PARODA, AND C. S. YINGThis paper focuses on the genetic conservation and exchange of ricegermplasm by lRRl and two major rice-growing and germplasm-richcountries, China and India. They serve as examples of active internationalcooperation. Attention is given to additional measures that will furtherstrengthen aspects of genetic conservation and use.Plant germplasm fuels all crop improvement activities. Rice researchers are blessedwith a remarkably rich and diverse array of genetic resources which have beencontinuously tailored by rice growers across ten thousand years of cultivation inmany parts of the world. The complex processes involved in attaining the enormousdiversity in rice germplasm have been discussed elsewhere (Chang 1985).The contributions of rice germplasm to rice crop improvement are uniqueamong the major food crops. The most notable contributions are• Semidwarfism, used to improve yield potential.• Resistances to and tolerances for many biotic and ecologic stresses.• Cytoplasmic male sterility, used in hybrid rice production.Rice researchers are active in international and interinstitutional exchange ofboth unimproved and elite germplasm. Multiple channels of exchanges anddissemination established in the 1960s have been continually expanding. IRRI hasbeen a major force in coordinating and implementing such collaboration, eitherinformally or through networks, such as with the IRTP nurseries.ChinaThe history of rice cultivation in China dates back at least 7,000 yr. Rice is thatcountry’s most important food crop. The planted area is more than 34 million ha(30% of the total crop area, with 40% of the total grain production). Cropenvironments that span a range from 18 °N to 53 °N latitudes, and from sea level to2,600 m altitude helped Chinese rice to diversify from its primary area ofdomestication in the warmer regions of south and southwest China.The national crop genetic resources program of China is under the leadership ofthe Institute of Crop Germplasm Resources (ICGR) of the Chinese Academy of

326 Chang et alAgricultural Sciences (CAAS) in Beijing. Operational aspects of exchange, storage,distribution, and evaluation of rice germplasm are handled by the China NationalRice Research Institute (CNRRI) in Hangzhou. A modern genebank capable ofstoring 400,000 accessions of crop seed over the long-term was completed at theICGR in 1986. It will be the site of the base collection of major crops, including rice.CNRRI is mandated to provide duplicate storage for the base collection of rice andto serve as the center for active rice collection within the national and internationalcommunity. CNRRI also coordinates participation of Chinese rice researchers ininternational testing.Size and composition of germplasm collectionThe assembling of rice varieties started in the 1930s, primarily in provinces south ofthe Yangtze River. During the mid-l950s, a massive nationwide canvassing andcollection project resulted in the gathering of 57,647 rice accessions from 15provinces. After comparison, evaluation, and cataloging, a total of 41,379traditional cultivars were maintained by various provincial academies in collaborationwith the CAAS (CAAS 1986). In 1978-82, during a supplementarysurvey and with additional collecting effort, more than 10,000 accessions wereacquired (Dong 1983). According to information assembled by CNRRI in 1986,about 60,000 rice accessions are conserved, 49,714 of which belong to the traditionaltype (Table 1).China is also rich in wild rice germplasm. Three wild species ( Oryza sativa f.spontanea/ O. rupifogon, O. officinalis, and O. meyeriana ) are known to be widelydistributed in Fujian, Guangdong, Guangxi, Hunan, Jiangxi, and Yunnan Provinces(Table 2). The geographical distribution of Chinese wild rices was depicted by theformer Kwangtung Agricultural and Forestry College (1975) and CAAS (1986). Thesix major regions of rice cultivation are1. the south region—hot and humid, double-cropping area;2. the central region—warm and moist, single- or double-cropping area;3. the northwestern region—semiarid, single-cropping area;4. the southwestern China plateau—moist, single-cropping area;5. the north region—semiarid, single-cropping area; and6. the northeastern region—mesophytic, early, single-cropping area.The rich genetic diversity falls into two ecogeographic races: hsien (indica) andkeng (sinica or japonica). Both ecotypes may be found in the warmer regions (1-4).The low-amylose japonica race is adapted to cooler regions and higher elevations(Ting 1961).Further delineation may be made by growing season (early, intermediate, orlate; or first crop or second crop), soil-water regime (wetland, upland, shallow water,and deep water), and cooking characteristic (nonglutinous or glutinous) (CAAS1986, Ting 1961).National system of genetic conservationIn recent years, Chinese rice workers have recognized the importance of germplasmin rice improvement and have cooperated fully in collecting rice germplasm, both at

Conservation and use of rice germplasm 327Table 1. Numbers of Chinese traditional rice cultivars collected and preserved indifferent provinces, July 1986.Province, municipality, orautonomous regionAccessionsGuangxi 8,798Yunnan 8,467Guangdong 6,204Hunan 4,872Guizhou 4,279Sichuan 3,255Jiangxi 2,991Fujian 1,969Jiangsu 1,816Zhejiang 1,653Hubei 1,440Taiwan1,360 aAnhui 608Shaanxi 540Henan 430Shanghai 304Hebei 292Shandong 85Heilongjiang 80Shanxi 76Jilin 66Liaoning 45Tianjin 27Ningxia 18Xinjiang 16Neimonggol 10Beijing 8Gansu 3Xizang 2a Including improved rice varieties.Total 49,714Table 2. Number of accessions of three wild species originating from six provincesof China, as of July 1986.Province orautonomous regionO. sativa f.spontaneaRoschev.O. officinalisWail.O. meyerianaBaill.SubtotalGuangdong 2,300 185 15 2,500Guangxi 1,716 201 – 1,917Yunnan 12 5 34 51Hunan 400 – – 400Jiangxi 181 – – 181Fujian 6 – – 6Total 4,615 391 49 5,055

328 Chang et althe provincial level or under special projects. The ICGR staff made special collectiontrips to Fujian, Guangdong, Sichuan, Tibet, and Yunnan. The semiarid and coldregion of Tibet yielded a considerable number of cultivars, but no wild rices werefound.The ICGR staff also has conducted many studies on the reaction of ricegermplasm to cold temperature, blast, yellow stem borer, brown planthopper, stemborers, and gall midge. CNRRI also has systematically characterized and evaluatedimproved materials. Materials have been screened for additional traits, includingdrought resistance, salinity and alkalinity tolerance, grain quality, and resistance tothe whitebacked planthopper.Annual conferences of crop germplasm workers and affiliated researchers heldeach year at different locations help national institutions strengthen theirconservation and evaluation efforts. The conferences also enlist the cooperation ofworkers at provincial and local levels and from the agricultural universities andcolleges.Genebank facilitiesThe ICGR has both medium- and long-term seed storage facilities. CNRRI is nowbuilding its seed storage facilities, which combine short-, medium-, and long-termrooms. The CNRRI staff inventoried 60,000 accessions, of which about 49,700 arethe traditional type. About 15,000 rice accessions are now stored at CNRRI, andthat institute will handle seed distribution in response to domestic and internationalrequests.International exchangeGermplasm exchange has expanded rapidly in the 1980s. ICGR supplied 1,322 seedsamples to foreign researchers in 1985, 1,240 in 1986. The International RiceGermplasm Center (IRGC) at the International Rice Research Institute (IRRI) isthe main recipient, averaging 1,000 accessions a year.Introduction from foreign sources ranged between 1,100 and 12,000 samples.IRRI supplied an average 2,200 samples a year from 1981 to 1986. Among theintroductions, IR8 had the largest planted area (0.78 million ha) in the 1970s;BG90-2 had the largest (slightly more than 1 million ha) in the 1980s. Numerousforeign introductions are being used by Chinese researchers in their varietalimprovement activities.Use of germplasmThe continuous expansion of the world’s rice-producing areas over the last fivemillennia was undoubtedly aided by exploitation of indigenous germplasm. Theearly-maturing indica rices of south and central China probably benefited fromgenes of the Champa rice originating in central Vietnam (cf. Chang 1987a).During the early 1930s, Prof. Y. Ting used crosses between rice cultivars and thecommon wild rice of Guangdong Province to breed Yatsen 1. Further selection andcrossing led to the development of Bao-tan 2 and Bao Tai-ai semidwarfs, two of thehighly pest-resistant cultivars of China. The Shanghai Academy also used a white-

Conservation and use of rice germplasm 329awned wild rice in breeding early japonica rices (Kwangtung College of Agricultureand Forestry 1975).Two semidwarf sources discovered in 1956, Ai-jiao-nan-te and Ai-zai-zhan,were used immediately by Chinese breeders. The series of high-yielding semidwarfsreleased in the late 1950s and the 1960s greatly upgraded rice production south of theYangtze River (cf. Shen 1980).The major source of cytoplasmic male sterility in hybrid rice breeding camefrom the wild abortive spontanea type found on Hainan Island (cf. Lin and Yuan1980). Its use was a major breakthrough in the production of hybrid rice, which nowoccupies almost 10 million ha in China.Chinese breeders also made extensive use of foreign introductions, notablyIRRI material, in both conventional breeding and hybrid rice improvement. IR8made the largest inroad in the warmer regions during the 1960s (CAAS 1986).Germplasm from China has supplied other rice-growing countries with manyuseful parents, such as Fortuna (in the U.S.) and China (parent of Peta and otherimproved varieties in Indonesia), Dee-geo-woo-gen and its semidwarf derivatives,Ai nan zao 1, and others, Leng kwang and China 1039 (cool temperature-tolerantsources for tropical regions), and several outstanding breeding stocks (used in Japanand Korea) (CAAS 1986).IndiaThe gene center in India is immensely rich in rice genetic resources, including landraces, special ecostrains, wild rices, and weedy types (Paroda and Arora 1986).Conservation of indigenous rice germplasm began in the early 1950s. The NationalBureau of Plant Genetic Resources (NBPGR) coordinates activities related toexploration, exchange, quarantine, evaluation, and preservation of numerous cropplants, in collaboration with specialized crop institutions/ cooperative projects andagricultural universities. The NBPGR also serves as the channel for internationalcollaboration.Exploration and collectionExploration and collection of rice germplasm have been undertaken by a greatvariety of institutions in India: rice experiment stations, agricultural colleges anduniversities, the Central Rice Research Institute (CRRI), the Directorate of RiceResearch (formerly All India Coordinated Rice Improvement Project), andNBPGR staff at headquarters and regional stations. Since 1985, NBPGR hasdevoted increasing efforts to the conservation of rice germplasm, especially thatfrom marginal rice-producing areas rich in land races and wild species of Oryza. TheBureau also conducts foreign expeditions in cooperation with the InternationalBoard for Plant Genetic Resources (IBPGR). One new species, Oryza indandamanica,recently was found on one of the Andaman Islands. Coordinatedcollection activities under the Indian Council of Agricultural Research since 1979have resulted in the assemblage of about 6,000 rice samples (Paroda and Sharma1986).

330 Chang et alThe national system of genetic conservationNBPGR was separated from the Indian Agricultural Research Institute in 1976. Itnow has a network of six regional stations, nine base centers, three quarantinestations, one satellite station, and one experimental farm (Fig. 1). NBPGRcollaborates closely with other research institutions in India to develop a nationwideprogram of genetic conservation. During early 1987, a national symposium enlistedgreater participation from other institutions and formulated future thrusts (NBPGR1987). NBPGR itself also has greatly expanded its storage facilities and activities1. NBPGR network in India. Based on Survey of India map with the permission of the Surveyor Generalof India. The territorial waters of India extend into the sea to a distance of 12 nautical miles measuredfrom the appropriate baseline.

Conservation and use of rice germplasm 331under its five divisions (Fig. 2): (1) plant exploration and collection, (2) germplasmevaluation, (3) germplasm conservation, (4) germplasm exchange, and (5) plantquarantine.NBPGR also has strengthened quarantine aspects of plant introductions andinternational exchange, to safeguard plant health (Paroda et al 1988).Major holdings of rice germplasm in India are kept in three centers: NBPGR—8,000 accessions; CRRI—18,000 accessions; and Regional Rice Research Station ofM.P. State at Raipur—20,000 accessions.Genebank facilitiesSince 1984, NBPGR has been adding cold storage facilities for long-term seedpreservation. The Bureau also has been providing storage space to CRRI (8,000samples) and the Raipur station (20,000 samples) until storage facilities areestablished at CRRI. By 1990, storage capacity will accommodate 50,000 samples.All rice breeders have been invited to rejuvenate and deposit their rice seed at thenational center. NBPGR also is serving as the distribution center for sources ofoutstanding tolerance/resistance supplied by IRRI.International exchangeNBPGR processes 25,000-50,000 rice seed samples a year. The majority of thematerials are for International Rice Testing Program (IRTP) nurseries. Hundreds ofIndian scientists are involved in the IRTP network, many more are receiving seedmaterial from the IRRI breeding program and the IRGC through NBPGR’squarantine facilities.2. Organizational setup of the NBPGR.

332 Chang et alNBPGR regional stations at Trichur, Bhowali, and Shillong are maintainingand increasing the Bureau’s rice collection, as well as receiving seed materials fromIRRI and distributing them to Indian workers. During 1976-86, the Bureauannually processed 2,103-73,115 introductions from IRRI and 61-5,494 exports toIRRI. NBPGR not only coordinates germplasm activities, but also developsguidelines on exchange, plant quarantine, preliminary evaluation, anddocumentation.Use of germplasmRice workers in India have made profitable use of indigenous rice germplasm inmeeting the ever-expanding demand for rice. Historical accounts of rice breeding atvarious stations/colleges were provided by Parthasarathy (1972) and Gangadharan(1985). Varieties developed by selection and purification of traditional varietiesnumber more than 400 and elite varieties evolved by hybridization total more than ahundred.Indian germplasm is particularly rich in resistance to diseases and insects, andtolerance for drought, salinity, flooding, and waterlogging. Indian rices havefurnished a major portion of the pest resistance genes used at IRRI. Theindica/japonica hybridization project has produced the popular variety Mahsuri,which is adapted to adverse conditions. The wild rice O. nivara collected from UttarPradesh State has furnished a useful Gsv gene which controls grassy stunt virusbiotype 1 (Chang et al 1982, Gangadharan 1985).Breeders also have made profitable use of foreign introductions from otherAsian countries and IRRI. The introduction of TN1 and crossing it with local ricestriggered the Green Revolution for rice in India. Since the late 1960s, IRRI materialand IRTP entries have been used extensively (Dalrymple 1986, Hargrove et al 1985,IRRI 1980).IRRIFrom its inception, IRRI has been intensely involved in the conservation andexchange of rice germplasm through its genetic resources program (IRRI 1985).Field collectionCoordinated worldwide field collection activities began in 1971-72. Fourteen Asiancountries, two African countries, several international and regional centers, andIRRI combined their resources to survey germplasm-rich areas, particularly inpreviously unexplored regions or areas with ecological stresses. This led to theassemblage of more than 43,000 samples by 1986. IBPGR joined the activities in1978. IRRI’s direct participation netted about 12,000 seed samples. Thiscollaborative venture is unprecedented in the history of genetic conservation (IRRI1983).While the collection of unimproved cultivars in some inaccessible remote areashas yet to be completed, in the future IRRI will focus on the conservation of wildspecies in the genus Oryza. This neglected segment will require close cooperation andtechnical expertise.

