JASP 3 -- 1985.pdf - International Herbage Seed Group
JASP 3 -- 1985.pdf - International Herbage Seed Group
JASP 3 -- 1985.pdf - International Herbage Seed Group
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Journal of Applied<strong>Seed</strong> ProductionVolume III, 1985 ISSN 8755-8750Table of Contents'Grasslands Maim' Lotus (Lotus pedunculatus Cav.) <strong>Seed</strong> Production. 3. Effect of Time of Closing andSeverity of Defoliation on <strong>Seed</strong> Yields.M.D. Hare .......... . ... . ... ... .. ... . . .. . . . ... ... . . .. .... ... . ....·... . ........ .. . . ..... . .. .PageScarification of Lotus <strong>Seed</strong>.M.D. Hare and M.P. Rolston . . .. . .... ... ....... ... .. .. ..... . ...... .. . . . .. . . ........ . .. .... . .. 6<strong>Seed</strong> Yield Response to Fungicide Application in Paclobutrazol Treated Perennial Ryegrass.J.G. Hampton and P.D. Hebblethwaite . .. .. ..................... .. . . .. .. . ... ... ... .. .......... . 11The Effect of Time of Application of the Growth Retardant Flurprimidol (ELSOO) on <strong>Seed</strong>Yields and Yield Components in Lolium perenne L.P.D. Hebblethwaite, J.G. Hampton , G.R. Batts and S. Barrett ...... ..... ............... .. ... ... .... 15A Comparison of the Effects of the Growth Retardants Paclobutrazol (PP333) and Flurprimidol(ELSOO) on the Growth, Development and Yield of Lolium perenne Grown for <strong>Seed</strong>.J.G. Hampton and P.D. Hebblethwaite ............. ... .. .... . . ............ . .... . ...... .. .. .. ... 19Immaturity as a Cause of Low Quality in <strong>Seed</strong> of Panicum maximum.J.M. Hopkinson and B.H. English .... . ... ... ............... . . . .... . . ....... . .. . .. ............. 24<strong>Seed</strong> Dormancy and Germination of Switchgrass from Different Row Spacings and Nitrogen Levels.R.E. Mullen , P.C. Kassel, T.B. Bailey, and A.D. Knapp ..... . ... . . . ......... .. .......... . ....... . 28Effect of Pesticide Residues in Alfalfa Pollen and Nectar on the Foraging and ReproductionActivities of Alfalfa Leafcutting Bees (Megachile rotundata).C.M. Rincker and D.A. George .. ............. ... . . . .. ... . . .. . ..... ... . .......... . .. .... .... .. 33Lodging Control and Yield Enhancement in Morex Spring Barley with Paclobutrazol Treatment.L.A. Morrison and D.O. Chilcote .. . . . . . ............................. .... .......... . ........ . . 37Seminar on Floret Site Utilization.W.J.M. Meijer . ...... ... ..... ........ .. ....... .......... . ... ... . .. ..... . . ...... ...... . .. ... 42Developmental and Physiological Aspects of <strong>Seed</strong> Production in <strong>Herbage</strong> Grasses.C. Marshall ...... . .. ... ....... . ... .. . . . . . . ................. .. . ... . .. . . . . . . .. .... .. .. . . .. . . 43Floret Site Utilization in Grasses: Definitions, Breeding Perspectives and Methodology.A. Elgersma .. . .. . .. ..... .... . .. ............ ...... . .. . . .. ... .. . .......... . .. ... .. ... . .. .. .. 50The Effect of Uneven Ripening on Floret Site Utilization in Perennial Ryegrass <strong>Seed</strong> Crops.W.J.M. Meijer . . ....... . ................ . .................... ... ..... ....... . .. . . ... . ...... 55The Influence of Environmental and Agronomic Factors on Floret Site Utilization in Perennial Ryegrass.P. D. Hebblethwaite .. . . . .... .. ... . ......... . . . .. .. .... .... ............ .... .... ... . . . ... .. ... 57Factors Affecting <strong>Seed</strong> Yield in Breeding Material of Kentucky Bluegrass (Poa pratensis L.).A.J.P. van Wijk . .... . . ....... . ............. ... .......... . ..................... . . ... . ....... 59
JOURNAL OF APPLIED SEED PRODUCTIONPublished annually at Corvallis, Oregon, U.S.ASubscription rate for current and back issues US$15.00 postpaid. Subscription requests should beaddressed to the Editor.Editorial and subscription correspondenceHarold Youngberg, EditorJournal of Applied <strong>Seed</strong> ProductionCrop Science DepartmentOregon State UniversityCorvallis, Oregon 97331EDITORIAL BOARDHarold W. Youngberg, Editor,Oregon State University, U.S.ADavid 0. Chilcote,Oregon State University, U.S.A.Donald F. Grabe, Oregon State University, U.S.A.Paul D. Hebblethwaite,University of Nottingham, U.K.Murray J. Hill, Massey University, N.Z.Vern L. Marble, University of California, U.S.AAssistant Editor: Janet BurchamFrom the EditorResearch and review papers on seed productiontopics for future issues are invited. Commentsfrom readers are welcome.We are pleased to include articles in this issuefrom a special seminar on Floret Site Utilizationpresented at Wageningen, the Netherlands inJune, 1985.The EditorUSEFUL CONVERSION FACTORSTo ConvertTo ConvertA to BB to AABMultiply by:Multiply by:LENGTH3.2810.3940.0394meter, mcentimeter, emmilimeter, mmfeet, Itinch, ininch, inAREA0.30482.54025.40247.12.471kilometer 2 , km 2hectare,acre, aacre, a0.004050.405ha (0.01 km 2 )10.760.1550meter 2 , m 2centimeters 2 , em 2 foot 2 , lt 2inches 2 , in 20.09296.452VOLUME- CAPACITY2.1141.0570.26420.22liter, Iliter, Iliter, Iliter, Ipint, ptquart (liquid), qt.US gallon, galImperial gallon0.4730.9463.7854.5450.0338 milliliters, ml fluid ounce, oz 29.57WEIGHT- MASS1.1022.2050.0353ton (metric) tkilogram, kg.gram, gton (short) tpound, lbounce, oz av0.90720.45428.35YIELD OR RATE0.446 ton (metric) ton (short)2.242hectare- 1 , t ha- 1 acre- 1 , t a- 10.892 kilogramshectare- 1 , kg ha- 1 poundsacre- 1 , lbs a- 1 1.1210.0930.4276plants m- 2liters hectare- 1 ,I ha- 1 plants W 2quarts acre- 1 ,qts a- 110.762.3380.1069 liters perhectare, I ha- 1 gallons acre- 1 ,gal a- 1 9.3540.6214 kilometer hou( 1 ,km h- 1 miles hou( 1 , mph 1.609PRESSURE14.22 kilogramspounds inch- 2 , psi 0.0703centimete( 214.50 barpounds inch- 2 , psiTEMPERATURE0.068951.80(C)+32 Celsius, CFahrenheit, F 0.555(F-32)CORRECTIONIn the article '"Grasslands Maku' Lotus (Lotus pedunculatus Cav.) <strong>Seed</strong> Production. 2.Effect of Row Spacings and Population Density on <strong>Seed</strong> Yields" on pages 65-68 ofVolume II, 1984 issue, the headings for Figure 1 and 2 were transposed. The figures arecorrect but the headings should be interchanged.
'Grasslands Maku' lotus (Lotus pedunculatus Cav.) seed production. 3. Effect of timeof closing and severity of defoliation on seed yields.tM.D. HarezABSTRACT'Grasslands Maim' (Lotus pedunculatus Cav.),syn. L. uliginosus(Schkuhr) seed yields of 47 g m-2were harvested from treatmentsleft uncut from the start of spring growth. Cutting to a groundlevel before bud appearance, in September and October, significantlyreduced seed yields to 28 g m-2 and 14 g m-2respectivelyand after bud appearance did not significantly affect seed yieldsbut topping after bud appearance reduced seed yields to 26 gm-2,INTRODUCTIONMany farmers close 'Grasslands Malm' lotus (Lotus pedunculatusCav.), syn. L. uliginosus (Schkuhr), from earlyspring to early summer according to their experiences withclover and lucerne seed crops. It is normal practice forfarmers to cut established lucerne stands for hay and thenharvest for seed later in the same season (Kowithayakorn andHill, 1982). White clover seed crops grazed until mid-Novemberand red clover seed crops closed in early Decemberafter grazing will give high seed yields (Clifford, 1980;Clifford and Anderson, 1980).Research by Clifford (1975, reported by Lancashire et al.,1980) found that marked reductions in Maku lotus seedyields occurred when crops were closed later than October1st. Neal (1983) also reports that by closing in mid-October,after close grazing or cutting, seed yields are decreased,compared with earlier closing dates. However, Neal (1983)preferred October closing, as there was less vegetative bulkat harvest and pod shattering was reduced by harvestingunder cooler conditions in March.By allowing an initial attack on Maku lotus flowerheads bypotato mirids (Calocoris norvegicus) and then spraying withan insecticide, Clifford et al., (1983) increased stem branchingand potential seed yields of Maku lotus. They concludedthat the increased stem branching was because the earlyapical dominance of the primary stems was impaired, eitherby way of physical mirid damage or some hormonal effectinduced by the injection ofmirid saliva. They also found thatflowerheads when protected with an insecticide applicationlA contribution of the Plant Science Department, Lincoln CollegeCanterbury, New Zealand. Received for publication 11 February1985.2Present address: Grasslands Division, DSIR, Private Bag,Palmerston North, New Zealand.following a mirid attack, shortened the period of flowering,thereby ensuring minimum seed losses at harvest. Makulotus has been found to have a long flowering period, floweringfrom mid-November until April, (Armstrong 1974),making harvesting difficult (Neal, 1983). Clifford et al.,(1983) also suggested, that in the absence of a mirid attack,some form of high topping management with a mower toremove only primary apical meristems, might promote stembranching in Maku lotus.The objective of this study was to impose a range ofclosing dates and different intensities of defoliation in orderto test the following hypotheses that:(i) any severe cutting treatment after the start of springgrowth may be detrimental to seed yield.(ii) a high topping may simulate mirid damage and concentrateflowering time allowing for easier harvestmanagement.MATERIALS AND METHODSThe study was conducted over two seasons ( 1981-83) on a0. 75 ha Maku lotus field at Lincoln College, Canterbury,New Zealand (43°S). The soil type was a Wakanui soilcomplex (Hare and Lucas, 1984) containing adequate nutrients.Maku lotus was sown on 5 November 1980 in 0.45 mrows, at a sowing rate of 3 kg ha-l. Each plot over the twoseasons averaged six plants m-2.Trial 1: Effect of time of defoliation, 1981-82The field was sprayed with paraquat at 0.5 a.i. ha-l in July1981, to control grass weeds.There were five treatments, a check and four cutting dates:(a) left uncut until seed harvest in January.(b) cut to ground level (30-50 mm above the ground)with a sickle-bar mower, 1.2 m wide, on 12 November,(c) 24 November, (d) 4 December, and (e) 15December, 1981.Each plot was 15m x 2.5 m, and there were six replicates.Dry matter yield measurements: At closing, material thelength of each plot was harvested, fresh weighed and dryweight determined. At seed harvest, 10 stems from each plotwere dried and the average stem dry weight multiplied by theaverage stem number m-2.<strong>Seed</strong> yield measurements: Optimum harvest time wasdetermined when approximately 5% of the pods had shattered,80% of the pods were light brown, 10% of the podswere green or purple and 5% of the umbels were still in theyellow flower stage (Hare and Lucas, 1984).1
2 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Just before seed harvest 20 stems were randomly cut fromeach plot for measurement of components of seed yield.<strong>Seed</strong>s per pod were not measured. At seed harvest two 2 x 1m areas per plot were cut, oven dried for four days at 35 C,threshed and cleaned to determine total seed yield. Theharvested areas were vacuumed to calculate shattered seedyield. To calculate the effect of delay of harvest upon seedyield, two more 2 x 1 m areas were harvested one week afterthe main harvest in the uncut treatment. All seed yields werecorrected to 12% moisture content. Vacuumed seed was notadded to final harvested seed yields in the results.Trial2: Effect oftime and severity of defoliation, 1982-83The field was mown on 4 May, 1982 and the cut materialremoved. Ioxynil ('Totril') was sprayed twice, two weeksapart, at 1.6 kg a.i. ha-l in August to control broad leavedweeds. Carbetarnide, ('Carbetamex 70') at 1.5 kg a.i. ha-l,was applied twice, two weeks apart, in September to controlPoa annua and barley grass (Hordeum murinum).Two hives of honey-bees were placed in the field inN ovember1982. No hives were in the field for the previous trial.Bromophos ('Nexion') at 0.4 a.i. ha-l, was applied on 16December to control potato mirids (Calocoris norvegicus)when rnirid populations in the field reached 15-20 per 20 netsweeps with a 400 mm sweep net (Clifford et al., 1983).The trial was a factorial design with three closing dates bytwo cutting heights, plus one uncut treatment, with fourreplicates. Closing dates were 29 September, 20 October,and 11 November, 1982, and cutting heights were (a) groundlevel with a sickle-bar mower and trimmed with rotary mower,and (b) 50-100 mm off the top of Maku lotus with asickle-bar mower. The uncut treatment plots were not cutuntil seed harvest in February 1983.Dry matter yield measurements: At closing two 2 x 1 mareas were cut from the ground level plots, fresh weighed anddry weight determined. Dry matter cuts were not taken fromtopped plots. At seed harvest two 0. 5 m-z areas were cut fromeach plot and all the material was dried and weighed.<strong>Seed</strong> yield measurements: Two 2 x 1 m areas were handharvested from each plot at the optimum seed harvest timeand slowly air dried over a period of four to six weeks. Thematerial was then threshed and the seed cleaned. Ten stemswere randomly cut from each plot for measurement of componentsof seed yield. As shattering was minimal sampleareas were not vacuumed. All seed yields were corrected to12% moisture content.RESULTSMeteorological Data1981-82 was a hot dry season with higher average maximumtemperatures, higher average vapor pressure deficitsand less total rainfall than the 1982-83 season (Table 1).Heavy hail fell on 19 January, 1983, before any seed washarvested, causing approximately 10% seed loss in all plots.Estimates of hail damage were made by taking 10 stemsrandomly from each plot and counting total pods, brokenpods and broken stems.Flowering at DefoliationAt closing dates in September and October no flower budswere visible. By mid-November green buds were forming,becoming orange by late November. In early Decemberyellow flowers were forming, reaching maximum bloom inmid-December.Defoliation at closing caused harvest dates to be delayedup to two months later than the uncut treatment harvest time.When uncut plots were harvested other plots were still flowering.Days From Cutting to <strong>Seed</strong> Harvest<strong>Seed</strong> harvest dates and days from cutting to seed harvestare given in Table 2. The cool weather caused pods to ripenvery slowly (Hare and Lucas, 1984) making optimum harvesttime very difficult to determine. From stem analysis atharvesting, there was a large proportion of small green podsand a very small proportion of shattered pods (light brownpods 55%, purple pods 9%, green pods 34%, shattered pods2%). The heavy December rainfall caused a mass of newvegetative growth to appear with new flowers forming inTable 1. Mean monthly temperatures, mean monthly vapor pressure deficits and total monthly rainfall for the 1981-82 and 1982-83seasons.MonthMean temperatures1981-82 1982-83Mean vaporpressure deficits1981-82 1982-83Totalrainfall1981-82 1982-83AugustSeptemberOctoberNovemberDecemberJanuaryFebruaryMarchApril(C)5.6 8.28.7 8.611.5 9.913.5 15.017.1 13.717.2 15.717.4 14.816.0 15.210.1 11.6(k pa)0.20 0.410.43 0.250.52 0.480.48 0.870.72 0.591.02 0.820.93 0.550.67 0.810.30 0.42(mm)122.5 23.415.0 20.894.4 87.634.6 52.215.1 94.228.2 30.815.5 18.512.2 24.046.6 101.4
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 3Table 2. Harvest dates and days from cutting to seed harvest.Time of closingDays fromand method of <strong>Seed</strong> harvest date cutting tocutting at closingseed harvest1981-82Uncut21 January12 November 9 February 89Cut to ground level24 November 18 February 86Cut to ground level4 December 16 March 102Cut to ground level15 December 22 March 97Cut to ground level1982-83Uncut8 February29 September 1-16 February 125-140Cut to ground levelTopped 1-16 February 125-14020 October 16-24 February 119-127Cut to ground levelTopped 1-24 February 104-12711 November 2 March 111Cut to ground levelTopped 16-24 February 97-105January. It was not possible to delay harvesting until thegreen pods were ripe, as the brown pods, which were inlarger proportion, would have shattered.Dry Matter YieldsDry matter at closing increased with the lateness of closingdates (Table 3). The maximum dry matter yield at seedharvest in 1982 was from the uncut treatment. This was threeto four times greater than the defoliated treatments whichaveraged 330 g m-2 of dry matter at harvest.Cutting to ground level on 11 November, 1982 significantlyreduced dry matter at seed harvest in 1983 comparedwith the topped treatment (Table 3). There were no significantdifferences in dry matter at seed harvest in 1983between methods of cutting at the two earlier closing dates.Stem Length at <strong>Seed</strong> HarvestIn 1981-82 cutting at closing reduced stem length at seedharvest by one half or more than the uncut treatments (Table4). Stem lengths were significantly reduced at harvest, byclosing in mid-December.In 1983 cutting at closing did not affect stem lengths atharvest except for the ground level cutting on 11 Novemberwhich was approximately 100 mm shorter in length.<strong>Seed</strong> YieldMaximum seed yields in both years were from the uncuttreatments; 47 g m-2 in 1981-82 (Table 5) and 48.8 g m-2 in1982-83 (Table 6).<strong>Seed</strong> yields in 1981-82 were significantly reduced byTable 3. Effect of closing date upon Maku lotus dry matteryields at closing, harvest and post-harvest in 1981-82.TreatmentsDry Matterg m-2Closing date Closing Harvest1981-82Uncut 113512 November 263 41624 November 406 3304 December 480 36515 December 408 208SE (mean) 55 1641982-83Uncut 104429 SeptemberGround 204 905Topped 94320 OctoberGround 288 1034Topped 99911 NovemberGround 350 806*Topped 1112SE (mean)cutting (Table 5). Plots cut in November and December1981, produced none or very little seed at all, as the very dryconditions caused the pods to shrivel and produce no harvestableseed.Later closing with cutting to ground level decreased seedyields in 1982-83 (Table 6). There was no significant differencein seed yield between closing dates when crops weresimply topped. However, crops that were topped yieldedsignificantly less seed than those that were uncut (Table 6).Table 4. Effect of closing date upon stem length at harvest.ClosingDate1981-82Uncut12 November24 November4December15 DecemberSE (mean)1982-83Uncut29 September20 October11 NovemberSE (mean)Methodof cuttingGround levelGround levelGround levelGround levelGround levelToppedGround levelToppedGround levelToppedStemlength(mm)86046042033028010371076073073073062071016.7
4 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 5. Effect of time of closing on Maku lotus seed yields in1981-82.Treatment(Closing date 1981)UncutSE (mean)12NovemberSE (mean)24November4December15 DecemberSE (mean)<strong>Seed</strong> yieldgm-2(12% moisture)47(4.8)1.2(0.25)001.5(0.47)Table 6. Effect of time of closing and method of cutting atclosing on Maku lotus seed yields in 1982-83.Treatment(Time of closing, 1982)29 September 198220 October 198211 November 1982SE (mean)SignificanceUncutMean of 6 cut treatmentsSE (mean)Significance!Linear 2Non-significant** Significance 1% level.<strong>Seed</strong> yieldCut to groundlevel28.213.66.74.24IL**48.825.85.8**g m-2(12% moisture)Topped39.941.125.97.392N.S.Topping produced significantly higher yields, than cutting atall closing dates.Pod shatter was rapid in 1981-82 as a result of hot dryconditions when harvesting was delayed. Uncut plots harvestedon 21 January 1982, had 11% of total seed on theground and eight days later 47% of total seed was on theground. Pod shattering was minimal in 1982-83 with only2% pod shatter in the uncut plots at harvest.Components of <strong>Seed</strong> YieldIn 1981-82 cutting reduced the number of umbels per stemand pods per umbel (Table 7). In 1982-83 seed yield per stemand seeds per pod when both topped and cut to ground level,showed highly significant (P < 0. 01) decreases from Septemberto November closing dates (Table 8). Cutting at groundlevel significantly (P< 0.01) reduced umbels per stem. Podsper umbel and 1,000 seed weight were not affected by successivelylater closings and severity of defoliation (Table 8).DISCUSSIONDelaying the date of closing and increasing severity ofdefoliation at closing depressed seed yields of Maku lotus.This pattern of reductions in seed yield following either lax orsevere defoliations, particularly after bud formation, has alsobeen reported in other herbage legumes e.g., Lotus corniculatus(Anderson and Metcalfe, 1957; Bader andAnderson, 1962), Medicago sativa (Kowithayakorn andHill, 1982), Stylosanthes guianensis (Loch et al., 1976), S.humilis (Loch and Humphreys, 1970; Fisher, 1973), Trifoliumsubterraneum (Rossiter, 1961; Collins, 1978) and Trifoliumpratense (Dade, 1966).Closing Maku lotus seed crops from November onwardssignificantly reduced seed yields as previously observed byClifford ( 1975; reported by Lancashire et al. , 1980). However,closing even earlier, in late September and October,with a close ground cutting, also decreased seed yields.These decreases of Maku lotus seed yields may be caused byeither slow recovery from severe defoliation, (Sheath, 1980)or slow growth under cool early spring temperatures(Charlton, 1977). In both trials warm spring temperaturesabove lYC were not reached until November.Both lucerne and white clover recover rapidly from defoliationand grow in the early spring when the average dailytemperatures are still about 10-15 C. Grazing can thereforebe practiced before closing crops for seed production. However,Maku lotus has relatively little winter or early springgrowth and therefore, spring grazing cannot be carried out ifmaximum seed yields are to be produced.Topping did not simulate mirid damage, as the stems didnot branch and produce more umbels per stem (Table 8) andconcentrate flowering. Instead there was a decrease in seedsper pod following topping. Clifford et al., (1983) found thatmirids only damaged the umbels. Topping in this studyremoved the umbels and 50-100 mm of stem, and this mayhave been too severe to allow Maku lotus to recover, branch,and produce more umbels per stem. However, it is impracticalfor farmers to remove any less stem by topping in Novemberor December, because of the height and unevengrowth of Maku lotus stands. There is a need, however, formore detailed study of the effect on seed yield on removingTable 7. Effect oftime of closing on components of seed yield ofMaku lotus in 1981-82.TreatmentUncutCut to groundlevel12 Nov24 Nov4 Dec15 DecSE (mean)Stemsm-232542734537334317.8Umbelsstem-t8.54.21.9Podsumbel-!8.05.22.61000seed wt(12%moisture)0.9300.9180.938
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 5Table 8. Effect of time of closing and method of cutting at closing on components of seed yield of Maku lotus in 1982-83.Treatment Stems <strong>Seed</strong> Umbelsm-2 Yieldstem-!(g)stem-!Pods <strong>Seed</strong>s 1000umbel-! pod-! seedweight (g)12% moistureCut to ground level29 Sept 452 0.1820 Oct 476 0.0911 Nov 502 0.02Significance N.S. IL**SE (mean) 30 0.03Topped29 Sept 449 0.2420 Oct 447 0.1911 Nov 374 0.08Significance N.S. L**SE (mean) 30 O.Q3ContrastUncut 481 0.18Mean of 6 450 0.13Cut treatmentsSignificance N.S. N.S.SE (mean) 30 0.03!Linear 2Non-significant**Significance 1% level.6.25.52.9L**0.86.46.35.6N.S.0.85.35.6N.S.0.85.5 5.6 0.9706.0 2.7 0.9776.7 1.2 0.9122N.S. L** N.S.0.3 0.7 0.0195.7 6.9 0.9445.7 5.6 0.9295.5 2.6 0.994N.S. L** N.S.0.3 0.7 0.0195.1 7.5 0.9265.8 4.1 0.954N.S. ** N.S.0.4 0.7 0.027only umbels as this may stimulate mirid damage more closely.The possibility of hormonal effects of mirids saliva(Clifford et al., 1983) needs further study as some growthregulatory substance may be involved.The main problem with Maku lotus at harvest is to dry themass of vegetation, especially the stems, before pods shatter.Neal ( 1983) closed fields late in order to have less vegetationand shorter stems to dry at harvest and to reduce pod shatter,although this meant a loss in potential seed yield. However,Neal (1983) maintained that it was better to be sure of a lowseed yield in the bag rather than risk a high seed yield withmost on the ground. It was found in this study that vegetationand stem length at harvest could only be significantly reducedby cutting to ground level from November onwards,but little seed was produced. In order, therefore, to get highseed yields, large amounts of vegetation and long stems areunavoidable and must be coped with at harvest. Harvesting atthe optimum time (Hare and Lucas, 1984) will allow sufficienttime for the vegetation and stems to dry, either aftermowing or chemical desiccation, before combine harvesting.After mowing, the stems should be turned upmost with ahay rake in order to dry quickly. The pods will be protectedfrom shattering under the stems (Lancashire et al., 1980).Flowering and seed ripening were not concentrated bylater closing dates as reported by Neal ( 1983). There were noobserved differences in length of flowering and seed ripeningbetween treatments cut to ground level or topped.CONCLUSION<strong>Seed</strong> yields ofMaku lotus in Canterbury were significantlyreduced by cutting to ground level after spring growth started.Topping only reduced seed yields when it was carried outafter bud appearance in November. A light topping cantherefore take place in the spring without detrimental effectson seed yields, but it is of no practical value.ACKNOWLEDGEMENTSAppreciation is expressed to the Leonard Condell FarmingScholarship Trust for awarding the author a scholarship in1982 and 1983, the Lincoln College Research Committee forproviding funds for the field research, Mr. R.J. Lucas forassistance in preparing the trial and advice in analyzing thedata, Mr. B.G. Love for statistical analysis and Mr. P.T.P.Clifford for advice throughout the research program.REFERENCES1. Anderson, S.R., and D.S. Metcalfe, 1957. <strong>Seed</strong> yields ofBirdsfoot Trefoil (Lotus corniculatus L.) as affected by preharvestclipping and by growing in association with three adaptedgrasses. Agron. J. 49:52-55.2. Armstrong, C.S. 1974. 'Grasslands Maku' tetraploid lotus(Lotus pedunculatus Cav.). N.Z. J. of Exp. Agric. 2:333-6.3. Bader, K.L., and S.R. Anderson. 1962. <strong>Seed</strong> yields of Birds-
