A Handbook of Rice Seedborne Fungi TW Mew and P ... - IRRI books

PrefaceSeed health testing has become an important componentof germplasm exchange between internationalcenters and national agricultural research and extensionsystem (NARES) partners. It assures the safemovement of seed, which is a carrier of pathogens,insect pests, and contaminants such as weed seeds.This handbook focuses on the importantseedborne fungi that cause diseases of the foliage,stem, leafsheath, root, grain, and inflorescence inrice. It provides information on more than 50 speciesthat have been detected in rice seed during routinetesting and analysis.Seed health testing is also a means of qualitycontrol that ensures the exchange of high-qualityseed among scientists or research centers. For thisreason, the Seed Health Unit at IFW functions as thegatekeeper of safe germplasm movement from andwithin IRRI, the Philippines, and outside.IRRI has always given high priority to the safetyof germplasm exchange. It has worked closely withthe Philippine Plant Quarantine Service to achievethis objective. As the volume of germplasm exchangeincreased annually, a Seed Health Unit wasestablished in 1982 and a new laboratory was developedand deputized by the Philippine Plant Quarantineto undertake major activities on rice seed healthtesting for plant quarantine certification. Besides itsregular activities on seed health testing of ricegermplasm, the unit also offers rice seed health trainingto NARES partners. To date, more than 100 scientistsfrom rice-growing countries worldwide havereceived such training.Rice seed, like seeds of other crops, carries alarge number of organisms, such as fungi describedin this book, bacteria, and nematodes. Theseseedborne organisms can be pathogens andsaprophytes; many of the bacteria or fungi canied byrice seed are also potential biological control agentsagainst other rice pathogens. Some also function topromote seed germination and seedling vigor.In quarantine regulations, seedborne pathogensoften serve as baniers to seed movement for researchand for trade. Misunderstanding arises becauseof insufficient biological and epidemiologicaldata to guide the development of plant quarantineregulations. Many seed-importing countries need thisinformation to determine whether seed carries thetargeted pathogens of "quarantine importance." Yetlittle is known about the pathogens carried by seed interms of crop damage and yield losses. Equally importantis the transmission of seedborne pathogens inrelation to disease establishment in the field and theconsequent effects on crop production. Not everypathogen carried by rice seed, for instance, is transmittedto the field when the seed is grown. The rateof transmission varies from one pathogen to anotherand in the same pathogen when the seed is sownunder different conditions for rice growth. These importantsubjects need further research.Since the early 1960s, IFW has conducted riceseed health testing to accomplish seed certification.As a result, the levels of rice seed infection causedby various microorganisms and the detection frequencyof a given microorganism from different ricegrowingcountries are well documented. The informationprovided on seedborne fungi in this handbookcan be used for teaching and as a reference whenconducting seed health testing in different laboratories.It should be used with reference to local conditions.