Conservation and use of rice germplasm 333The mid-1987 holdings of rice germplasm in the IRGC are as follows: 72,550 O.sativa accessions, 2,983 O. glaberrima strains, 2,268 populations of wild species, 695genetic testers and mutants, 1,972 recently planted O. sativa samples (unregistered),and 1,541 newly received and unplanted samples.Exchange and dissemination of seedThe volume of seeds and material distributed by IRGC in the last 5 yr is given inTable 3. Although the total number of samples remains the same, the number of seedrequests has continuously increased, signifying expanding research activities innational programs and at IRRI. Workers in biotechnology have greatly increasedthe demand for exotic germplasm (wild species and temperate-zone cultivars). TheIRGC staff also has tightened quality control for seed purity, genetic identity, andseed viability (Chang et al 1987).Technical assistance to other genebanksIn recent years, efforts directed to training germplasm workers and improvinggenebank facilities in national and regional programs have increased. Examples ofsuch new activities are assistance to the genebanks of China, India, Thailand, theInternational Institute of Tropical Agriculture, and the West Africa RiceDevelopment Association. A 12-mo training course on genetic resources conservationand management was completed in 1986; 12 workers were awardedAssociateship of IRRI diplomas. Short-term training of germplasm workers hasbeen provided many national programs.Public informationConcern about the ownership and security of germplasm collections is growing.Social-political activists have questioned the free access of developing countries tobase collections, most of which came from such countries but which primarily arestored in developed countries and the International Agricultural Research Centers.IRGC is a custodian of many national rice collections, and has returned wholecollections to several donor countries. It also has intensified an information programto allay unwarranted fears. A duplicate set of IRGC holdings is deposited at theNational Seed Storage Laboratory at Ft. Collins in the U.S. for security. CanvassingTable 3. Progress of the International Rice Gamplasm Center (IRGC) in seeddistribution, 1982 to 1986.YearNo, of O. sative samplesdistributed (no. of requests)Inside IRRlNationalprogramsNo. of O. glaberrima genetictesters/wild rices distributed(no. of requests)Inside IRRlNationalprograms1982198319841985198633,975 (279)23,443 (287)28,170 (277)30,709 (306)39,135 (327)11,075 (154)3,756 (150)6,619 (146)4,736 (172)9,897 (187)378 (26)342 (20)83 (17)1,138 (24)2,253 (13)438 (20)972 (38)448 (29)1,174 (36)595 (28)

334 Chang et alis being done to ensure consolidation and coordination among genebanks. Nationalscientists have been freely supplied with characterization and evaluation datagenerated at IRRI.Use of the base collectionShortly after IRRI began its research operations, in late 1961, the evaluationprogram was streamlined and expanded. The GEU (Genetic Evaluation andUtilization) program was formalized in 1973 (Brady 1975). Evaluation activitiesranged from extensive and nearly comprehensive tests for blast, bacterial blight,protein content, and drought to intensive studies on biotypes of insects, races ofpathogens, and adverse soil factors. Outstanding sources of resistances andtolerances have been identified (Chang et al 1982, Heinrichs et al 1985, Khush andVirmani 1985).Reports of profitable use of diverse sources of important traits by breeders atIRRI and in different country programs may be found in numerous publicationsand reports. Brief mention is made here of the following outstanding achievements:• The sd 1 gene for semidwarfism from Dee-geo-woo-gen.Multiple-resistance genes to diseases and pests found in Indian cultivars,such as in TKM6, ASD7, and PTB.• The Gsv gene for resistance to grassy stunt from O. nivara of North India.• Early-maturity genes with high yielding backgrounds pooled from Chineseand Indian sources.Recent efforts by IRRI scientists have added several potentially useful traitsfrom land races and wild relatives. Selected examples include• O. brachyanta, an African species, the only known source of resistance to thewhorl maggot Hydrellia philippina.• The Rayada rices of Bangladesh that combine 11-mo duration, absence ofgrain dormancy, and 5-m elongation ability.• Resistance to the recently identified biotype 2 of grassy stunt, present only inthe perennial strain Guan-keng/ O. rufipogon// O. longistaminata (Aguieroet al 1984).• Resistance to multiple insects in wild species having the C genome ( O.officinalis, eichingeri, and minuta ).• Resistance to the leaffolder in land races of Bangladesh and Sri Lanka,recently collected by international efforts.• Tolerance for or field resistance to the brown planthopper in the Indonesianland race Utri Rajapan.Meanwhile, IRRI scientists are focusing research efforts on increasing andstabilizing rice yields in unfavorable environments, where yields fluctuate morewidely than in the fully irrigated areas. The widespread drought in many Asiancountries in 1987 will focus increased attention to the plight of the subsistence ricefarmers.In the long run, IRRI’s progress in rice improvement will likely be surpassed bynational efforts, initially stimulated by the IRRI approach and continuallyexpanded and coordinated within countries. Programs similar to the GEU scheme

Conservation and use of rice germplasm 335have been established in several countries (cf. Harahap et al 1982) and evaluationmethods using local sources have been further refined. We can look forward to evenmore rewarding results from the use of diverse rice germplasm in different riceproducingcountries.Areas for considerationAlthough progress in international collaboration, exchange, and use of ricegermplasm has been most impressive, continuous and expanded efforts in someareas are still important.Completion of field collectionKnowledge about the geographic and ecologic distribution of wild species and landraces in specialized ecological niches should be strengthened. This area requiresmore national input. IRRI will continue to train field collectors for nationalprograms.Security of existing collectionsMany national programs are adding genebank facilities, Efforts should be made toproperly design or improve those physical facilities so that operations will be moreefficient and seed longevity markedly extended. The cost factor is high, andgenebank managers must try to reduce operating and maintenance expenses.Public information and national systemsEvery genebank needs to extol the value of rice germplasm, so that public supportwill be increased and ensured. On the professional level, advisory committees fromall disciplines working on rice should be organized to broaden the scientific base andto provide increased support to the national germplasm systems.Incentives to germplasm workersGermplasm workers in general suffer from inadequate incentives for professionaldevelopment. The workers themselves should seek ways to expand their areas ofscientific endeavor, while cooperating with other disciplines to broaden the scope ofscientific and related activities. A spirit of service is an essential prerequisite ofgermplasm workers. Every rice germplasm worker should strive to be a source ofinformation on the rice germplasm of his/her country or province.Use of germplasmCommunication between germplasm workers and users (the evaluators andbreeders) historically has been less than adequate. It is up to the germplasm workersto explain the unexploited traits in conserved stocks to present and potential users.This requires improved documentation and information. A national cropimprovement scheme should include this phase of cooperation and coordination.From our experience over the last two decades, we are confident that ricegermplasm will play an even greater role in crop improvement. The magnitude of

336 Chang et alsuch advances will depend partly on the quality of service provided by germplasmworkers. Meanwhile, germplasm users in public institutions should make greater useof unexploited genetic diversity, so that they can continue to provide a muchappreciatedservice to rice farmers. Genetic diversity in elite cultivars and hybridrices needs to be reinstated by tapping new gene cytoplasm in little-used germplasm(Chang 1984).Whatever biotechnology may achieve in fixing or transferring desirable genesin plants, the basis for improving crop varieties remains a varied stock of germplasm(Chang 1987b).References citedAguiero V M, Cabauatan P Q, Hibino H (1984) A possible source of resistance to rice grassy stunt virus(GSV). Int. Rice Res. Newsl. 9(3):11-12.Brady N C (1975) Rice responds to science. Pages 62-96 in Crop productivity .... research imperatives.Charles F. Kettering Foundation, Ohio.CAAS—Chinese Academy of Agricultural Sciences (1986) Chinese rice science [in Chinese]. AgriculturalPublishing Society, Beijing. 746 p.Chang T T (1984) Conservation of rice genetic resources: luxury or necessity? Science 224:251-256.Chang T T (1985) Crop history and genetic conservation. Rice - a case study. Iowa State J. Res.59:425-455.Chang T T (1987a) The impact of rice on human civilization and human population. Interdisc. Sci. Rev.12(1):63-49.Chang T T (1987b) Saving crop germplasm. SPAN 3(2).Chang T T, Adair C R, Johnston T H (1982) The conservation and use of rice genetic resources. Adv.Agron. 35:37-91.Chang T T, Seshu D V, Khush G S (1987) The rice seed exchange and evaluation programs of IRRI.Pages 21-32 in Rice seed health. International Rice Research Institute, P.O. Box 933, Manila,Philippines.Dalrymple D (1986) Development and spread of high-yielding rice varieties in developing countries.United States Agency for International Development, Washington, D.C. 117 p.Dong Yu-Shen (1983) Survey of conservation activities in Asian countries and proposals for future action- China. Page 30 in 1983 Rice gemplasm conservation workshop. International Rice ResearchInstitute, P.O. Box 933, Manila, Philippines.Gangadharan C (1985) Breeding. Pages 73-109 in Rice research in India. Indian Council of AgriculturalResearch, New Delhi.Harahap Z, Pathak M D, Beachell H M (1982) Genetic evaluation and utilization—a multidisciplinarystrategy. Pages 81-98 in Rice research strategies for the future. International Rice Research Institute,P.O. Box 933, Manila, Philippines.Hargrove T R, Cabanilla V L, Coffman W R (1985) Changes in rice breeding in 10 Asian countries:1965-84. Diffusion of genetic materials, breeding objectives, and cytoplasm. IRRI Res. Pap. Ser.111. 18 p.Heinrichs E H, Medrano F G, Rapusas H R (1985) Genetic evaluation for insect resistance in rice.International Rice Research Institute, P.O. Box 933, Manila, Philippines. 356 p.IRRI—International Rice Research Institute (1980) Five years of the IRTP a global rice exchange andtesting network. P.O. Box 933, Manila, Philippines. 33 p.IRRI—International Rice Research Institute (1983) 1983 Rice germplasm conservation workshop. P.O.Box 933, Manila, Philippines. 109 p.IRRI—International Rice Research Institute (1985) Genetic resources. Pages 41-47 in International riceresearch: 25 years of partnership. P.O. Box 933, Manila, Philippines.Khush G S, Virmani S S (1985) Breeding rice for disease resistance. Pages 239-279 in Progress in plantbreeding. G. E. Russell, ed. Buttenvorths, London.Kwangtung Agricultural and Forestry College (1975) The species of wild rice and their geographicaldistribution in China [in Chinese, English summary]. Acta Genet. Sin. 2(1):31-36.Lin S C, Yuan L P (1980) Hybrid rice breeding in China. Pages 35-52 in Innovative approaches to ricebreeding-selected papers from the 1979 International Rice Research Conference. P.O. Box 933,Manila, Philippines.

Conservation and use of rice germplasm 337NBPGR—National Bureau of Plant Genetic Resources (1987) National symposium on plant geneticresource—proceedings and recommendations. New Delhi. 16 p.Paroda R S, Arora R K (1986) Plant genetic resources - an Indian perspective. NBPGR Sci. Monog.10:1-34.Paroda R S, Nath R, Reddy A P K, Singh B P (1988) Indian plant quarantine systems for rice. Pages77-89 in Rice seed health. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Paroda R S, Sharma S D (1986) Collection of rice germplasm in India—current status and future plans.Paper presented at the All-India Annual Rice Workshop, 14-17 Apr 1987, Narendra DevaUniversity of Agriculture and Technology, Faizabad.Parthasarathy N (1972) Rice breeding in tropical Asia up to 1960. Pages 5-28 in Rice breeding.International Rice Research Institute, P.O. Box 933, Manila, Philippines.Shen J H (1980) Rice breeding in China. Pages 9-30 in Rice improvement in China and other Asiancountries. International Rice Research Institute, P.O. Box 933, Manila, Philippines.Ting Y (1961) Chinese culture of lowland rice [in Chinese]. Agricultural Publishing Society, Beijing.NotesAddresses: T. T. Chang, International Rice Germplasm Center, International Rice Research Institute, P.O. Box 933,Manila, Philippines; Y. S. Dong, Institute of Crop Germplasm Resources, Chinese Academy of Agricultural Sciences,Beijing, China R. S. Paroda, National Bureau of Plant Genetic Resources, New Delhi, India; C. S. Ying, GeneticResources Department, China National Rice Research Institute, Hangzhou, ChinaCitation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Findings from the internationalirrigated rice nurseries,with special reference to ChinaD. V. SESHU AND ZHANG YIHUAThe International Rice Testing Program (IRTP), coordinated by theInternational Rice Research Institute, has established a global network forexchanging elite cultivars and breeding lines among rice scientists aroundthe world and for evaluating those rices under diverse environments. IRTPnurseries are designed to screen for resistance to important biological,physical, and chemical stresses under different cultural systems. One setis targeted to irrigated conditions. Since the inception of the IRTP in themid-1970s, worldwide evaluation of the irrigated trials has identifiedseveral promising varieties of different growth durations, some of whichshow wide adaptability. Varieties have been specifically identified fortolerance for extreme temperatures and adverse soil conditions. Severalpromising lines possess resistance to one or more of the major ricediseases and insect pests. Some entries have been released for cultivationin several countries and some have been used as parents in nationalbreeding programs. The impact of IRTP on rice varietal improvement andproduction in China is cited as a case study.The International Rice Testing Program (IRTP), coordinated by the InternationalRice Research Institute (IRRI) and funded by the United Nations DevelopmentProgramme, was initiated in 1975 to facilitate exchange of elite genetic materialamong rice scientists around the world and to provide a mechanism for testingbreeding material generated by individual rice improvement programs.The international nurseries are broadly grouped into two categories: targetenvironment nurseries and stress screening nurseries. The target environments forwhich nurseries are composed and tested are irrigated and rainfed. The rainfedcategory in turn includes upland, lowland (shallow water), deep water, floating rice,and tidal wetlands.This paper summarizes salient findings from the IRTP irrigated nurseriesevaluated across locations in different rice-growing countries since its inception in1975 and highlights experiences in China.The irrigated trials include both yield and observational nurseries. Yieldnurseries are divided into 4 growth duration groups—very early (about 100 d), early(100-120 d), medium (120-140 d), and late (more than 140 d). Only very early, early,and medium nurseries are organized regularly. Observational nurseries also havesubsets based on growth duration.

340 Seshu and ZhangIrrigated nurseries also are organized specifically for low-temperature and aridregions. Screening nurseries include those for identifying resistance to blast,bacterial blight, tungro virus, stem borer, gall midge, brown planthopper, andwhitebacked planthopper. One nursery is composed for screening against salinityand alkalinity. A special nursery, the International Rice-Weather Yield Nursery(IRWYN), organized 1982-84, studied the impact of major climatic factors on thegrowth and yield of irrigated rice.Irrigated yield and observational nurseriesVarietal performanceEntries that performed well across locations and years in different maturity groupsand their relative yield rankings in different years are summarized in Table 1 (Seshu1986). Entries that produced the highest average yields across locations in the 1986irrigated yield nurseries and observational nurseries and their agronomic traits andreactions to diseases and insects are given in Tables 2-5.Table 1. Yield ranking of promising entries in the International Irrigated RiceYield Nursery (IRYN) trials, 1978-85.Yield rankEntry designation1978 1979 1980 1981 1982 1983 1984 1985BG276-5BG367-4BG367-7lR25588-7-3-1lR25924-51-2-3IR50lR9729-67-3UPR103-80-1-2Location (no.)Entries (no.)Chianung sen yu 13lR13429-196-1IR36lR9828-91-2-3KAU1727Taichung sen yu 285Locations (no.)Entries (no.)BG400-1BR51-282-8IR13540-56-3-2-1lR21820-154-3-2-2-3IR28118-138-2-3IR42IR54Location (no.)Entries (no.)162828IRYN — Very Early10 414 455372821 230 2820 25IRYN — Early5 42 42 4 2 21 2130 43 41 5228 28 28 20IRYN — Medium5 156 1 1 21 15 41 229 3728 294412441281133373828271823228331332473016143729111930304481445308241301414253011315382443342514222528

Tabla 2. Entries in the 1986 IRYN (Very Early) that produced the highest average yields over 25 locations in 11 countries and their agronomic andstress resistance characteristics.Reaction to stress aa Locations reporting the reactions: BI (leaf blast) - Los Baños; BLS (bacterial leaf streak) - Los Baños; BLB (bacterial leaf blight) - Milyang, Chainat,Comille, Mingora; RTV (rice tungro Virus) - Los Baños; ShR (sheath rot) - Comilla; ShB (sheath blight) - Los Baños; WBPH (whitebacked planthopper)- Kala Shah Kaku; GLH (green leafhopper) - Los Baños; YSB (yellow stem borer) - Los Baños; BPH (brown planthopper) - Los Baños.Table 3. Entries in the 1986 IRYN (Early) that produced the highest average yields over 26 locations in 10 countries and their agronomic and stressresistance characteristics.Reaction (score) to stress aa Locations reporting the reactions: BI (leaf blast) - Los Baños; BLB (bacterial leaf blight) - Los Baños, Chainat, Camilla, Joydebpur, Mingore; RTV(rice tungro virus) - Los Baños, Joydebpur; ShB(sheath blight) - Los Baños, Joydebpur; ShR (sheath rot) - Joydebpur; WBPH (whitebacked planthopper)- Kala Shah Kaku; GLH (green leafhopper) - Los Baños; BPH (brown planthopper) - Los Baños; SB (stem borer) - Los Baños.Designation OriginYield(t/ha)Days tofloweringPlant height1 2 3Bl BLS BLB RTV ShR ShB WBPH GLH YSB BPHbiotype(cm)Wei-You 64 China 5.4 88 88 – – 6 – 5 5 5 – – 5 5 7IR50 IRRl 5.3 88 87 8 5 5 4 3 7 7 5 5 3 3 3lR39357-133-3-2-2-2 IRRl 5.1 88 97 1 5 4 4 5 5 5 3 5 3 5 7IR25884-94-3-2 IRRl 4.9 85 91 8 5 6 7 7 7 7 5 3 3 3 3IR28598-60-2-3 IRRl 4.9 85 90 4 5 7 6 7 5 – 3 5 5 5 5Designation OriginYield Days to(t/ha) floweringPlant 1 3BI BLB RTV ShB ShR WBPH GLH BPH SBheight biotype(cm)2 lR13240-108-2-2-3 lRRl 5.1 97 85 4 6 6 4 7 5 7 3 7 3 –Chianung sen yu 26 Taiwan (China) 5.0 102 99 4 4 6 7 7 5 7 3 7 3 5C662083Taiwan (China) 4.9 91 85 7 5 6 6 7 5 7 3 9 3 5IR13524-21-2-3-3-2-2 IRRI4.9 96 82 8 7 5 7 7 5 3 3 7 5 5IR31805-20-1-3-3 IRRl 4.9 101 93 4 6 6 5 7 5 3 3 3 3 3lR32843-92-2-2-3 IRRl4.9 96 89 1 6 6 7 5 – 3 3 3 3 5

1 2 3a Locations reporting the reactions: BI (leaf blast) - Los Baños; NBLS (narrow brown leaf spot) - Pusa; BLS (bacterial leaf streak) - Los Baños; LSc (leafscald) - Barisal, Joydebpur; BLB (bacterial leaf blight - Los Baños, Joydebpur; RTV (rice tungro virus) - Los Baños; ShB (sheath blight) - Los Baños;GLH (green leafhopper) - Los Baños; SBDH (stem borer deadhearts) - Los Baños; SBWH (stem borer whiteheads) - Los Baños; LF (leaffolder) - Joydebpur;BPH (brown planthopper) - Los Baños.Table 5. Entries in the 1986 International Rice Observational Nursery (IRON) with overall good phenotypic acceptability ratings and their agronomicand stress resistance characteristics.1 2 3Table 4. Entries in the 1986 IRYN (Medium) that produced the highest average yields over 14 locations in 7 countries and their agronomic and stressresistance characteristics.DesignationOriginYield Days to(t/ha) floweringReaction (score) to stress aPlantheight BI NBLS BLS LSc BLB RTV ShB GLH SBDH SBWH LF BPH(cm) biotypelR29723-143-3-2-1 IRRl 5.2 112 103 4 9 9 6 6 3 9 3 5 3 8 3 3 3BG380-2 Sri Lanka 5.0 103 97 4 3 9 6 8 9 5 9 5 7 7 7 9 9BR316-15-4-4-1 Bangladesh 4.7 100 107 4 5 7 4 7 9 3 9 5 3 7 5 9 9lR18349-135-2-3-2-1 IRRl4.7 101 96 7 3 9 6 7 6 7 3 5 5 7 5 9 7OR447-20 India4.7 100 98 6 3 9 6 7 9 9 9 – 7 7 7 9 7lR3180983-3-2-2 IRRl4.7 105 93 1 5 7 5 6 7 9 3 3 3 7 3 9 5Designation OriginPhenotypic biotypeDays to Plant Seedling Reaction to stress aacceptability flowering height vigorscore (cm) BLB RTV ShB BPH AlkC702015 Taiwan (China) 4.2 102 97 3 4 8 3 3 5 7 3lR35295-82-2-1-3-2 IRRl4.4 10089 4 5 6 5 3 3 3 5lR39357-133-3-2-2-2 IRRl4.6 91 97 4 4 7 3 3 3 7 5PDR76-D10-D8-D1 Pakistan 4.6 104 99 4 4 5 5 3 5 3 1Si-pi 692033 Taiwan (China) 4.6 102 98 4 4 9 3 3 7 7 5a Locations reporting the reactions: BLB (bacterial leaf blight) - Los Baños, Van Dien; RTV (rice tungro virus) - Los Baños; ShB (sheath blight) - LosBaños; BPH (brown planthopper) - Los Baños; Alk (alkalinity) - Culiacan.