6 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985foot Trefoil, Lotus corniculatus L., as affected by preharvestclipping combined with control of injurious insects. Agron. J.54:306-309.4. Charlton, J.F.L. 1977. Establishment of pasture legumes inNorth Island hill country. N.Z. J. of Exp. Agric. 5:385-390.5. Clifford, P.T.P. 1980. Research in white clover seed production.pp. 64-67. In Lancashire, J.A. (ed.) <strong>Herbage</strong> seed production.N.Z. Grassl. Assoc., Paimerston North.6. Clifford, P.T.P., and A.C. Anderson. 1980. Red clover seedproduction. Research and practice. pp. 76-79. In Lancashire,J.A. (ed.) <strong>Herbage</strong> seed production. N.Z. Grassl. Assoc. PalmerstonNorth.7. Clifford, P.T.P., J.A. Wightman, andD.N.J. Whitford 1983.Mirids in 'Grassland Maku' lotus seed crops: friends or foes?Proc. N.Z. Grassl. Assoc. 44:42-46.8. Collins, W.J. 1978. The effect of defoliation on inflorescenceproduction, seed yield and hard-seededness in swards of subterraneanclover. Australian J. of Agric. Res. 29:789-801.9. Dade, E. 1966. Effects of clipping on red clover seed yields andseed-yield components. Crop Sci. 6:348-350.10. Fisher, M.J. 1973. Effects of times, height and frequency ofdefoliation on the growth and development of Townsville styloin pure ungrazed swards at Katherine, N.T. Australian J. ofExp. Agric. and Animal Husb. 13:389-397.II. Hare, M.D., and R.J. Lucas 1984. 'Grasslands Maku' lotus(Lotus pedunculatus Cav.) seed production. I. Development ofMaku lotus seed and the determination of time of harvest formaximum seed yields. J. of Applied <strong>Seed</strong> Prod. 2:58-64.12. Kowithayakom, L., and M.J. Hill, 1982. A study of seedproduction of lucerne (Medicago sativa) under different plantspacing and cutting treatments in the seeding year. <strong>Seed</strong> Sci.and Techno!. 10:3-12.13. Lancashire, J.A., J.S. Gomez, and A. McKellar. 1980.'Grasslands Maku' lotus seed production: Research and practice.pp. 80-86. In Lancashire, J.A. (ed.) <strong>Herbage</strong> seed production.N.Z. Grassl. Assoc., Palmerston North.14. Loch, D.S., and L.R. Humphreys 1970. Effects of stage ofdefoliation on seed production and growth of Stylosanthes humilis.Australian J. of Exp. Agric. and Animal Husb. 10:577-581.15. Loch, D.S., J.M. Hopkinson, and B.H. English 1976. <strong>Seed</strong>production of Stylosanthes guyanensis 2. The consequences ofdefoliation. Australian J. of Exp. Agric. and Animal Husb.16:226-230.16. Neal, G.W. 1983. Maku lotus seed production in practice.Proc. of N.Z. Grassl. Assoc. 44:36-41.17. Rossiter, R.C. 1961. The influence of defoliation on the componentsof seed yield in swards of subterranean clover (Trifoliumsubterraneum L.). Australian J. of Agric. Res. 12:821-833.18. Sheath, G. W. 1980. Production and regrowth characteristics ofLotus pedunculatus Cav. cv. 'Grasslands Maku'. N.Z. J. ofAgric. Res. 23:201-109.Scarification of Lotus <strong>Seed</strong>1M.D. Hare and M.P. RolstonzABSTRACT<strong>Seed</strong> of 'Grasslands Maku' tetraploid lotus (Lotus pedunculatusCav. syn. L. uliginosus Schkuhr) was scarified by hotwater, sulphuric acid and mechanical treatments.Hot water treatments were effective at 80 C and 90 C for 1minute immersion. <strong>Seed</strong> death increased as time of immersionand the temperature of the hot water were increased. All sulphuricacid treatments above 10 minutes immersion in acidsignificantly increased seed germination, the optimum immersiontime occurring at between 60 and 75 minutes.A commercial Eddy-Giant Huller and Scarifier fitted withrubber concaves scarified seed effectively by impaction whenseed was passed quickly through the machine, the optimumspeed being 800-900 rpm (73% germination). Increasing thespeed and number of passes increased abnormal germinatingseed significantly. Higher normal germinations (78%) wereachieved using a Westrup polisher which significantly reducedhardseededness in Maku lotus.The problems of scarifying Maku lotus seed on a commercialscale are discussed and recommendations for commercial scarificationpresented.Additional index words: normal germinating seed; abnormal germinatingseed; hard seed; seed processing; seedlot quality.INTRODUCTIONIA contribution of Grasslands Division, Department of Scientificand Industrial Research, Palmerston North, New Zealand. Receivedfor publication 26 August 1985.2Scientists, Grasslands Division, DSIR, Private Bag, PalmerstonNorth, New Zealand.Hardseededness is a characteristic of many herbage legumes(Rolston, 1978; Tran and Cavanagh, 1984) whichenables seed to persist through unfavorable conditions, and isimportant in regeneration and persistence of many annualspecies (Quinlivan, 1971; Suckling and Charlton, 1978).'Grasslands Maku' tetraploid lotus (Lotus pedunculatus Cav.),syn. (L. uliginosus Schkuhr) machine harvested seed lines
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 7can contain high levels of hardseededness (Scott andHampton, 1985); hand harvested lines contained up to 87%hard seed (Hare and Rolston, unpub. data). This may be anattribute in helping establish Maku lotus in marginal areaswhere it is used as a pioneer legume (J.F.L. Charlton, DSIR,Palmerston North, pers. comm.), but not for seed cropswhere quick even establishment is needed.Of the certified Maku lotus seedlots tested by the Ministryof Agriculture Official <strong>Seed</strong> Testing station, PalmerstonNorth, New Zealand in 1983 and 1984,34% and62%respectivelyhad germinations of less than 80%. These seedlotscontained, on average, 15% hard seeds and 10% abnormalseeds. By contrast only 6% and 3% of 'Grasslands Pitau'white clover (Trifolium repens L.) seedlots had germinationsof less than 80% in 1983 and 1984.In herbage legumes hardseededness is a physical conditionwhich prevents the movement of water through the seed coat.This seed coat impermeability develops as seeds ripen andlose moisture in accordance with atmospheric relative humidity(Hyde, 1954; Quinlivan, 1971) or vapor pressuredeficits (Hare and Lucas, 1984). The proportion of hardseeds before harvest will vary according to seasons; hardseedednesswas increased by hot dry weather in Maku lotus(Hare and Lucas, 1984), and by low temperatures in Trifoliumpratense (Puri and Laidlaw, 1984) and T. subterraneum(Quinlivan, 1965; Taylor and Palmer, 1979). Hardseedednesswill first occur after seed maturity is reached as found inMaku lotus (Hare and Lucas, 1984), Medicago sativa(Kowithayakom and Hill, 1982) and Trifolium pratense(Win Pe, 1978). Hardseededness, however, can be reducedin seedlots by the types of mower and combine header usedand the pre-harvest treatment of the seed crop (Clifford andMcCartin, 1985).The seed dries further in storage and often a seed moisturecontent of less than 10% will be reached before the seed istested for germination, thereby further increasing hardseededness(Win Pe, 1978; Kowithayakorn and Hill, 1982).When below 10% seed moisture content, permeability can berestored to hard seeds only by artificial softening (Hyde,1954) or natural softening in the field by exposure to changesin soil temperature (Quinlivan, 1971; Mott et al., 1981;McKeon and Mott, 1982).For seed production purposes artificial softening is thequickest and most practical means to reduce hardseedednessin seedlots. Methods of softening hard seeds have beendescribed by Porter ( 1949) and Bilsland et al., ( 1984) andreviewed by Rolston (1978). Abrasive or impaction scarificationusing centrifugally forced contact with carborundumor rubber concaves is most commonly used in New Zealandto remove dirt particles and incidentally reduce hard seedlevels (K.A. Young, MAF <strong>Seed</strong> Testing Station, PalmerstonNorth, pers. comm.). However, in order to use scarifierseffectively, the seed scarification requirements of variousspecies need to be known (Bilsland et al., 1984). To datethere have been no reported studies on scarifying lotus seed,and given the high content of hard and abnormal seeds incertified seedlots, means of reducing both and improvinggermination needed to be investigated.Initial experiments investigated whether hard seed of Makulotus in small seedlots could be softened by hot water andacid treatments. Further experiments evaluated mechanicalscarification of larger seedlots, using impaction rather thanabrasion to improve germination by reducing the percentageof hard seed whilst minimizing any increases in abnormalseedlings or non-viable seed. The final objective was todevelop a recommendation for scarifying large seedlots ofMaku lotus seed.MATERIALS AND METHODSTwo seedlots of Maku lotus seed were used for the experiments;one seedlot for the hot water and sulphuric acidtreatments and another seedlot for the mechanical scarificationtreatments. Both seedlots were combine harvested inFebruary and the seed cleaned and then stored in calico bagsat room temperatures until experimentation between Augustand December.Hot Water TreatmentsDuplicate samples of 100 seeds were soaked in water at50, 60, 70, 80, 90 and 100 C for 1, 2, 5 and 10 minutes. Theseeds were drained and placed on moist filter paper in petridishes and germinated ( 16 hours light and 8 hours darkness ata constant temperature of 20 C). The number of germinatedseeds after 6 and 9 days was recorded.Sulphuric Acid TreatmentsDuplicate samples of 100 seeds were immersed in 5 ml ofconcentrated sulphuric acid (36 N, commercial grade) for 0,5, 10, 15, 20, 30, 45, 75, 90, 105 and 120 minutes. The acidwas drained off and the seed washed in a fine stainless steelgauze strainer for 10 minutes under running water. Afterdraining, the seeds were germinated under the same conditionsas for the hot water treatments.To obtain samples containing only hard seed, seeds wereplaced on moist filter paper for 9 days in a growth cabinet (20C with 16 hours light and 8 hours dark). All the seeds whichgerminated or imbibed water were discarded. The hard seedswere dried at room temperature on the laboratory bench.These hard seeds were then treated with 5 ml of concentatedsulphuric acid for 60, 90, and 120 minutes. After washing,the seeds were germinated as above.Mechanical Scarification TreatmentsAn Eddy-Giant Huller and Scarifier (Blount IndustrialProducts, Indiana, USA) fitted with rubber concaves wasused in the first and second mechanical scarification treatments.Rubber concaves scarify the seed by impaction. <strong>Seed</strong>at two moisture contents (SMC) (12 and 10%) were passedthrough the scarifier quickly (150 g min-I) and slowly (5 gmin-I), one and two times, at speeds of 1000, 1500 and 2000rpm.In the second mechanical scarification treatment, seed( 10% SMC) was passed quickly through the same scarifier atspeeds of 500, 600, 700, 800, 900, 1000, 1500 and 2000rpm.A Westrup polisher scarified the seed in the third mech-
8 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985anical scarification treatment. The polisher was fitted with a40 em long x 20 em diameter woven steel wire screencylinder with a 1.5 mm x 1.8 mm internal grid. Two nylonbrushes rotated inside the cylinder against the wire screen.With the cylinder rotating at 630 rpm, seed was passedthrough the polisher one, two and three times and collectedfrom the center (pushed through the screen) and from the end(traveled right through).<strong>Seed</strong> in the mechanical scarification treatments were germinatedon top of filter paper in 8 hours light (30 C) and 16hours darkness (20 C) with four replications of 100 seeds.RESULTSHot Water TreatmentsThree treatments, 1 minute at 80 and 90 C and 2 minutes at70 C, significantly increased germination percentages overthe control (no hot water immersion) treatment (Table 1). Allother treatments did not significantly increase germinationover the control treatment, and reductions were significant at80 and 90 C with immersion times of 5 and 10 minutes. The100 C treatment almost totally killed seed, especially aslength of immersion was increased (Table 1).Table 1. Effect of hot water treatment on germination of Makulotus seed.Water Temp.(C)Germination %Immersion Time (min.)2 5 1050 53 61 56 5960 61 60 66 6170 63 70 61 3180 74 61 31 1290 75 65 11 9100 12 4Control (no hot water) 57LSD 0.05 10.8Sulphuric Acid TreatmentsAll treatments, except the 5 minute immersion in acid,significantly increased germination over the control (no acidimmersion) treatment (Figure 1). The optimum treatmentwas 75 minutes immersion in acid, as there were no furthersignificant increases in germination above this time.Sulphuric acid significantly increased germination of thesolely hard seed samples (Table 2), but there were no significantdifferences between the 60, 90 and 120 minute acidimmersion treatments.Mechanical Scarification TreatmentsIn the first experiment the speed of the rotating cylinder(rpm) significantly increased normal and abnormal germinatingseed, and reduced hard seed, but had no effect on dead100 •"90.. •..~= 0 801~ Y = 71•4 + 0•282X70•R 2 =0·77-~'-~'LSD(005) I60 (8 treatment means)0 30 60 90 120Time in acid (minutes)(•treatment means )Figure 1. Effect of concentrated sulphuric acid on thegermination of Maku lotus seed.seed (Table 3). Increasing the number of passes from one totwo reduced hard seeds but significantly reduced normalgerminating seed and increased abnormal germinating seed.The optimum treatments were one pass through the scarifierat either 1000 or 1500 rpm. <strong>Seed</strong> moisture content and theflow rate through the scarifier had no significant effects on allseed germination categories.Increasing speed of scarification significantly increasedthe normal and abnormal germinating seeds and reduced hardseeds in the second experiment (Figure 2). There were nosignificant differences between normal germinating seeds(LSD 0.05 = 6.5%) at speeds between 700 and 1500 rpm.However, there were significant differences between hardseeds (LSD 0.05 = 5.2%) and abnormal seeds (LSD 0.05 =4.9%) at these speeds; higher speeds totally eliminated hardseeds but increased abnormal seeds (Figure 2).Scarifying the seed right through to the end of the Westruppolishing cylinder, instead of discharging through the screenfrom the center, significantly decreased hard seeds and increasednormal germinating seeds (Table 4). The number ofpasses through the polisher did not affect normal germinatingTable 2. Effect of concentrated sulphuric acid on the germinationof hard seed samples containing only hard seed.Acid immersion (min.) 0 60 90 120Germination(%) 94 96 99LSD 0.05 9.8
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 9Table 3. Effect of speed of revolution and number of passesthrough the Eddy-Giant Scarifier on germination of Makulotus seed.Table 4. Effect of number of passes and the position ofdischarge of each pass through a Westrup Scarifier on thegermination of Maku lotus seed.Speed Passes(rpm) (no)NormalgerminatingseedHardseedAbnormalgerminatingseedDeadseedPasses Position Normal Hard Abnormal Dead(No) of germinating seed germinating seeddischarge seed seed----------------------------(%) ---------------------------Control' 38.8 55.5 a* 5.5 0.21000 71.5 2.2 b 25.0 1.32 60.2 0.2 c 37.8 1.81500 1 69.4 0.8 c 28.6 1.22 65.6 0.1 d 32.9 1.42000 65.9 Od 33.0 1.12 61.9 Od 37.4 0.7LSD 0.05 4.63 4.31 N.S.*Means followed by the same letter are not significantly different(P 0.05) as indicated by LSD tests for arc sin square roottransformed data.'No scarification100 ...,.----250LSD(0·05) I5 10 15 20Speed (rpm xlOO)NormalAbnormal • Y=1•17 ·1•ssxHard • Y=42•3->•ssx R 2 =0•73'• v=JB•3·6•91X-0•21BX 2 R 2 "'o•a1···R 2 =0•7B"Figure 2. Effect of increasing rotation speed of an EddyGiant Scarifier on Maku lotus seed germination.------------------------(%) ----------------------·Controll 38.8 55.5 5.5 0.21 Center 59.8 23.0 15.8 1.4End 78.8 7.5 11.8 1.92 Center 59.3 7.3 31.3 2.1End 76.0 0.8 21.3 1.93 Center 59.0 0.5 38.0 2.5End 78.3 0.5 20.3 0.9LSD 0.05 6.68 4.20 4.91 N.S.1No scarificationseeds, but as passes were increased, hard seed and abnormalseed were significantly reduced and increased respectively.The optimum treatment was one pass through to the end ofthe cylinder as this had the highest percentage of normalgerminating seeds and significantly the highest percentage ofviable seeds (normal and hard).DISCUSSIONOur results show that small seedlots of Malm lotus seedcan be very effectively scarified with sulphuric acid, as hasbeen found with many other legume seeds (Rolston, 1978).For researchers wishing to scarify small hand harvestedquantities of Maku lotus seed, sulphuric acid immersion issafe and effective. Hot water immersion can be difficult, astemperatures close to boiling point will significantlydecrease germination and most lower temperatures have nosignificant effect on softening hard seeds. Hot water immersionis not recommended as an effective method of scarification.For larger seedlots, mechanical scarification can significantlyreduce hard seed. However, it was not possible toreduce hard seed without significant increases in the abormalportion of germinated seeds compared with unscarifiedseed. None of the mechanical scarification treatmentstested could increase normal germinating seeds above 80%.The abnormal seeds may have originally been normal seedsbut scarification was too severe on them. Scarification,therefore, may well convert equal proportions of hard seedinto normal seed and normal seed into abnormal seed. Becausehard seed retains the potential to grow, it is better toaccept lower normal seed proportion, with more hard seedsand less abnormal seeds, than a high normal seed proportionwith more abnormals which will not produce vigorous seedlings.Hence, with the Eddy-Giant Scarifier the best scarifyingspeeds would be between 800-900 rpm giving optimumgermination, with the best balance between normal, hard and
10 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985abnormal seeds (Figure 2). These speeds also gave the highestEsvalues (Bilsland et al., 1984).Severity of scarification is extremely important in producingnormal germinating seeds. Increasing the number ofpasses through the rubber concaves increased impaction andlowered normal germinating seed percentages. Grant (1979)also found that increasing the number of passes in a similarFerrell Scarifier with rubber concaves lowered germinationof Stylosanthes guianensis var. intermedia cv. Oxley. Theuse of carborundum concaves is often too abrasive on herbagelegumes, producing too many abnormal seedlings(Grant, 1979). Preliminary tests before experiments on Makulotus began showed that at any speed, too many split andcracked seeds were produced when carborundum concaveswere used.Forcing seed through the mesh screen on the WestrupPolisher bruised and damaged seed, resulting in abnormalgerminating seedlings. However, smaller size grid meshscreens can be fitted and the bottom of the screen blocked offso that all seed travels through to the end of the cylinder.Operating speed of scarification equipment is important.Jones (1971) found that a speed of 17 50 rpm was the optimumspeed in a hammer mill to scarify Cotalaria ochroleucaseed; 1700 rpm was the optimum speed to scarify Oxley finestem stylo in a Ferrell Scarifier with rubber concaves (Grant,1979). With Maku lotus in a similar scarifier, 800-1000 rpmwere the optimum scarifying speeds.The mechanical scarification treatments were evaluatedusing the formula developed by Bilsland et al., (1984). Inthis formula the overall effectiveness of scarification (E 5)will range from 1.00 to -1.00; 1.00 indicates optimum scarification,0 indicates no net improvement from scarificationand negative values indicate seed damage. In these experimentsthe highest Es value was 0. 70 from the Westrup Polisherwith one pass through to the end of the cylinder. Thehighest Es value for the Eddy-Giant Scarifier was 0.61 fromthe speed of 900 rpm and 0.60 from 800 rpm. These valueswere lower than the optimum values for M. sativa (Es =0.77) and T. vesiculosum (Es = 0.82) that Bilsland et al.,(1984) achieved. The lower values for Maku lotus werebecause of the high numbers of abnormal germinating seedsproduced. With the highest normal germinating seed percentage(78. 8) and the highest Es value (0. 70), scarification bythe Westrup Polisher was the most effective.About half the seedlots of Maku lotus have normal seedgerminations less than 80% (Official <strong>Seed</strong> Testing Station,MAP, pers. comm.) because of high hard seed content. Theproportion of hard seed depends on climate during seedmaturation and harvest (Hare and Lucas, 1984) and scarificationduring mowing and threshing (Clifford and McCartin,1985). There is a difficulty in commercially scarifying seedlotswith high hard seed content to achieve normal germinationsabove 80%, as was found in this experiment. Thisillustrates the importance of buying seed with purity andgermination certificates provided. Farmers wishing to oversowpastures may prefer having a high hard seed content tospread the period of germination; whereas those sowing seedfor seed production which needs a rapid, even establishment,especially when spraying for weed control is necessary, willprefer seed with the highest normal seed germination.CONCLUSIONLarge seedlots of Maku lotus can be scarified effectively ina Westrup Polisher. Scarfication can be carried out in anEddy-Giant Huller and Scarifier if rubber concaves are usedat speeds of approximately 800-900 rpm. Sulphuric acidscarification can still be effectively used on small seedlots ofMaku lotus.ACKNOWLEDGEMENTSMr. George Hill, Plant Science Department, Lincoln College,Canterbury, for suggesting the initial experiments; theMAP Official <strong>Seed</strong> Testing Station, Palmerston North forgermination tests and seed data; Mr. Kenyon Moore ofGrasslands Division, DSIR, for technical assistance.REFERENCES1. Bilsland, D.M., N.R. Brandenburg, and A.G. Berlage. 1984.A procedure for evaluating scarification processes. J. of Appl.<strong>Seed</strong> Prod. 2:45-49.2. Clifford, P.T.P., and J. McCartin. 1985. Effects of pre-harvesttreatment and header types on seed loss and hard seed content atmowing, recovery, and separation when harvesting a whiteclover seed crop. N.Z. J. of Exp. Agric. 13: 307-316.3. Grant, P.J. 1979. Mechanical scarification of Stylosanthes guianensiscv. Oxley seed. Proc. Grassl. Soc. Southern Africa.14:137-141.4. Hare, M.D., and R.J. Lucas. 1984. Maku lotus (Lotus pedunculatusCav.) seed production. 1. Development of Makulotus seed and the determination of time of harvest for maximumseed yields. J. of Appl. <strong>Seed</strong> Prod. 2:58-64.5. Hyde, E.O.C. 1954. The function of the hilum in some papilionaceaein relation to the ripening of the seed and the permeabilityof the testa. Ann. of Bot. 18:241-256.6. Jones, M.E. 1971. <strong>Seed</strong> scarification. Rhodesia Agric. J.68:25-31.7. Kowithayakorn, L., and M.J. Hill. 1982. A study of lucerneseed development and some aspects of hard seed content. <strong>Seed</strong>Sci. and Technol. 10:179-186.8. McKeon, G.M., and J.J. Mott. 1982. The effect of temperatureon the field softening of hard seed of Stywsanthes humilis and S.hamata in a dry monsoonal climate. Aust. J. Agric. Res.33:75-85.9. Mott, J.J., G.M. McKeon, C.J. Gardener, andL. 'tMannetje.1981. Geographic variation in the reduction of hard seed contentof Stylosanthes seeds in the tropics and subtropics of NorthernAustralia. Aust. J. Agric. Res. 22:861-869.10. Purl, K.P., and A.S. Laidlaw. 1984. The effect of temperatureon components of seed yield and on hard seededness in threecultivars of red clover (Trifolium pratense L.). J. of Appl. <strong>Seed</strong>Prod. 2:18-23.11. Porter, R.H. 1949. Recent developments in seed technology.Bot. Rev. (Lancaster) 15:221-344.12. Quinlivan, B. J. 1965. The influence of the growing season andthe following dry season on the hardseededness of subterraneanclover in different environments. Aust. J. of Agric. Res.16:277-291.13. Quinlivan, B.J. 1971. <strong>Seed</strong> coat impermeability in legumes. J.Aust. Inst. of Agric. Sci. 37:283-295.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 1114. Rolston, M.P. 1978. Water impermeable seed dormancy. Bot.Rev. 44:365-396.15. Scott, D.J., and J.G. Hampton. 1985. Aspects of seed quality.pp. 43-52. In M.D. Hare and J.L. Brock (eds.) Producingherbage seeds. Grasslands Research and Practice Series No. 2,N .z. Grassland Assoc., Palmerston North.16. Suckling, F.E. T., and J.F.L. Charlton. 1978. A review of thesignificance of buried legume seeds with particular reference toNew Zealand agriculture. N.Z. J. of Exp. Agric. 6:211-215.17. Taylor, G.B., and M.J. Palmer. 1979. The effect of someenvironmental conditions on seed development and hardseedednessin subterranean clover (Trifolium subterraneum L.).Aust. J. of Agric. Res. 12:227-238.18. Tran, V.N., and A.K. Cavanagh. 1984. Structural aspects ofdormancy. pp. l-44 In D.R. Murray (ed.). <strong>Seed</strong> physiology.vol. 2., Germination and reserve mobilization. Academic Press,Sydney.19. Win Pe. 1978. A study of seed development, seed coat and seedlongevity in 'Grasslands Pawera' red clover (Trifolium pratenseL.). Ph.D. thesis, Massey University, Palmerston North, N.Z.<strong>Seed</strong> Yield Response to Fungicide Application in PaclobutrazolTreated Perennial RyegrasstJ.G. Hampton3 and P.D. HebblethwaitezABSTRACTFungicide application (triadimefon plus carbendazim pluscaptafol) at monthly intervals from tillering (February) untilharvest (July) to perennial ryegrass cv. S24 treated with thegrowth retardant paclobutrazol (PP333) at spikelet initiation(March), increased seed yield in 1981 and 1982 by increasing thenumber of seeds per spikelet. <strong>Seed</strong> yield responses to fungicideapplication in these non-lodged crops were not as great as thosepreviously reported for lodged crops.The incidence of leaf pathogens in both years was low. Fungicideapplication increased leaf area duration by delaying thesenescence of photosynthetic tissue. The importance of sourcesize and duration in the perennial ryegrass seed crop isdissussed.Additional index words: Lolium perenne L., seed production,seeds per spikelet, leaf senescence, leaf area duration.INTRODUCTION<strong>Seed</strong> yields in the perennial rye grass (Latium perenne L.)seed crop are usually around one-tenth of the theoretical!Contribution from Department of A_griculture and Horticulture,School of Agriculture, University of Nottingham, Sutton Bonington,Loughborough, Leics., U.K. Received for publication 28 June1985.2Qraduate Research Fellow and Reader in Agronomy respectively,University of Nottingham School of Agriculture, Sutton Bonington,Loughborough, Leics., U.K ..3Present address: Official <strong>Seed</strong> Testing Station, Ministry of Agricultureand Fisheries, P.O. Box 609, Palmerston North, NewZealand.potential because of poor seed site utilization (Hampton andHebblethwaite, 1983). Recent experiments with chemicalmanipulation of the crop have shown that both growth retardantand fungicide application can significantly increase seedyield (Hebblethwaite et al., 1982; Hampton andHebblethwaite 1984; 1985a).Poor seed site utilization resulting from seed abortion hasbeen associated with lodging of the crop (Hebblethwaite etal., 1980). Hampton and Hebblethwaite (1985a) suggestedthat seed abortion occurred because of assimilate shortage,due to competition from the elongating stem (Clemence andHebblethwaite, 1984) and from vegetative tillers (Hampton,1983), as well as from a loss of photosynthetic tissue in alodged canopy.Fungicide application to lodged crops increased seed yieldby increasing the number of seeds per spikelet. Hampton andHebbethwaite (1984) showed that these increases were associatedwith an increased leaf area duration brought aboutby delays in senescence of photosynthetic tissue. <strong>Seed</strong> yieldincreases in response to growth retardant application havealso been associated with increased numbers of seeds perspikelet (Hebblethwaite et al., 1980; 1982), although recentexperiments with paclobutrazol (PP333) have demonstratedthat increased fertile tiller production also contributed to seedyield increases (Hampton and Hebblethwaite, 1985a).Paclobutrazol has fungicidal properties (Froggatt et al.,1982), and Hampton and Hebblethwaite (1985a) showed thatone effect of its application was to increase leaf area duration.However, the effects of the fungicidal properties of thechemical and the delay in leaf tissue death because of theabsence of lodging could not be differentiated. Trials in 1981and 1982 examined whether the substantial seed yield increasesobtained from paclobutrazol application could befurther increased by fungicide application.
14 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985assimilate was still down the plant to the vegetative tillers.Results from this trial suggest that even in non-lodged paclobutrazoltreated plants, the area of actively photosynthesisingtissue was insufficient to meet all the demands from thevarious sinks. Delaying leaf tissue senescence through fungicideapplication may have provided a greater photosyntheticsource and allowed more seeds per spikelet to be retainedthrough until harvest.The use of fungicides in the perennial ryegrass seed croprequires further investigation. Trials in both lodged and uprightcrops have demonstrated that sequential fungicide applicationsdelayed leaf tissue senescence in the absence ofleaf pathogens, and possible reasons for this have been previouslydiscussed (Hampton and Hebblethwaite, 1984).However, there is still little information available as to theeffects of pathogens on seed production (Labruyere, 1980),and the effects of single critically timed fungicide applicationson seed yield, as sequential applications are not financiallyviable. Recent work (Hampton, 1983; Hampton andHebblethwaite, 1985a) has suggested that the photosyntheticcapacity of the plant between ear emergence and anthesisstrongly influences the number of seeds retained per spikelet.The effects of fungicide application at this time need to beevaluated.ACKNOWLEDGEMENTSWe gratefully acknowledge the financial assistance andgrowth retardant supplied by ICI (Plant Protection Division)Plc.; the financial assistance and fungicide provided byBayer (U.K.) Ltd., the technical assistance of Mr. J.Travers, Mrs. S. Manison and other staff of the Agronomysection. J.G.H. also gratefully acknowledges the NewZealand National Research Advisory Council for the awardof a Fellowship to undertake the Ph.D. studies from whichthis paper originated.REFERENCES1. Anon. 197 6. Manual of plant growth stages and disease assessmentkeys. MAFF., Harpenden, Herts., U.K.2. Clemence, T.G.A., and P.D. Hebblethwaite. 1984. An appraisalof ear, leaf and stem t4C0 2 assimilation, '4C-assimilatedistribution and growth in a reproductive seed crop of amenityLolium perenne. Ann. App. Biol. 105:319-327.3. Evans, L.T., I.F. Wardlaw, and R.A. Fischer. 1975. Wheat.pp. 101-149 In L.T. Evans (ed.) Crop physiology-some casehistories. Cambridge University Press.4. Froggatt, P.J., W.D. Thomas and J.J. Batch. 1982. The valueoflodging control in winter wheat as exemplified by the growthregulator PP333. pp. 71-87 In A.F. Hawkins and B. Jeffcoat(eds.) Opportunities for manipulation of cereal productivity,Monograph 7. British Plant Growth Regulator <strong>Group</strong>, Wantage.5. Hampton, J.G. 1983. Chemical manipulation of Loliumperenne grown for seed production. Ph.D. thesis, University ofNottingham, U.K.6. Hampton, J.G., and P.D. Hebblethwaite. 1983. Yield componentsof the perennial ryegrass (Lolium perenne L.) seedcrop. J. Appl. <strong>Seed</strong> Production. 1:23-25.7. Hampton, J.G., and P.D. Hebb1ethwaite. 1984. The effect offungicide application on seed yield in perennial ryegrass cv.S24. Ann. Appl. Biol. 104:231-239.8. Hampton, J.G., and P.D. Hebblethwaite. 1985a. The effect ofthe growth regulator paclobutrazol (PP333) on the growth,development and yield of Lolium perenne grown for seed.Grass and Forage Sci. 40:93-101.9. Hampton, J.G., and P.D. Hebblethwaite. 1985b. The effect ofgrowth retardant application on floret site utilization and assimilatedistribution in ears of perennial ryegrass cv. S24. Ann.Appl. Bioi. 107:127-136.10. Hebblethwaite, P.D., D. Wright, and A. Noble. 1980. Somephysiological aspects of seed yield in Lolium perenne. pp.71-90 In P.D. Hebblethwaite (ed.) <strong>Seed</strong> production. Butterworths,London.11. Hebblethwaite, P.D., J.G. Hampton, and J.S.McLaren. 1982. The chemical control of growth, develop-mentand yield of Lolium perenne grown for seed. pp. 502-523 InJ. S. McLaren ( ed.) Chemical manipulation of crop growth anddevelopment. Butterworths, London.12. laggard, J.W., D.K. Lawrence, and P.V. Biscoe. 1982. Anunderstanding of crop physiology in assessing a plant growthregulator on sugar beet. pp. 139-150 In J.S. McLaren (ed.)Chemical manipulation of crop growth and development. Butterworths,London.13. Labruyere, R.E. 1980. Fungal diseases of grasses grown forseed. pp. 173-187 In P.D. Hebblethwaite (ed.) <strong>Seed</strong> production.Butterworths, London.14. Mohamed, G.E.S. and C. Marshall. 1979. Physiological aspectsof tiller removal in spring wheat. J. Agric. Sci., Cambridge.93:457-463.15. de Wit, C.T. 1965. Photosynthesis ofleafcanopies. Agric. Res.Rep. No. 633, Verslagen Landbouwk Onderzoet. pp. 1-57.16. W oledge, J. 1972. The effect of shading on the photosyntheticrate and longevity of grass leaves. Ann. Bot. 36:551-561.
The Effect of Time of Application of the Growth Retardant Flurprimidol (ELSOO) on<strong>Seed</strong> Yields and Yield Components in Lolium perenne L.rP.D. Hebblethwaite2, J.G. Hampton 3,s, G.R. Batts 4 and S. Barrett 3ABSTRACTThe effects of the growth retardant flurprimidol (ELSOO) ongrowth, development and yield of perennial ryegrass (Loliumperenne L.) following application at double ridge (DR), spikeletinitiation (SI) and floret initiation (FI) were investigated. AllELSOO applications significantly increased seed yields in bothyears. In 1983, no significant differences in stem length, lodging,dry matter accumulation, photosynthetic area index or seedyield were recorded between ELSOO application times. Howeverin 1984, lack of rain following the FI application delayed growthretardant activity so that lodging occurred before anthesis, andalthough fertile tiller numbers were eventually increased, seedyield was significantly lower than that for DR and SI applicationbecause of a reduction in the number of seeds per spikelet.DR application produced the greatest number of seeds perunit area in each year because of an increased production offertile tillers. Reasons for this are discussed. However, seed yieldwas not significantly different from that of other applicationtimes because of a failure to fill seeds to the same thousand seedweight.Additional index words: perennial ryegrass, seed production,double ridge, spikelet initiation, floret initiation.reduces internode enlongation of a broad range of both monocotyledonousand dicotyledonous plants (Anon., 1983).The mode of action involves a reduction in gibberellin biosynthesis.Hampton and Hebblethwaite (1985b) compared the effectsof EL500 and PP333 on perennial ryegrass seed yields andalso compared EL500 application rates (1.0 and 2.0 kg a.i.ha -1). In this paper we report the effects of time of EL500application on perennial ryegrass growth, development andseed yield.MATERIALS AND METHODSExperiments were carried out at the University of Nottinghamexperimental farm, Sutton Barrington, Loughborough,Leics., on soil of the Astley Hall series. Certified basic seedof perennial rye grass cv. S24 was sown in the autum of 1982and 1983 at 12 kg ha-t with a row width of 15 em and in plots1. 5 x 12m. Details of experimental management are given inTable 1.Table 1. Experimental details.INTRODUCTIONRecent reports of stem retardation and lodging preventionin the perennial' rye grass (Lolium perenne L.) seed crop havediscussed the effects of paclobutrazol (PP333)(Hebblethwaite et al., 1982; Hampton and Hebblethwaite,1985a). However, other products have also been investigated(Hampton, 1983), one of which is flurprimidol(EL500) = -( 1-Methylethyl)- -[ 4-(trifluoromethoxy) phenyl]-5-pyrimidine-methanol. Like paclobutrazol, flurprimidol isa foliar and root absorbed plant growth regulator whichSowing datePrevious cropHerbicide:AutumnSpring198323 August 1982PotatoesCambilene,4.91 ha-lNortron,9.81 ha-lNortron,4.91 ha-t198426 August 1983PotatoesCambilene,4.91 ha-tNortron,9.81 ha-l'Contribution from Department of Agriculture and Horticulture,School of Agriculture, University of Nottingham, Sutton Bonington,Loughborough, Leics., U.K. Received for publication 28 June1985.2Reader in Agronomy, 3Graduate Research Fellows and 4undergraduatestudent, University of Nottingham, School of Agriculture,Sutton Bonington, Loughborough, Leics., U.K.5Present Address: Official <strong>Seed</strong> Testing Station, Ministry ofAgriculture and Fisheries, P.O. Box 609, Palmerston North, NewZealand.Fertilizer:Application dateApplication rateELSOO application:Double ridgeSpikelet initiationFloret initiation<strong>Seed</strong> Harvest14 April120 kg N ha-l1 March29 March15 April15 July30 March120 kg N,60 kg P,60 kg K ha-l24 February28 March20 April18 July15
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 17Table 4. The effect of time of ELSOO application on vegetativetiller numbers at final harvest, 1983 and 1984.Vegetative tiller numbers m~2Application time 1983 1984Nil 2454 4283DR 1004 1769SI 65 1050FI 810 4954S.E. diff. (9 d.f.) 612.8 1009.5LSD .05 1385 2281numbers were increased (Table 5), although this differencewas significant only for the DR application. At final harvestin 1984 vegetative tiller numbers were significantly lower forthe DR and SI application times (Table 4), but the tillernumbers for the FI application time differed from the previousyear in that both vegetative and fertile tiller numberswere increased (Tables 4, 5).Dry Matter Accumulation and DistributionThe dry matter (DM) accumulation of vegetative tillerswas increased by EL500 application at all 3 times prior toanthesis, but at anthesis, differences were not significant.Vegetative tiller DM was significantly reduced at final harvestin both years for the DR and SI application times, but in1984, vegetative tiller DM for the FI application did notdiffer from that of untreated plots.EL500 effects on fertile tiller DM accumulation weresimilar to those previously reported for PP333 (Hampton andHebblethwaite, 1985a; 1985b), in that fertile tiller stem DMwas reduced, but leaf and ear DM were not. Time of EL500application did not significantly alter DM accumulation ordistribution within fertile tillers in 1983, but in 1984, fertiletiller stem DM, while still reduced from that of untreatedplots, was greater than that for DR and SI plots.Photosynthetic Area IndexData were collected in 1983 only. No significant differencesin total photosynthetic area index (P AI) between untreatedand EL500 treated plots, or between EL500 applicationtimings were recorded. Within fertile tillers, PAl didnot differ significantly between EL500 application times foreither stem, leaf or earP AI. At an thesis, EL500 had reducedstem P AI, but increased fertile tillerleaf P AI. At final harvest,stem P AI was significantly less than that of untreated plots,and ear PAl was significantly increased.<strong>Seed</strong> Yield-Potential, Actual and ComponentsAt anthesis in both years, potential seed yield was similarfor all treatments, as no significant differences were recordedin the number of fertile tillers, florets per spikelet orspikelets per tiller (Batts 1984; Hampton and Hebblethwaite,1985b). Actual seed yield was significantly increased for allthree EL500 application times in both years (Table 5) as aresult of increased tiller numbers and significant increases inthe number of seeds per spikelet for the DR and SI applicationtimes. In 1983, seed yield did not differ betweenEL500 application times, but in 1984, the seed yield from theFI application was significantly lower than that from the DRand SI applications. In both years, the greatest number ofseeds was produced from the DR application (Table 5), butbecause thousand seed weight was significantly reduced eachyear, the DR application did not consistently outyield thelater application times. The 1984 FI seed yield differed fromthe other EL500 responses, in that the increase over that ofTable 5. The effect of time of ELSOO application! on seed yield and yield components, 1983 and 1984.HarvestApplication Yield g m-22 data not recorded.Time <strong>Seed</strong> Straw index1983Nil 148.8 994.7 0.13DR 217.6 610.4 0.26SI 225.2 792.0 0.22FI 226.2 793.0 0.22S.E. diff. (9 d.f.) 16.3 50.3 0.02LSD .05 36.8 113.7 0.051984Nil 127.4 1213.2 0.09DR 275.5 963.8 0.22SI 262.9 1000.6 0.21FI 192.8 1203.4 0.14S.E. diff. (9 d.f.) 16.9 181.9 0.03LSD .05 38.2 411.1 0.0712 kg a.i. applied per hectare.Fertile Spikelets <strong>Seed</strong>s per TSW <strong>Seed</strong> numbertillers per tiller spikelet (g) m-2 x 104(m-2) (calc) (calc)3146 19.9 1.25 1.89 7.854498 17.7 1.69 1.61 13.523735 19.9 1.76 1.72 13.093388 _2 _2 1.73 13.08439.9 (6 df) 1.35 (6 df) 0.14 0.08 1.17994 3.2 0.33 0.18 2.642978 19.6 1.06 2.05 6.213932 19.2 2.23 1.63 16.903593 18.6 1.95 2.02 13.014173 20.4 1.11 2.03 9.49455.5 1.23 0.32 0.16 2.291029 2.8 0.72 0.36 5.18
18 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985the untreated plots was a result solely of increased fertiletiller numbers, as the number of seeds per spikelet was notincreased.DISCUSSIONThe objective of applying growth retardants to perennialryegrass seed crops has been to prevent lodging(Hebblethwaite et al. , 1980) and increase seed yield byreducing seed abortion (Hampton et al., 1985). However,seed yield increases following growth retardant applicationhave also resulted, either partly or solely, from increasedfertile tiller production (Hampton and Hebblethwaite1985a). For example, PP333 is known to reduce apicaldominance and increase tillering, the response being greaterwhen the growth retardant is applied early in the phase oftiller development (Froggatt et al., 1982). Hampton (1983)suggested that growth retardant application prior to apicaldifferentiation may lead to a greater synchronous emergenceof tillers and a greater proportion of fertile tillers, as previouslydemonstrated in wheat (Hofner and Kuhn, 1982) andbarley (Matthews et al., 1982).In both 1983 and 1984, the greatest number of seeds,though not necessarily the greatest seed yield, resulted fromEL500 application prior to apical differentiation. In 1983,fertile tiller number increases were consistent with EL500application time i.e. greatest with the earliest application,and it is possible that the same pattern would have followedin 1984. However a dry April (Table 6) meant that growthretardant activity following the FI application (20 April) wasdelayed - stem length reductions were not as great as theprevious year, and the lodging pattern followed that of untreatedplots. EL500's requirements for water before soilactivation are similar to those of PP333 (Hampton andHebblethwaite, 1984a). However, once water became available(at ear emergence), the response was an increase in tillerproduction in plots already lodged, similar to that reported inthe 1982 season (Hampton and Hebblethwaite, 1984b). Althoughfertile tiller numbers were significantly increased,seed yield was reduced because of a reduction in the numberof seeds per spikelet.EL500 application at DR allowed the production of morefertile tillers, but not a greater proportion of fertile tillers assuggested by Hampton (1983). In both years, the greatestproportion offertile tillers was achieved with SI application,as fewer vegetative tillers were produced. However, tillernumber differences between DR and SI application timeswere not significant, and the proportion of fertile tillers forboth times was over 75%, compared with around 50% foruntreated plots, a result also reported for PP333 (Hamptonand Hebblethwaite, 1984b).Hofner and Kuhn (1982) suggested that in wheat, growthretardant application, by altering the balance between GA3and GA3 inhibitors, may influence apical differentiation bysynchronizing and reducing the growth rate of individualspikelets, and lead to an increase in the number of spikeletsand of seeds per spikelet. EL500 application prior to apicaldifferentiation had no effect on the number of spikelets pertiller in either year, and differences in the number of seedsTable 6. Rainfall data, February-July; longterm average, 1983and 1984, Sutton Bonington.Rainfall (mm)Month Longterm 1983 1984average-1February 41 27.0 45.4March 45 32.9 58.3April 39 87.7 7.4May 49 78.6 59.9June 48 8.4 73.4July 51 28.6 24.0IJ9!6-1982per spikelet were not significant from that of EL500 appliedat SI. While the number of seeds per spikelet for FI plots wasreduced in 1984, Hampton and Hebblethwaite (1985a) obtainedmore seeds per spikelet from FI application of PP333than from SI application. In perennial ryegrass, increases inthe number of seeds per spikelet are more likely to result fromreduced seed abortion because of reduced competition forassimilates than any 'antigibberellin' effects of growth retardants(Hampton and Hebblethwaite, 1985c).EL500 application at DR produced the greatest number ofseeds per unit area in each year, but this potential was notachieved in terms of seed yield because of reduced thousandseed weight (TSW). This suggests either that plants treated atDR could not support the number of seeds retained in eachspikelet, or that maturity was delayed even more than the 3-5days recorded for SI application (Hampton, 1983) so that DRplots were harvested before adequate seed filling had beenallowed to occur. This requires further investigation. <strong>Seed</strong>yield results did not show any significant differences betweenDR and SI application times, but the 1984 results confirm thepossible inconsistency of FI application (Hampton andHebblethwaite, 1985a) for growth retardants which requirewater for activation.ACKNOWLEDGEMENTSWe gratefully acknowledge the financial assistance of theBritish <strong>Seed</strong>s Council, the growth retardant supplied byBlanco Ltd., the technical assistance of Mr. J. Travers, Mrs.P. Tetlow, Mrs. S. Manison, and Mrs. B. Hull. J.G.H. alsogratefully acknowledges the New Zealand National ResearchAdvisory Council for the award of a fellowship to undertakethe Ph.D. studies from which part of this paper originated.REFERENCESI. Anon. 1983. Technical report on EL500. Lilly Research Laboratories,Eli Lilly and Co., Indianapolis, U.S.A.2. Batts, G.R. 1984. The effect of growth regulators on seedproduction in Lolium perenne L.: a timing investigation. B.Sc.(Hons.) dissertation, University of Nottingham, U.K.3. Froggatt, P.J., W.D. Thomas, andJ.J. Batch. 1982. The valueof lodging control in winter wheat as exemplified by the growthregulator PP333. pp. 71-87. In A.F. Hawkins and B. Jeffcoat