International irrigated rice nurseries 343Some entries, such as IR36 and BG367-4, perform well under both irrigatedand rainfed upland conditions. Since 1975, IR36 has consistently been among thetop five entries in the IRTP irrigated trials. It was included in the internationalupland rice yield trials 1976-79 and was among the top five entries in three of thoseyears. BG367-4 has been among the highest yielding entries in irrigated trials indifferent years and was the overall highest yielding entry in the 1985 upland yieldnursery.Yield trendsThe highest yields obtained for any entry at any location are 7.7-10.4 t/ha for thevery early group (1980-85), 8-10.8 t/ha for the early group (1975-85), and 7.6-12.8t/ ha for the medium group (1975-85). The varieties and locations relative to thosehighest yields are given in Tables 6 to 8.Yield-weather relationshipsSeshu and Cady (1984) studied yield-weather relationships in rice, using results fromthe IRTP irrigated yield trials (early group) conducted at several locations indifferent countries 1976-81. They used two weather variables measured during theripening stage-average daily solar radiation (RAD) in mWh cm 2 and average dailyminimum temperature (MINT) in °C—to develop the following model to explainthe relationship:Values in parentheses are standard errors of the estimated coefficients.Temperature stress nurseriesLow-temperature stressThe International Rice Cold Tolerance Nursery (IRCTN) is aimed at identifyingappropriate breeding lines for low-temperature rice-growing areas, such as canTable 6. Highest yields obtained in IRYN (Very Early), 1980-85.YearHighest yieldingentryYield(t/ha)Days toflowering1980 IR19728-9-3-2 7.7 631981 lR19746-28-2-21982 Reiho (local check)1983 IR501984 UPR103-80-1-21985 Kexuan 93 (localcheck)9.610.110.410.29.78210688105105SiteMean CV (%)Location and mean flowering forlatitude for yield durationyield(t/ha) (d)Rangsit, Thailand 5.2 61 12.114°NChangsha, Chine 6.8 84 13.828°NSakha, Egypt 7.6 101 10.431°NSwat, Pakistan 7.9 88 11.335°NAmol, Iran 8.2 106 19.536°NHaukou, China 7.6 97 5.930°N

7778911 0091–93116117110106CV (%)for yield12.07.68.822.725.718.722.88.112.69.87.4Table 7. Highest yields obtained in IRYN (Early), 1975-85.Year Highest yielding entryYield Days to Location and latitude(t/ha) floweringSite mean Mean floweringfor yield duration(t/ha) (d)19751976197719781979198019811982198319841985IET1444BG 34-8Farro 15RP79-5TNAU8870BAU19-3IR36Giza 172 (local check)KAU1727IR13240-108-2-2-3910 (local check)8.09.08.510.010.59.78.710.110.810.710.573731208896–93118108110108Pattambi, India10°NMaha Illupallama,Sri Lanka, 8°NHyderabad, India17°NDokri, Pakistan28°NDokri, Pakistan28° NDokri, Pakistan28°NKyeukse, Burma21°NSakha, Egypt31°NSakha, Egypt31°NWangdiphodrang, Bhutan27°NHaukou, China30°N6.57.66.46.77.47.26.86.47.48.67.8

Mean floweringduration(d)CV (%)for yieldTable 8. Highest yields obtained in IRYN (Medium), 1975-85.Year Highest yielding entryYield(t/ha)Days tofloweringLocation andlatitudeSite meanfor yield(t/ha)1975 BR51-91-6 7.6 92 Pattambi, India 6.3 9010.81976 lR2863-38-1-2 12.8 106 10°NPalmira, Colombia 8.0 10227.11977 BR51-46-5 10.9 109 3°NHyderabad, India 8.3 109 10.61978 IR4422-98-3-6-1 9.5 117 17°NPalmira, Colombia 7.0 11412.91979 lR4422-98-3-6-1 10.7 94 3°NTitabar, India 7.8 91 16.01980 lR13540-56-3-2-1 9.1 108 26° NRejendranagar, India 7.0 113 12.11981 PAU143-B-4-2-PA505 9.3 110 17°NDokri, Pakistan 6.3 118 12.21982 IR13540-56-32-1 8.9 90 28°NRangsit, Thailand 5.3 95 12.314°N1983 ITA212 11.2 108 Gambella, Ethiopia 8.9 105 10.61984 BR153-2B-10-1-3 9.2 1098°NMendalay, Burma7.610812.11985 BR380-2 11.2 10921°NDokri, Pakistan 7.711718.928°N

346 Seshu and Zhangoccur in dry-season crops of some areas in the tropics. Low temperature stress canoccur at one or more growth stages, depending on geographical location. This stresscan cause stunting, leaf discoloration, delayed flowering, incomplete panicleexsertion, and spikelet sterility; the type of injury depends on the time of stressrelative to the growth stage of the crop. Several promising lines have been identifiedfrom IRCTN multilocation evaluations; although predominantly japonicas, theyinclude some indicas. Interaction between varietal tolerance and growth stage wasobserved in several instances. Some lines that have consistently performed well atmost growth stages over different years are as follows:• Japonica: Stejaree 45, Eiko, Ching-shi 15, K335, Ta tsu mi mochi, Fuji 120,Jodo, Barkat• Indica: K39-96-1-1-2, K31-163-3, China 1039A comparison of flowering durations at selected sites in tropical, subtropical,and temperate regions shows that K335 has good stability in days to flowering(Table 9).Salinity and alkalinity stress nurseriesSaline and sodic soils are widespread in many rice-growing countries in the tropicsand subtropics (Bangladesh, Burma, Cambodia, Egypt, Gambia, Guinea, India,Indonesia, Iran, Iraq, Nigeria, Pakistan, Philippines, Senegal, Sierra Leone, SriLanka, Thailand, and Vietnam). Such soils are major obstacles to increasing riceyields in the arid and coastal areas. The International Rice Salinity and AlkalinityTolerance Observational Nursery (IRSATON) is designed to identify linesTable 9. Varietal differences in stability of days to flowering, 1984 IRTP ColdTolerance Rice Nursery.Days to flowering at different site aVariety Subtropical TropicalTemperate High altitude Plains High altitude Plains1 2 3 4 5 6Tolerent entriesStejaree 45Ching-shi 5BarkatK335China 1039Nontolerant entrylR19746-26-2-3-3138 110149 118131 96116 88138 11095 9094 9388 8980 7785 8898 75108 7196 7884 7396 69NF NF 96 94 105 73a 1 = Szarvas, Hungary (latitude: 4°N; elevation: 85 m); 2 = Vercelli, Italy (45°N;132 m); 3 = Wangdiphodrang, Bhutan (37°N; 1500 m); 4 = Changsha, China(37°N; 30 m); 5 = Banaue, Philippines (17°N; 1200 m); 6 = Joydebpur, Bangladesh(23°N; 8 m). NF = did not flower.

International irrigated rice nurseries 347genetically tolerant of these soil problems. IRSATON entries that have consistentlyperformed well over different locations and years areSalinity• Traditional: Pokkali, Nona Bokra, Nona Sail (sel.), Patnai 23• Improved: Pokkali derivatives: IR4595-4-13, IR4630-22-2-5-1-3Nona Bokra derivatives: IR8236-B-B-336-3-2, IR9884-54-3,IR10198-66-2Alkalinity• Traditional: Pokkali, Getu• Improved: IR4595-4-1-13, IR10206-29-2, IR11248-23-3-2, IR9884-54-3,IR11418-15-2, IR4227-109-1-3-3, IR9764-45-2-2, IR46, CSRlThe salt-tolerant improved rices confer a comparative yield advantage of 2 t/ha(Ponnamperuma 1984).Disease nurseriesNurseries to screen for major rice diseases are organized as part of IRTP. Thediseases include blast ( Pyricularia oryzae ), bacterial blight ( Xanthomonascampestris pv. oryzae ), and tungro virus transmitted by the green leafhopperNephotettix virescens.BlastBlast is widely prevalent and occurs in both irrigated and rainfed rice. Uniform blastnurseries were in progress even before IRTP was initiated. Most screening tests ofthe International Rice Blast Nursery (IRBN) are confined to seedling blast.Differential reactions in several IRBN entries across locations are evident,confirming the prevalence of different races of the pathogen (Seshu et al 1986). SomeIRBN entries that have shown resistance to seedling blast at most locations overseveral years are as follows:• Traditional: Tetep, Tadukan, Carreon, Ta-poo-cho-z• Improved: Suweon 300, IRAT104, CIAT-ICA5, IR5533-PP850-1, IR1905-PP11-294, IR27325-27-3-3, IR1416-128-5-8, IR4547-4-1-2, IR3259-5-160-3,IR19660-00948-1Among the japonicas, Fukunishiki and Toride 1 showed a broad spectrum ofresistance.Several improved derivatives of Tetep showed resistance across locations, butin differing patterns. From the nature of their reactions, it appears that Tetepresistance is governed by several major genes.Bacterial blightBacterial blight has become a major disease of rice in Asia during the last twodecades, causing severe crop damage. No effective chemical control method hasbeen found. Increasing nitrogen fertilizer application rates to obtain optimum yieldsalso encourages an increase in the incidence and severity of this disease. Some of thepromising resistant lines that have been identified through the International RiceBacterial Blight Nursery (IRBBN) include• Traditional: DV85, BJ1

348 Seshu and Zhang• Improved: BR51-282-8, Cisadane, IR13423-17-1-2, IR444246-3-3, IR26717-1-1-2, RP633-76-1, IR54, IR64IRBBN results show variation in pathogen strains. The strains in South Asiaappear to be more virulent than those in East and Southeast Asia.Tungro virusTungro, one of the most destructive rice diseases prevalent in South and SoutheastAsia, is a virus transmitted by green leafhoppers. Both the virus and the vectordamage the crop; resistance to each is known to be independently controlled. Someentries in the International Rice Tungro Nursery (IRTN) found promising forresistance over different years and locations include• Traditional: ARC11554, Utri Merah, Utri Rajapan, Gam Pai 30-12-15,Naria Bochi• Improved: IR7929-67-3, IR9828-91-2-3, RP825-45-1-3, R51-315-4Insect nurseriesIRTP nurseries targeted to major insect pests include those designed to identifyresistance to stem borer—primarily yellow stem borer Scirpophaga incertulas andstriped stem borer Chilo suppressalis— gall midge Orseolia oryzae, brownplanthopper Nilaparvata lugens, and whitebacked planthopper Sogatella furcifera.Stem borerStem borer occurs in almost all rice-growing countries, although the species maydiffer from region to region. The insect damages rice at both the vegetative andheading stages, causing deadhearts and whiteheads. Screening for resistance is doneprimarily in the field and, where facilities exist, in the screenhouse. Varietiesidentified in the International Rice Stem Borer Nursery (IRSBN) as havingmoderate to good resistance across different locations include• Yellow borer: Traditional TKM6, CO 18, W1263, MTU15Improved: IR1820-522-4, IET2845, IR9828-23-1, IR3941-9-2, IR15723-45-3, IR13639-34• Striped borer: Traditional TKM6, Taitung 16, W1263Improved: IET2845, IET5540, CR157-392-4, IR1514A-E666,IR2798-143-3, IR20, IR36Gall midgeThe gall midge is a serious rice pest in South and Southeast Asia and parts of WestAfrica. Damaged plants are stunted and affected tillers produce no panicles.Presence of the larva causes the leaf sheath to develop into a gall, called a silvershoot.The International Rice Gall Midge Nursery (IRGMN) has revealed distinct biotypicdifferences in the insect between different countries and within large countries likeIndia (IRRI 1981). Some varieties identified as resistant through the multilocationevaluation include• Traditional: W1263, PTB18, PTB19, PTB21, Leuang 152, Eswarakora• Improved: RPW6-17 (Phalguna), Kakatiya, CR157-392-4, BG380-2, IR36

International irrigated rice nurseries 349Brown planthopperThe brown planthopper, a serious pest of rice throughout Asia, causes the feedingdamage called hopperburn. In addition, it transmits the virus disease known asgrassy stunt. Because of the economic importance of this insect, rearing and varietalresistance screening programs are well established in many countries. Mostscreening tests of the International Rice Brown Planthopper Nursery (IRBPHN) indifferent countries are conducted in the greenhouse. IRBPHN results reveal distinctdifferential reactions at different sites for most test entries, suggesting the occurrenceof selection for biotypes within hopper populations (Seshu and Kauffman 1980).Biotypes of the insect in South Asia have proved to be more virulent than those inEast and Southeast Asia. Some entries rated resistant at most locations are• Traditional: PTB33, Rathu Heenati, Babawee, Balamawee, Suduru Samba• Improved: Rathu Heenati derivatives: IR13540-56-3, IR17494-32-1,IR12912-131-2PTB33 derivatives: IR19660-45-1, IR19661-23-3, IR56, BG367-2, RP1756-121Whitebacked planthopperThe whitebacked planthopper is prevalent in most Asian countries; damage issimilar to that caused by the brown planthopper. Rearing and screeningmethodologies used are also similar. Multilocation evaluation of the InternationalRice Whitebacked Planthopper Nursery (IRWBPHN) has provided evidence ofbiotype differences in the insect. Some promising IRWBPHN entries include• Traditional: ASD8, ADR52, PTB19, PTB33, Rathu Heenati, VellathilCheera, WC1240• Improved: IR13458-117-2-3, IR15529-253-3-2, IR17492-18-6-1, IR17307-11-2-3, IR2035-117-3Utilization of IRTP entries in national programsTo date, 139 entries originating from 17 countries and from IRRI have been releasedas varieties in 47 countries in Asia, Africa, and Latin America. In addition, severalhundred entries have been used as parents in national breeding programs.IRTP experiences in ChinaChina formally joined the IRTP network in 1979. The Chinese Academy ofAgricultural Sciences (CAAS), in collaboration with several provincial academies,organized IRTP nurseries in the major rice-growing regions of the country. By 1987,these organizations had joined the IRTP network:• Guangdong Academy of Agricultural Sciences,• Guangxi Autonomous Regional Academy of Agricultural Sciences,• Fujian Academy of Agricultural Sciences,• Hunan Academy of Agricultural Sciences,• Jiangsu Academy of Agricultural Sciences,• Zhejiang Academy of Agricultural Sciences,

350 Seshu and Zhang• Shanghai Academy of Agricultural Sciences,• Sichuan Academy of Agricultural Sciences,• Germplasm Research Institute, CAAS, and• China National Rice Research Institute.About 50 Chinese scientists are involved in IRTP activities. Their experimentsinclude yield nurseries, observational nurseries, and different stress screeningnurseries. Evaluation of IRTP nurseries has led to the identification of a largenumber of promising materials, some of which are applied directly to production.Others are used as parents in hybridization (Tables 10-16). They have contributedsignificantly to rice varietal improvement in China.From time to time, varieties and breeding lines developed in China are enteredinto IRTP nurseries. Some early-maturing lines from China have been utilizedeffectively in IRRI breeding programs. Chinese rice scientists have participatedactively in IRTP-sponsored monitoring tours. One Chinese scientist serves as amember of the Global IRTP Advisory Committee.Table 10. Some IRTP entries named as varieties in China.Region Designation Origin Name givenYearreleasedSouth ChinaSouth ChinaJiangsuHunanHunanFujianFujianGuangxiGuangxiGuangdongGuangdongSichuanSichuanJiangsuIR24IR26BG90-2Chianung sen yu 13PNA237-F4-130-1Suweon 287lR21929-12-3-3lR21015-80-3-3-1-2IR15853-89-7E-P3IR9965-48-2lR9129-102-2DR92BR203-70-B-1M114IRRlIRRlSri LankaTaiwan (China)ColombiaKoreaIRRlIRRlIRRlIRRlIRRlBangladeshBangladeshIndiaIR24IR26BG90-2E108Xiangxuan 8325Minyin 1Minkang 108N304N90Waiyin 35GuojiyouzhanDR92–80851980198019831980198219811986198319811981198619861981Table 11. Some varieties or lines developed in China from crosses utilizing IRTP entries asparents.Province Relaased variety cross RemarksGuangdong Sanhuangzhan 2Sanhuangzhan 4Sanhuangzhan 8Sanguizhan 2IR9965-48-2/TuanhuangzhanIR9965-48-2/TuanhuangzhanIR9965-48-2/TuanhuangzhanGui-Chao 2/IR9965-48-2Good quality, highresistance to blast(BI), medium resistanceto bacterialleaf blight (BLB)High yield, Bi resistance,mediumresistance to BLBcontinued on opposite page