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 19(eds.) Opportunities for manipulation of cereal productivity,Monograph 7. Wantage: British Plant Growth Regulator <strong>Group</strong>.4. Hampton, J.G. 1983. Chemical manipulation of Loliumperenne grown for seed production. Ph.D. thesis, University ofNottingham, U.K.5. Hampton, J.G., and P .D. Hebblethwaite. 1984a. The influenceof rainfall on paclobutrazol (PP333) response in the perennialryegrass (Lolium perenne L.) seed crop. J. Appl. <strong>Seed</strong> Production2:8-12.6. Hampton, J.G., and P.D. Hebblethwaite. 1984b. Experimentswith vegetative tiller manipulation in the perennial ryegrass(Lolium perenne L.) seed crop by the application of growthregulators. J. Appl. <strong>Seed</strong> Production 2:1-7.7. Hampton, J.G., and P.D. Hebblethwaite. 1985a. The effect ofthe growth regulator paclobutrazol (PP333) on the growth,development and yield of Lolium perenne grown for seed.Grass and Forage Sci., 40:93-102.8. Hampton, J.G., and P.D. Hebblethwaite. 1985b. A comparisonof the effects of the growth retardants paclobutrazol(PP333) and flurprimidol (EL500) on the growth, developmentand yield of Lolium perenne grown for seed. J. Appl.<strong>Seed</strong> Production 3:19-23.9. Hampton, J.G., andP.D. Hebblethwaite. 1985c. The effect ofgrowth retardant application on floret site utilization and assimilatedistribution in ears of perennial ryegrass cv. S24. Ann.Appl. Bioi. 107: 127-136.10. Hampton, J.G., T.G.A. Clemence, and B.L. McCloy. 1985.Chemical manipulation of grass seed crops. pp.9-14. In M.D.Hare and J.L. Brock (eds.) Producing herbage seeds. Grasslandresearch and practice series no. 2. N.Z. Grassld. Assoc. (Inpress).11. Hebblethwaite, P.D., D. Wright, and A. Noble. 1980. Somephysiological aspects of seed yield in Lolium perenne. pp.71-90. In P.D. Hebblethwaite (ed.), <strong>Seed</strong> production. Butterworths,London.12. Hebblethwaite, P.D., J.G. Hampton, and J.S. McLaren.1982. The chemical control of growth, development and yieldof Lolium perenne grown for seed. pp. 505-523. In J.S.McLaren (ed.), Chemical manipulation of crop growth anddevelopment. Butterworths, London.13. Hafner, W., and H. Kuhn. 1982. Effect of growth regulatorcombinations on ear development, assimilate translocation andyield in cereal crops. pp. 375-390. In J.S. McLaren (ed.)Chemical manipulation of crop growth and development.Butterworths, London.14. Matthews, S., G.O. Koranteng, and W.J. Thomson. 1982.Tillering and ear production: opportunities for chemical regulation.pp. 88-96. In A.F. Hawkins and B. Jeffcoat (eds.).Opportunities for manipulation of cereal productivity, Monograph7. Wantage: British Plant Growth Regulator <strong>Group</strong>.15. Wright, D. 1978. Control of growth, development and seedproduction in Lolium perenne. Ph.D. thesis, University ofNottingham, U.K.A Comparison of the Effects of the Growth Retardants Paclobutrazol (PP333)and Flurprimidol (ELSOO) on the Growth, Development and Yield ofLolium perenne Grown for <strong>Seed</strong>tJ.G. Hampton3 and P.D. HebblethwaitezABSTRACTApplication of the growth retardants paclobutrazol(PP333) and flurprimidol (ELSOO) to perennial ryegrass (Loliumperenne L.) seed crops at spikelet initiation can substantially!Contribution from Department of Agriculture and Horticulture,School of Agriculture, University of Nottingham, Sutton Bonington,Loughborough, Leics., U.K. Received for publication 28 June1985.2Graduate Research Fellow and Reader in Agronomy respectively,University of Nottingham School of Agriculture, Sutton Bonington,Loughborough, Leics., U.K.3Present address: Official <strong>Seed</strong> Testing Station, Ministry of Agricultureand Fisheries, P.O. Box 609, Palmerston North, NewZealand.increase ryegrass seed yields. The mode of action of these twoproducts is similar, both being gibberellin inhibitors, whichresults in stem internode retardation.A comparison of the effects of these two growth retardantsdemonstrated that at the same rate of active ingredient, plotstreated with PP333 outyielded plots treated with ELSOO, primarilybecause of a greater retention of seeds per spikelet. Thegreater activity of PP333 allowed less lodging, and prolongedreproductive photosynthetic leaf area. For comparable effectson perennial ryegrass plant growth and seed yield, ELSOO hadto be applied at double the active ingredient rate of thatrequired for PP333.Additional index words: perennial ryegrass, seed production,growth retardants, seed abortion.INTRODUCTIONThe use of growth retardants to increase seed yield inperennial ryegrass crops through the prevention of lodging
20 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985has been investigated for over 10 years. Recent attentionhas focu,sed on two products, paclobutrazol (PP333) andflurprimidol (EL500), both of which have significantlyincreased ryegrass seed yields by increasing fertile tillerproduction and reducing seed abortion (Hampton andHebblethwaite, 1985a;b Hebblethwaite et al., 1985).Both retardants are root active with some foliar activity,and both are inhibitors of gibberellin biosynthesis whichresults in prolonged stem retardation and internode compression(Shearing and Batch, 1982; Anon., 1983). In thispaper we compare the effects of PP333 and El500 onperennial ryegrass growth and seed yield.MATERIALS AND METHODSExperiments were carried out at the University of Nottinghamexperimental farm, Sutton Bonington, Loughborough,Leics., on soil of the Astley Hall series. Certifiedbasic seed of perennial ryegrass cv. S24 was sown on 18August 1981 and 23 August 1982 at 12 kg ha- 1 with a rowwidth of 15 em and in plots 1.5 x 12 m. Details ofexperimental management have been previously described10Lodging 1982(Hampton and Hebblethwaite, 1985a; Hebblethwaite et al. ,1985).PP333 and EL500 were applied at spikelet initiation (25March 1982; 29 March 1983) at active ingredient rates of1.0 and 2.0 kg ha-l for both products in 1982, and 1.0 kga.i. ha-l for PP333 and 2.0 kg a.i. ha-l for EL500 in 1983.Growth retardant treatments plus an unsprayed control werereplicated four times in a randomized complete blockdesign.Growth analyses were carried out at regular intervals;techniques used for data accumulation have been previouslypublished (Hampton and Hebblethwaite, 1985a). <strong>Seed</strong> washarvested at 40% seed moisture content in both years bycutting 5.5 m2 per plot in 1982 and 2.8 m2 per plot in 1983with a reciprocating knife mower (Mayfield). The cutmaterial was placed in cloth bags and cool air dried to12-15% straw moisture content before the seed was threshed,cleaned and weighed. Yield results are expressed at 0%moisture content.RESULTSLodging and Stem LengthIn untreated plots, lodging began at ear emergence inboth years, and was severe by anthesis. Growth retardantapplication delayed the onset of lodging until after anthesisin 1982 (Figure 1), with PP333 at 2.0 kg a.i. ha-l preventinglodging completely. In 1982 (Figure 1) and 1983, lodgingin plots which had received EL500 at 2.0 kg a.i. ha-l wasnot significantly different from that for plots which hadreceived PP333 at 1.0 kg a.i. ha-l.PP333 and EL500 reduced stem length in both years. In1982, the stem length of plants treated with PP333 at 2.0 kga.i. ha-l was significantly less than that of plants treatedwith EL500 at the same rate of active ingredient by 56 daysafter application (Table 1). Greater retardation occurred atinternodes three and four (base of stem = one) in PP333treated plants. In 1983, the pattern of internode lengthreduction was similar for PP333 at 1.0 kg a.i. ha-l andEL500 at 2.0 kg a.i. ha-l.Table 1. The effect of growth retardants on stem length,1982.Treatment Days after growth retardant application,1982kg a.i. ha-l 34 56 69 99Stem lengthMAY JUNE JULYFigure 1. The effect of growth retardants on lodging, 1982.( e =nil; Ill = PP333, 1.0 kg a.i. ha-1; j = PP333 2.0 kga.i. ha-1; o = ELSOO 1.0 kg a.i. ha-t; 0 = ELSOO. 2.0 kga.i. ha-t; E = peak ear emergence; A = peak anthesis; I = S.E.diff.16 d.f.-----------------------(em)---------------------------nil 28.5 49.5 53.7 60.2EL500 2.0 11.3 29.8 40.7 51.6PP333 2.0 9.2 21.6 24.6 33.1S.E. diff. 1 1.53 2.61 3.73 3.16LSD .05 3.75 6.39 9.14 7.74
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 21Table 2. The effect of growth retardants on tiller numbers, 1982 and 1983.1982Tiller number m-2Treatment and Peak ear emergence Peak anthesis Final harvestrate a.i. ha-lVegetative Fertile Vegetative Fertile Vegetative Fertilenil 3487 2387 3044EL500 2.0 6674 2526 1681PP333 2.0 8298 2204 4128S.E. diff. (6 d.f.) 1011.6 331.4 306.9LSD .05 2478.4 811.9 751.93206 59844406 51843478 6197403.7 1381.6989.1 3384.9246830483285234.6574.8Fertiletillersurvival(%)76.969.286.41983nil 4239 1761 1384EL500 2.0 7301 1899 4498PP333 1.0 6099 1901 39882816 24542802 652412 35331463735414780.088.992.3S.E. diff. (6 d.f.) 1008.6 116.7 301.6LSD .05 2471.1 N.S. 738.9246.2 612.8N.S. 1501.4439.9N.S.Tiller ProductionIn both years, growth retardant application increased thetotal number of tillers present at ear emergence by increasingthe production of vegetative tillers (Table 2). Atanthesis in 1982, vegetative tiller numbers in PP333 treatedplots were significantly greater than those of ELSOO treatedplots, but fertile tiller numbers did not differ either atan thesis or final harvest. In 1983, tiller numbers in plotstreated with PP333 at 1.0 kg a.i. ha-l did not differ fromthose plots treated with ELSOO at 2.0 kg a.i. ha- 1 • At finalharvest, vegetative tiller numbers in both PP333 and EL500treated plots were significantly reduced (Table 2).Dry Matter Accumulation and DistributionBoth growth retardants reduced fertile tiller stem drymatter (DM) in both years, had no effect on fertile tiller leafDM and increased ear DM, although differences from theuntreated check were not always significant. Vegetativetiller DM at final harvest was reduced in 1983.Differences in DM accumulation and distribution betweenPP333 and ELSOO were not significant in either year.Table 3. The effect of growth retardants on the photosynthetic area index of fertile tillers, 1982 and 1983.Photosynthetic area index1982Treatment Ear Stem Leafand ratea.i. ha -1 Anthes is Final An thesis Final An thesis Finalharvest harvest harvestnil 1.0 0.9 2.3 1.6 2.1 0.2EL500 2.0 1.1 1.0 1.5 1.6 2.2 0.4PP333 2.0 1.2 1.4 1.1 1.5 2.8 1.0S.E. diff. (6 d.f.) 0.26 0.18 0.31 0.27 0.22 0.02LSD .05 N.S. 0.44 0.76 N.S. 0.54 0.051983nil 0.6 0.8 2.4 2.2 2.2 0.1EL500 2.0 0.7 1.1 1.1 1.5 1.9 0.4PP333 1.0 0.7 1.1 0.9 1.5 2.2 0.4S.E. diff. (6 d.f.) 0.21 0.18 0.20 0.21 0.41 0.11LSD .05 N.S. N.S. 0.49 0.51 N.S. 0.27
22 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Photosynthetic Area IndexTotal reproductive photosynthetic area index (PAl) wasdecreased by growth retardant application prior to anthesisin both years because of a reduction in stem PAl (Table 3).By final harvest in both years, fertile tiller leaf PAl wasincreased by EL500 and PP333. However in 1982, thedifference between PP333 at 2.0 kg a.i. ha-l and EL500 atthe same rate was significant (Table 3). In 1983, the fertiletiller leaf PAl of plants treated with EL500 at 2.0 kg a.i. ha-ldid not differ from that of plots treated with PP333 at 1.0 kga.i. ha-l.Table 4. Effect of growth retardants on florets per basal, middleand penultimate spikelet and spikelets per tiller at anthesis,1982.Florets per spikeletTreatmentSpike letskg a.i. ha-l basal middle penultimate per tillernil 8.1 8.7 5.7 22.3EL500 2.0 7.8 8.5 5.4 21.7PP333 2.0 8.3 8.9 5.4 21.9S.E. diff.l 0.28 0.24 0.44 0.56LSD .05 N.S. N.S. N.S. N.S.16 d.f.<strong>Seed</strong> Yield--Potential, Actual and ComponentsAt anthesis, potential seed yield was similar for alltreatments, as no differences were recorded in the numberof florets per spikelet and spikelets per tiller (Table 4), orfertile tillers (Table 2). However, actual seed yield wassignificantly increased by growth retardant application inboth years as a result of increased fertile tiller numbers anda significant increase in the number of seeds per spikelet(Table 5). Other yield components did not differ. In 1982,plots treated with PP333 at 1.0 and 2.0 kg a.i. ha-lsignificantly out-yielded plots treated with EL500 at 1.0 and2.0 kg a.i. ha- 1 respectively, because of an increase in thenumber of seeds per spikelet. The seed yield of plots treatedwith PP333 at 1.0 kg a.i. ha-l and EL500 at 2.0 kg a.i. ha-ldid not differ in either year.DISCUSSIONIn 1982, seed yield from plots treated with PP333 at 1.0kg a.i. ha-l was 36.5 g m-2 (20%) greater than that of plotstreated with EL500 at the same rate of active ingredient.Similarly, for plots treated with PP333 at 2.0 kg a.i. ha-lseed yield was increased by 42.5 g m-2 (20%) over thoseplots treated with EL500 at the same rate. In both 1982 and1983, seed yields from plots which had received PP333 at1.0 and EL500 at 2.0 kg a.i. ha-l did not differ. <strong>Seed</strong> yielddifferences between the two growth retardants resultedprimarily from a greater num-ber of seeds per spikelet.Hampton and Hebblethwaite ( 1985b) showed that thegreater retention of seeds per spikelet in non-lodged perennialryegrass plots occurred because seed abortion wasreduced. <strong>Seed</strong> abortion may occur because of an assimilateshortage due to competition from the enlongating stem(Clemence and Hebblethwaite, 1984), competition fromvegetative tillers (Hampton and Hebblethwaite 1984a), andloss of photosynthetic tissue in a lodged canopy (Hamptonand Hebblethwaite 1984b). At anthesis, yield potential didnot differ between the growth retardants. However, whilePP333 at 2.0 kg a.i. ha -1 completely prevented lodging,EL500 at 2.0 kg a.i. ha-l allowed some lodging afteranthesis. Stem length was reduced more by PP333 thanEL500, although the theory that reduced stem size mayTable 5. The effect of growth retardants on seed yield and yield components, 1982 and 1983.seeds perTreatment yield g m-2 harvest fertile tillers spikelets spikelet 1000 seed seed numberkg a.i. ha-l seed straw index m-2 per tiller (calc.) weight (g) m-2 x 1041982nil 111.3 749.1 0.13 2468 20.7 1.19 1.85 6.04EL500 1.0 186.3 716.7 0.21 3228 20.3 1.67 1.73 10.76EL500 2.0 213.8 643.7 0.25 3048 20.9 1.59 1.78 12.00PP333 1.0 222.8 716.6 0.24 3096 20.6 1.89 1.77 12.63PP333 2.0 256.3 612.2 0.30 3285 20.3 2.21 1.76 14.59S.E. diff. (12 d.f.) 8.1 37.6 O.Dl 373.6 1.11 0.19 0.96 0.67LSD .05 17.6 81.9 0.02 814.4 N.S. 0.41 N.S. 1.461983nil 148.4 994.7 0.13 3146 19.9 1.25 1.89 7.85EL500 2.0 225.2 792.0 0.22 3735 19.9 1.76 1.72 13.09PP333 1.0 229.6 694.7 0.25 4147 17.2 1.89 1.70 13.57S.E. diff. (6 d.f.) 16.3 50.3 0.02 439.9 1.35 0.14 0.08 1.17LSD .05 39.9 123.2 0.05 N.S. N.S. 0.34 N.S. 2.87
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 23reduce the stem sink capacity to the benefit of the ear(Hebblethwaite et al., 1982) has still to be confirmed(Hampton and Hebblethwaite, 1985a). Vegetative tillernumbers did not differ significantly between growth retardantsafter anthesis, but fertile tiller leaf photosynthetic areaindex was significantly greater in PP333 treated plots overthe same period.Both PP333 and EL500 can substantially increase perennialryegrass seed yields (Hampton and Hebblethwaite, 1985a;Hebblethwaite et al., 1985). However, PP333 has greateractivity in the perennial ryegrass plant than does EL500,and for comparable effects on plant growth and seed qualitythe latter retardant needs to be applied at double the rate ofactive ingredient.ACKNOWLEDGEMENTSWe gratefully acknowledge the financial assistance andgrowth retardants supplied by ICI (Plant Protection Division)Pic. and Elanco Ltd.; the financial assistance of the British<strong>Seed</strong>s Council; the technical assistance of Mr. G. Batts, Mr.J. Travers, Mrs. P. Tetlow and Mrs. S. Manison. J.G.H.also gratefully acknowledges the New Zealand NationalResearch Advisory Council for the award of a fellowship toundertake the Ph.D. studies from which this paper originated.REFERENCES1. Anon. 1983. Technical report on ELSOO. Lilly ResearchLaboratories, Eli Lilly and Co., Indianapolis, U.S.A.2. Clemence, T.G.A., and P.D. Hebblethwaite. 1984. An appraisalof ear, leaf and stem I4C0 2 assimilation, I4C-assimilatedistribution and growth in a reproductive seed crop of amenityLolium perenne. Ann. Appl. Bioi. 105:319-327.3. Hampton, J.G., and P.D. Hebblethwaite. 1984a. Experimentswith vegetative tiller manipulation in the perennial ryegrass(Lolium perenne L.) seed crop by the application of growthregulators. J. Appl. <strong>Seed</strong> Production. 2:1-7.4. Hampton, J.G., andP.D. Hebblethwaite. 1984b. The effect offungicide application on seed yield in perennial rye grass cv.S24. Ann. Appl. Bioi. 104:231-239.5. Hampton, J.G., and P.D. Hebblethwaite. 1985a. The effect ofthe growth regulator paclobutrazol (PP333) on the growth,development and yield of Lolium perenne grown for seed.Grass and Forage Sci. 40:93-101.6. Hampton, J.G., and P.D. Hebblethwaite. 1985b. The effect ofgrowth retardant application on floret size utilization andassimilate distribution in ears of perennial ryegrass cv. S24.Ann. Appl. Bioi. 107:127-136.7. Hebblethwaite, P.D., J.G. Hampton, and J.S. McLaren.1982. The chemical control of growth development and yieldof Lolium perenne grown for seed. pp. 139-150. In J.S.McLaren (ed.) Chemical manipulation of crop growth anddevelopment. Butterworths, London.8. Hebblethwaite, P.D., J.G. Hampton, G.R. Batts, and S.Barrett. 1985. The effect of time of application of the growthretardant flurprimidol (EL500) on seed yields and yieldcomponents in Lolium perenne L. J. Appl. <strong>Seed</strong> Production3:15-19.9. Shearing, S.J., and J.J. Batch. 1982. Amenity grass retarationsome concepts challenged. pp. 467-483. In J.S. McLaren(ed.) Chemical manipulation of crop growth and development.Butterworths, London.