International irrigated rice nurseries 351Table 11 continued.Province Released variety Cross RemarksSanguizhan 5Sanguizhan 6Sanguizhan 8Chun-hua-ai 6Gui-Chao 2/IR9965-48-2Gui-Chao 2/IR9965-48-2Gui-Chao 2/IR9965-48-2IR20/QinglanaiHigh yield, goodquality, BLBresistanceGuangxiJiangsuWan-hua-ai 1Zhi 20579007Tie 6Gui 32Gui 33Gui 34Gui 44Gui 45Gui 47Nanjing 3736Nanjing 3714Nanjing 51148004780079IR20/QinglanaiIR29/Gui-Chao 2IR22/Zhen zhu aiIR26/Tie-er-ailR36/IR24-32lR36/IR24-33IR30/IR24IR36//IR24/TaiyinXian 146/IR30IR36/IR24IR24/BG90-2Chianung si-pi 861032lR5982-7-6-1 selection350/Xihai 134//Xiang yang zao/lR29Kao cha 1/American Rice 1//Xiang yang zao/lR29High yield, goodquality, BLBresistanceHigh yield, goodquality, BLBresistanceHigh yield, goodquality, BLBresistanceResistance to BLBand brown planthopper(BPH)As restorer for hybridcombinationsAs restorer for hybridcombinationsAs restorer for hybridcombinationsAs restorer for hybridcombinationsAs restorer for hybridcornbinationsAs restorer for hybridcombinationsHigh yield, BLBresistance, goodqualityHigh yield, BLBresistance, goodqualityHigh yield, BLBresistance, goodqualityJaponica type,BPH resistanceJaponica type,BPH resistanceShanghaiP339P152P127H46H5C48/4/Kao cha 1/lR26//Nongfu 6//Aikeng 23/5/C8014Linfeng//Fengwo/Mudgo//Texikuxibali//Kao cha 1/IR26/4/HanfengFuke 43/1R26//Shuang-Feng 1Shuang-Feng 1/lR26//Shuang-Fang 1Hanfeng/4/Nongfu 6/IR36//Nongfu 6///C241Late japonica,BLB resistanceLate japonica,BPH resistanceLate japonica,BPH resistancecontinued on next page

352 Seshu and ZhangTable 11 continuedProvince Released variety Cross RemarksHunan IR36/Xiang Ai Zao 8IR50/79-1163IR42/Shuang-er-zhanIR50/Shuang-er-zhanMilyang 50/79317-41952/KS282Chianung sen yu 13/248-279317-6/Chianung sen yu 13High yield, goodquality, BLBresistanceGood plant type,high yield, goodqualityGood plant type,high yield, goodqualityGood plant type,high yield, goodqualityGood plant type,high yield, goodqualityGood plant type,high yield, goodqualityHigh yield, goodresistance to BLBHigh yield, BLBresistanceTable 12. Some IRTP entries selected in Jiangsu Province, China, for good planttype, high yield, disease resistance, and good quality, 1980-86. aTainung sen 12Taichung sen yu 321Taichung sen yu 223Chianung sen yu 13C662083Si-pi 681032Chianung si-pi 661020Milyang 23Milyang 53Suweon 290a All have been used in hybridization.Iri 347IR24IR36IR56IR60lR9698-16-3-3-2IR9729-67-3IR13240-108-2-2-3IR13539-100-2-2-2-3lR17525-278-1-1-2lR21931-47-3-3lR2558845-1-2lR25621-105-1-2BR161-2B-59AD9246PAU14-2-13-9-2-1-1UPR82-1-7UPR103-80-1-2RNR142975704-36Table 13. IRTP entries used as restorers for hybrid rice in China.ProvinceGuangdongHunanGuangxiJiangsuEntriesIR24, IR26, IR36, IR64Milyang 49, lR9782-111-2-1-2, IR9218-156-1-3,lRl9575-85-2-2-3, UPR103-80-1-2, UPR254-24-1,HPU71, Chianung si-pi 662098, Chianung si-pi661020Suweon 287, lR31775-30-3-2-2-2, lR19762-2-3-3PAU41-B-31-1-PR407, PAU41-10-1-3-PR385,PAU41-306-1-2-PR404, PAU41-306-1-4PR422,PAU41-306-2-1-PR405, PAU41-306-2-2-PR406

International irrigated rice nurseries 353Table 14. IRTP entries identified in China as resistant to various diseases, 1980-86.DiseaseInstitute/provinceEntriesRemarksBIast CNRRI a Chianung si-pi 661020, lR8608-82-1-3-1-3, RD23, MRC603-303, Iri 347,lR21848-65-32-2, lR25925-84-3-2,lR11297-170-3-2, lR9782-111-2-1-2,lR25884-94-3-2, ARC6650, lR13423-17-1-2-1Bacterial leaf blightHunanFujianZhejiangGuangdongGuangxiCNRRIGuangdongFujianGuangxia China National Rice Research Institute.IR94633-2-2-2-2, IR1416-128-5-8,lR28154-101-3-2, lR11248-83-3-2-1-3,IR13429-299-2-1-3, IR4568-86-1-3-2,IRAT104, IRAT109, IRAT13, ITA118,BR319-1, Milyang 45, Milyang 55,Pokhereli Masino, Suweon 290,Camponi SML, Ceysvoni SML, CIAT-ICA5Tetep, Raminad Str. 3, Carreon,lR19672-140-2-3-2lR2061-427-1-17-7-5, lR9782-111-2-1-2,IR13458-117-2-3-2-3, IR9209-249-1-2-3-2IR36, lR9129-102-2, lR9965-48-2IR30, IR36, IR54, IR56, BR319-1,BR161-2B-59, BR169-19-12, CIAT-ICA5,Huan-sen-goo, IRAT130, P1577-1-23M-5-1M-4C712315, C702344, IR13146-45-2,lR25916-15-3-2, lR19660-46-1-3-2-2,lR28224-21-2-2-1IR20, IR22, IR26, IR29, IR30,IR36, IR54, DV85lR32799-107-3-3-2, lR32720-138-2-1-1-2, lR33059-26-2-2IR11288-B-B-288-1, B24B4B-PN-28-3-MR-5, IR54BG35-2, BG90-2, BJ1, BR51-282-8,BR109-74-2-2-2, BR171-2B-8, DV85,IR20, IR22, IR26, IR30, IR42, IR52,IR54, IR8608-231-2-2-3-2, IR1529-680-32, IR2061, IR2006P-12-2-2,IR13429-287-3, UPR70-30-7,KMP40, Rasht 507, RP633-76-1,TKM6, UPR4-25-1Also resistant tobrown planthopperGood agronomiccharacters

Insect lnstitute/province Entries RemarksTable 15. IRTP entries identified in China as resistant to various insects, 1980-86.Brown planthopperCNRRI a IR36, IR56, IR58, IR62, IR64, lR19374-25-2-2,lR8608-75-31-3, PY2, ARC6650, Kannaki.RP1015-39-89-1, Ratna, Taichung sen 12, Taichung sen yu 285,C702080Hunan Sinna Sivappu (Acc. 15444). Sudu Hondarawala (Acc. 15541),Rathu Heenati, BG367-4, BG379-3, Babawee, ASD7,lR13429-196-1-2-1, lR14252-13-2-2-5, lR17492-18-10-2-2-2,lR19670-177-1, lR13240-39-3, IR46, Utri Rajapan,Suduru Samba, Hondarawala, C1321-9, C701045, C1322-28,lR9761-19-1, lR4619-57-1-1-2-1, lR3858-6, lR14875-98-5,lR13564-109-1, C1117-2, C702043, C711125, C712068,lR11418-19-2-3, lR13415-9-3Fujian (312 entries selected)lR21929-12-3-3lR25588-7-3-1Shanghai IR26, IR36Guangxi lR9732-119-3, lR9782-111-2-1-2. lR18348-36-3-3Good agronomic charactersGlutinous and high grain-set rateAlso resistant to bacterial leafblightASD7Also resistant to leaf rollerand bacterial leaf blightGuangdongPTB33IR36, Sinna SivappuAlso resistant to leaf roller

WhitebackedplanthopperStem borerCNRRICNRRlHunanPTB33, Rathu Heenati, BKNBR76025-10-8-1-2KLG-1-1-1-7,lR10232-17-2, lR11418-15-2, lR13427-45-3-1-2-2-2,IR13429-86-3-3-2-2, IR14875-98-5, IR15498-167-3-2-2,lR15869-1131, IR18350-93-2, IR19256-88-1, lR19431-72-2,lR25587-67-1-3-3-3, IR46, lR27316-78-3-3, lR2815084-3-3-2,IR28154-101-3-2, lR28224-3-2-3-2, lR29692-94-2-1-3,lR29692-99-32-1, lR29723-186-2-2-3, lR2972388-2-3-3,lR29725-109-1-2-1, lR29725-3-1-3-2, lR32272-67-3-2-3,lR32429-130-2-2-2, IR32429-68-3-3-3, lR32822-2-2-3-2,lR35323-931-3-1, IR45, lR476373-1-11, IR60, IR8154-95-1,lR9763-11-2-2-3, RNR3070, Mudgo, C711125, C712068,lR11418-19-2-3, IR13564-95-1, lR15718-28-2-2, lR15847-135-1-1,lR15849-12-3-3, lR17494-32-2-2-1-3, IR20878-1-P1, lR25586-108-1-2-2-2, IR25588-7-3-1, lR28228-12-3-1-1-2, lR29692-65-2-3C711140, lR15797-74-1-3-2, Chemparampandi,Cheriya chittari, Djambon, lR2035-117-3, Valsara Champara,Bahbolon, GH147 (M) Krad 78, GH147 (M) 40 Krad 89TKM6, IR40, IR56, W1263, lR13535-21-2-3-3-2,lR2101580-3-3-1-2lR11288-B-B-118-1 Resistant to striped stem borera China National Rice Research Institute.

356 Seshu and ZhangTabla 16. IRTP entries identified in China as resistant to low temperature and salinity, 1980-86.Stress Institute/province Entries Remarks aCold tolerance Fujian ADT14, AUS 339, Hwang hae do,IR9099-K1, lR9129-33-3-3,K39-96-1-1-2, MR365,IR19743-46-2-3, IR9224-K1,K143-1-2, China 1039, Ching-shi15, Corallo, SR3044-78-3,Strella, Wasetoramochi, Tainungsen yu, lR13525-118-3-2-2-2,Chu cheng (Acc. 1395), Ju ku(Acc. 1144). Suweon 303,Suweon 306, Ta-ma-shan(Acc. 4283), Fang chi (Acc. 1385).Stejaree 45. Ta tsu mi mochi,Giza 159Hunan lR19746-28-2-2-3, IR2061- Also resistant to BPH522-6-9IRM-78-1-3, lR9202-33-4-2-1 Also resistant to BLBK315, K434 Also resistant to BIYR2379-87-2, B2978B-SR-2-6-2-2-2P33-C-30, HPU741AromaticSalinity JiangsuM114, IR10206-29-2, A69-1a BPH = brown planthopper, BLB = bacterial leaf blight, BI = leaf blast.References citedIRRI—International Rice Research Institute (1981) Reactions of differential varieties to the rice gallmidge. Orseolia oryzae. in Asia. Report of an international collaborative research project. IRRI Res.Pap. Ser. 61. 14 p.Ponnamueruma F N (1984) Role of cultivar tolerance in increasing rice production on saline lands. Pages255-271 in Salinity tolerance in plants: strategies for crop improvement. R. C. Staples and G.H.Toenniessen, eds. John Wiley & Sons, New York.Seshu D V (1986) Rice varietal performance in international irrigated trials. Paper presented at theSymposium on Rice Farming Systems: New Directions, 31 Jan-3 Feb 1987, Sakha, Egypt.Seshu D V, Cady F B (1984) Response of rice to solar radiation and temperature estimated frominternational yield trials. Crop Sci. 24:649-654.Seshu D V, Kauffman H E (1980) Differential response of rice varieties to the brown planthopper ininternational screening tests. IRRI Res. Pap. Ser. 52. 13 p.Seshu D V, Kwak T S, Mackill D J (1986) Global evaluation of rice varietal reactions to blast disease.Pages 335-351 in Progress in upland rice research. International Rice Research Institute, P.O. Box933, Manila, Philippines.NotesAddresses: D. V. Seshu, International Rice Testing Program, International Rice Research Institute, P.O. Box 933,Manila, Philippines; Zhang Yihua, China National Rice Research Institute, Hangzhou, People’s Republic of China.Citation information: International Rice Research Institute (1989) Progress in irrigated rice research. P.O. Box 933,Manila, Philippines.

Abstracts 357ABSTRACTS: INTERNATIONAL COLLABORATIONIRRl and national agricultural researchsystems: challenges and opportunitiesK. KANUNGOIRRl scientists spend considerable effort in collaborative research andtraining activities with their counterparts in national agricultural researchsystems and with scientists in advanced research institutions anduniversities in both developed and developing countries. Some suggestionsfor furthering that international collaboration were presented at themeeting on Strengthening national agricultural research systems: wheatand rice research and training in Rome, 26-28 Jan 1987. Three areas ofopportunities for national agricultural research workers’ professionalgrowth and development were identified—for young professionals, formidcareer scientists, and for experiment station managers. Meeting theneed would reinforce current levels of collaborative research and trainingand would support durable and sustainable new linkages.K. Kanungo, Agricultural Scientists’ Recruitment Board, Indian Council of AgriculturalResearch, New Delhi.China’s collaborative relationship with IRRlZHANG YIHUA AND D. L. UMALIThe collaborative relationship between China and the International RiceResearch Institute (IRRI) began during the 1970s. Mutual understandingwas promoted through exchange visits of officials and scientists. After1979, the relationship entered the collaborative agreement phase. Chinahas joined international collaboration networks (International Rice TestingProgram, International Network on Soil Fertility and Fertilizer Evaluationfor Rice, and Asian Rice Farming Systems Network) organized by IRRI.Collaborative research activities on rice have involved the ChineseAcademy of Agricultural Sciences, Provincial Academies of AgriculturalSciences, Rice Research Institutes, Agricultural Universities, ChineseAcademy of Agricultural Mechanization Sciences, and Academia Sinica.Research areas include germplasm resources, plant breeding, tissueculture, soil and plant nutrition, plant protection, agricultural engineering,and agricultural economics. International symposiums and conferencesand special training courses have been jointly sponsored. A large numberof students have been trained at IRRl through graduate degrees andshort-term nondegree courses. Chinese scientists have conductedpostdoctoral research as visiting scientists at IRRI. China’s agricultural

358 Abstractsuniversities have started graduate degree programs with IRRI. The manyyears of interaction have proven that such collaboration is of mutualbenefit. China holds the viewpoint that the close collaboration with IRRlhas helped promote the development of the country’s rice researchscience and production and that the collaborative relationship should befurther developed.Zhang Yihua, China National Rice Research Institute, Hangzhou, People’s Republic of China;D. L. Umali, International Rice Research Institute, P.O. Box 933, Manila, Philippines.Educational technology and its implicationsfor rice technology transferD. R. MINNICKKnowledge and information about technology increase exponentiallyacross time. The need is to find more efficient means of transferringknowledge and technological skills. A systems training concept that useseducational technology to expedite human resource development isadvanced. The systems concept consists of four basic strategies: coursedevelopment and implementation, instructional resource development,course transfer, and educational feedback. The methodology combinesprogrammed instruction, lecture, guided design, group dynamics, and theprinciples of adult learning as components in course development andimplementation. Instructional resource development provides supportmaterials for course development and implementation. The componentsused include media, programmed instruction, course materials, andlearning objectives fashioned into databases and computer-aided andmanaged instruction. A five-step strategy for information and technologydissemination through human resources development is advanced. Threecritical components of training competencies and courseware areexplored. Feedback and assessment are based on educational research.Ways to evaluate methodology and learning objectives, courseware, andthe course transfer model are suggested. The new educational technologiesof human resource development, learning styles, computermemory, compact disks, CD-ROM, CDI, CD-WORM, and expert systems ofartificial intelligence are discussed.D. R. Minnick, Training and Technology Transfer Department, International Rice ResearchInstitute. P.O. Box 933, Manila, Philippines.