Immaturity as a Cause of Low Quality in <strong>Seed</strong> of Panicum maximum1J.M. Hopkinson and B.H. EnglishzABSTRACTMethods were devised for measuring the mature seed contentof samples of pure seed of Panicum maximum cv. Petrie (greenpanic) and cv. Gatton. Tests conducted on mature and immaturefractions confirmed the great inferiority of immatureseed in terms of laboratory germination, field emergence, viabilityand longevity. A close correlation was obtained betweenmature seed content of commercial seed samples measuredshortly after harvest and subsequent viability, germination andplanting value. Mature seed content of numerous samples fromseed crops of both cultivars averaged just below 60%, withvariation between about 30 and 90%. It was concluded thatimmaturity was a reason for the low general quality of seed ofthese grasses and a major cause of variation in quality. Possiblereasons for variation were suggested.Additional index words: maturity, germination, emergence, viability,longevity, tropical pasture grass.INTRODUCTION<strong>Seed</strong> of most species of tropical pasture grasses has areputation for low quality. Examination of many seed samplesover a long time led us to the opinion that one reason wasthe presence of high proportions of immature seed. Thecondition generally passes unnoticed because its detection inmost grass seeds requires spikelet dissection, and there islittle specific, useful, published information on the subject.Descriptions of the behavior of other species were of somevalue. They provided evidence of the general inferiority ofseed harvested before maturation (Austin, 1972) and ampleindication of the presence and low quality of immature seedin temperate grasses (Hill, 1980).It could be inferred that a proportion of the seed of standingcrops of at least one tropical pasture grass, Panicwn maximwn,must be immature, even at harvest ripeness, because of thecombination of unsynchronized spikelet development andbrief retention after ripening (Hopkinson and English, 1982a).Immature seed would then be carried through in unchangedproportions to the marketed product, first because conven-!Contribution from Department of Primary Industries, WalkaminResearch Station, Walkamin, Queensland 4872, Australia. Receivedfor publication 26 September 1985.2Pasture Agronomist and Experimentalist at W alkamin ResearchStation.tional combine harvesting does not selectively exclude immatureseed (Hopkinson and English 1982b), next becausethe pure seed fraction is never altered during cleaning.There was thus little doubt about the ubiquity of immatureseed in Panicum maximum seed lots. There was, however,no indication of how much is normally present, how low is itsquality, or to what extent its content varies and causes qualityto vary. The objective of this investigation was to obtaininformation on the importance of seed immaturity to lowseed quality.The first task was to reach practicable definitions of maturityand immaturity and to devise methods for their quantification.The methods were then used on seed from bothcommercial and experimental sources to provide an accumulationof information. Several species were covered, but thisaccount is restricted to two cultivars of one species for whichthe most thorough records were obtained. These are greenand Gatton panic of Panicum maximum (described as cv.Petrie and cv. Gatton, Barnard, 1972).METHODS AND RESULTSDefmition and Measurement of MaturityMeasurements were made on dried samples of pure seed asdefmed by the <strong>International</strong> <strong>Seed</strong> Testing Association (Anon.,1985). The unit of seed was thus the individual spikeletcontaining a single recognizable caryopsis.After much preliminary trial, it was decided to measurematurity in terms of the percentage content of mature seeds.Two classes only of seed were to be recognized, mature andimmature. This was obviously artificial, since maturation isprogressive and a gradation of stages of maturity must exist.Nevertheless, it was practical and realistic. Intermediateswere few, normally less than 5% of a sample, and couldreadily and consistently be allocated to the class they resembledthe more closely. Germination tests failed to detectdifferences between fractions created within the mature seedclass. From this and from the difference between classes (seelater results), we concluded that our point of separationbetween classes was appropriate.A mature seed was defined as one in which the caryopsishad completed, or virtually completed, its development basedon visual evaluation. The caryopsis fully occupied the huskcavity, its final growth having forced the overlapping edgesof the lemma and palea together in a tight seal which wasmaintained after drying because the caryopsis did not shrink.24
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 25The embryo was outwardly perfect, the endosperm plumpand translucent.The caryopsis of an immature seed did not fully occupy thehusk cavity when dry, and the seal between lemma and paleawas consequently slack. The embryo might or might not befull sized, but the endosperm was always undersized, opaque,and usually chalky in texture.Normally at least two sub-samples of 100 seeds each weretaken for maturity measurement. With proper attention tomixing and sub-sampling, reproducibility within the theoreticalrange was readily achieved. Each seed was examinedindividually at x12 magnification under a dissecting microscope,the caryopsis being exposed for observation wherevernecessary. This will be referred to as the direct method.Two other methods were sometimes used. One was employedwhen seed was needed for germination testing andmust not, therefore, sustain husk damage. It involved detachingthe membranous tissues of the spikelets by rubbing thesub-sample gently with ball of thumb on palm of hand, thenaspirating in a blower of the type used in purity analysis.Using a setting determined by prior trial and error, this neatlyseparated mature and immature seeds with the same degreeof reproducibility as that of the direct method. Its accuracy ofseparation was monitored by observation under magnification.We refer to this as the aspiration method.The third method was used to obtain retrospective estimatesof mature seed contents from old records, and consistedsimply of the establishment of a regression equationrelating mature seed content to 100 seed weight. Values wereobtained for 43 different seed lots of Gatton panic, matureseed content being measured by the direct method and 100seed weights from the means of paired sub-samples (standarderrors averaged ± 2.4% of the mean). The equation y =0.989x + 0.1 was derived (y =mature seeds per 100 spikelets;x = 100 seed weight in mg of intact spikelets dried toabout 10% moisture; r = 0.883). This is referred to as theregression method.Comparisons Between Mature and Immature <strong>Seed</strong>Three sets of records are summarized to illustrate thedifferences in quality between mature and immature seed(Table 1). The following details apply to them:Germination tests. Results reported are average germinationpercentages of mature and immature fractions, separated bythe aspiration method, derived from 89 separate tests conductedon 30 different seed lines of Gatton panic. Each testconsisted of 100 seeds germinated in standard conditions(35/15 C, 8 hour day, 0.2% KN0 3 ). <strong>Seed</strong> was one year old attest, having been stored since harvest at about 10% moistureand ambient temperature (average about 22 C).Field emergence. Records are of seedlings emerging fromsoil as a percentage of seed sown. They are average valuesderived from 18 separate tests on 6 different lines of seed ofboth green and Gatton panic, each test consisting of threereplicates of 200 seeds of either fraction separated by theaspiration method. One year old seed stored as for the germi-Table 1. Comparative quality of mature and immature seed ofGatton panic. Values are averages of many tests, with standarddeviations of means for different seed lines quoted wherelegitimate for untransformed data.MatureImmatureLaboratory germination (%) 69.3 ± 25.0 13.2Field emergence(%) 34.4 ± 5.2 3.8 ± 1.6Viability(%)Storage age (years)0.2 96.7 49.0 ± 17.51.5 88.9 + 8.9 16.2 ± 12.12.2 83.2 ± 13 8.6Estimated mean viabilityperiod (years) 4.3 0.1nation tests was sown into conventional field seedbeds insummer in Atherton, north Queensland.Retention of viability. Records are of percentage viability ofstored seed of green panic measured by tetrazolium aftervarious intervals of storage. Each figure is the average valuefor 29 different lines of seed. Each test on each line used100-300 seeds in various replications. Methods of testingwere similar to those described in an earlier paper (Harty,Hopkinson, English, and Alder, 1983). Mean viability period(Roberts, 1972) was estimated from the linear regression ofprobits of viability on time rather than by formal probitanalysis. Storage age means time spent at ambient temperature(average about 22 C) and 10% moisture. Mature andimmature seeds were separated by the direct method.The results confirm the inferiority of immature seed andillustrate just how poor its quality is. The initial viability islow and subsequent deterioration rapid. Performance at theage and conditions when the seed is most likely to be used isvery weak in both laboratory and field. Though not entirelyworthless, the immature fraction of a seed lot clearly contributesso little to overall performance.Relation Between Mature <strong>Seed</strong> Content and QualityIn view of the differences between mature and immatureseed, it was to be expected that a relationship would existbetween mature seed content and potential quality. Providedother factors affecting quality did not blur the relationship itought to be possible to use mature seed content measured onnewly harvested seed as a guide to future usefulness.The opportunity to check these expectations arose with thecollection for other purposes of green panic seed from sevenseparate commercial harvests in 1981. Mature seed contentwas recorded during initial processing. Details of harvest,handling and drying differed between lots, but storage conditionswere identical. Tests of quality were conducted overthe following three years. The quoted values (Table 2) areaverage viability over four occasions by the tetrazolium test;average germination on three occasions by the routine test;and average soil survival of seed of three ages (the valuequoted is the sum of emerging seedlings and surviving dor-
26 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 2. Correlations between mature seed content and threeindices of quality, obtained with seven lots of commercialgreen panic seed. Each row represents a separate seed lot.Mature seedcontentViability Germination Soilsurvival-------------------------------------(%) --------------------------------------72 74 34 5188 89 59 7355 64 37 46~ ~ ~ ~59 64 30 4461 62 29 43m w ~ ~Correlationcoefficient ( r) 0.943 0.865 0.898mant seeds from pot tests). Each value is the average ofdeterminations made on 600 to 1600 seeds.The results show that correlations were close, and thatmature seed content provided a reasonable indication offuture quality. Of the causes of variation in quality that have aprestorage origin, variation in maturity was clearly an importantone.Records of Mature <strong>Seed</strong> ContentMethods. Mature seed content was determined for mostcommercial and experimental samples of green and Gattonpanic that came to hand from 1971 onwards. The regressionmethod was used for Gatton panic from 1974 and earlier, thedirect method otherwise. Records were kept from 63 crops ofgreen panic and 31 of Gatton panic from central and northernQueensland. These include complete records of all Gattonpanic seed crops grown on an area ofKairi Research Station,north Queensland, under identical management since 1971.They consist of estimates made on seed harvested from eachstanding crop, plus values for fallen seed collected in trapsbelow the canopy of six crops (see Hopkinson and English,1982a for details).Results. The overall average and standard deviation of matureseed content of seed of green panic was 59.9% ± 12.3.For Gatton panic it was 57.5% ± 11.0. The extremes were 31to 90% and 31 to 86% respectively. Few consistent patternscould be detected that allowed mature seed content to beassociated with particular conditions, though sometimes therewere marked differences between years. For example, of thegreen panic crops grown in north Queensland, the 12 recordsfor 1977 averaged 69% ranging from 61 to 82%, while the 8records for 1980 averaged 48% with a range from40 to 52%.Also, very low values were always derived from crops thathad experienced stress, either as a result of drought, excessiverainfall, or low temperature through their being grownout of season.The 27 Gatton panic records from Kairi averaged 59.5% ±12 .4 with a range from 31 to 86%, despite uniform management.The differences can only be attributed to the effects ofvarying seasonal conditions. Mature seed content changedlittle with time over the life of any one crop, except fortending to be low very early in the crop's life. Standarddeviations of successive samplings averaged only 5. 9% forthe 9 crops sampled. Illustrated examples of sequences havealready been published (Hopkinson and English, 1982a).Choice of harvest time is clearly not an important cause ofvariation in mature seed content, except perhaps in cases ofextreme misjudgement.Those records that included mature seed content of shedseed as well as from the standing crop are shown in Table 3.Shed seed always had a higher mature seed content thanstanding crop, but still contained significant and variablepercentages of immature seed. On the occasion when thevalue for shed seed was relatively low, so also was theequivalent figure for standing seed. Obviously some seedundergoes abscission before it has completed its maturation,and the proportion of seed doing so is variable.DISCUSSIONImmature seed is almost worthless, yet constitutes onaverage more than 40% of the pure seed present in green andGatton panic seed samples. If standards of quality are basedon the expectation that high quality seed should all be potentiallyuseful, then immaturity is certainly an important causeof low quality in these grasses.Variation in mature seed content is clearly a major cause ofvariation in quality. This was readily discernible over a rangeof maturities between 54 and 88% (Table 2). Over the recordedrange of 30 to 90%, the differences in potential qualitymust be assumed to be massive.The investigation was not designed to find out why matureseed content varies, but the question inevitably arises, andthe records allow some reasons to be rejected while raisingthe possibility of others. Choice of harvest time, for example,which might seem to be an obvious reason for variation inmaturity, has proved to be unimportant. Seasonal differencesin weather, on the other hand, appear to be a major cause ofvariation. The association of high immature seed contentwith stress and the variable immature seed content of fallenseed suggest that a variable degree of premature sheddingmight be the cause of variation.Table 3. Records of mature seed contents of standing and shedseed of Gatton panic. Values quoted are averages of successivesamplings over the ripening period except for 1976-2when only a single sample was taken at harvest ripeness.Year and crop197319741975-11975-21976-11976-2Standing seedShed seed------------------(%) -----------------66.9 82.255.6 65.663.0 90.675.7 92.362.5 85.870.5 87.0
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 27If a high proportion of seed falls prematurely, the immatureseed content of the standing crop must be high (e.g. 1974crop, Table 3). Variation in the time taken for caryopsis todevelop relative to the time taken for the abscission layer toform would affect the extent of premature shedding. Stressfulconditions are likely to slow down caryopsis development,and if they did so without equally delaying abscission,premature shedding would occur, and lead to high proportionsof immature seed in the standing crop ...Similarly, it is likely that conditions that favor retentionwill lead to high mature seed contents. It is often observedthat in calm conditions seed remains loosely attached to theculm despite having a well-developed abscission layer. Suchconditions have a reputation for producing good seed andprolonged retention probably raises the proportion of matureseed present. Both possibilities warrant experimental attention.Although this account has been restricted to two cultivarsof Panicum maximum, we have observed similar degrees ofimmaturity in other tropical pasture grass seeds, and believethat our conclusions apply in a general sense to any speciesthat share similar habits of spikelet tum-over. We find themeasurement of mature seed content widely useful, particularlywhere explanations of variation in quality or earlywarnings of low quality are needed.ACKNOWLEDGEMENTSThe financial support of the Australian Meat ResearchCommittee and the cooperation of colleagues in StandardsBranch of Q.D.P.I. are gratefully acknowledged.REFERENCES1. Anonymous. 1985. <strong>International</strong> rules for seed testing.<strong>International</strong> <strong>Seed</strong> Testing Association. Rules 1985. Annexesto chapter 3. <strong>Seed</strong> Sci. and Technol. 13:395-420.2. Austin, R.B. 1972. Effects of environment before harvestingon viability. pp. 114-149. In E. H. Roberts (ed.) Viability of<strong>Seed</strong>s. Chapman and Hall, London.3. Barnard, C. 1972. Register of Australian <strong>Herbage</strong> Plant Cultivars.Technical Papers Division of Plant Industry, CSIRO.Australia.4. Harty, R.L., J.M. Hopkinson, B .H. English, and J. Alder.1983. Germination, dormancy and longevity in stored seedofPanicum maximum. <strong>Seed</strong> Sci. and Technol. 11:341-351.5. Hill, M.J. 1980. Temperate pasture grass-seed crops: formativefactors. pp. 137-149. In P.D. Hebblethwaite (ed.)<strong>Seed</strong> Production. Butterworths, London.6. Hopkinson, J.M., and B.H. English. 1982a. Spikelet populationdynamics in seed crops of Panicum maximum'Gatton'. <strong>Seed</strong> Sci. and Technol. 10:379-403.7. Hopkinson, J.M., and B.H. English. 1982b. Harvest efficiencyin seed crops of Gatton panic (Panicum maximum) and signalgrass (Brachiaria decumbens). Tropical Grasslands, 16:201-205.8. Roberts, E.H. 1972. Storage environment and the control ofviability. pp. 14-58. In E.H. Roberts (ed.) Viability of <strong>Seed</strong>s.Chapman and Hall, London.
<strong>Seed</strong> Dormancy and Germination of Switchgrass from Different Row Spacingsand Nitrogen Levels1R.E. Mullen, P.C. Kassel, T.B. Bailey, and A.D. Knapp2ABSTRACTVarious levels of seed dormancy in switchgrass (Panicumvirgatum L.) influence germination results. However, mostgermination data in switchgrass seed production managementstudies have not considered seed dormancy. The purpose of thisstudy was to determine whether seed dormancy varies withmanagement practices. <strong>Seed</strong> dormancy and germination responseof three switchgrass cultivars to different row spacingand nitrogen (N) treatments on 2- and 3-year-old stands wereexamined. Field experiments were conducted in 1979 and 1980on a predominantly Webster loam (Typic Haplaquoll) soil nearAmes, Iowa. Blackwell, Cave-in-Rock, and Pathfinder cultivarswere seeded in a clean-tilled seedbed on 18 May 1978 at arate of 230 seeds mt of row in 20-, 60-, and 100-cm rows andfertilized with 0, 90, and 180 kg ha-t ofN. Prechill germination(PG), short-term dormancy (STD), long-term dormancy (LTD),and viable seed did not appreciably differ among cultivars atdifferent row spacings. Prechill germination and STD valuesincreased with additions of N fertilizer to 180 kg ha-t forCave-in-Rock, but N fertilizer decreased these values forBlackwell and Pathfinder. <strong>Seed</strong> dormancy and germinationamong cultivars significantly varied between years. Prechillgermination values averaged 37, 48, and 44% in 1979 and 16,40, and 38% in 1980 for Cave-in-Rock, Blackwell, and Pathfinder,respectively. Short-term dormancy among cultivars wasgreatest for Cave-in-Rock in 1979 but least in 1980. Long-termdormancy was greater for all cultivars in 1980 than in 1979 andinfluenced pure live-seed yields. Results indicated that for 2-and 3-year-old stands of cultivated switchgrass, germinationand seed dormancy can vary among cultivars, years, andN-levels. The 2-week prechilling treatment commonly used instandard switchgrass germination procedures may not uniformlybreak seed dormancy for different cultivars.Additional index words: native grasses Panicum vergatum L.,prechill germination, pure live-seed yield, seed quality, tetrazoliumtest, viable seed, warm germination test, warm-seasongrasses.IJoumal Paper No. J-11996 of the Iowa Agric. and Home Econ.Exp. Stn., Ames, IA 50011. Project 2470. Received for publication30 September 1985.2Associate professor, Dept. of Agronomy; extension crop productionspecialist, Spencer, IA (formerly graduate research assistant);professor, Dept. of Statistics, and associate professor, Dept. ofPlant Pathology, <strong>Seed</strong> and Weed Sciences, Iowa State Univ.,Ames, IA 500 II, respectively.INTRODUCTION<strong>Seed</strong> dormancy frequently has been observed in switchgrass(Panicum virgatum L.) and other warm-season grasses(Blake, 1935; Robockeret al., 1953; Sautter, 1962; Shaidaeeet al., 1969). The degree and length of dormancy and treatmentsnecessary to overcome seed dormancy in native grassesvary with species and locations of production. Variable seeddormancy and the resultant variable germination have complicatedresults of seed-quality experiments in switchgrass.Switchgrass germination has been improved by exposingseeds to freezing (Blake, 1935) or to a chilling temperature of10 C (Sautter, 1962; Norris and Decker, 1943). Norris andDecker (1943) suggested that switchgrass germinates best at17/30 C, or 20/30 C for 16/8 h cycles. <strong>Seed</strong>lings can becounted at 7, 14, 21 , and if needed, 28 days after planting.New seed should be prechilled for 2 weeks at 10 C. Thisgermination procedure was similar to the procedure of theAssociation of Official <strong>Seed</strong> Analysts (A.O.S.A.) (Anon.,1978). Combine-harvested and recleaned switchgrass, cv.Pathfinder, seed germinated 84 and 94%, respectively, whena30-dayprechill period at5 C was used (T.N. Shiflet, 1970).Unpublished studies of germination and seedling growth ofswitchgrass. Dept. of Agronomy, Univ. of Nebraska, LincolnNE). Germination values were 30 and 35% less, respectively,when prechilling was not used. Shiflet concluded thatprechilling increased the germination percentage of switchgrassseed that was less than 1 year old and increased thegermination rate of switchgrass seed stored over 1 year.Improved germination has been observed for native grassseed stored after harvest. Robocker et al. ( 1953) reported thatgermination percentages were greatest 2 years after seedharvest for big bluestem (Andropogon gerardi Vitman) andswitchgrass and 1 year after seed harvest for indiangrass(Sorghastrum nutans (L.) Nash). Hoover et al. (1947) andWheeler and Hill (1957) reported that switchgrass had 30%germination the year after seed harvest and that germinationpercentage may double if seeds are stored more than 1 year.Shaidaee et al. (1969) found that 'Grenville' switchgrassseed, 7 years after harvest, had greater field emergence thanyounger seed. It seems that seed of switchgrass in dry storagefor several years may exhibit less dormancy and may becapable of producing better stands in the field.Cultural practices and other factors have influenced seedquality of switchgrass and other native grasses. Smika andNewell (1968) found that side-oats grama (Bouteloua curtipendulaMichx.) produced heavier caryopsis weight whengrown in 101-cm rows than in solid stands. Kneebone and28
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 29Cremer (1955) studied the relationship of seed size to seedlingvigor in several native grasses, including buffalograss(Buchloe dactyloides Nutt.), indiangrass, side-oats grama,and switch grass. Switchgrass showed pronounced differencesin germination percentages in response to seed size, but otherspecies showed no response. 'Blackwell' switchgrass seedsized on 1.27-, 1.15-, and 1.06-mm screens emerged 82, 64,and 31% respectively, in sphagnum moss. Smaller switchgrassseed also required 7 days longer to germinate thanlarger seed.The effect of nitrogen management on seed quality varieswith species of native grasses. Austenson and Peabody (1964)found no differences in seed germination tests or purity testsamong row spacing or N level treatments in several coolseasonspecies grown for seed. Cosper et al. (1967) thatgermination of western wheatgrass (Agropyron smithii Rydb.)slightly increased as N level increased up to 88 kg ha-l,although the trend was not statistically significant. Smikaand Newell (1966) found that seed weight of western wheatgrasswas not influenced by N level but that seed weight wasincreased by irrigation at growth initiation and heading stagesof growth. Smika and Newell (1965) also showed that seedweight of side-oats grama was increased by N applications upto 88 kg ha-l.It is evident from the literature that seed dormancy associatedwith native grasses can influence germination responseand complicate interpretations of treatment effects on seedquality. Primary emphasis of experiments measuring effectsof cultural management on seed quality of switchgrass havecentered on germination without regard to seed dormancy.Row spacing and nitrogen fertilization are important managementconsiderations for seed production of switchgrass,but little or no information is available on row-spacing ornitrogen-level effects on switchgrass seed dormancy andsubsequent germination capability. This study was conductedto compare seed dormancy and germination response of threeswitchgrass cultivars to three N levels and three row spacingson 2-, and 3-year-old stands.MATERIALS AND METHODSField experiments were conducted in 1979 and 1980 on apredominately Webster Loam (Typic Haplaquoll) soil at theAgronomy and Agricultural Engineering Research Centerlocated near Ames, Iowa. The study site contained someNicollet loam (Aquic Hapludoll) soil and was blocked accordinglyin experimental layout. Blackwell (B), Cave-inRock (C), and Pathfinder (P) cultivars of switchgrass wereused in the experiment. Cave-in-Rock switchgrass is a bottomlandecotype and was developed by the Soil ConservationService in Elsberry, Missouri. Selections were initially fromsouthern Illinois. Cave-in-Rock was the tallest cultivar studied,having coarse stems and leaves. Pathfinder switchgrass, asynthetic cultivar and upland ecotype, was developed inNebraska. It has fine leaves and stems. Blackwell switchgrassis an upland ecotype and was collected in northernOklahoma on fine-textured soils. It was further developed inKansas and has vegetative characteristics similar to those ofPathfinder.Cultivars were seeded in a clean-tilled seedbed on 18 May1978 at a rate of230 seeds m-1 of row in 20-, 60-, and 100-cmrows, which corresponds to seedling rates of 13.5, 4.5, and2.7 kg ha-l, respectively. Four-row plots were used in the20-cm row seedings, and 3-row plots were used in the 60-and 100-cm row seedings. Each plot was 3.7 min length.After seeding, the soil was firmed with a roller packer, andno fertilizer was applied. Atrazine (2 chloro-4-ethylamino-6-isopropyl amino-1, 3-5-triazine) was applied to plots at a rateof 3.36 kg ha-l active ingredient was a preemergence treatmentin 1978 and as a postemergence treatment during springgrowth initiation in subsequent years. Hand hoeing was usedeach year as an additional weed control measure and tomaintain row-spacing treatments. Plots were fertilized withurea in May 1979 and 1980 at rates ofO, 90, and 180 kg ha-lofN.The experimental design consisted of three whole plotsreplicated three times. Row spacing treatments were randomlyassigned to each of the whole plots. Nitrogen treatmentswere applied in random strips across each whole plot,and cultivars were assigned in random strips perpendicular toN treatments for each whole plot.<strong>Seed</strong>s were hand-harvested during 22 to 29 September1979 and 20 to 27 September 1980. Cave-in-Rock maturedapproximately 1 week later than Blackwell and Pathfindercultivars. Harvest was initiated when seed from the top of thepanicle had begun to shatter and the seed from lower paniclebranches was hard and brown. <strong>Seed</strong> was harvested from a 3.2m length of one row in the center of each plot. Harvestedinflorescences were dried in a 38 Cheated-air oven for 7 daysand stored at 10 C until threshed. Inflorescences were threshedwith a hammer mill at 850 rpm with a 4.8-mm screen. <strong>Seed</strong>was cleaned with a Clipper bench-type seed cleaner with aNo. 8 (3 .0 mm) screen for preliminary cleaning and a No. 6(2.3 mm) screen for additional cleaning. A 1-mm screen wasused as a lower screen in all cleanings. Unthreshed seedswere separated from remaining trash with a 1. 8-mm screen,hand threshed, cleaned, and returned to the sample. <strong>Seed</strong>subsamples were threshed by hand rubbing to remove glumes,sifted in a 1.8-mm screen, and cleaned in an air-columnseparator.Standard germination tests, with prechill (PG) and without(WG) prechill, were conducted on units of 100 seeds(A.O.S.A. Anon., 1978). <strong>Seed</strong>s were planted on blotterpaper moistened with 0.2% KN0 3• <strong>Seed</strong>s were prechilled at5 C for 2 weeks. The germination test was conducted ingrowth chambers set at 15/30 C temperatures for 16/8 hcycles for 28 days with light during the warm cycle, accordingto A.O.S.A. (Anon., 1978) specifications. Germinationwas counted at 7, 14, 21, and 28 days after planting. <strong>Seed</strong>germination was defined according to A.O.S.A. (Anon.,1978). Ungerminated firm seeds from the prechill test werecut in half and stained with 0.1% tetrazolium to determineviability. <strong>Seed</strong> viability (V) was expressed by the equation,V = c + t, in which c = germinated seeds (prechill test) per100 seeds, and t = ungerminated firm seeds per 1 00 seedsthat were alive based on the tetrazolium test. <strong>Seed</strong> dormancywas divided into short-term (STD) and long-term (LTD)dormancy in which STD = prechill test % - warm test % and
30 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 1. Mean squares for seed quality measurements.Prechill Short-term Long-term Total seedDegree of germination dormancy dormancy viabilitySource Freedom 1979 1980 1979 1980 1979 1980 1979 1980Replication 2 286 759 28 534 20 282 286 116Row Spacing (S) 2 236 39 100 13 16 12 118 47Error A 4 113 147 95 128 7 90 147 84Cultivar (V) 2 896** 4788** 714** 3714** 1353** 9607** 217* 895*CvsPBt (1) 1513* 9491* 1300* 7428* 2705* 18517* 172* 1494*PvsB (1) 280* 86 128 0 0 697* 262* 294*V X S 4 63 75 82 75 14 39 37 68CvsPB x S-linear (1) 78 3 49* 118* 3 84Error B 12 43 79 69 83 8 37 43 58Nitrogen (N) 2 137 136 49 66 15 156 241Nx S 4 30 41 144 78 2 42 23 20Error C 12 125 152 50 118 24 67 92 69VxN 4 132* 123 139** 89 7 80 102 62CvsPB x N-Linear (1) 184* 352* 247* 290* 2 30 149 176VxNxS 8 42 14 56 33 7 55 19 56Error D 24 46 48 25 54 12 46 45 66*, **Significant at .05 and .Ollevels, respectively.t C, P, and B represent Cave-in-Rock, Pathfinder and Blackwell cultivars, respectively.LTD = V - prechill test %. Pure live-seed yields werecalculated by multiplying the percentage germination (prechilltest) by the amount of pure seed harvest per plot.The effects of cultivars, row spacing and nitrogen, andtheir interactions were tested by using analysis of variance(ANOVA) F-tests. Treatment and interaction effects weretested at P s 0. 05 except where noted. Whenever cultivar byrow spacing, or cultivar by nitrogen, interaction effects weresignificant, they were interpreted by partitioning the degreesof freedom and sums of squares into meaningful comparisons.RESULTS AND DISCUSSIONPrechill germination (PG), short-term dormancy (STD)and viable seed (V) means did not differ among cultivars atTable 2. Long-term seed dormancy of switchgrass cultivarsgrown in three row spacings.Row spacing (em)CultivarCave-in-RockBlackwellPathfinderYear19791980197919801979198020 60100------------------------------ (%) -------11.2 14.7 14.954.4 52.1 51.41.6 1.4 0.816.0 17.4 17.61.0 2.2 1.022.1 23.3 27.1Table 3. Prechill test and short-term seed dormancy values for switchgrass cultivars fertilized at three N levels.Cu1tivarTest N-leve1 Cave-in-Rock Blackwell Pathfinder1979 1980 1979 1980 1979 1980(kg ha -I) --------------------------------------------------------------------------------- (%) --------------------------------------------------------0 35.3 14.5 53.1 44.5 48.7 43.4Pre chill 90 38.9 16.2 43.6 37.1 42.7 37.0test 180 36.8 18.1 48.7 39.8 40.3 33.50 26.3 12.8 23.0 38.3 26.4 39.5Short-term 90 31.8 15.0 15.8 33.0 22.3 33.9dormancy 180 30.1 16.9 19.3 34.3 18.6 32.1
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 31different row spacings in either year of the experiment.Long-term dormancy (LTD) varied among cultivars at differentrow spacings (Table 1). The orthogonal contrast ofCave-in-Rock versus Blackwell and Pathfinder at differentrow spacings was significant for 1979 and 1980, but themaximum range of differences in LTD was within 5 percentagepoints and was not considered to be of practical significance(Table 2). The results show that row spacing treatmentsin this study had little or no influence on seed germinationand dormancy of switchgrass.Cultivar values for PG and STD were influenced by Nlevel (Table 1). Prechill test and STD values for Cave-inRock increased with added N, but these values decreased forBlackwell and Pathfinder with additions of N fertilizer (Table3). Cave-in-Rock was lodging resistant, but Blackwell andPathfinder lodged throughout the study regardless of rowspacing or N level. Possibly, N additions accentuated lodgingeffects for Blackwell and Pathfinder, resulting in poorseed fill and decreases in seed quality; however, this seemsunlikely because cultivar values for 100-seed-weight werenot influenced by N level (Kassel et al., 1985).A significant year X variety interaction was obtained in acombined-year ANOV A (data not shown). The greatest variationobtained in means of seed quality measurements in bothyears was due to cultivars, and most of the variation wasaccounted for in the orthogonal comparison of Cave-in-Rockversus Blackwell and Pathfinder (Table 1). Prechill germinationvalues averaged 37, 48, and 44% in 1979 and 16, 40,and 38% in 1980 for Cave-in-Rock, Blackwell and Pathfinder,respectively (Fig. 1). Blackwell differed from Pathfinder inPG in 1979 but not in 1980 (Table 1).Germination values were appreciably less than those reportedin the literature and those advertised for switchgrass inindustry. Environmental factors, cultivar, age of seed, ordifferent germination testing procedures may have contributedto the higher germination values reported elsewhere for switchgrass.The majority of switchgrass seed is produced in statesreceiving less rainfall than Iowa. Possibly, less rainfall andhumidity increases subsequent germination values of switchgrass.Sautter (1962) reported 84% germination for scarifiedseeds of switchgrass and Shaidaee et al. ( 1969) reported 90%germination of Greenville switchgrass in 2 out of 3 yearsusing alternating temperatures of 30 C for 16 h and 20 C for 8h. Low prechill test germination values may also be related toseed size of switchgrass. Kneebone and Cremer (1955) observedslower emergence and reduced germination percentageswith smaller seed. Possibly, decreased seed weights ofswitchgrass seed in this experiment contributed to reducedPG values. <strong>Seed</strong> weights in this experiment ranged from 110to 130 mg for 100 seeds. Expected 100-seed-weights ofswitchgrass range from 120 mg per 100 seeds (Atkins andSmith, 1967) to 180 mg per 100 seeds (A.O.S.A., Anon.,1978). <strong>Seed</strong> weights of switchgrass may have been below thecritical level necessary for high germination in this experiment.The large difference in PG values observed between Cavein-Rockand the other two cultivars support conclusions byShaidaee et al. (1969) that differences in germination abilityexist among cultivars. Cultivar differences in PG were relatedto seed dormancy. Although PG values in both yearswere lowest for Cave-in-Rock, this cultivar had the highestpercentage of viable seed (Fig.1). These results indicate thatthe greatest amount of seed dormancy was associated withCave-in-Rock. Cave-in-Rock is a lowland ecotype, andBlackwell and Pathfinder are upland ecotypes. Possibly,seed dormancy was associated with differences in growthcharacteristics or adaptation between lowland and uplandecotypes.Short-term dormancy in our study was the total amount ofseed dormancy that was broken with a 2-week prechillingtreatment conducted in accordance with A.O.S.A. (Anon.,1978) standards. Long-term dormancy was the remainingviable, but nongerminated seeds after the conclusion of theprechill germination test. In 1979, STD accounted for 86%of the total seed dormancy of Cave-in-Rock and was significantlygreater than the STD for Blackwell and Pathfinder.For Cave-in-Rock in 1980, however, STD accounted foronly 25% of the total seed dormancy and was significantlylower that STD for Blackwell and Pathfinder. Long-termdormancy was greater for all cultivars in 1980 than in 1979Table 4. Prechill test germination values and calculated pure live seed yields of three switchgrass cultivars for different testing dates.Dateof harvestCultivarPure seedyieldGerminationPLS yieldb/GerminationPLS yield22-29 Sept.1979Cave-in-RockBlackwellPathfinder(kg ha-l)1002289287Tested: 4-l-SOa/(%) (kg ha-l)37 37148 13944 126Tested: 5-1-81(%) (kg ha-l)75 75258 16867 19220-27 Sept.1980Cave-in-RockBlackwellPathfinder813349491Tested: 2-1-81(%) (kg ha-l)16 13040 14038 187Tested: 5-1-81(%) (kg ha-l)31 25260 20956 275a/ Germination was tested in accordance with Association of official <strong>Seed</strong> Analysts ( 1978) standards.b/ PLS = Pure live seedPLS yield = (kg of pure seed harvested) x (% prechill test germination + 100)
32 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985-+-'(/)Q)-+-'0-+-'OJ)c::::·- -cc::::0Cl.(/)Q).._-cQ)Q)(/)-0Q)OJ)ro-+-'c::::Q)u .._Q)c...7060C = Cave-in-RockB = BlackwellP = Pathfinderlliilli] Warm testbSSJ Prechill test~ Short-term~dormancyD dormancyLong-term<strong>Seed</strong> viability =uppermostboundaryof column...--..~-_..-o~~~~~--~~~~-1979 1980Harvest date (year)Figure 1. <strong>Seed</strong> quality of three switchgrass cultivars harvestedin 1979 and 1980 and tested in April, 1980 and in February,1981. Values are averaged over row spacings and nitrogenlevels.(Table 1 and Figure 1). Results indicate that STD and LTDfor switchgrass can vary among cultivars and years. It alsoappears that the 2- week prechilling treatment recommendedfor switchgrass germination by A. 0. S .A. may not uniformlybreak seed dormancy of seed from different cultivars. Rulesby the A.O.S.A. acknowledge that dormant seeds may remainat the end of the germination test for switchgrass.The increased amounts of LTD obtained in all cultivars in1980, compared with 1979, may be related to seed storagetime. <strong>Seed</strong> harvested in 1980 was in dry storage approximately8 weeks less than seed harvested in 1979 beforeinitial germination testing. Germination tests conducted on 1May 1981 resulted in increased PG values for all cultivars,cwith increases ranging from 20 to 100% (Table 4). Theimproved PG observed for older seed would lower LTD andsuggests that a period of storage is needed for maximumgermination. Blake (1935), Robocker et al. (1953), and 1Coukos ( 1944) have also shown increased germination valuesof switchgrass with increased time in dry storage. The failureof the 2-week prechilling treatment to adequately breakswitchgrass seed dormancy in this study indicates that purelive seed (PLS) yields of freshly harvested seed would increasewith additional storage time. PLS yields obtained in1979 increased for all cultivars and more than doubled forCave-in-Rock when PLS yield was calculated from the highergermination values obtained from the later testing date(Table 4). Frequently, switchgrass seed is marked on a PLSbasis, and the reduced dormancy and resulting improvementin germination with additional storage time observed in thisstudy would be of obvious importance to firms or buying andselling seed. The greater initial seed dormancy and greaterrate of improvement in germination with additional storagetime for Cave-in-Rock compared with Blackwell or Pathfinder(Table 4) also indicates that time between harvest andmaximum germination of seed in storage will vary amongcultivars.In our study, seed viability was determined by tetrazoliumstaining of ungerminated seeds remaining from the PG test.Viability of switchgrass seed harvested in 1979 and measuredon 1 April 1980 was 51% or less for all cultivars (Fig. 1), butwhen PG tests were conducted on the same seedlots on 1 May1981, PG values ranged from 58% for Blackwell to 75% forCave-in-Rock (Table 4). The method of determining viabilityin our study underestimated the germination of seeds aftera storage period. Recent rule changes for germination procedures(Anon., 1985) require that the viabiity of ungerminatedseed remaining at the end of the germination test beevaluated. For switchgrass, a tetrazolium test on "fresh"seed before germination may be a better indication of potentialviability than a tetrazolium test on the ungerminated seedremaining after the germination test. Additional work wouldbe necessary to identify the best method of tetrazolium testingfor determining viability of switchgrass seedlots.Results of this study indicated that row spacing was not animportant factor influencing germination and seed dormancy.Nitrogen fertilizer did influence germination and STD, butthe N response varied among cultivars. Nitrogen fertilizerimproved germination and decreased dormancy of recentlyharvested seed of the lowland ecotype, Cave-in-Rock, butnot of the upland ecotypes, Blackwell and Pathfinder. Rowspacing and nitrogen treatments in this study were imposedon 2- and 3-year-old cultivated stands, and results may differfor older or noncultivated stands of switchgrass. Long-termseed dormancy was greatest for Cave-in-Rock in both years,and subsequent improvement in germination of Cave-in-Rockduring storage was greater than for Blackwell and Pathfinder.The amount of short-term dormancy and the effectiveness ofa 2-week prechilling treatment in breaking seed dormancywill vary with cultivars and years. Tetrazolium staining ofungerminated seeds remaining after the conclusion of theprechill germination test may underestimate germination potentialof switchgrass seeds after a period of storage.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 33REFERENCES1. Anonymous. 1978. Rules for testing seeds. Association ofOfficial <strong>Seed</strong> Analysts. J. <strong>Seed</strong> Techno!. 3(3):29-118.2. Anonymous. 1985. Association of Official <strong>Seed</strong> Analysts.Newsletter. 59(3):43-50.3. Atkins, M.D., and J.E. Smith, Jr. 1967. Grass seed productionand harvest in the Grain Plains. U.S. Dept. Agric. FarmersBull. 2226.4. Austenson, H.M., and D.V. Peabody, Jr. 1964. Effects of rowspacing and time of fertilization on grass seed production.Agron. J. 56:461-463.5. Blake, A.B. 1935. Variability and germination of seeds andearly life history of prairie plants. Ecol. Monogr. 5:405-460.6. Cosper, H.R., J.R. Thomas, and A.Y. Alsayeh. 1967. Fertilizationand its effect on range improvement in the NorthernGreat Plains. J. Range Mange. 20:216-222.7. Coukos, C.J. 1944. <strong>Seed</strong> dormancy and germination in somenative grasses. J. Am. Soc. Agron. 36:337-345.8. Hoover, M.M., J.E. Smith, A.L. Ferber, andD.R. Cornelius.1947. <strong>Seed</strong> for regrassing Great Plains areas. U.S. Dept. Agric.Farmers Bull. 1985.9. Kassel, P.C., R.E. Mullen, and T.B. Bailey. 1985. <strong>Seed</strong> yieldresponse of three switchgrass cultivars for different managementpractices. Agron. J. 77:214-218.10. Kneebone, W.R., and C.L. Cremer. 1955. The relationship ofseed size to seedling vigor in some native grass species. Agron.J. 47:472-477.11. Norris, E.L., and A. Decker. 1943. Report of the committee onrange grass studies. Proc. Assoc. Off. <strong>Seed</strong> Anal. 35:63-67.12. Robocker, W.C., J.T. Curtis, andH.L. Ahlgren. 1953. Somefactors affecting emergence and establishment of native grassseedlings in Wisconsin. Ecology 34:194-199.13. Sautter, E.H. 1962. Germination of switchgrass. J. RangeMange. 15:108-110.14. Shaidaee, G., B.E. Dahl, and R.M. Hansen. 1969. Germinationand emergence of different age seed of six grasses. J.Range Mange. 22:240-243.15. Smika, D.E., and L.C. Newell. 1965. Irrigation and fertilizationpractices for seed production from established stands ofside-oats grama. Nebr. Agric. Exp. Stn. Res. Bull. 218.16. Smika, D.E., and L.C. Newell. 1966. Cultural practices forseed production from established stands of western wheatgrass.Nebr. Exp. Stn. Res. Bull. 223.17. Smika, D.E., and L.C. Newell. 1968. <strong>Seed</strong> yield and caryopsisweight of side-oats grama as influenced by cultural practices.J. Range Mange. 21:402-404.18. Wheeler, W.A., and D.D. Hill. 1957. Great Plains Grasses.pp. 591-592. In Grassland seeds. D. Van Nostrands Co., Inc.,New York.Effect of Pesticide Residues in Alfalfa Pollen and Nectar on the Foragingand Reproduction Activities of Alfalfa Leafcutting Bees Megachile rotundatalC.M. Rincker and D.A. GeorgezABSTRACTForaging and reproduction activities of alfalfa leafcutting bees(Megachile rotundata F.) were not affected when alfalfa wastreated with various insecticides. Treatments consisted of recommendedand 1.5 times recommended rates of demeton, oxydemeton-methyl,aldicarb, trichlorfon, dimethoate and carbofuranapplied to alfalfa grown for seed in 1980 and 1981. Exposureof the bee larvae to insecticide residues in the pollennectarball within the reproductive cell did not adversely affectpercent live larvae nor emergence and flight of bees in thesucceeding year.Additional index words: Medicago sativa, seed production, pollinators,insecticides.!Contribution of Agricultural Research Service, USDA. Received19 Sept. 1985.2Research Agronomist, Agricultural Research Service, USDA,lrrig. Agric. Res. & Ext. Center, Prosser, WA 99350, andResearch Chemist, Agricultural Research Service, USDA, YakimaAgric. Res. Lab., Yakima, WA 98902.INTRODUCTIONAlfalfa leafcutting bees (Megachile rotundata F.) are oneof the most important pollinators of alfalfa grown for seed inthe Pacific Northwest (McGregor, 1976). <strong>Seed</strong> growers,therefore, must use considerable care to protect these beesfrom toxic insecticides applied to seed fields for control ofinsects detrimental to seed production. Use of insecticides iseven more of concern to seed growers since leafcutting beesare more susceptible to most insecticides than either honeybees (Apis mellifera L.) or alkali bees (Nomia melanderi Ckll)(Johansen 1983; Capizzi et al., 1982).George and Rincker (1982) reported residues of demeton(Systox ®), trichlorfon (Dylox®), dimethoate (Cygon®), carbofuran(Furadan®), and/or their respective metabolites werefound in the pollen-nectar ball collected by leafcutting bees.Waller (1969) studied the susceptibility of alfalfa leafcuttingbees to various insecticides. He found azinphosmethyl(Guthion®) most toxic and carbaryl (Sevin®) least toxic.More recently we found residues of oxydemeton-methyl(Metasystox-R®) and it's metabolite in pollen-nectar balls.Leafcutting bees collect pollen and nectar from flowering
34 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985alfalfa and store it as a pollen-nectar ball in the reproductivecells they construct in nesting boards. The female bee lays anegg on the pollen-nectar ball before sealing the cell. Afteregg hatch, the bee larva consumes the pollen-nectar ball asfood. This study was initiated to determine if residues ofcommercially used insecticides applied to alfalfa grown forseed were present in the pollen and nectar collected by thebees, and if so, whether the levels were high enough to betoxic to the bee larvae.MATERIALS AND METHODS'Arc' alfalfa was planted August 17, 1977, to supplyindividual plots, 3.6 X 6.0 min size. Each plot consisted offour rows, 90 em apart and was managed for alfalfa seedproduction in 1978,1979, 1980and 1981. Aportionoftheseplots was utilized in 1978 and 1979 for pilot studies. In 1980,the study was expanded to include additional insecticidescurrently used by growers in seed production. A summary ofresidue data (George and Rincker, 1982) showing residuesfound in the pollen-nectar ball from the cell, and leaffrom thecell is presented in Table 3. In 1980 and 1981, commerciallyused insecticides were applied to individual plots of alfalfa atrecommended rates (kg a.i. ha-t) as follows: demeton, 0.28;dimethoate, 1.68; trichlorfon, 1.68; carbofuran, 1.12; and at1. 5 times these rates. Aldie arb (Temik®), a pesticide presentlyunregistered for commercial use on alfalfa, in the PacificNorthwest, was also used in the pilot study in 1978 and 1979at 3.36 and 5.04 kg a.i. ha-t. It was not applied in 1980 or1981 but continued observations were made to determine ifresidues carried over from year to year. Aldie arb was appliedto a new plot at the lower rate in 1980 only. Oxydemetonmethyl(0.56 and 0.84 kg a.i. ha-t) was applied in 1981instead of demeton. Aldicarb was applied as a granularsidedressing in mid-May. All other insecticides were appliedas foliar sprays. Carbofuran and dimethoate were appliedonce about mid-May, but the others were applied threetimes during bloom stage near June 3, June 24 and July 8,each year.The first spring-growth of alfalfa was clipped and removedthe last week of April each year. Before the alfalfa regrowthbegan flowering, about June 1 each year, each plot wascovered with a Saran screen cage of 18 X 14 mesh (6 X 6 X1.8 m in height) to prevent the bees from becoming contaminatedwith unknown insecticides from outside their testarea.Laminated wooden bee nesting boards were provided ininsulated shelters inside each cage. A fresh supply of loosecells from wild-trapped leafcutting bees were used in 1980.The loose cells were incubated in a laboratory incubator set at30 C and 60% R.H. Freshly emerged bees were counted,sanitized (quick dip in a 0.5% solution of sodium hypochlorite)to control chalkbrood (Ascosphaera aggregata),and released into each cage after the alfalfa began flower-ing.The bees were introduced into each cage in groups of 10 to 15over a period of about one month. Total bees/cage were 104in 1980 and 140 in 1981. Bee cells recovered from eachtreatment in 1980 were identified and retained for use in plotswith the same treatments in 1981 to determine if there wasany adverse accumulative treatment effect the following year.Bees from the 1980 demeton treatments were used with theoxydemeton-methyl treatments in 1981.Pollination activities of the bees were observed at leasttwice a week to determine if bee numbers were declining orpollination was not being achieved due to loss of bee vigor.Sampling procedures and results of residue analyses onTable 1. Number and status ofleafcutting bee cells recovered from alfalfa seed plots treated in 1980 and 1981 with variousinsecticides.Rate Total No. of Cells %of Total CellsConstructed With CocoonsInsecticide (kg a.i. ha-l) 1980 1981 19801981%of Cocoons With %of Total CellsLive Larvae With Pollen Balls1980 1981 1980 1981Control 680 602 74Demeton 0.28 870 82Demeton 0.42 816 70Aldicarb 3.36 609 78Trichlorfon 1.8 368 790 58Trichlorfon 2.52 848 567 73Dimethoate 0.56 653 471 79Dimethoate 0.84 558 421 77Carbofuran 1.12 452 654 81Carbofuran 1.68 366 492 80A1dicarb(NT) 1 566 384 64A1dicarb(NT)2 585 75Oxydemeton-methyl 0.56 565Oxydemeton-methyl 0.84 801!Treated in 1978 and 1979 @ 3.36 kg of a.i. ha-l, but not in 1980 and 1981.ZTreated in 1978 and 1979 @ 5.04 kg of a.i. ha-l, but not in 1980 and 1981.38T2- 129 128 723 693 - 09 08 065558524461465770696789 93 12 3093 890 1596 1187 90 19 32100 92 12 3984 90 9 4690 88 11 3090 95 9 4190 97 10 3693 97 15 2593 1195 2497 25
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 35Table 2. Residues of oxydemeton-methyl +metabolite (determined as the sulfone) in alfalfa leaves, pollen, nectar, pollen-nectar (p-n)ball, and leaf from bee cells from alfalfa treated with oxydemeton-methyl in 1981.TreatmentSampling intervalResidue found (ppm)Nectar21.81(kg a.i. ha-t) (days) LeafPollenp-n ballLeaf-cell0.50 2nd spray 0.5 28.901.5 20.003.0 10.1014.0 2.653rd spray 4.0 9.051.34ND2___ J2.50 0.910.601.861.890.557.550.75 2nd spray 0.5 51.801.5 43.283.0 42.0014.0 0.103rd spray 4.0 36.001.881.4720.411.56 2.070.341.552.180.702.48tNo sample taken.2Below the lower limit of sensitivity of the method: 0.10 ng of sulfone.alfalfa leaf, pollen, nectar, pollen-nectar balls from the beecell, and leaf from the bee cell for 1980 are previously reported(George and Rincker, 1982). Over 430 residue samples werecollected and analyzed in 1980 and 1981.After pollination was completed, the alfalfa seed matured,and the bees had ceased activities, all bee nesting boards wereidentified by plot, removed from the cages and stored at 5 C.During the winter months the cells were carefully removedfrom the bee boards of each pesticide treatment and counted.Cells with pollen balls only collapsed easily, whereas goodcells contained cocoons spun by the fourth-instar larvae anddid not collapse when gently squeezed. The percentage of cellswith pollen balls only was determined. One hundred cellscontaining cocoons from each treatment were excised andexamined to determine percentage with live larvae. Thosecells either incomplete or parasitized were not used in calculatingpercentages of living larvae.Due to the nature of the research, availability of screenedcages, and the large number of residue samples removed fromeach plot for analysis, it was not feasible to replicate eachyear's study; thus eliminating a statistical analysis of the datacollected.RESULTS AND DISCUSSIONDemetonThe effect of previously reported demeton residues (Table3) upon leafcutting bee activities appear to be nil (Table 1).More bee cells were constructed in the demeton treated plotsthan the control plots, or most other treatments, which indicatesno adverse effect upon the pollination activities in1980. The percent live bee larvae was slightly higher than thecontrol and about the same as most other treatments. Beecells recovered from the 1980 demeton treatment were usedon the oxydemeton-methyl treatments in 1981, where theyperformed very well, suggesting no adverse carryover effect(Table 1). The bees produced 6% fewer cells on the higherrate than the recommended rate.TrichlorfonThe effect of trichlorfon residues (Table 3) upon the pollinationactivities of the bees appeared to be nil, but not clearcut because of differences between the low and high treatmentrates (Table 1). When averaged over two years, thebees on the plots treated at the higher rate performed betterthan the control or most other treatments, suggesting noadverse effect upon the bees. However, the bees on the plottreated at the recommended rate in 1980 performed ratherpoorly compared to the control in number of cells constructed,percent cells with cocoons, and percent pollen balls.Apparently trichlorfon was not responsible for this poorcomparison since the higher rate did not adversely affect thebees. In 1981, the bees on plots treated at the recommendedrate compared very favorably with the control, indicating nocarryover affect.DimethoateResidues of dirnethoate were not detached in alfalfa pollen,nectar, pollen-nectar balls, or the leaf from bee cells (Table3). Therefore, logically the pollination activities of the beesshould not be impacted. The number of cells constructed in1980 and 1981 on the dimethoate-treated plots averaged 11%fewer in 1980, and 26% fewer in 1981 than the control (Table1). This was due to lack of control of the detrimental insects,Pea aphids (Acyrothosiphon pisum) and Lygus bugs (Lygushesperus and L. elisus) within the plots in mid- to lateseason,which in tum adversely affected continued floweringof the alfalfa and reduced the availability of pollen and nectarfor the bees. Two year averages for percent cells with cocoons,percent live larvae, and percent pollen balls for the higherrate were comparable to the control. These results from therecommended rate, however, compare less favorably to thecontrol, particularly in 1981. Since the higher treatment rateindicates no adverse effect of this insecticide, the unfavorablecomparison for the recommended rate apparently wasnot due to dimethoate.