Abstracts 359International linkages in rice farming systemsV. R. CARANGAL AND GUO YIXIANThe International Rice Research Institute provides the coordination forinternational collaboration on rice farming through the Asian RiceFarming Systems Network (ARFSN). The network involves Bangladesh,Bhutan, Burma, China, India, Indonesia, Madagascar, Malaysia, Nepal,Pakistan, Philippines, Korea, Sri Lanka, Taiwan, Thailand, and Vietnam.Farming/cropping systems research methodologies developed within thenetwork are used, with some modification, by nationally coordinatedcropping/farming systems programs. The collaboration also involvesInternational Center for Maize and Wheat Improvement, InternationalCenter for Living Aquatic Resources Management, International CropsResearch Institute for the Semi-Arid Tropics, International Institute ofTropical Agriculture, International Center for Tropical Agriculture, InternationalPotato Center, and national research institutes and universities.The network collaborates with the International Development ResearchCenter, United States Agency for International Development, AsianDevelopment Bank, Food and Agriculture Organization, InternationalFund for Agricultural Development, Australian Center for InternationalAgricultural Research, Canadian International Development Agencyfundedprojects, and other organizations. Collaborative research onproduction systems and component technology includes cropping patternstesting, women in rice farming, crop - animal systems research, rice -wheat cropping systems, prosperity through rice - rice - fish farming,impact of cropping systems research, varietal improvement and testing ofupland crops for rice farming, long-term cropping pattern and fertilizerstudies, and farm implements for intensified cropping. Sharing researchinformation and methodologies is achieved through workshops, monitoringtours, and ARFSN Working Group meetings, as well as publications.V. R. Carangal, Rice Farming Systems Program, International Rice Research Institute, P.O. Box933, Manila, Philippines; Guo Yixian, Farming Systems Program, Institute of Crop Breeding andCultivation, Chinese Academy of Agricultural Sciences, 30 Bai Shi Quiao Lu, West Suburbs,Beijing, China.Computer networkingin international agricultural researchG. N. LINDSEYThe international data network which has come to be known as theCGNET is the result of a successful attempt to use computers andcommunication technology to increase the effectiveness and efficiency ofthe international agricultural research system. The project began as afeasibility study. It is now an operational network. How internationalaccess to value-added networks is accomplished, the step-by-stepprocedure to establish network access, and the economic implications ofthe electronic network are explained.G. N. Lindsey, CGNET Services International, 680 Waverley Street, Palo Alto, CA 94301, USA.

360 AbstractsMultilanguage copublication:IRRl design and policiesT. R. HARGROVE, V. L. CABANILLA, R. C. CABRERA, AND L. R. POLLARDThe International Rice Research lnstitute (IRRl) developed its copublicationprogram-cooperative ventures with national agencies and privatepublishers to translate and publish IRRl books—to alleviate the languagebarrier in the transfer of agricultural technology. By May 1987, at least 108non-English editions of 27 IRRl books had been copublished in 40languages. Another 45 editions of 12 books are in press. IRRl’s mostsuccessful copublication ventures have been with extension- and farmlevelbooks designed to facilitate easy and inexpensive translation andprinting. The most popular is A farmer’s primer on growing rice, a highlyillustrated book that describes the hows and whys of improved ricefarming. The handbook Field problems of tropical rice has 172 color photosto help rice workers identify insects, diseases, weeds, and problem soils.Field problems has been published in 20 languages. The effectiveness ofthe translations has been tested in two studies in the Philippines. Readingin their native language significantly increased knowledge amongextension workers and farmers. A survey of translators and copublishersin 12 Asian countries showed that translators initiated most projects. Aninformal copublication network would move more information abouttechnology into various languages and countries.T. R. Hargrove, V. L. Cabanilla, R. C. Cabrera, and L. R. Pollard, Communication and PublicationsDepartment, International Rice Research Institute, P.O. Box 933, Manila, Philippines.

Highlightsand recommendationsThe global rice situationHighlightsThe traditional political dilemma of the food economy is especially acute in rice,where new technologies and breeding have achieved unprecedented yield increases.The dilemma is maintaining prices for the farmer that encourage increased outputand induce technological change while at the same time lowering prices forconsumers, especially the poor.The dilemma is particularly acute in rice, the staple consumption commodity ofthe poor. An increase in rice prices is likely to drive the poor to nutritionally inferiorconsumption or to famine and starvation.Traditionally, the food-price dilemma has been solved by applying technologythat decreases unit price but increases profits (yield-increasing, cost-decreasingtechnology), and/ or by government subsidies for the staple commodity of the poor.It is likely we are realizing the limits of these traditional approaches. In manycountries, land constraints (and thus mechanization constraints) and budget deficitsmake it difficult to contemplate dramatic cost reductions in producing food or incontinuing subsidies for consumers.Research prioritiesIn the interest of maintaining low prices of the staple commodity of the poor withoutstifling farmer income and incentives, regulating and segmenting the market for rice(depending on different demand characteristics for each rice use) and applyingseveral tiers of prices could be examined. Another question is the extent to which theworld market price of rice affects domestic prices to producers and consumers.If there is more emphasis on producers’ interests and on induced technologicalchange, one may wish to maintain high rice prices, so long as the incomes of the pooralso increase so that they can afford to pay those prices. The macroeconomicquestion is, what are the feedbacks between strategies for agricultural development(rice production specifically) and income distribution, so that higher farmer incomesfeed back into decreased poverty, not only for farm workers but also for othersegments of society?

362 Highlights and recommendationsPhysiological aspects for increasing productionHighlightsCorrelations between sink size and temperature during the vegetative stage andbetween sink size and growth duration are strongly negative. Sink formationefficiency (sink size per biomass at heading) is important in further improving yieldpotential.Higher yields of F 1 hybrids are attributed to higher harvest index.It appears possible to enhance yield ability by producing highdensity grain.Physiological traits of newly bred high-yielding varieties and lines in Japan areattributed to higher sink size without accompanying excessive growth.Less carbohydrate in the culm and sheath causes green withering and low grainfilling.Growth retardants will effectively control yield.High-yielding indica varieties and indica/japonica hybrids have deeper rootsystems and higher water-supplying abilities.Physiological characteristics of high-yielding varieties in China have 130-150 dgrowth duration, 0.50-0.55 harvest index, erect leaves with’ a 0.4 extinctioncoefficient, large sink size, higher photosynthesis rate, and higher nutrient uptakeability.Physiological characteristics of high-yielding varieties in Korea include anoptimum leaf area index of 7-9 for indica-japonica high-yielding varieties, higherthan for japonica varieties. Extremely high yields of 10 t milled rice (14 trough rice)per hectare were reported. Growth durations of recent high-yielding varieties areshorter than those of traditional varieties. Mean air temperature at ripening andyield are highly correlated.High-yielding varieties for acid soils in Vietnam were developed by selectingmaterials with high photosynthesis rates. Varieties with high tolerance for acid soilsgive yields similar to those of IR8 grown on nonacid soils.Research prioritiesMorphological and physiological traits for further improvement of yield potentialthat should be studied include• Increased harvest index— Increased sink sizeIncreased sink formation efficiencyGreater partitioning of assimilates for sink formationFaster nitrogen uptake in shortduration varieties— Increased spikelet fillingOptimum manipulation of senescenceHigher percentage of highdensity grainEfficient translocation of photosynthateMaintenance of higher sink activityMaintenance of healthy root systemIncreased lodging resistance

Highlights and recommendations 363• Increased biomass production— Reduced carbon consumption for maintenance— Increased canopy photosynthesisPlant characteristics for yield improvement and determination of geneticvariability need to be studied.Understanding of the physiological basis of heterosis in rice is needed.Effective selection criteria for screening higher yield potential should beestablished.The physiological and morphological traits required to reach yield potentialshould be examined across tropical, subtropical, and temperate regions. Aninternational research collaboration to build a database on yield characteristics ofhigh-yielding varieties and lines is recommended.Interdisciplinary collaboration should be established to study• Prototype breeding with desirable physiological traits (by breeder andbiotechnology groups).• Simulation of the dynamic process of growth and yield determination (withcrop modeling scientists).Yield potential under stress, such as adverse soils and unusual weather, shouldbe improved.Moderator: S. ObienRapporteur: S. AkitaDisease and insect problemsHighlightsIn addition to cultivar susceptibility or pathogen virulence, disease epidemics bear aclose relationship to cropping intensity and crop management. Some experimentshave shown a significant negative correlation between nitrogen fertilizer level andresistance to rice blast in some varieties, but not in others.Many rice cultivars that appear to possess durable resistance to rice diseaseshave been identified.Varietal resistance to sheath blight has not been found. Several effective andsafe chemicals have been recommended. One or two applications before and/or atpanicle initiation can control the disease.Several wild species of Oryza are highly resistant to leafhoppers andplanthoppers. Embryo rescue techniques have been used to transfer resistance tobrown planthopper and whitebacked planthopper from O. officinalis acrosscrossability barriers to cultivated rice.Research prioritiesSources of resistance to diseases and insects are still very limited. Germplasmscreened to identify additional sources of resistance should include additional wildspecies.

364 Highlights and recommendationsSources of resistance to some diseases (such as sheath blight) are not known.We should redouble our efforts to identify donors for resistance. Because of theurgency of the problem, minor genes for resistance to sheath blight should beaccumulated through male sterility-facilitated recurrent selection programs.More basic studies should search for the causes of the tremendous variability ofthe blast fungus.The existence of disease and insect races and biotypes complicates breedingprograms. Collaborative research to identify the races and biotypes of majordiseases and insects of rice should be strengthened.Known donors for resistance should be genetically analyzed to identify diversegenes for resistance.Isogenic lines with diverse genes for resistance to each major disease and insectshould be developed. Such lines can be powerful tools in identifying races andbiotypes of diseases and insects.Genes for resistance from wild species should be transferred to cultivated riceusing the modern techniques of cytogenetics and biotechnology. Emergingtechniques in genetic engineering and cellular biology should be used to transfernovel genes for resistance from unrelated species.Durable resistance to diseases and insects should be the ultimate objective ofresistance breeding programs. However, durable resistance needs to be clearlydefined and its components elaborated.In the absence of strong resistance, tolerance can play a useful role in diseaseand insect control. Improved germplasm with good levels of tolerance should bedeveloped.Integrated pest management strategies with a strong emphasis on hostresistance should be adopted.Pest management programs should examine control of vertebrate pests andweeds, in addition to diseases and insects.Moderator: F. BernardoRapporteur: G. S. KhushNutrient managementNitrogenHighlightsThe use of inorganic fertilizer has increased dramatically throughout Asia, whereasapplication of organic substrates has declined. Green manure and organic fertilizercan substitute for inorganic fertilizer, but inorganic N fertilizer is essential to sustainhigh yields of irrigated rice.Extensive research has demonstrated that poor utilization (only 20-40%) ofapplied N fertilizer is largely due to N losses. Ammonia volatilization has beenidentified as a major loss mechanism in irrigated rice. Denitrification may accountfor most of the still-unidentified loss of about 30% of the N applied.Better understanding of N loss mechanisms has led to the development of

Highlights and recommendations 365management practices that greatly increase agronomic N fertilizer efficiency. Theyinclude• incorporation of urea before transplanting with no standing floodwater.• coating of urea, resulting in slow release.• deep placement of fertilizer.• use of urease inhibitors.Research prioritiesUrease inhibitors offer an alternative strategy for reducing N loss, although ureaseinhibitors so far evaluated have not matched grain yield achieved by deep placementof urea or sulfur-coated urea. Methods for measuring denitrification losses arehighly needed.The effectiveness of integrated N management depends on season, climate, soiltype, water management, rice variety, cropping pattern, and farming systems. Morework is needed on N management strategies for particular environments.Farm-grown sourcesHighlightsOrganic amendments have been important sources of nutrients in traditionalagriculture, but the contribution of farm-grown nutrient sources (green manure,farmyard manure, rice straw) has declined with intensified rice cropping in irrigatedfields. Organic amendments, especially green manure and farmyard manure, cansubstitute for inorganic N-fertilizer. Using rice straw as a substitute for N-fertilizer ishighly restricted because of its high C-N ratio, which in the tropics results in netimmobilization of nitrogen under flooded rice soils.To sustain the soil nitrogen pool and high yields of irrigated rice, theaccumulation-decomposition balance is decisive. In some areas, organic amendmentsare essential to maintaining the soil nitrogen pool and high rice yields; in otherareas, no additional organic inputs are needed. Decomposition of organic matter inflooded rice soils in the tropics can be as fast as in upland soils.Research prioritiesLittle is known about the nature and mineralization pattern of soil nitrogen or aboutthe transformation of N when it is combined with organic manure and inorganicfertilizer in irrigated rice soils. There is a need to explore these transformationprocesses in major rice-growing environments to develop sound integrated nutrientmanagement practices.Nutrient kinetics and availabilityHighlightsNutrient kinetics are closely interlinked with fermentation of organic substrates inflooded rice soils. The production of CO 2 by the fermentation of organic matter is animportant factor in determining the pH and the precipitation of elements ascarbonates in most flooded rice soils. After redox chemistry, the importance ofcarbonate chemistry in flooded soil cannot be overemphasized.The high oversaturation of ions (as great as 100-fold) in flooded soils inducesprecipitation of carbonates and sulfides; the rates of precipitation are slow.

366 Highlights and recommendationsApparently, blocking of crystal growth sites by organic ligands is important for ironand manganese carbonates as well as for calcite.The most important effect of flooding on P availability is the increase indiffusivity, not an increase in solution concentration. In neutral and calcareous soils,P availability may even decrease after flooding.Thermodynamic analysis has shown that the only pure phase that could controlZn in the soil solution is zinc sulfide. Coprecipitation or adsorption in Fe-Mncarbonate or other minerals may be another important factor contributing to loss ofavailable Zn in continuously flooded soils.Research prioritiesFactors that affect nutrient availabilities and nutrient uptake of elements other thannitrogen are still not well understood.Phases of phosphates, carbonates, sulfides, and silicates that control thesolubility of nutrients in flooded rice soils have yet to be identified.Mechanisms to block crystal growth in flooded rice soils are needed, tounderstand the mechanisms that result in high oversaturation of ions in soil solution.The importance of floodwater chemistry and floodwater biology on N losseshas been demonstrated, but little is known about their effects on the kinetics of othernutrients.Managing acid sulfate soilsHighlightsVietnam has about 1.7 million ha of acid sulfate and potentially acid sulfate soils. InSouth China, about 67,000 ha of acid sulfate soils are cultivated. Irrigated rice can begrown successfully on acid sulfate soils. On Hainan Island, after some years ofreclamation, farmers were able to add banana, pineapple, and coconut to thecropping system.In Vietnam and China, farmers and researchers have developed integratedmanagement practices, including water control by empoldering, special drainage,and irrigation systems to keep pyritic layers submerged; early plowing before dryseason; submergence seeding of first rice crop; dry seeding of second rice crop; splitapplication of P fertilizer; application of ashes and lime; topdressing N after panicleinitiation; green manuring between crops; raising topsoil; and adoption of tolerantrice varieties.In China, hybrid rices are recommended for acid sulfate soils.Research prioritiesAcid sulfate soils include a wide range of soil types; wide variations in specificproperties and nutrient toxicities and deficiencies must be elucidated. Determining Pkinetics and improving P management should be emphasized. Some managementpractices developed by farmers are still not understood.Weed control practices for zero tillage, direct-seeded rice, and dry seeded riceneed to be developed.Moderator: I. ManwanRapporteur: H. U. Neue

Highlights and recommendations 367Water management and farming systemsA common theme is that agriculture, and rice production in particular, is not a singleevent but an integrated system with internal feedback mechanisms involving plantphysiology, biology, soils, economics, etc.Drainage practicesHighlightsTwo water management schemes were compared: draining and sun-drying at certainstages of plant growth and submergence. China reports substantial yield increasesfor draining and sun-drying. Other participants indicate submergence is better.Research prioritiesThe processes involved in increasing yields in environments selected for differentsoils and different temperatures should be determined. The economic feasibility ofeach system should be explored. Collaborative research on water use and drainageshould likewise be explored.Irrigation system principles and practicesHighlightsIntervention for water reliability at the allocation level includes diagnosing specificconditions in an irrigation system, identifying technical and managerial deficiencies,determining appropriate interventions (with farmer participation), and testing theinterventions.Research prioritiesWith lagging national investment in irrigation, water may need to be viewed as ascarce resource. Comprehensive research is needed to better understand how waterused for rice culture can be minimized and conserved. Irrigation systems in Southand Southeast Asia have been designed for rice production. Research is needed onmore effective water distribution and management to increase the productivity ofrice-based cropping systems that include upland crops.Rice - wheat crop rotationHighlightsOf the 60 million ha of wheat grown in Asia, 18 million ha are in rice - wheatcropping systems. Yields are declining in both rice and wheat. The many constraintsinclude late seeding of wheat because of late harvest of rice, establishing wheat inpreviously puddled soils, weed infestation, and suboptimal fertilizer use in bothcrops.Research prioritiesThe collection and synthesis of a database from the many long-term fertilizer trials inrice - wheat cropping systems in different countries, especially in India and China,should be coordinated. That information could become the foundation of a networkto study sustainability problems. The approach could also be used for other ricebasedcropping systems.