36 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985CarbofuranResidues of carbofuran or the metabolites were not detectedin alfalfa pollen, nectar or pollen-nectar balls (Table3). Therefore, as with dimethoate, logically the pollinationactivities of the bees should not be impacted. However, thenumber of bee cells constructed on the carbofuran-treatedplots averaged 40% fewer in 1980, and 5% fewer than thecontrol in 1981 (Table 1). Lack of control of detrimentalinsects in mid- to late-season reduced alfalfa flowering.Therefore, the reduced availability of pollen and nectar forthe bees accounts for the reduced number of bee cells. Thepercent cells with cocoons, percent live larvae, and percentpollen-nectar balls compare favorably with the control, withthe exception of percent pollen-nectar balls in 1981. We haveno explanation for the increased pollen-nectar balls in 1981.AldicarbResidues of aldicarb and its metabolites were previouslyreported detected in alfalfa leaves, nectar, and leaf from beecells but not in the pollen-nectar ball (Table 3). Low levels ofaldicarb residues and its metabolites (Table 3) were detectedin samples from plots not treated in 1980 but previouslytreated in 1978 and 1979. High levels of residue were detectedin samples from the leaf from cells from the single plottreated and sampled in 1980.The number of cells constructed in 1980 were I 0% fewerin the aldicarb plot than the control (Table 1). However, thepercent cells with cocoons, percent live larvae and percentpollen-nectar balls generally compares favorably with thecontrol. The one exception is in 1980 when the percent ofcells with cocoons from the untreated aldicarb (treated in1978 and 1979 at 3.36 kg of a.i. ha-I rate) plot produced 64%good cells compared to 74% for the control. Lack of controlof detrimental insects in the nontreated plots resulted infewer alfalfa flowers and thus a diminishing supply of pollenand nectar for the bees. Aldicarb appears to have no adverseeffect on leafcutting bees and their pollination activities at therates used in this study, particular! y when the results of 197 8and 1979 are considered. The aldicarb-treated plots producedthe highest seed yields and had more live bee larvae than thecontrol or the demeton or trichlorfon treated plots in 1978 and1979.Oxydemeton-methylOxydemeton-methyl was applied for the first time in 1981and residues in alfalfa leaves, pollen, nectar, pollen-nectarballs, and leaf from the bee cells are reported (Table 2). Leafsamples for residues of oxydemeton-methyl and its sulfonemetabolite were taken 12 hrs to 14 days after the second spraytreatment and 4 days after the third spray treatment. Residuesranged from a high of 28.9 ppm (12 hrs) to 2.65 ppm (14Table 3. Summary of residues in pollen-nectar (p-n) ball and alfalfa leaf collected by Megachile rotundata from alfalfa seed plotstreated with several insecticides in 1980. (Condensed from George and Rincker, 1982).InsecticideTreatment(kg a.i. ha-l)Sampling interval(Days after application)p-n ballResidue found (ppm)leaf-cellDemeton0.280.42389213892148948926 to 6926 to 6926 to 5426 to 544756600.44 0.020.30 NDI0.27 O.Q70.02 0.050.10 0.020.03 0.060.21 2.970.10 0.0715.675.45 5.770.64 1.080.27 1.140.75 1.240.68 4.48nonenonenonenonenone 0.6 to 10.0none 0.6 to 10.0ND 2.09ND 0.610.12 9.27Trichlorfon1.682.52DimethoateCarbofuranAldicarb0.560.841.121.683.36IBelow lower limit of sensitivity of the method used.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 37days) after treatment at the recommended rate and 51. 8 ppmto 0.10 ppm, respectively, at the higher rate. High residueswere detected in the nectar 12 hrs after treatment. However,these high residues were not detected in the pollen-nectar ballor leaf from the cell. In spite of these levels of residues, thebees performed well in the treated plots and the insecticideprovided good control of the detrimental insects in the alfalfa.The number of bee cells constructed in 1981 averaged 13%above those from the control (Table 1). Also, the percentcells with cocoons, percent live larvae, and percent pollenballs reflected no adverse effect of oxydemeton-methyl onthe bees or their pollination activities. Oxydemeton-methylwas applied again in 1982 with similar results regarding beeactivities (Rincker, unpublished data).In summary, residues in the leaves and/or the pollen-nectarballs show no adverse effect on bee larvae in this study evenat 1.5 times recommended rates. Bees from cells retainedfrom the 1980 treated plots performed as well in 1981 as beesfrom the control plots. The effect of pesticide residues in thepollen-nectar ball on leafcutting bee larvae has not beenreported previously. Results from this study are not a basisfor using more than the recommended rates of the respectiveinsecticides but are reported as experimental data only.ACKNOWLEDGEMENTWe thank the Washington Alfalfa <strong>Seed</strong> Commission forpartial support of this research project.REFERENCES1. Capizzi, J., G. Fisher, H. Homan, C. Baird, A. Retan, and A.Antonelli. 1982. Pacific Northwest Insect Control Hand-book.pp 23.2. George, D.A., and C.M. Rincker. 1982. Residues of commerciallyused insecticides in the environment of Megachilerotundata. J. Econ. Entomol. 75:319-323.3. Johansen, Carl. 1983. How to reduce bee poisoning frompesticides. Western Region Ext. Publ. (WREP) 15. pp 1-11.4. McGregor, S.E. 1976. Insect pollination of cultivated cropplants. USDA Agric. Handbook No. 496:36-39.5. Waller, G.D. 1969. Susceptibility of an alfalfa leafcutting beeto residues of insecticides of foliage. J. Econ. Entomol.62(1):189-192.Lodging Control and Yield Enhancement in Morex Spring Barley withPaclobutrazol TreatmenttL.A. Morrison and D.O. ChilcotezABSTRACTPaclobutrazol, an experimental plant growth regulator (PGR),is reported to control lodging through height reduction and stemstrengthening and thereby enhance yield. This field experimenttested Paclobutrazol under two levels of nitrogen on a knownlodging-susceptible spring barley cultivar (Hordeum vulgare cv.Morex).Paclobutrazol caused significant shortening of the basal internodesbut did not improve stem strength. Due to delayed lodging,treated plots reflected significant yield increases over the controlplots. The higher treatment rates (800 and 1000 g ha-1) alsoshowed significant yield increases over the lower treatment rates(400 and 600 g ha-1).IA Contribution of the Crop Science Department, OregonState University. Received for publication 30 September,1985.2Formerly Graduate Assistant and Professor of Crop Physiology,respectively, Department of Crop Science, OregonState University, Corvallis, Oregon 97331, USA.The results point to a clear association of reduced height withlodging control and concomitantly with yield increases. Theabsence of improved stem strength raises questions concerningthe mechanism ofPaclobutrazol's effect on lodging in the barleyspecies and the mechanism of its effect in combination withnitrogen fertility.~-------------------------Additional index words: Height reduction, Hordeum vulgare,Parlay, plant growth regulator, stem strength.INTRODUCTIONLodging can be a management problem in intensive culturalsystems where high nitrogen levels and optimum moisturerelations are used to promote yield (Mulder, 1954;Pinthus, 1973). Under these conditions, lodging-susceptiblecereal cultivars , which are typically tall and weak-strawed,show a greater tendency to lodge. Yield losses can be significant,particularly when plants lodge during the earlylodgingperiod that occurs at heading (Laude and Pauli,1956; Pinthus, 1973).Plant growth regulators (PGR's) which affect the stemelongation event by manipulating the endogenous hormonesystems have proven useful in controlling lodging (Froggatt
38 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985et al., 1981; Humphries, 1968; Pinthus, 1973). The experimentalPGR, Paclobutrazol (Parlay), is an inhibitor of gibberellin(GA) synthesis and has been shown to be effective inreducing plant height and thereby controlling lodging incereal and grass seed crops (Froggatt et al., 1981; Johnstonand McLeod, 1980; Chilcote et al. 1982, 1983). Parlay'smechanism of action appears to be similar to that of Chlormequat(CCC), a GA-synthesis inhibitor that is widely usedfor cereal lodging-control in Europe (Froggatt et al., 1981;Humphries, 1968).Cereal crop research with Parlay has produced variableresults. Most often the grain yield-enhancing attributes of thechemical are realized when the tested cultivars show a susceptibilityto lodging (Froggatt et al., 1981; Johnston andMcLeod, 1980). When they do not, the data indicate thatbenefits of Parlay treatment are lessened. In Oregon, Parlaytreatment of the typically lodging-resistant semidwarf whitewinter wheats can cause to yield reductions (Chilcote et al.1982, 1983). This study was designed to evaluate Parlay onMorex barley, a cultivar known to be susceptible to lodgingunder growing conditions of the Pacific Northwest.MATERIALS AND METHODSMorex is a six-row, spring malting barley with a mediumtall,moderately strong-strawed stem (Anon., 1985). It wasplanted on March 12, 1984 at the Oregon State UniversityAgricultural Research and Extension Center in Hermiston,Oregon. The soil was an Adkins loamy sand which carried 31kg ha-' of residual nitrogen.The experiment was arranged in a split-plot design. Themain plots received two nitrogen levels of 112 and 168 kgha-l, and the subplots received four Parlay treatments and acontrol. <strong>Seed</strong> was drilled in 18-cm rows at 45 kg ha-'.Subplots measured 2 x 6 m. Preplant nitrogen of 56 kg ha-'was applied to both main plots. After seedling emergence,nitrogen treatments of 56 and 112 kg ha-l, respectively, werebroadcast by hand. Plants were treated with Parlay at rates of400, 600, 800, or 1000 g ha-l a.i. at Freekes Scale Stage 6(Large, 1954). Parlay application was made by a Cooper-Pegler backpack sprayer and a hand-held spray boom fittedwith 8002LP nozzles. Application pressure was 242 kg cm-2.Precipitation from planting to harvest totaled 436 mm. Asprinkler irrigation system delivered 326 mm of water atincrements of 6, 59, 120, and 141 mm during the months ofMarch, April, May, and June, respectively. Rainfall duringthis period totaled 110 mm. No rainfall was recorded afterJuly 1984.Lodging was scored periodically during the growing seasonfollowing Parlay treatment. A lodging scale of one to fivewas used. One indicated no lodging and five indicated severelodging. The degree of lodging was measured by percent ofthe plot lodged.Prior to harvest, 30-cm-length row samples were cut byhand sickle. Subsamples of five fertile tillers were selectedand measured for stem length, internode lengths, and yieldcomponent data. The basal internode region was cut to two10-cm sections. The sections were weighed to give the specificstem weight (SSW) value which constitutes the dryweight per unit length of stem (Hunter, 1984). SSW is adensity measurement which has been shown to correlate withbreaking strength (Atkins, 1938). It was used in this study inplace of stem strength measurements.RESULTSPlant HeightParlay decreased plant height significantly for all Parlaytreatment rates (Table 1). Height reductions ranged from 15to 27%. The high treatment rates (800 and 1000 g ha- 1 ) alsodecreased height significantly over the low treatment rates(400 and 600 g ha-'). The number of nodes was decreasedsignificantly from the control in the high Parlay treatmentrates due probably to a compression of the lower stem internodes(Table 1).The most significant shortening attributable to Parlay treatmentoccurred in the first three internodes (Table 2). Shorteningof the first, second, and third internodes was significantlycorrelated to both treatment rate and height reduction (TableTable 1. Effect of Parlay treatment rate on yield and stem morphology of Morex barley grown in Hermiston, Oregon under twonitrogen treatments, 1984.ParlayRate(g ha-l)FertileTillersTSW'(g)Yield CST2 Spike- Nodeslets3(kg ha-l)Height(em)SSW4(mg cm-1)0 26400 25600 31800 281000 27LSD .01LSD .05NSNS40383737374395 25 20.8 7.485815 34 20.9 7.165976 30 20.6 7.136704 36 20.9 7.086776 38 20.8 6.93645 10 0.36NS124 23.6106 17.2101 15.795 16.491 15.45 4.0'Thousand seed weight.2Calculated seeds per tiller.3The three spikelets at each rachis node were counted as one. Rudimentary spikelets were also counted.4Specific stem weight.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 39Table 2. Effect of Parlay treatment rate on internode length of Morex barley grown in Hermiston, Oregon under two nitrogentreatments, 1984.InternodeParlayRate1st2nd3rd 4th 5th 6th 7th(g ha-l) -------------------------------------------------------------------(em)-------------------------------------------------------------------04.2 12.6 17.3 18.7 22.4 30.1 36.44002.1 6.7 11.1 15.7 24.0 35.1 40.76002.4 6.5 10.4 15.1 23.4 34.8 41.78002.0 5.2 8.8 14.1 23.8 33.4 42.61000 2.2 5.0 8.6 14.7 24.5 36.2 42.1LSD .01LSD .050.9 1.3 1.7 2.6 NS NS 3.2NS 4.23). Significant increases in length occurred in the sixth andseventh internodes of the Parlay-treated plants (Table 2). TheSSW value for the Parlay-treated plants was significantlylower than the control (Table 1).Grain YieldParlay significantly increased grain yield for all treatmentsover the control (Table 1). Yield increases ranged from 32 to54%. The high Parlay treatment rates (800 and 1000 g ha-l)also significantly increased yields over the low treatmentrates (400 and 600 g ha-l). Yield was found to be significantlycorrelated with Parlay treatment rate and plant height reduction(Table 3).Tillering tend to increase in the Parlay treatment ratesabove 400 g ha-l. Thousand seed weight (TSW) showed asignificant decline in the treated subplots (Table 1). Nosignificant differences were evident in spikelet number andseeds per spike although the latter did show a trend forincrease with Parlay treatment (Table 1). Another measurement,calculated seeds per tiller (CST), was taken as anempirical calculation of actual yield 1. CST values for thehigh treatment rates (800 and 1000 g ha-l) were significantlyincreased over the control. CST values for the low treatemntrates (400 and 600 g ha-l) did show a trend of increasingvalues although these were not significant (Table 1).LodgingLodging began in the control subplots during anthesiswhich started on or about May 30, 1984. Lodging in thetreated subplots first occurred between the June 6, and June20, 1984, lodging evaluations. The control plots were lodgedmore severely than the treated subplots until July 7, 1984,!Calculated seeds per tiller is derived from TSW, seed yield,and tiller data and calculated by the following formula:seedgramXgrams of seedsXtillersCSTwhen they all attained approximately the same lodging scoreand severity rating (Figure 1). The high Parlay treatmentrates (800 g ha-l and1000 g ha-l) received lower scores thandid the low treatment rates (400 g ha-l and 600 g ha-l)throughout the evaluation peiod (Figure 1). At harvest onAugust 1, 1984, plants were lying flat on the ground, and allsubplots received a score of 5. Human error in score assignmentmay account for the decline in the lodging scores for thecontrol on July 7, 1984.Table 3. Correlation coefficients for Parlay treatment effect onMorex barley 19841ParlayTreatmentPlantHeightCST2Yield 0.90 -0.86 0.73CST 0.61 -0.57Height -0.931st Jn3 -0.65 0.712nd Jn3 -0.89 0.943rd Jn3 -0.90 0.96SSW4 -0.78 0.771R2 values were nonsignificant for CST. R2 was significant at the.05 level for the 1st internode/treatment correlation coefficient,and significant at the . 01 level for all other coefficients.2Calculated seeds per tiller3Length measurements for first, second, and third internode.4Specific stem weight.FertilityThe high nitrogen rate caused tiller number to significantlyincrease and TSW to significantly decrease. High nitrogenalso caused a trend toward increased height with a correspondingdecrease in yield (Table 4). No interaction betweenParlay treatment and nitrogen level was found.DISCUSSIONPlant HeightThe lodging scores showed that Parlay can delay lodgingunder conditions of high fertility and high moisture. The
40 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985expected inverse relationship of height and SSW was notevident in the plant sample data. Presumably, Parlay wouldcontrol lodging by reducing plant height and increasing stemstrength as has been shown in previous studies of lodging(Mulder, 1954; Pinthus, 1973). However, these data onlyshowed that Parlay delayed lodging by decreasing basalinternode elongation.The decrease in stem unit weight with Parlay treatment,evident from the SSW values, raises questions concerningthe mechanism of stem strength vis-a-vis Parlay treatment,The time at which stem weakening occurred cannot be concludedfrom these data. Changes in stem unit weight mayhave been progressive. If so, this would help to explain thelodging control during the early-lodging period as a result ofboth stem shortening and stem strength, the latter decreasingas the plant matured.Parlay and nitrogen, acting alone or in combination, mayhave influenced stem weakening. The SSW values generallye 4.o~bJl-~ 3.0]2.06-1 6-6 6-20 6-27 7-7 8-1Date (Month-Day)0 = 0 + = 400 ¢ = 600 b. = 800 X = 1000Figure 1. Lodging Scores: Morex Barley, 1984. Average of twonitrogen treatment rates. Parlay rate g ha-tdecreased with increasing Parlay treatment rate (Table 1).Responses to nitrogen application may have been suppressedby a hypernutrition effect which results in an imbalance ofthe carbohydrate to nitrogen ratio that is associated with stemstrengthening (Mulder, 1954; Welton, 1931). Genetics shouldalso be considered since Cenci's work with barley stemmorphology and anatomy showed that an inverse relationshipbetween stem height and stem wall thickness does notnecessarily hold (Cenci, 1984).The elongation that occurred in the fifth, sixth, and seventhinternodes of treated plants is difficult to explain. The mechanismthat apparently causes the plant to grow out of theParlay-treatment effect may depend on levels and activity ofGA during different growth stages, on uptake of Parlay, or ona bioregulatory response. This last response may lead to ahigher rate of GA synthesis following a period of chemicallyinducedinhibition. Interaction between GA and the otherendogenous plant hormone systems should be consideredwith each of these possibilities.Yield EnhancementThe control plots lodged during the early-lodging periodand suffered a significant yield loss. The Parlay-treated plotsbegan to lodge during the late-lodging period (post-heading)and showed a significant increase in yield over the controls.These differences in time of lodging and in yield agree withLaude's distinction between early and late lodging vis-a-visyield loss (Laude and Pauli, 1956).According to the literature, the possible methods for grainyield improvement include improved tillering through increasedfertile tiller production and survival, improved seednumber through delayed head emergence, and improvedseed weight through redistribution of dry matter (Humphries,1968; Pinthus, 1973). Parlay may influence grain yield foreach method through its action on the endogenous hormonesystems. Since the chemical is usually applied betweenFeekes Scale Stages 3-5 (Froggatt et al., 1981), a time whenthe plant is preparing for elongation and entering reproductivedevelopment, it would seem likely that Parlay's effect onendogenous hormone systems would not be limited to stemelongation.Due to weather conditions, Parlay treatment was delayedto Feekes Stage Scale 6 when production of viable fertiletillers was nearing completion and floret structures weredifferentiated. The failure of the tiller number, seed number,and TSW data to account for the observed grain yield increasesupports a conclusion that Parlay in this experiment,by virtue of late application date, did not exert a beneficialinfluence on the development of individual yield components.The CST explains the treated plots' grain yield increase(Table 1) as resulting from a greater number of seed produced.This explanation would agree with the conclusion thatTable 4. Effect of nitrogen treatment rate on yield and stem morphology of Parlay-treated Morex barley, Hermiston, Oregon, 1984.Nitrogen(kg ha· 1)Fertile TSW 1Tillers(g)Yield CST 2 Spikelets3(kg ha- 1 )Nodes Height SSW 4(em) (mg/cm- 1 )tl2168LSD .0526 3929 363 26065 33 20.75816 32 20.9NS NS NS7.11 102 17.07.20 105 18.3NS NS NS'Thousand seed weight.2Calculated seeds per tiller.3The three spikelets at each rachis node were counted as one. Rudimentary spikelets also were counted.4Specific stem weight.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 41seed production was lowered in the controls due to theadverse effects of early lodging on seed developmentFertilityThe absence of a Parlay by nitrogen interaction and thenonsignificant differences for nitrogen effect on plant heightand grain yield can be explained in part by the rates ofnitrogen selected for the field experiment The low nitrogenrate apparently was in the upper range of nitrogen fertilityrequired for maximum nitrogen response. Thus, the high andlow rates were not sufficiently different with respect to theirlodging-promoting effects to produce a variation in plantresponse.CONCLUSIONSParlay's potential effectiveness as a chemical lodgingcontrolagent for cereals depends upon the lodging susceptibilityof the particular crop. Morex barley is a susceptiblecultivar (tall and relatively weak-strawed) that lodged underthe high nitrogen and moisture conditions of this experimentParlay treatment promoted yield by delaying lodging.The data show that lodging delay was attributable to shorteningof the basal internodes. The expected inverse relationshipbetween stem height and stem strength was notfound. Questions arise concerning the nature of the stemweakening--was it progressive, was it attributable to Parlaytreatment, or a combination of the effect of Parlay treatmentwith nitrogen or due to barley genetics? Additional researchon Parlay rates, timing of application, and the mechanism ofstem weakening may resolve these questions and conflictswith previous PGR experiments and provide further tests ofits possible beneficial effects on reproductive developmentREFERENCES1. Anonymous. 1985. Barley variety dictionary. AmericanMalting Barley Association Inc. Milwaukee, WI.2. Atkins, I.M. 1938. Relation of certain plant characters tostrength of straw and lodging in winter wheat. J. Agric. Res.56:99-119.3. Cenci, C.A., S. Grando, and S. Ceccarelli. 1984. Culmanatomy in barley (Hordeum vulgare). Can. J. Bot. 62:2023-2027.4. Chilcote, D.O., H.W. Youngberg, and W.E. Kronstad. 1982.Cereal seed yield enhancement with growth regulators. pp.4-5. In H.W. Youngberg (ed.) <strong>Seed</strong> production research atOregon State University. Dept. Crop Sci. Oregon State University.USDA-ARS Cooperating.5. Chilcote, D.O., D.T. Ehrensing, H.W. Youngberg, W.C.Young, III, L.A. Morrison, and W.E. Kronstad. 1983. Cerealcrop response to plant growth retardants. pp. 19-20. InH.W. Youngberg (ed.) <strong>Seed</strong> production research at OregonState University. Dept. Crop Sci. Oregon State University.USDA-ARS Cooperating.6. Froggatt, P.J., W.D. Thomas, and J.J. Batch. 1981. Thevalue of lodging control in winter wheat as exemplified by thegrowth regulator PP333. Pages 71-87. In British Plant GrowthRegulator <strong>Group</strong>, Monograph 7.7. Humphries, E.C. 1968. CCC and cereals. Field Crop Abstracts.21:91-99.8. Hunter, J.L. 1984. Tillering, lodging, dry matter partitioning,and seed yield in ryegrass (Lolium spp.) as affected by theplant growth regulator paclobutrazol. M.S. Thesis. OregonState University.9. Johnston, H.W., and J.A. McLeod. 1980. Growth regulatorsfor cereals. Page 21. In Research Summary 1980. ResearchStation Charlottetown, P.E.I. Canada.10. Large, E.C. 1954. Growth stages in cereals. Pl. Path. 3:128-129.11. Laude, H.H. and A. W. Pauli. 1956. Influence of lodging onyield and other characters in winter wheat. Agron. J. 48:452-455.12. Mulder, E.G. 1954. Effect of mineral nutrition on lodging ofcereals. Plant and Soil. 5:246-306.13. Pinthus, M.J. 1973. Lodging in wheat, barley, and oats: thephenomenon, its causes, and preventative measures. Adv.Agron. 25:209-263.14. Welton, F.A., and V.H. Morris. 1931. Lodging in oats andwheat. Ohio Agric. Exp. Stat. Bull. 471.