368 Highlights and recommendationsWomen’s concerns in rice farming systemsHighlightsDifferent types of household and agricultural labor are not exact substitutes for oneanother. Women are involved in many different farm activities in rice-based systems.Many agricultural activities, especially those in decisionmaking, production, andmarketing, are gender-specific.Research prioritiesA database from different environments of income flow and labor use that aregender-specific should be developed. Information on gender-specific tasks should beincorporated into the development of agricultural technology and appropriateextension schemes devised. Policy workers, planners, and researchers should bemade aware of the policy implications of these concerns. Women’s concerns shouldbe incorporated into research on farming systems in different rice environments.Moderator: P. YotopoulosRapporteur: V. CarangalInnovative breeding methodsHybrid riceHighlightsOutside China, hybrid technology is still experimental. Viable hybrid rice seedproduction techniques developed in China are being adapted to other countries.Chinese cytosterile lines are unsuitable as parents for hybrid developmentelsewhere because of their susceptibility to major diseases and insects and their poorgrain quality. Several better-adapted CMS lines developed in IRRI, India, andKorea are being evaluated. To diversify cytoplasmic male sterility system, some newcytosterility sources have been identified in China and at IRRI. China is using someof these to reduce total dependence on the ‘WA’ CMS source.Several suitable restorers have been identified among indica rice cultivars inseveral countries. Restorers in japonica rices are bred by transferring restorer gene(s)from indica rices.An economic analysis indicated that the higher yields of commercial hybrids inChina are due primarily to the genetic superiority of hybrids; management practicesdid not contribute significantly to increased yields.A photoperiod-sensitive genetic male sterility (PSGMS) system identified inChina results in complete pollen sterility under long-day conditions and partialfertility under short-day conditions. The system appears to be effective above 23°Nlatitude. Chemical emasculating agents (viz., zinc methyl arsenate and sodiummethyl arsenate) have been found effective in developing F 1 rice hybrids that yieldhigher than CMS-derived hybrids. Using chemical emasculating agents lessensdependence on a single cytosterility system.

Highlights and recommendations 369Research problems• Available commercial hybrids have poor grain quality.• Extremely narrow cytoplasmic bases of commercial hybrids make thempotentially vulnerable to disease and insect epidemics associated with the‘WA’ cytosterility system.• Disease or insect resistance in available hybrids is low.• Effective restorers are lacking among sinica (japonica) rice cultivars.• The complex seed production system and low seed yields increase seedproduction costs.• Outstanding and stable CMS lines to produce superior and stable hybrids areneeded.• The economic feasibility of hybrid rice cultivation and seed production inrice-growing countries outside China should be established.Research priorities• CMS and restorer lines and heterotic rice hybrids possessing acceptable grainquality and multiple disease and insect resistance should be developed for thetropics and subtropics.• New sources of cytoplasmic male sterility need to be identified throughinterspecific or intraspecific crosses.• Numerous restorer lines should be bred in japonica rices, using indica/japonica hybridization combined with anther culture.• The two-line method of hybrid breeding, using photoperiod-sensitive malesterility gene or chemical emasculation agents to simplify hybrid seedproduction and to increase the frequency of heterotic hybrids should bedeveloped.• Research to improve yield in hybrid seed production plots must beintensified.• Prospects of clonal propagation methods (viz., somatic embryogenesis as analternative to large-scale hybrid seed production) should be studied.• Outstanding CMS and restorer lines adapted to tropical conditions need tobe developed.• Heterosis in indica/japonica hybrids must be exploited by utilizing widecompatibilitygene(s) in rice.• Apomixis in rice to develop a one-line method of hybrid breeding must bestudied.• The economics of hybrid rice in countries outside China should be studied.Tissue culture and genetic transformationHighlightsAnther culture techniques have been developed for japonica and indica/japonicaderivative crosses. For indica rices, radiation treatment has shown some promise.Anther culture helps shorten the breeding cycle and improve selection efficiency,resulting in gametoclonal genetic variability.

370 Highlights and recommendationsSomatic cell culture and regeneration techniques have been developed toincrease genetic variability through somaclonal variation. In vitro selection forresistance to blast and bacterial blight and tolerance for salt and cold is beingpracticed in China. Embryo rescue techniques have been used to overcomepostfertilization barriers in wide crosses. Protoplast fusion and regenerationtechniques have been developed for japonica rice cultivars.DNA-mediated protoplast transformation involving a kanamycin resistancegene has been demonstrated on the callus of a japonica rice cultivar. Plants wereregenerated from the transformed callus, but whether the regenerated plants aretransformed needs to be established.Research problems• Regeneration ability of indica rices in anther and protoplast cultures is low;high frequencies of albinos occur among the seedlings regenerated in antherculture.• Mechanisms of somaclonal variation are not understood.• Knowledge of specific genes that need to be transformed and their locationon the molecular marker map in rice is lacking.Research priorities• Techniques to improve regeneration ability of indica rices in anther andprotoplast culture should be developed; these techniques will be used onappropriate breeding material, including japonica and indica/japonicacrosses.• Indica rices that have good plant regeneration ability must be identified intissue and cell culture.• Specific genes to be used in rice transformation must also be identified.• RFLP maps in rice should be developed and promising genes for use intransformation studies tagged.• Protoplast fusion techniques should be used to transfer salt tolerance fromSclerophyllum (Porteresia) coarctatum to cultivated rices.• Protoplast fusion techniques must be used to develop CMS lines in rice.• The molecular basis of cytoplasmic male sterility in rice must be studied.Other breeding approachesHighlightsRapid generation advance (RGA) involving single seed descent (SSD) breeding hasbeen used extensively by Japanese rice breeders. It speeds the breeding cycle,increases the number of favorable genotypes, and reduces breeding costs.Shuttle breeding using different ecological environments increases breedingefficiency and helps develop varieties with wider adaptability.Indica/japonica hybridization has been used in China, Korea, and Egypt tobreed rice cultivars possessing high yield and blast resistance.Genes for resistance to grassy stunt virus, brown planthopper, and whitebackedplanthopper have been successfully transferred from wild species of Oryza intoseveral rice cultivars. Wide hybridization can be used to transfer other resistance/tolerance genes and to search for unique genetic variability.

Highlights and recommendations 371Rice/sorghum hybrids have been successfully bred in China through repeatedhybridization. Hybrid types and a wide range of variations have been obtained andnew cultivars with elite economic traits were released for production.Research problemsKnowledge about the efficiency of nonconventional breeding methods (viz.,RGA/SSD, male sterility facilitated recurrent selection procedures) compared withthe pedigree method of breeding under tropical conditions is inadequate.Research priorities• Single-seed descent breeding must be explored in the tropics.• Shuttle breeding must be used to increase breeding efficiency and wideadaptability.• Wild rices must be screened systematically for resistance to or tolerance forbiotic and abiotic stresses.• Interspecific hybridization must be used to transfer useful genes forresistance to or tolerance for biotic and abiotic stresses and to identify uniquegenetic variability in rice.• The search for bridging species in rice must be continued.• Methods to overcome prefertilization barriers in wide crosses must bestudied.• Rice cultivars derived from rice/sorghum crosses for drought tolerance mustbe evaluated.• Male sterility facilitated recurrent selection must be tested as a way toimprove resistance to sheath blight and stem borer.Moderator: S. PushpavesaRapporteur: S. S. VirmaniGrain qualityHighlightsImproving rice grain quality has become an important issue as countries thattraditionally have imported rice have attained self-sufficiency and export occasionalsurpluses. In the international market, price premiums for quality are substantial. Indomestic markets, rapid growth in consumer income has increased demand forquality.At the same time, innovative breeding approaches have created newopportunities for significant progress in improving grain quality. Improved grainquality has the potential to raise the value of rice production and to increaseconsumer satisfaction without reducing farmer income.Grain quality characteristics typically are classified by• chemical properties—amylose content, gel consistency, gelatinizationtemperature, etc.• physical appearance—percentage of broken grains, shape, whiteness,translucency, aroma, etc.• nutritional content, especially protein.

372 Highlights and recommendationsIt is important to quantify the relative contribution of the factors that affectgrain quality (variety, environment, postharvest handling, and processing). Many ofthe physical or technical relationships between the factors and grain qualitycharacteristics are already known; only a few attempts have been made to estimatethe value consumers place on grain quality and its individual characteristics.Historically, consumer preferences have been analyzed by asking individuals torank their preferences for different types of cooked rice. With this approach, thevalue of individual quality characteristics and the price consumers would be willingto pay for quality cannot be determined.IRRI has used the Hedonic price model to identify the value consumers placeon rice quality characteristics. In a study of representative urban markets inThailand, Indonesia, and the Philippines, intermediate amylose content, fewerbrokens, and aroma were identified as desirable characteristics in those countries.In the world market, quality appears to be defined in terms of percent brokensand grain length; rice is also differentiated by country of origin. Thai rice hasintermediate to high amylose content and hard to soft gel consistency. Quality ricesfrom Pakistan, India, USA, and Australia have intermediate or low amylosecontent, low to intermediate final gelatinization temperature, and soft to medium gelconsistency.The parboiled rice consumed in India, Bangladesh, Nepal, Pakistan, and SriLanka constitutes half the rice consumed in South Asia and about a fifth of worldconsumption. Most parboiled rice is processed by the conventional method ofsoaking, draining, and steaming. A shift to dry-heat and pressure parboiling isexpected.Parboiling increases milling recovery, raises vitamin and mineral levels,transfers oil from the grain to the bran, and reduces insect susceptibility. However,parboiled rice requires longer cooking time, is subject to discoloration, and involvesprocessing costs. The quality characteristics of parboiled rice differ from raw rice.Research prioritiesIn breeding, greater attention should be paid to• achieving synchronous maturation of grains, reducing grain indentation,achieving a high rate of translucency and fissuring resistance, and eliminatingwhite belly to improve milling recovery and reduce percentage of brokens.• increasing yields of aromatic rice by screening germplasm, introducingdwarfing genes, insect and pest resistance, etc.• raising protein content.• improving shelf life of seed by exploiting available genetic variability.• exploring means to reduce cooking time of parboiled rice.Adoption of improved postharvest practices and drying and milling technologyhas been slow, largely because there is little economic incentive at the farm andmilling level. Government policies that insulate the domestic market from the pricepremiums for quality in the world rice market, such as government monopoly ofinternational and domestic trade in Burma, Philippines, and Indonesia, are keyconstraints.

Highlights and recommendations 373Two studies are needed:• The effect of cultural management practices and agroclimatic conditions ongrain quality (e.g., timing of harvest and fertilizer application).• A map of consumer preferences for rice quality in different Asian countries,as well as in the international market.Collaborative research to assess the value of rice grain quality characteristics inthe Philippines, Indonesia, Thailand, Bangladesh, and the world market should beextended to Burma, India, Malaysia, and Pakistan, to provide insights into therelative value of different quality characteristics and to evaluate the economictrade-off between improving quality and increasing quantity.Moderator: R. S. ParodaRapporteur: C. C. DavidFarm machinery and postharvest managementHighlightsMechanization of irrigated rice production involves hand tools, animal draft power,and mechanical power; all three can coexist in a given rice production area.The introduction of new machines involves complex socioeconomic issues.Balanced national mechanization policies are crucial. In general, mechanization oflabor-intensive operations almost always results in displacement of farm labor.Where sufficient off-farm income opportunities are available, the social effects maynot be severe. Where income opportunities are not available, introducing powermachinery can cause social hardships.The trade-off between increased production efficiency through mechanizationand displacement of agricultural labor and tenant farmers poses a crucial policydilemma for labor-abundant, land-scarce economies with little opportunity foroff-farm and nonfarm income. Adverse effects can be aggravated by suchgovernment policies as cheap credit for purchase or manufacture of machines thatcause large-scale labor displacement.Types, sizes, and performance standards of current farm machinery,particularly transplanting and harvesting machines, need to be modified to fitrapidly growing rural economies in which the agricultural labor force is steadilytransferring to other professions.Mechanization inputs have limited divisibility and are subject to economies ofscale. The economic efficiency of a given machine or piece of equipment depends onrelative factor prices, especially the cost of labor vs the cost of the machine, and on itsefficient application. Lack of institutional and infrastructural support services formechanization may substantially increase private and social costs.Basic objectives of mechanization must be clarified before the type ofmechanization needed is identified and the means to attain its efficient useestablished. Those objectives depend on resource endowments, rate of economicgrowth and development, and existing policies and programs of each country.

374 Highlights and recommendationsResearch prioritiesThe research issues are related to (a) opportunities for off-farm income available tothe rural population, (b) land-population ratio in the rural areas, and (c) existinglevels of mechanization.Land preparation. Current machines should be adapted to local conditions.Land preparation machines should enhance labor productivity and improve timelycrop establishment.Transplanting. Mechanical transplanters are inappropriate for land-scarce,labor-abundant economies. Where labor is moving from agriculture to industry, apriority is to develop efficient transplanters. Improved performance of currentlyused transplanters, which function well for the first rice crop but not for a second riceor hybrid rice crop, is urgent.Harvesting. Thailand needs institutionalized and efficient extension servicesand credit facilities for farmer adoption of existing reapers. China needs to improvethe efficiency of currently available harvesters and to develop efficient small combineharvesters. In most other developing rice-growing countries, harvesting is best left asa manual operation.Drying. Current IRRI research on drying, utilizing such innovative ideas asmultipurpose use, agricultural waste as an energy source, wind for aeration, andlocally available construction materials, needs to be evaluated in terms of its value tosmall farmers.Irrigation. East Africa needs nonfossil fuel-dependent machines to clearvegetation from irrigation canals.From a social equity and employment point of view, mechanization of waterlifting would be desirable.Research directionsWith the diversity of agroclimatic, technical, socioeconomic, and political systems ofrice-growing countries, most research and extension needs must be addressed byappropriate national institutions. However, experience gained in one country canhelp guide the mechanization programs of another country. Collaboration betweenIRRI and the Regional Network for Agricultural Machinery Testing (RNAM)should remain strong for effective knowledge sharing. Collaborative regionalresearch and training programs should enhance appropriate agricultural machinerydesign and testing.IRRI’s agricultural machinery development program should continue to focuson designing machines to increase rice production and to support experimentalresearch at IRRI and its collaborating institutions.Moderator: Z. ToqueroRapporteur: S. I. Bhuiyan

Highlights and recommendations 375International collaborationHighlightsIRRI’s collaborative relations with Asian and other rice-growing countries aredesigned to share seeds, research techniques, cultural practices, farm machinery, andtechnical information. Genetic conservation at IRRI now focuses on traininggermplasm workers in field collection and resource management. National plantgermplasm systems need to be established or strengthened to augment the security ofconserved stocks. IRTP provides a major, effective channel to pool, evaluate, anduse elite germplasm. Information transfer involves actual field trials (e.g., croppingpattern trials of the Asian Rice Farming Systems Network), training, andinformation transmission.Research priorities• Movement to adverse environments. As research emphasis expands toinclude not only irrigated rice but also rainfed lowland, upland, deepwater,and problem soils environments, IRRI must seek new and more intensivecollaboration with national agricultural research systems (NARS) at theepicenters of the problem areas.• Career development. IRRI should develop training programs for youngprofessionals, midcareer scientists, and NARS experiment station managers.• Relationship between private industry and the international agriculturalresearch system. IRRI traditionally has provided seed and information freeto institutions and individuals, with the sole objective of increasing riceproduction worldwide. IRRI also has benefited enormously from the freeflow of information from advanced country scientists and laboratories.Institutions in the public domain, such as IRRI, should carefully consider theissues before establishing collaborative relations with private sectorcompanies.• Copublication network. An informal network of publishers representinginternational, national, and private agencies could help move informationinto many more countries and languages.• Computer and communication technologies provide the capability forelectronic networks among rice researchers to improve scientific communication,at dramatically reduced costs.Recommendations• The genetic diversity of test and breeding material should be increased.• Observational nurseries for adverse ecologies should be strengthened.• Appropriate linkages between IRTP and the International Network on SoilFertility and Fertilizer Evaluation for Rice and the Asian Rice FarmingSystems Network should be sought.• Training needs of NARS scientists involved in research in adverseenvironments should be examined, so that collaboration can be based onequality.

376 Highlights and recommendations• The content and resources required for training programs in Young ScientistDevelopment, Midcareer Scientist Development, and Experiment StationManager Development should be considered.• The potential for private seed company growth in Asia and the level ofinteraction IRRI and NARS will have with such companies should beexamined.• Currently available information on transmission technology, especiallyelectronic technology, should be examined to make information transferbetween IRRI and NARS more efficient and cost-effective.• The establishment of an informal network for copublication should beexamined.• At training sessions and conferences, less time should be spent on sendingand receiving information and more time on discussing and problem solving.Moderator: S. C. LeeRapporteur: P. Pingali

ParticipantsADBA. J. RijkAsian Development BankP.O. Box 789, Metro ManilaPhilippinesBURMAOhn KyawAgricultural Research InstituteYezin, PyinmanaA. MundtAgricultural Research InstituteYezin, PyinmanaCHINACao JinminJilin Academy of Agricultural SciencesGonzhulinChen ChuangqunZhejiang Commission of Science andTechnologyHangzhouChen ZhanglianBeijing UniversityBeijingChen ZiyuahZhejiang Agricultural UniversityHangzhouCheng WinfuShenyang Agricultural UniversityShenyangChuge GenzhangZhejiang Academy of AgriculturalSciencesHangzhouFeng BinyuanChinese Academy of AgriculturalMechanization SciencesBeijingFeng DingfuAgricultural PressBeijingGao LianzhiJiangsu Academy of AgriculturalSciencesNanjingGao ZhengchenYunnan Provincial GovernmentKunminGuan ZhiheBeijing Agricultural UniversityBeijingMinister He KangMinistry of Agriculture, AnimalHusbandry, and FisheryBeijingHuang HeqingHunan Academy of AgriculturalSciencesChangshaHuang ZuhuiZhejiang Agricultural UniversityHangzhouJin ShichaoZhejiang Provincial GovernmentHangzhou

378 ParticipantsJing PengyanZhejiang Academy of AgriculturalSciencesHangzhouKuang TingyunChinese Academy of SciencesBeijingLi DachenMinistry of Agriculture, AnimalHusbandry, and FisheryBeijingLi JingpenAgricultural UniversityGuangdongLi LiangcaiChinese Academy of SciencesBeijingLiang ChenyeSouth China Botanical InstituteGuangzhouLin QihongJiangsu Provincial GovernmentNanjingLin YiziZhejiang Academy of AgriculturalSciencesHangzhouLin ZhengyouYunnan Provincial GovernmentKunminLiu BiaoxiSichuan Academy of AgriculturalSciencesChenduLiu ChungchuFujian Academy of Agricultural SciencesFuzhouLiu TianlinGuangxi Agricultural MachineryResearch InstituteNanningLiu YansongJiangsu Academy of AgriculturalSciencesNanjingLu YonggenSouth China Agricultural UniversityGuangzhouMa YueZhejiang Agricultural BureauHangzhouMao ChangxiangHunan Hybrid Rice Research CenterChangshaMou TongminHubei Academy of Agricultural SciencesWuchangRen GuahuaMinistry of Agriculture, AnimalHusbandry, and FisheryBeijingShao QiquanInstitute of GeneticsAcademia SinicaBeijingShen ZongtanZhejiang Agricultural UniversityHangzhouSun ShuyuanZhejiang Academy of AgriculturalSciencesHangzhouTsiu JilingJiangsu Academy of AgriculturalSciencesJiangsuTu ZengpingGuangdong Academy of AgriculturalSciencesGuangzhouWan BanghuiSouth China Agricultural UniversityGuangzhouWang BingInstitute of GeneticsAcademia SinicaBeijingWang CailinJiangsu Academy of AgriculturalSciencesNanjingWang ZhaoqianZhejiang Agricultural UniversityHangzhouWen QixiaoInstitute of Soil ScienceNanjing

Participants 379Wu GuangnanJiangsu Academy of AgriculturalSciencesNanjingWu ShangzhongGuangdong Academy of AgriculturalSciencesGuangzhouXia YingwuZhejiang Agricultural UniversityHangzhouXiong HongSichuan Academy of AgriculturalScienceLuzhouGovernor Xue JuZhejiang Provincial GovernmentHangzhouXue QingzhongZhejiang Agricultural UniversityHangzhouYan QisongAnhui Academy of Agricultural SciencesHefeiYan RencuiFujian Agricultural CollegeFuzhouYang ShourenShenyang Agricultural UniversityShenyangYang ZhenyuLiaoning Academy of AgriculturalSciencesShenyangYe YanfuZhejiang Academy of AgriculturalSciencesHangzhouYuan LongpingHunan Hybrid Rice Research CenterChangshaZhang ZhenhuaShanghai Academy of AgriculturalScienceShanghaiZhang ZhongshanMinistry of Agriculture, AnimalHusbandry, and FisheryBeijingZhang JunlongMinistry of Agriculture, AnimalHusbandry, and FisheryBeijingZheng QinjieZhejiang Provincial GovernmentHangzhouZhou YuediZhejiang Provincial GovernmentHangzhouZhu DeyaoJiangxi Academy of AgriculturalSciencesNanchangZhu ZhaoliangInstitute of Soil ScienceNanjingZhu ZuxiangZhejiang Agricultural UniversityHangzhouCIMMYTD. SaundersInternational Maize and WheatImprovement CenterDepartment of AgricultureBangkhen, Bangkok, ThailandEGYPTM. S. BalalMinistry of Agriculture A.R.E.Rice Research and Training ProjectField Crops Research InstituteGizaHUNGARYI. K. SimonDepartment of Breeding and CultivationResearch Institute for Irrigation5540 SzarvasSzabadzag u. 2.IFPRlL. A. GonzalesInternational Food Policy ResearchInstitutec/o IRRlP.O. Box 933, ManilaPhilippines

380 ParticipantsllMlS. MirandaInternational Irrigation ManagementInstituteP.O. Box 20755A Schofield PlaceColombo 3, Sri LankaINDIAK. R. BhattacharyaCentral Food Technology ResearchInstituteMysoreE. P. GhildyalIRRl382 Samrat Hotel, ChanakyapuriNew DelhiK. KanungoPlanning CommissionGovernment of IndiaNew DelhiR. S. ParodaNational Bureau of Plant GeneticResourcesNew DelhiA. K. SinghRajendra Agricultural UniversityPusa 848125 (Samastipur)BiharRamashrit SinghRajendra Agricultural UniversityPusa 848125 (Samastipur)BiharE. VenkateswarluDirectorate of Rice ResearchRajendranagarHyderabadINDONESIADjoko DamardjatiSukamandi Research Institute for FoodCropsSukamandi, SubangWest JavaZ. HarahapCentral Research Institute for FoodCropsJalan, Merdeka 99BogorI. ManwanCentral Research Institute for FoodCropsBogorPudjiwati SajogyoBogor Agricultural UniversityJalan Malabar No. 1BogorD. M. TanteraCooperative DEPAGRI-IRRI ProgramP.O. Box 107Bogor 16001IVORY COASTE. A. AkinsolaWARDA Regional Upland Rice Station10 B.P. 2551BouakeJAPANK. MaruyamaNational Agricultural Research CenterYatabe, lbaraki 305I. NishiyamaCentral Agricultural Research CenterTsukuba Science CityYatabe, lbaraki 305A. TanakaLaboratory of Plant NutritionFaculty of AgricultureHokkaido University, SapporoK. ToriyamaZen-Noh, 8-3 Ohtemachi1-Chome, Chiyoda-ku. TokyoH. UchimiyaUniversity of TsukubaInstitute of Biological ScienceSakura-mura, Niihari-gunlbaraki 305T. YamaguchiChugoku National AgriculturalExperiment StationNishi-fikatsu 6-12-1Fukuyama, Hiroshima 721T. YamamotoTropical Agriculture Research CenterMAFF, YatabeTsukuba, lbarakiKOREASoo Yeon ChoRural Development Administration250 Seodun DongSuweon 170Tae Young ChungRural Development Administration250 Seodun DongSuweon 170

Participants 381Mun Hue HeuCollege of AgricultureSeoul National UniversitySeoulE. J. LeeRural Development Administration250 Seodun DongSuweon 170Hong Suk LeeCollege of AgricultureSeoul National UniversitySeoulSeung Chan LeeDepartment of Agricultural BiologyCollege of AgricultureChonnam National UniversityKwangju 500Seog Hong ParkRural Development Administration250 Seodun DongSuweon 170MADAGASCARJ. R. HooperIRRI, B.P. 41 51AntananarivoJeanine RaharinirinaDivision of Agro-geneticsFOFIFA, B.P. 1444AntananarivoPierre RasolofoDivision of PedologyB.P. 1444, AntananarivoClet Pascal RavohitrarivoFOFIFA, B.P. 1690AntananarivoLala RazafinjaraDivision of PedologyFOFIFA, B.P. 1444AntananarivoB. B. ShahiIRRI, B.P. 41 51AntananarivoNIGERIAI. O. AkobunduInternational institute for TropicalAgriculturelbadanPHILIPPINESJ. HernandezAgronomy DepartmentUniversity of the Philippines at LosBañosCollege, LagunaSantiago R. ObienPhilippine Rice Research InstituteUniversity of the Philippines at LosBañosCollege, LagunaR. RoblesAgronomy DepartmentUniversity of the Philippines at LosBañosCollege, LagunaZenaida ToqueroIDRC Post Harvest ProjectSEARCACollege, LagunaTANZANIAG. C. MremaDepartment of Agricultural EngineeringSokoine University of AgricultureMorogoroTHAILANDChak ChakkaphakAgricultural Engineering DivisionDepartment of AgricultureBangkhen, Bangkok 10900Suvit PushpavesaRice Research InstituteDepartment of AgricultureBangkhen, Bangkok 10900Praves SaengpetchDepartment of AgricultureBangkhen, Bangkok 10900Aamphol SenanarongDepartment of AgricultureBangkhen, Bangkok 10900Praphas WeerapasDepartment of AgricultureBangkhen, Bangkok 10900USAA. AppThe Rockefeller foundation1133 Avenue of the AmericasNew York, N.Y. 10036

382 ParticipantsH. M. BeachellManagement Farms of Texas Co.Chocolate Bayou Research DivisionP.O. Box 1305Alvin, Texas 77512C. N. BollichTexas Agricultural Experiment StationThe Texas A & M University SystemBeaumont, Texas 77706R. DildayUSDA-ARSP.O. Box 287Struttgart, ArkansasG. LindseyCGNET Services400 WebsterPalo Alto, CA 94310P. YotopoulusFood Research InstituteStanford, CA 94305UNITED KINGDOME. C. CockingDepartment of BotanySchool of Biological SciencesThe University of NottinghamUniversity ParkNottingham NG7 2RDVIETNAMDao The TuanVietnam Agricultural InstituteVan Dien, HanoiVo Tong XuanCantho UniversityCantho, HaugiangSPONSORING INSTITUTESChinese Academy of AgriculturalSciencesChen ShangbaoFang CuinongGan XiaosongGuo YixianHe GuitingLi BaochuLi XianghuiLiang MingzhaoLin ShichenLiu GuangshuLou XichiLu LiangshuPang ZhongmeiXing ZuyiXu GuanrenXu ShiweiZhang QiChina National Rice Research InstituteBao SiqiCha LiqunChen YaliChen ZhongxiaoDong BingyuFei HuailinHu GenshenHuang YuminJin LiandengLi DebaoLi JiahouLin RonghuiLin ZhongdaLu ZitongLuo YukunMin ShaokaiSong SitoXiong ZhenminXu YunlianYing CunshanShang BaozhaoZhang WeiZhang YihuaZen YankunZheng KangleIRRlS. AkitaF. BernardoS. I. BhuiyanV. R. CarangalT. T. ChangC. C. DavidS. K. De DattaK. K. JenaY. W. JeonG. S. KhushC. H. KimD. R. MinnickH. U. NeueT. OgawaP. PingaliL. R. PollardR. C. SaxenaD. V. SeshuL. A. SitchM. S. SwaminathanD. L. UmaliB. S. VergaraS. S. VirmaniF. J. Zapata

Varietal index 383Varietal indexRice4, 3515, 35126 Zhai zao, 234II 32, 227-22870X-46, 10879-1163, 352248-2, 352350, 351910, 3441952, 3528085, 35075704-36, 35279007, 35179317-4, 35279317-4, 35280047, 35180079, 351829042, 266837003, 268A 69-1, 356A7929, 267-268A8315, 268AD9246, 352ADR52, 115, 349ADT14, 356ADT27, 273Ai nan zao 1, 329Ai-jiao-nan-te, 3, 329Ai-zai-zhan, 329Aikeng 23, 97, 351Akenohoshi, 48, 68Aki-bare, 100,108American Rice 1, 351ARC6650, 120-121, 353-354ARC10239, 115ARC11554, 117, 348ARC13829-16, 229Asahan, 27ASD7, 116-117, 119-121, 126, 334, 354ASD8, 126, 349Asominori, 106-108AUS 339, 356B 2484B-PN-28-3-MR-5, 353B2978B-SR-2-6-2-2-2, 356Babawee, 117, 121, 349, 354Baegam, 103-104Baegunchalbyeo, 105Baegyang, 101Bahbolon, 35, 355Balamawee, 349Bao Tai-ai, 97, 328Bao Xuan 2, 97Bao-tan 2, 328Barito, 35Barkat, 225, 346Basmati, 19, 21, 278, 287BAU19-3, 344Bengawan, 27BG34-8, 344BG35-2, 353BG90-2, 328, 350-351, 353BG276-5, 340BG367-2, 349BG367-4, 340, 343, 354BG367-7, 340BG379-3, 354BG380-2, 342, 348BG400-1, 84, 340BG2767-5, 84Binato, 44, 142-143BJ1, 82, 347, 353BKNBR76025-10-8-1-2KLG-1-1-1-7, 355Bongkwang, 99-104BPI 121-407, 279BR51-46-5, 345BR51-91-6, 345BR51-282-8, 340, 348, 353BR309-74-2-2-2, 353BR153-2B-10-1-3, 345, 352-353

384 Varietal indexBR161-2B-59, 353BR169-19-12, 353BR171-2B-8, 353BR203-70-B-I, 350BR316-1544-1, 342BR319-1, 353BR380-2, 345Brantas, 27C4-63, 27C4-63G, 279C40, 102C41, 102C48, 351C241, 351C1117-2, 354C1321-9, 354C1322-28, 354C5924, 245C8014, 351C662083, 341, 352C701045, 354C702015, 342C702043, 354C702080, 354C702344, 353C711125, 354-355C711140, 355C712068, 354-355C712315, 353Camponi SML, 353Carreon, 81, 347, 353Ceysvoni SML, 353Champa, 328Chang Hui 22, 227Chemparampandi, 355Chengte 232, 234Cheongcheong, 101,105Cheonma, 100,103-104Cheriya chittari, 355Chiag, 101Chianung sen yu 13, 340,350,352Chianung sen yu 26, 341Chianung si-pi 661020, 352-353Chianung si-pi 662098, 352Chianung si-pi 861032, 351Chikong, 101,104China, 329China 1039, 329,346,356Ching-shi 5, 346Ching-shi 15, 346, 356Chu cheng (Am. 1395), 356Chucheong, 100-107, 109Chukoku 45, 108Chun-hua-ai 6, 351CIAT-ICA5, 347, 353Cikapundung, 35Cipunegara, 35Cisadane, 33-36, 348Citanduy, 35Citrum, 27CO 18, 348Colombia 1, 81Colombo, 115Corallo, 356CR94-13, 84CR157-392-4, 348CSRI, 347D254, 278Daechang, 100,102,105Daecheong, 104Daeseong, 100-105Dahanala 2220, 119-120Dawn, 81Dee-geo-woo-gen, 329, 334Dewi Tara, 27Diket, 208Djambon, 355Dobong, 100-101,103Dongjin, 101DR92, 350DV85, 347,353DZS97, 228E 108, 350Eai Nou, 98Early Tong-il, 108Eiko, 346Erwan 5, 97Eswarakora, 348F ang chi (Acc. 1385), 356Farro 15, 344FB24, 83Fengwo, 351Fortuna, 329Fu She 94, 98Fu-Gui, 240Fuji 120, 346Fujiminori, 253Fuke 43, 351Fukunishiki, 349G am Pai 15, 81-82, 88Gam Pai 30-12-15, 348Gang-Er-Hua-Shuang-Gui, 238Gang-Hua 2, 49, 238Gang-Hua-Da-Zha, 239Gang-Hua-Qing-Hua 6, 240Gang-Hua-Qing-Lan, 238-239, 241Gaya, 105-107,109Getu, 347GH147(M)40 Krad 89, 355GH147(M)Krad 78, 355Giho, 101,103Giza 159, 356Giza 172, 344Giza 175, 273Gokyoku, 108Guan-keng, 334Guangchang Ai, 3

Varietal index 385Gui 32, 351Gui 33, 351Gui 34, 351Gui 44, 351Gui 45, 351Gui 47, 351Gui-Chao, 240Gui-Chao 2, 350-351Guojiyouzhan, 350H4, 281H5, 351H46, 351H105, 81Hanfeng, 351Hokuriku 93, 258Hondarawala, 354Hong 410, 95HPU71, 352HPU741, 356HR21, 82Hua 30, 262Huan-sen-goo, 353Hwang hae do, 356Hwaseong, 101I 353, 100I 355, 100IET1444, 344IET2845, 348IET5540, 348Intan, 82IR5, 83, 85, 279IR8, 42, 59, 83-85, 89-90, 98-99, 117, 122,125-126, 279, 304-305, 328-329, 362IR20, 42, 82-85, 96, 277, 348, 351, 353IR22, 82-83, 85,351, 353IR24, 42, 82-83, 85, 229, 350-352IR24-32, 351IR24-33, 351IR26, 42, 82-86, 89, 112, 115-117, 122, 124-126, 229, 350-351, 353-354IR28, 42, 82-86, 126, 229IR29, 82-83, 85-86, 116-117, 126, 129, 351,353IR30, 82-86, 126, 351, 353IR32, 35, 82-45, 279, 281IR34, 82-83, 85-86IR36, 27, 33, 35, 42, 82-86, 89-90, 95, 99, 101,103, 117, 122-128, 137-139, 141-142, 222,229, 279, 340, 343-344, 348, 351-354IR38, 35, 82-86IR40, 82-85, 129, 355IR42, 229, 277, 279, 340, 352-353IR44, 44, 46, 50, 82, 85IR45, 355IR46, 35, 82-85, 115-116, 122, 126, 128, 229,347, 354IR48, 82-83, 85, 279IRM, 35, 82-86, 101, 103, 226, 229, 340-341,352IR52, 35, 42, 82-83, 85, 353IR54, 35, 82-86, 226, 229, 231, 340, 348, 353IR56, 44, 46, 50, 82-83, 85-86, 117, 122-127,229, 349, 352-355IR58, 42, 44-46, 48, 53, 55-58, 82-83, 85, 137,229, 279, 354IR60, 82-83, 85-86, 124, 126-127, 229, 352,355IR62, 82-86, 117, 126, 279, 354IR64, 35, 42, 45-46, 48-49, 53, 56, 58, 61-64,67, 82-85, 96, 117,125,142-143, 222,224,226, 229, 231, 279, 348, 352, 354IR65, 85, 208IR66, 85, 96, 117,279IR440-78-1-3, 356IR946-33-2-2-2-2, 353IR1416-128-5-8, 347, 353IR1514A-E666, 348IR1529-680-3-2, 353IR1539-823-14, 84IR1695, 107IR1820-52-2, 841R1820-52-24, 348IR1905-PP11-29-4, 347IR1917-3-19, 84IR2006-P-12-2-2, 353IR203.5-117, 83IR2035-117-3, 115, 119-120, 349, 355IR2061, 353IR2061427-1-17-7-5, 353IR2061-522-6-9, 356IR2798-143-3. 348IR2863-38-1-2, 345IR33259-5-160-3, 347IR3858-6, 354IR3941-9-2, 348IR4227-109-1-3-3, 347IR4422-98-3-6-1, 345IR4422-480-2-3-3, 226IR444246-3-3, 348IR45474-1-2, 347IR4568-86-1-3-2, 353IR45954-13, 347IR459541-13, 347IR4619-57-1-1-2-1, 354IR4630-22-2-5-1-3, 347IR4763-73-1-11, 355IR4763-73-3-11, 228IR5533-PP850-1, 347IR5982-7-6-1 selection, 351IR7929-67-3, 348IR8154-95-1, 355IR8236-BB336-3-2, 347IR8608-75-3-1-3, 354IR8608-82-1-3-1-3, 353IR8608-231-2-2-3-2, 353IR9909-K1, 356IR9129-33-3-3, 356IR9129- 102-2, 350, 353IR9202-5-2-2-2, 225IR9202-3342-1, 356

386 Varietal indexIR9209-249-1-2-3-2, 353IR9218-156-1-3, 352IR9224-K1, 356IR9698-36-3-3, 352IR9729-67-3, 340,352IR9732-119-3, 354IR9761-19-1, 222, 226, 231, 354IR9761-19-1-64, 231IR9763-11-2-2-3, 355IR9764-45-2-2, 347IR9782-111-2-1-2, 352-354IR9828-23-1, 348IR9828-91-2-3, 340, 348IR39884-54-3, 347IR996548-2, 350-351, 353IR10154-23-3-3, 228IRl0176-24-6-2, 228IR10179-2-3-1, 228IR1019862, 347IR10206-29-2, 347, 356IR10232-17-2, 355IR11248-23-3-2, 347IR11248-83-3-2-1-3, 353IR11288-B-B-118-1, 355IR11288-B-B-288-1, 353IR11297-170-3-2, 353IR11418-15-2, 347, 355IR11418-19-2-3, 354-355IR12912-131-2, 349IR12979-24-1, 228IR13146-45-2, 353IR13240-39-3, 354IR132M-108-2-2-3, 341, 344, 352IR13415-9-3, 354IR13419-113-1, 231IR13423-17-1-2-1, 348,353IR1342745-3-1-2-2-2, 355IR13429-86-3-3-2-2, 355IR13429-196-1, 340IR13429-196-1-2-1, 354IR13429-287-3, 353IR13429-299-2-1-3, 353IR13458-117-2-3, 349IR13458-117-2-3-2-3, 353IR13524-21-2-3-3-2-2, 341IR13525-118-3-2-2-2, 356IR13535-21-2-3-3-2, 355IR13539-100-2-2-2-3, 352IR13540-56-3, 349IR13540-56-3-2-1, 340, 345IR13564-95-1, 355IR13564-109-1, 354IR13639-34, 348IR14252-13-2-2-5, 354IR14753-120-3, 225IR14875-98-5, 354-355IR15498-167-3-2-2, 355IR15529-253-3-2, 349IR15718-28-2-2, 355IR1572345-3, 348IR15795-151-2-3-2-2, 228IR15797-74-1-3-2, 355IR15847-135-1-1, 355IR15849-132-3-3, 355IR15853-89-7E-P3, 350IR15869-113-1, 355IR17307-11-2-3, 349IR17492-184-1, 349IR17492-18-10-2-2-2, 354IR17494-32-1, 349IR17494-32-2-2-1-3, 355IR17525-278-1-1-2, 228, 352IR18348-36-3-3, 354IR18349-135-2-3-2-1, 342IR18350-93-2, 355IR19256-88-1, 355IR19374-25-2-2, 354IR19392-211-1, 224-226IR19431-72-2, 355IR19575-85-2-2-3, 352IR19657-34-2-2-3-3, 228IR19657-87-3-3, 228IR19660-45-1, 349IR196604-1-3-2-2, 353IR19660-00948-1, 347IR19661-23-3, 349IR19661-283-1-3-2, 228IR19670-177-1, 354IR19672-140-2-3-2, 353IR19728-9-3-2, 343IR19728-9-3-2-3-3, 228IR1974346-2-3, 356IR19746-26-2-3-3, 346IR19746-27-3-3-1-3, 228IR19746-28-2-2, 343IR19746-28-2-2-3, 356IR19762-2-3-3, 352IR19774-23-2-2-1-3, 228IR19792-15-2-3-3, 228IR19805-32-1-3-1-2, 228IR19807-21-2-2, 228IR19809-12-3-2-1, 228IR20878-1-PI, 355IR20933-68-21-1-2, 226IR21015-80-3-3-1-2, 350, 355IR21820-154-3-2-2-3, 340IR21845-90-3, 228IR21848-65-3-2-2, 353IR21929-12-3-3, 350, 354IR21931-47-3-3, 352IR22103-262, 228IR254744 1-2-3-2, 228IR25586-45-1-2, 352IR25586-108-1-2-2-2, 355IR2558767-1-3-3-3, 355IR25588-7-3-1, 340, 354-355IR25621-105-1-2, 352IR25884-94-3-2, 341, 353IR25916-15-3-2, 353IR25924-51-2-3, 340

Varietal index 387IR25925-84-3-2, 353IR26717-1-1-2, 348IR27316-78-3-3, 355IR27325-27-3-3, 347IR28118-138-2-3, 340IR28150-84-3-3-2, 355IR28154-101-3-2, 353, 355IR28224-3-2-3-2, 117, 355IR28224-21-2-2-1, 353IR28228-12-3-1-1-2, 117, 355IR2859840-2-3, 341IR29512, 44, 69IR29512-81-2-1, 226IR2969245-2-3, 355IR29692-94-2-1-3, 355IR29692-99-3-2-1, 355IR29723, 47,49IR29723-88-2-3-3, 355IR29723-143-3-2-1, 44, 46-49, 51, 69, 139,142-143, 342IR29723-143-7-2, 46IR29723-186-2-2-3, 355IR29725-3-1-3-2, 355IR29725-309-1-2-1, 355IR31775-30-3-2-2-2, 352IR31787-24-3-2-2, 228IR31805-20-1-3-3, 341IR31809-83-3-2-2, 342IR31868442-3-3-3, 117IR3227247-3-2-3, 355IR3242947-3-2-2, 117IR3242948-3-3-3, 355IR32429-130-2-2-2, 355IR32453-20-3-2-2, 117IR32720-138-2-1-1-2, 353IR32799-107-3-3-2, 353IR32822-2-2-3-2, 355IR32843-92-2-2-3, 341IR333059-26-2-2, 353IR35295-82-2-1-3-2, 342IR35323-93-1-3-1, 355IR35366-90-3-2-1-3, 222IR39357-133-3-2-2-2, 341-342IR40094-1-5-2, 225IR40094-4-5-5, 225IR44668-85-1-2-2-3, 222IR44707-31-1-3-2, 222IR46826, 228IR46827, 228IR46828, 228IR46829, 228IR46830, 44, 222, 226, 228, 231IR46831, 228IR48483, 228IR54752, 69, 222, 225-226, 228, 231IR54753, 228IR54754, 228IR54755, 229IR54756, 228IR54757, 228IR54758, 228IR58019, 228IR58020, 228IR58021, 228IR58022, 228IR58023, 228IR58024, 228IR58025, 228IR58026, 228IR58027, 228IR58052, 228IR58053, 228IR58054, 228IR58055, 228IR58056, 228IR58057, 228IR58058, 228IR465831, 231IRAT13, 353IRAT104, 347, 353IRAT109, 353IRAT130, 353Iri 347, 352-353Iri 356, 228Iri 372, 100, 103-104Iri 373, 103Iri 377, 104-105ITA118, 353ITA212, 345J angseong, 103Jarhu 5, 97Jikkoku/Seranai 52-37, 228Jin heung, 108, 262, 266Jingying 1, 262,266Jingying 39, 221Jingying 47, 266Jingying 83, 267Jingyue 1, 98Jingza 1, 262Jinju, 103, 105Jcdo, 346Ju ku (Am. 1144), 356Jukkoku, 108Jungweon, 105K 31-163-3, 346K39-96-1-1-2, 346, 356K143-1-2, 356K315, 356K335, 346K434, 356Kakatiya, 84, 348Kannaki, 354Kao cha 1, 351KAU1727, 340, 344Kelara, 35,83Kencana, 115-116, 122Kexuan 93, 343Kinmaze, 106, 108

388 Varietal indexKMP40, 353Kogyoku, 106Koshihikari, 70, 258Krueng Aceh, 35KS282, 352Kwanag, 103Kwangmyoung, 100L 301, 227, 231Leng kwang, 329Leuang 152, 348Li-You 57, 221, 268Linfeng, 351Luwan 4, 97M 15, 100M55, 100M59, 101M80, 105M82, 105MI 14, 350, 356Mahsuri, 273, 276Mai Zheng Chang, 98Majigu, 98Malagkit Sungsong, 82, 107Malinja, 273Milyang 8, 103Milyang 15, 108Milyang 23, 49, 65, 100, 102, 104, 106-108,276, 352Milyang 30, 99-104Milyang 40, 99Milyang 42, 99-104Milyang 45, 353Milyang 46, 224-225, 229Milyang 49, 352Milyang 50, 352Milyang 53, 352Milyang 54, 229Milyang 55, 353Milyang 57, 101, 103Milyang 82, 103Minehikare, 100Minkang 108, 350Minyin 1, 350MNP119, 84Moddai Karuppan, 117Mokotou, 98Moroberekan, 82MR365, 228, 356MRC603-303, 353MTUI5, 348Mudgo, 117, 120-122, 124, 128-129, 351, 355Muskhan 41, 115N’Diang Marie, 88N22, 83, 114-115N32, 115N90, 350N304, 350Nagdong, 100-104Namyang, 101Nan 81, 268Nanjing 3714, 351Nanjing 3736, 351Nanjing 51 14, 351Naria Bochi, 348Nga Kywee, 278Nippon-bare, 253Nira, 119-120Nobaeg, 104Nona Bokra, 347Nona Sail (sel.), 347Nongbaek, 100-101, 103-105Nongfu 6, 351Nongken 58, 97Nonhu 6, 97Nopung, 99, 108Norin 1, 100, 105O dae, 103-104OR447-20, 342P 33-C-30, 356P127, 351P152, 351P339, 351P1577-I-23M-5-1M-4, 353Palasithari, 117Palgeum, 102-103Pankhari 203, 82, 117, 126Patnai 23, 347PAU14-2-13-9-2-1-1, 352PAU41-10-1-3-PR385, 352PAU41-306-1-2-PR404, 352PAU41-306-14PR422, 352PAU41-306-2-1-PR405, 352PAU41-306-2-2-PR406, 352PAU41-B-31-I-PR407, 352PAU143-B42-PR505, 345PAU269-1-8-4-1-1-1, 228PB5, 27PB8, 27PB26, 27PB28, 27PB32, 27PB34, 27PB36, 27PB38, 27PDR76-D10-D8-D1, 342Pelita 1-1, 27Pelita 1-2, 27Perurutong, 281Peta, 44, 82-83, 305Phalguna, 84,348Pinidwa, 225PNA237-F4-130-1, 350Podiwi A8, 114-115Pokhareli Masino, 353Pokkali, 347PTBI, 117PTB18, 82, 84, 117, 348

Varietal index 389PTB19, 348-349PTB20, 122PTB21, 348PTB33, 117, 120-121, 124, 349, 354-355Pusa 167-120-3-2, 228PY2, 228,354Q in-ai, 268Qing Gan Nou, 98Qing-Hua-Ai 6, 240Qing-Hua-Fu-Cui, 238-240Qing-Hua-Cui-Chao, 238, 240Qinglanai, 351Qiu Guang, 231R 29, 231R51-315-4, 348Raegyeong, 99Raminad Str. 3, 305, 353Ranta Mas, 108Rasht 507, 353Rathu Heenati, 117, 121, 348-349, 354-355Ratna, 354Rayada, 334RD23, 353Reiho, 343Reimei, 98Rexoro, 120RNR1429, 352RNR3070, 355RP79-5, 344RP633-76-1, 348, 353RP825-45-1-3, 348RP1015-39-89-1, 354RP1756-121, 349RPW6-17, 348S 264, 101S287, 100S341, 105S342, 105S345, 102S346, 102Saathi, 117Sadang, 35Sadri, 278Samgang, 99, 100-105San Zhao Qi, 98Sangju 5, 100, 103, 105Sangju 6, 100, 105Sanguizhan 2, 350Sanguizhan 5, 351Sanguizhan 6, 351Sanguizhan 8, 351Sanhuangzhan 2, 350Sanhuangzhan 4, 350Sanhuangzhan 8, 350Sasanishiki, 70Semeru, 35Seolag, 101, 103Seomjin, 99-107Seonam, 102-103Seonlag, 100Seraya, 27Shakti, 84Shan-You 2, 95, 231, 238Shan-You 6, 231Shan-You 30, 241Shan-You 63, 230Shin 2, 108Shinkwang, 105Shinsunchal, 99-105Shuang-er-zhan, 352Shuang-Feng 1, 351Shuang-Feng 4, 98Si-pi 681032, 352Si-pi 692033, 342Sigadis, 27, 81-83Sinna Sivappu, 116, 354Sinna Sivappu (Acc. 15444), 354Sobaeg, 100-101, 105Songjeon, 101, 104SR3044-78-3, 356Stejaree 45, 346, 356Strella, 356Sudu Hondarawala (Acc. 15541), 354Suduru Samba, 349, 354Surekha, 84Suweon 161, 228Suweon 251, 108Suweon 264, 101, 103, 108Suweon 287, 229,350Suweon 290, 352-353Suweon 294, 225, 229Suweon 300, 347Suweon 303, 356Suweon 306, 356Suweon 310, 228Suweon 342, 100Syntha, 27T a tsu mi mochi, 346, 356Ta-ma-shan (Acc. 4283), 356Ta-poo-cho-z, 347Tadukan, 347Taebaeg, 99-105Taichung sen 12, 354Taichung sen yu 223, 352Taichung sen yu 285, 340, 354Taichung sen yu 321, 352Tainung sen 12, 352Tainung sen yu, 356Taitung 16, 348Taiyin, 351TAPL796, 117Tetep, 81-82, 108, 347, 353Texikuxibali, 351Tie 6, 351Tie-er-ai, 351Tjeremas, 83TKM6, 81-82, 84, 87, 120, 126, 334, 348, 353,355

390 Varietal indexTN1, 115-117, 119-123, 128, 332TNAU8870, 344Tong-il, 94-95, 99, 108, 229, 273, 276, 321Toride 1, 273,347Toride 2, 273Triveni, 115-117, 122-123Tuanhuangzhan, 350U -1, 231Unbong, 100-101, 104UPR4-25-1, 39UPR70-30-7, 353UPR82-1-7, 352UPR103-80-1-2, 340, 343, 352UPR254-24-1, 352Utri Merah, 82, 116-117, 348Utri Rajapan, 82, 115-117, 122-123, 128, 334,348, 354V 20, 224-226, 234Valsara Champara, 355Vellathil Cheera, 349Vikram, 84W 1263, 84, 88, 348, 355Waiyin 35, 350Wan-hua-ai 1, 351Wase Aikoku, 106, 108Wasetoramochi, 356wc1240, 349Wei-You 2, 231Wei-You 6, 231Wei-You 64, 222, 225, 341Wonpung, 103X iabei, 266Xian 146, 351Xiang Ai Zao 4, 98Xiang Ai Zao 9, 98Xiang Ai Zao 8, 352Xiang Kang, 98Xiang yang zao, 351Xiangxuan 8325, 350Xihai 134, 351Xiu Qing Zao, 227-228Xiu-You 57, 221Xue Li Dong, 98Y atsen 1, 328Yeomyeongbyeo, 100-101, 104Yeomyoung, 102Yinfang, 262, 264, 266Youngdug, 100, 103-104Youngmun, 101, 104Youngsan, 100, 102-105YR2379-87-2, 356Yushin, 108Z ao Bai Dao, 98Zenith, 107Zhai Ye Qing 8, 95Zhekeng 66, 3, 91Zhen Luon 13, 98Zhen Shan 97, 98Zhen zhu ai, 351Zhi 205, 351Zhijing Non, 97Zhong dan 2, 95Zhong Shan Hong, 97-98Zhonghua 8, 3Zhonghua 9, 3Zi Mang Tao, 98MaizeHuanong 2, 262SorghumHegari, 262-264, 266Pingluowawatou, 266Yuanza 10, 262Sorghum/Rice3277, 2664437, 2655216, 266-26777125, 263, 265A7505, 262-263, 267D7846, 268WheatCappelle-Desprez , 97Joss Camber, 97