Seminar on Floret Site UtilizationWageningen, the Netherlands 1June 10, 1985INTRODUCTIONGrass production in the Netherlands provides green fodder,green manure, persistent ground cover for amenity purposes,and most importantly stabilization of dikes. For all thesepurposes, stem growth and flowering is undesirable. Therefore,breeding and selection of new varieties are concernedmainly with the vegetative plant characteristics. As a result,seed production characteristics are more or less neglected orare not considered until the final stages of selection.The issue is complicated by the perennial nature of mostgrass species. In the reproductive phase, grass plants are anintegrated system of reproductive and vegetative tillers.Despite the complexity of the physiology, experimentswith a single variety indicate that variation in seed yielddepends upon two components--the number of inflorescencesper unit area and the proportion of the florets that produceharvestable seeds.Most previous seed production research has concentratedon increasing the number of inflorescences per unit area.Presently it is fairly well known how to enhance inflorescenceproduction in most species from northern latitudes.During the last decade fundamental and applied researchhas focused on floret site utilization as a means of increasingseed yield. Dr. Paul Hebblethwaite and co-workers at NottinghamUniversity initiated this work and proved the importanceof fertilization and seed set percentage to seed yield.Recent research in several countries on use of growth retardantsand fungicides coupled with successes in breeding forseed retention demonstrate that innovative developments ingrass seed production are at hand. A prerequisite will be abetter understanding of the physiological processes that causethe wide variation in floret site utilization. An excellent basisis available from results of studies of assimilate productionand distribution patterns at Bangor University (UK).The objectives of this seminar were:- to summarize current information and examine problemsin floret development, fertilization, seed abortion,seed filling and ripening processes in grasses- to involve plant physiologists and cytologists in thesesubjects- to stimulate interest by plant breeders in seed productionaspects in their programsThe following five articles are from this seminar.Willem MeijerOrganizertSeminar held at Wageningen, the Netherlands on June 10,1985 was organized by the Research Station for ArableFarming and Field Production of Vegetables (PAGV) atLelystad and sponsored by the National Council for AgriculturalResearch (N. R. L. 0.), the Netherlands. Professor L.'t Mannetje, Department of Field Crops and Grassland Science,Agricultural University, Wageningen, presided overthe seminar.42
Developmental and Physiological Aspects of <strong>Seed</strong> Production in <strong>Herbage</strong> GrassesC. Marsh aliiABSTRACTThe developmental and physiological factors determining thepotential seed yield of the grass inflorescence are discussed,especially in relation to the productivity of florets. Analysis ofthe difference between potential and actual seed yield of theinflorescence reveals that a large proportion of florets are unproductive;many set seed but then abort developing seeds. Thephysiological factors influencing seed abortion are not well understoodbut nutritional factors, particularly carbohydrate supply,may be important. The inflorescence is the major source ofassimilate for seed growth and development, but some evidencesuggests that vegetative tillers may compete with developingseeds for assimilate produced by the inflorescence. Such competitionmay be important in initiating, at least in part, the abortionof some developing seeds. The productivity of florets is increasedby the application of certain plant growth regulators and fungicides,and this may be related to an improvement in the supply ofassimilate to developing seeds.Additional index words: florets, seed set, seed abortion, seedgrowth, source-sink relations, 14C-assimilate, growth regulators,fungicides.---------------------------INTRODUCTIONThe reproductive potential of the grass inflorescence is setby the number of spikelets and the number of fertile floretsper spikelet. The degree to which this potential is realized interms of yield depends on the proportion of florets thatproduce seed and the size of individual seed. Both herbagegrasses and cereals show a characteristic pattern of underutilization of reproductive potential in that the number ofseed produced per inflorescence is substantially less than thenumber of fertile florets, and this is especially the case ingrasses where there may be a sevenfold difference betweenfloret and seed numbers (Hebblethwaite et al., 1980). Thisemphasises the importance of the developmental processesoccurring from anthesis onwards, namely pollination, fertilization,seed set and seed growth, and there is good evidencethat deficiencies in each of these sequential steps restrictspotential seed yield of the inflorescence (Hill, 1980). Agronomicstudies suggest that there is a close relationship betweenthe number of seeds produced per unit area and the yield ofseed, and that this is primarily related to the number of seeds'Senior Lecturer, School of Plant Biology, University College ofNorth Wales, Bangor, Gwynedd LL57 2UW, U.K.per spikelet rather than to the number of fertile tillers producedby the crop (Hebblethwaite et al., 1982; Hampton andHebblethwaite, 1983). However, in the field it is evident thatseed production falls far short of its potential due to thelodging of the crop canopy, as large increases in seed yieldresult if lodging is prevented or reduced (Hebblethwaite andIvins, 1978; Hampton and Hebblethwaite, 1985a).This paper will consider some of the phsysiological anddevelopmental factors underlying the establishment of theyield potential of the grass inflorescence, and the subsequentutilization of this potential especially with respect to the fateof fertile florets.The Components of YieldIn perennial grasses the population of flowering shoots iscomposed of tillers of varying age and origin, and thesedisplay a considerable range of yield potential. Studies on theyield components of the inflorescence of Lolium perennehave revealed relatively small differences in spikelet numberbetween inflorescences of tillers appearing during the summerand winter months, but large differences in the numberof florets formed per spikelet (Ryle, 1964; Hill and Watkin,1975; Colvill and Marshall, 1984). In this species up to 14florets may be produced per spikelet, but not all of thesebecome fertile and produce a seed. The grass inflorescencethus produces far more florets than seeds and this is evidentfrom the results shown in Fig. 1 where the inflorescences ofsuccessively appearing primary tillers display a progressivedecline in the numbers of florets and seeds, with just underthree-quarters of all florets bearing a seed. The differencebetween floret and seed numbers is less in later than earlierproduced tillers, e.g. 65% of florets yield seeds in the firsttwo primary tillers (Tl and T2) compared with almost 80%for the T7-Tll group, thus spikelets with relatively fewflorets tend to be more productive than those with a highernumber of florets.Despite these differences the seed yield of the inflorescenceof the main shoot and early primary tillers is significantlygreater than that of later appearing primary tillers asthey produce many more seeds. This developmental patternreflects the relationship between the time of tiller appearanceand its reproductive potential, and also emphasizes the hierarchicalstructure of the reproductive capacity of the tillers ofan individual plant, as shown by Darwinkel ( 1978) for winterwheat.Observations on the pattern of floret production within aninflorescence of ryegrass have shown that the number offlorets per spikelet varies relatively little with position, butthat in certain cultivars the mid-region of the ear tends to bemore productive than basal and tip regions (Burbidge et al.,43
44 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 19851978). The percentage of florets setting seed is more or lessindependent of spikelet position, but where lodging occursthere is a marked profile of decreasing seed production perspikelet from the base to the tip of the ear (Burbidge et al.,1978). The latter observation matches the normal pattern offloret production in branching inflorescences foot and meadowfescue where the branches at the base of the inflorescencedevelop many more florets than those in the mid and apicalregions (Ryle, 1964). This difference in floret distribution inthese species is particularly evident in inflorescences borneby summer produced tillers compared with those of tillersappearing in early spring.An analysis of reproductive development at the level of thetiller apex allows some explanation for the differences inspikelet and floret production in inflorescences of tillers ofdifferent age. As temperate grasses such as L. perenne initiateinflorescences in long days following vernalization(Langer, 1979), tillers appearing in the summer initiatespikelet primordia at more or less the same time as laterappearing tillers and so have only a slightly earlier date ofinflorescence emergence (Anslow, 1963; Ryle, 1964). Thusdifferences in spikelet number between tillers arising at differenttimes primarily reflect differences in the size of thetiller apex, i.e. the availability of axillary sites for spikeletprimordia to be laid down. As leaf primordia tend to accumulatewith time in vegetative tillers (Langer, 1979) and asspikelet primordia arise in the axils of leaf primordia, then atthe onset of spikelet initiation tillers appearing in summerand autumn will have additional sites for spikelets to developcompared with later appearing tillers (Ryle, 1964). The degreeto which the apex continues to elongate to producefurther sites for spikelet primordia is also importanUn determiningfinal spikelet number, but it is not clear if thisdiffers in tillers appearing at different times of the year.In field experiments the application of nitrogen fertilizer inthe spring has relatively little effect on spikelet productionbut greatly influences floret production, the greater the supplythe higher the number of florets per spikelet (Hi,ll andWatkin, 1975; Hebblethwaite and Ivins, 1977, 1978.) Ittherefore seems likely that the greater floret number of spikeletsfrom summer appearing tillers, compared with laterappearing tillers, reflects the greater availability of nitrogenwithin the older and correspondingly larger tillers during thecritical period of floret differentiation. On the other hand, asshading at this time has been found to reduce the number offlorets produced per spikelet (Ryle, 1966, 1967) differencesin floret production may also reflect the availability of assimilatefor floret development, with older tillers able tocontribute assimilate more readily than smaller, youngertillers. This would particularly be the case if the latter becomeshaded within the crop canopy; alternatively someassimilate utilized by the differentiating apex may be derivedfrom the seasonal decline in fructan level that occurs prior tothe commencement of spring growth (Pollock and Jones,1979; Pollock, 1981), in which case younger tillers might beexpected to have a smaller pool of accumulated fructanreserve than older tillers.<strong>Seed</strong> Set and <strong>Seed</strong> DevelopmentAs previously described many florets are unproductive.The reasons for this are not readily resolved as there is littleinformation on the proportion of florets that are innatelysterile, or those that are fertile but are not successfully pollinatedor fertilized, or those that become fertilized but abortembryos or developing seeds. The situation is further complicatedby the fact that some mature seeds may be lost byshedding prior to harvest. These uncertainties can only beresolved by detailed observations on the development andSpike lets per inflorescenceMS Tl T2 T3 T4 TS-617-11Florets per spikeletMS T1 T2 T3 T4 TS-6 17-11100<strong>Seed</strong> yieldperinflorescence(mg) 50Florets per inflorescenceMS T1 T2 T3 T4 TS-6 17-11<strong>Seed</strong>s per inflorescenceMS T1 T2 T3 T4 TS-6 17-11O MS Tl T2 T3 T4 TS-6 17-11Figure 1. The components of seed yield and seed yield perinflorescence in relation to the identity of primary tillers in L.perenne ( + S.E.). MS = main shoot; T1- T11 =primary tillersarising from the axillary buds of main shoot leaves 1-11.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 45fate of individual florets with time from the emergence of theinflorescence to its maturation.Agronomic studies on the effects of lodging on seed production,where seed yield may be reduced by as much as60%, have however provided some pertinent data on thecapacity of florets to produce harvestable seed (Burbidge etal., 1978). Examination of florets from peak anthesis toharvest has revealed that about 60% of the florets set seedwithin three weeks (i.e. they are successfully pollinated andfertilized), but that by the final harvest after 4-5 weeks only40-50% of these yield seed. Thus many more seeds are setthan are harvested and the major proportion of this loss can beattributed to the abortion of developing seeds. It is not clearprecisely which seeds are most prone to abortion, i.e. theirposition within the various spikelets.In general the reduction in the number of seeds that initiallydevelop to a level that can be supported to maturityseems a common feature of the reproductive biology of manyspecies, and may account for the relative constancy of seedsize observed in plants growing in a range of stressed conditions(Harper, 1977). Silvertown (1982) has suggested thatflorets which abort their developing seeds or fruits play animportant role in reproduction by acting as 'pollen donors'and thereby maximizing the pollen production of the inflorescence,their female function being redundant. It thus seemsprobable that the loss of developing seeds by abortion isregulated by some internal control system and Burbidge et al.( 1978) suggested that this might be related to a shortfall in thesupply of substrates to sustain seed growth, or to the involvementof a hormonal mechanism inhibiting the growth anddevelopment of certain seeds within each spikelet.Within an individual spikelet in rye grass there is a markeddecline in the capacity of florets to set seed from the basal tothe distal floret, with basal florets tending to produce heavierseeds than distal ones (Anslow, 1963, 1964; Burbidge et al.,1978). These patterns of development suggest that there maybe competition for assimilate or mineral nutrients within thespikelet, with the earlier maturing basal florets developing atthe expense of distal florets, i.e. the latter may be moresusceptible to seed abortion. There is some evidence thatspike lets with relatively few florets have a higher percentageseed set at harvest than spike lets with a higher floret numberand this may be explained in terms of reduced competitionfor resources within the spikelet; for example, the greaterseed setting capacity of florets from inflorescences of tillersproduced over winter compared with those from tillers appearingin summer, and the observations of Hebblethwaiteand Ivins (1978) where the delayed application of nitrogenfertilizer in the spring results in an improvement in seed set inspikelets with fewer florets than those produced by controlinflorescences. In general, increasing the supply of nitrogenreduces the percentage seed set in field crops of ryegrass(Spiertz and Ellen, 1972; Hebblethwaite and Ivins, 1977) butthis response is confounded by increased lodging. Neverthelessany increase in competition between florets within theinflorescence at the higher nitrogen levels seems likely toreflect the need for assimilate rather than any other substratefor seed development. There is some evidence to support thisview in that shading the crop in the spring reduces seed setInflorescence Appearancef---------lAnthesis1-----i<strong>Seed</strong>-filling10 20 30 40Days from inflorescence appearance50 60Figure 2. The fixation of 1 4C0 2by the inflorescence and leavesof L. perenne with time from inflorescence appearance ( +S.E.). Whole tiller exposed to 1 4C0 2for 10 minutes and thenharvested. IIIII , inflorescence; -A- , flag leaf; - - A- - , flagleaf sheath; 0 , penultimate leaf; o , upper internode; •remaining stem. (From Ong et al., 1978a).(Spiertz and Ellen, 1972) but there seem to have been fewspecific studies on this aspect of development in grasses,whereas in temperate cereals the results of glasshouse andfield work show that grain set is greatly reduced by shadingduring anthesis and the immediate post-anthesis period(Wardlaw, 1975).The Assimilate Supply for <strong>Seed</strong> GrowthThe production of assimilate by the various parts of theflowering tiller and its supply to developing seeds can beevaluated by measuring the uptake of t4C0 2and followingthe distribution of t4C-assimilate from source to sink. In afield study of the assimilatory capacity of the inflorescenceand leaves of ryegrass, Ong et al. (1978a) found that theinflorescence was the major assimilatory organ of the floweringtiller accounting for almost half of the t4CQ 2fixed by thetiller during anthesis (Fig. 2). This proportion increased withtime as leaf laminae progressively senesced. With the exceptionof the developing seeds all parts of the inflorescenceshowed significant photosynthetic capacity, the lemmas andpaleas contributed 40% of the t4C0 2 fixation at anthesis, theglumes 20%, and the rachis the remainder. There was significantexport of t4C-assimilate from the inflorescence after 24hours as also reported in ryegrass by Clemence andHebblethwaite (1984) and as found for Poa annua by Ongand Marshall (1975), but over 70% of the t4C in the floweringtiller was retained by the inflorescence, and the majority of
46 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985this was probably located in the developing seeds (Fig. 3c).The assimilate supply to seeds was not recorded separately inthis experiment but in a similar study with Poa annua approximately70% of the t4C in the inflorescence was recoveredfrom seeds (Ong and Marshall, 1975). During anthesis theterminal internode was the major sink for assimilate exportedfrom the ryegrass inflorescence and this suggests that theremay be competition for assimilate between newly developingseeds and the elongating internode. Assimilate exported fromthe flag leaf and lower leaves was utilized almost entirely bythe stem (Fig. 3 a, b) and thus in contrast to most other workon source-sink relationships in grasses and cereals (Ong andMarshall, 1975; Wardlaw, 1975) these leaves did not make asignificant contribution to the growth and development ofseeds. They did, however, support the development of theinflorescence in the pre-anthesis period.Although these results suggest that the photosynthetic604020(a)inflorescence appearanceanthesis1----1seed fillingseed ripeningactivity of the inflorescence is wholly adequate to supportseed growth, observations in another season revealed that20% of the t4C in plants four weeks after supplying t4CQ 2tothe entire tiller at anthesis was recovered from the seeds (Fig.4). Thus the current assimilation of the inflorescence may besupplemented by the mobilization of material previouslyassimilated by the leaves and temporarily stored in the lowerinternodes in the post-anthesis period as described for wheat(Austin et al.,l977).10080I 601l~ 40[u::';(a)inflorescence appearancean thesisseed filling• 0 ••....·::.·seed ripening040(b)0(b) 1002040602080060(c)40202000 10 2030 40Days from inflorescence appearance50 60Figure 3. The percentage distribution of 14C-labelled assimilateafter 24 hours from (a) flag leaf, (b) penultimate (PL) or basal(BL) leaf, and (c) inflorescence, at different stages of reproductivedevelopment ( + S.E. ). IS] ,inflorescence; ~ , leavesand upper internode; D , rest of stern; IIIII , other tillers; ill] ,root. (From Colvill and Marshall, 1984).04060Days from inflorescence appearanceFigure 4, The redistribution of 14C-labelled assimilate with timein L. perenne. Main tiller supplied with 14{;0 2 at (a) flag leafemergence, or (b) anthesis. EJ , inflorescence; 0 , upperinternode; 0 , rest of stern and leaves; § , seeds;• , other tillers; IIIII1 , root. (From Colvill & Marshall,1984).
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 47A recently reported field study on I4C-assimilate distriutionin L. perenne during seed filling by Clemence andHebblethwaite (1984) shows an interesting additionalsource-sink link compared with the previously describedstudy of Ong et al. ( 1978a) and Colvill and Marshall (1984).The latter was conducted on a sward supplied with a relativelylow input of nitrogen fertilizer to minimize lodging andobservations were made in an unusually dry season, whereasHebblethwaite and co-workers studied crops well suppliedwith nitrogen. The higher input of nitrogen fertilizer stimulatestillering as well as causing early and extensive lodging(Hebblethwaite and Ivins, 1977; Hebblethwaite eta!., 1980)and so in this situation young tillers which rely on importedassimilate for their development (Colvill and Marshall, 1981)will form a significant sink for assimilate, a demand that canonly be met by established flowering tillers. Correspondingly,Clemence and Hebblethwaite (1984) found that I4C-assimilatewas readily supplied to developing tillers by theinflorescence and flag leaf during seed filling whereas Ong etal. (1978b) and Colvill and Marshall (1984) recorded only atrace of assimilate moving out of a flowering tiller to subtendingtillers at this time. However, inPoa annua, Ong andMarshall (1975) also found that young tillers were a majorsink for assimilate from the inflorescence. In contrast, Colvilland Marshall (1984) found that developing tillers were supportedby the mobilization of reserve materials rather than bycurrent assimilate as one sixth of the I4C in a plant four weeksafter supplying I4C0 2 to the shoot at anthesis was localized innew tillers (Fig. 4). In a lodged rye grass crop the flag leaf andother leaves thus supply assimilate to two major sinks, developingtillers and the stem, and as a result there is onlyminor support to growing seeds, but even so both Clemenceand Hebblethwaite (1984) and Hampton and Hebblethwaite( 1985b) recorded a relatively greater allocation of assimilatefrom the flag leaf to the inflorescence than that observed byColvill and Marshall (1984).It is evident from these I4C-studies that the inflorescence isthe principal assimilatory organ of the flowering tiller andsupplies the majority of the assimilate utilized by developingseeds. A significant proportion of current assimilate is exportedfrom the inflorescence and in view of this Colvill andMarshall (1984) concluded that the production of assimilatewas far greater than that needed for seed growth. This view issupported by experiments where lodging is prevented eitherby mechanically supporting the crop (Burbidge et a!., 1978)or chemically (Wright and Hebblethwaite, 1979; Hamptonand Hebblethwaite, 1985b) where the growth and developmentof many more seeds per inflorescence can be supported,but this response may in part reflect an improvement in thewithin-crop environment. However, the setting of seeds andtheir successful early growth is a far more critical developmentalstage than their overall growth to maturity and thus ifthere is some degree of competition between vegetative andreproductive sinks for assimilate (mainly from the inflorescence)then this could perhaps influence the abortion ofdeveloping seeds.Effects of Growth Regulators and FungicidesAny experimental treatment that modifies source-sinkrelations to the advantage of reproductive growth and development,for example the application of growth regulatorsthat reduce stem development and thereby reduce lodging,might be expected to enhance floret and seed development.Whilst the results of experiments with growth regulators suchas Ancymidol and Paclobutrazol indeed show large increasesin seed yield, mainly associated with an increase in seednumber per spikelet, the mechanism underlying this improvementis not clear (Hebblethwaite eta!., 1982; Hamptonand Hebblethwaite, 1985b).In particular, three aspects need to be resolved. Firstly,whether the number of fertile florets per spikelet at an thesis isinfluenced by the application of growth regulators: someobservations suggest that this is unaltered (Wright andHebblethwaite, 1979) but others show a significant increase(Hampton and Hebblethwaite, 1985b). Secondly, whetherthe reduction in lodging of the crop associated with theapplication of chemicals provides a more favorable environmentfor the production, release and dispersal of pollen,and so correspondingly results in an increase in the proportionof florets that become fertilized and set seed (Griffiths eta!., 1980; Hill, 1980). Thirdly, whether the loss of developingseeds by abortion is reduced by the altered growth patternof the crop following the application of growth regulators.This has frequently been claimed but is not supported bydetailed observations on seed number per spikelet with time.However, in a recent publication Hampton and Hebblethwaite( 1985b) provide some evidence that Paclobutrazol applicationat the time of spikelet initiation significantly reduced theabortion of seeds. This may reflect a direct effect of thegrowth regulator in suppressing the growth of vegetativetillers that compete with developing seeds for assimilate, orindirectly reflect improved light relations within the cropassociated with reduced lodging, i.e. tillers may, by virtue ofenhanced photosynthetic capacity, make less demand forassimilate from other parts of the plant.In general it can be concluded that competition for assimilatebetween reproductive and vegetative sinks especiallyduring anthesis and the early period of seed growth is importantin regulating seed yield. This view is supported by theresults of recent experiments in which fungicides have beenapplied to lodged crops of ryegrass; the crop remains lodgedand seed production per spikelet is significantly increased(Hampton and Hebblethwaite, 1984). This increase in seedyield was brought about in the virtual absence of pathogenicfungi and was related to an increase in the leaf area durationof the canopy resulting from delayed leaf senescence. Astreatment with fungicide did not influence floret number perspikelet at anthesis and did not alter the structure of the cropcanopy, the improvement in seed production per inflorescencemust largely be due to a reduction in seed abortion. Itcan, therefore, be suggested that treatment with fungicidemaintained the photosynthetic activity of tillers and resultedin an improved supply of assimilate to developing seeds at atime when they are normally prone to abort. In addition it ispossible that fungicides also exert a direct hormonal effect ondeveloping seeds via a cytokinin-like action. This wouldstimulate the sink activity of developing seeds and sustaintheir import of assimilate and other substrates, thereby re-
48 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985ducing their susceptibility to abortion.It is clear that precise physiological studies are required tocharacterize the assimilate requirements of developing seeds.Information on the pattern of assimilate supply with time toindividual seeds within a spikelet is needed to identify anydifferences between those seeds which abort, presumably theyoungest and most distal within the spikelet, and those thatmaintain their growth to maturity. However, as the pattern ofassimilate distribution may be markedly influenced by thehormonal relations of the sink (Wareing, 1977, 1979), thenthe hormonal background of individual developing seedsmay be the critical feature that determines their fate. Thiscould form the basis of a mechanism of hormonal inhibitionof seed development (Evans et al., 1975) and this possibilityneeds to be resolved. It is important to note that even wherethe application of plant growth regulators increases seednumbers per inflorescence the percentage of florets that setseed is at best only about two-thirds of the total (Hamptonand Hebblethwaite, 1985b). Thus considerable yield potentialremains to be realized.<strong>Seed</strong> Size<strong>Seed</strong>s that grow to maturity follow a characteristic patternof rapid increase in size and fresh weight in the first 10 daysafter fertilization, the period when they are most likely to besusceptible to abortion, and this is followed by a furtherperiod of dry weight increase during which reserves areaccumulated and the percentage water content of the seeddeclines (Hill, 1980). The maximum dry weight of seeds isreached at the end of this stage, approximately four weeksafter peak anthesis in perennial ryegrass. The final weight ofan individual seed depends mainly on its position within theinflorescence, although the earlier appearing inflorescencesof tillers produced in the summer tend to produce slightlylarger seeds than those of tillers produced later in the year(Anslow, 1964). Basal spikelets produce slightly larger seedsthan upper ones, but within a spikelet the basal florets tend toproduce much larger seeds than more distal florets. Thispattern reflects the relative activity of the individual seedsinks within the inflorescence and may well be related to theonset of fertilization of individual florets. Thus, seeds developingin upper florets within a spikelet compete poorly withthose in lower positions for mineral nutrients and assimilatemoving into the spikelet; on the other hand, if the lemma andpalea associated with each growing seed supply a substantialproportion of the carbohydrate required for growth (Ong etal., 1978a), then differences in the duration of the seedfillingperiod may be important in accounting for differencesin size between adjacent seeds within a spikelet.The results of field and glasshouse studies show that thelevel of nitrogen supply, or mineral nutrient regime in general,have relatively little effect on mean seed weight(Hebblethwaite and Ivins, 1977; Ong et al., 1978c). Overallit seems clear that variation in seed size is a minor componentof the yield structure of the grass inflorescence, and thisfollows the general pattern displayed by most plants, namelythat seed size tends to be relatively constant in a range ofconditions.CONCLUSIONSThe large difference between potential and actual seedproduction of the grass inflorescence is due to the poorcapacity of florets to yield mature seeds. This under-utilizationof floret potential is associated with the lodging of thecrop but even when this is reduced there is still a largediscrepancy between the numbers of florets and seeds. Thephysiological factors underlying the poor productivity offlorets are not fully understood but the evidence to datesuggests firstly, that many florets do not become pollinatedor fertilized, and secondly that a high proportion of developingseeds receive insufficient assimilate to sustain their growthat a critical period of their development, and as a result theyabort. The latter situation seems to be related to the demandsfor assimilate elsewhere in the plant and this aspect requiresmore detailed investigation. There is scope to increase thepotential seed yield further, for example by increasing theproportion of high yielding early-appearing tillers with a highnumber of florets per spikelet, but this approach is unrealisticuntil its potential can be realized. Currently the use of growthregulators to reduce lodging offers the best approach toimproving the productivity of florets in field crops, and alsoprovides a useful physiological tool to analyze the factorsunderlying this improvement.REFERENCES1. Anslow, R. C. 1963. <strong>Seed</strong> formation in perennial ryegrass. I.Anther exsertion and seed set. J. Br. Grassl. Soc. 18:90-96.2. Anslow, R.C. 1964. <strong>Seed</strong> formation in perennial ryegrass. II.Maturation of seed. J. Br. Grassl. Soc. 19:349-357.3. Austin, R.B., J.A. Edrich, M.A. Ford, and R.D. Blackwell.1977. The fate of dry matter, carbohydrates and 14 C lost fromthe leaves and stems of wheat during grain filling. Ann. Bot.41:1309-1321.4. Burbidge, A., P.D. Hebb1ethwaite, and J.D. Ivins. 1978.Lodging studies in Lolium perenne grown for seed. 2. Floretsite utilization. J. Agric. Sci., Cambridge 90:269-274.5. Clemence, T.G.A., and P.D. Hebb1ethwaite. 1984. An appraisalof ear, leaf and stem 14 C0 2 assimilation, t4 Cassimilate distribution and growth in a reproductive seed cropof amenity Lolium perenne. Ann. Appl. Bioi. 105:319-327.6. Col viii, K.E., and C. Marshall. 198 L The patterns of growth,assimilation of '4C0 2and distribution of t4C-assimilate withinvegetative plants of Lolium perenne at low and high density.Ann. Appl. Bioi. 99:179-190.7. Colvill, K.E., and C. Marshall. 1984. Tiller dynamics andassimilate partitioning in Lolium perenne with particularreference to flowering. Ann. Appl. Bioi. 104:543-557.8. Darwinkel, A. 1978. Patterns of tillering and grainproduction of winter wheat at a wide range of plant densities.Netherlands J. Agric. Sci. 26:383-398.9. Evans, L.T., I.F. Wardlaw, and R.A. Fischer. 1975. Wheat.pp. 101-149. In L.T. Evans (ed.) Crop Physiology: Some casehistories. Cambridge University Press.10. Griffiths, D.J., J. Lewis, and E.W. Bean. 1980. Problems ofbreeding for seed production in grasses. pp. 37-49. In P.D.Hebblethwaite (ed.) <strong>Seed</strong> production. Butterworths, London.11. Hampton, J.G., and P.D. Hebblethwaite. 1983. Yield componentsof the perennial rye grass (Lolium perenne L.) seedcrop. J. Appl. <strong>Seed</strong> Prod. 1:23-25.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 4912. Hampton, J.G., and P.D. Hebblethwaite. 1984. The effect offungicide application on seed yield in perennial ryegrass cv.S.24. Ann. Appl. Bioi. 104:231-239.13. Hampton, J.G., andP.D. Hebblethwaite. 1985a. The effect ofthe growth regulator paclobutrazol (PP333) on the growth,development and yield of Lolium perenne grown for seed.Grass and Forage Sci. 40:93-101.14. Hampton, J.G., andP.D. Hebb1ethwaite. 1985b. The effect ofgrowth retardant application on floret site utilization andassimilate distribution in ears of perennial ryegrass cv. S.24.Ann. Appl. Bioi. 107:127-136.15. Harper, J.L. 1977. Population Biology of Plants. AcademicPress, London.16. Hebblethwaite, P.D., J.G. Hampton, and J.S. McLaren.1982. The chemical control of growth, development andyield of Lolium perenne grown for seed. pp. 505-523. InJ.S. McLaren (ed.). Chemical manipulation of crop growth anddevelopment. Butterworths, London.17. Hebblethwaite, P.D., and J.D. Ivins. 1977. Nitrogen studiesin Lolium perenne grown for seed. I. Level of application. J.Br. Grassl. Soc. 32:195-204.18. Hebblethwaite, P.D., and J.D. Ivins. 1978. Nitrogen studiesin Lolium perenne grown for seed. II. Timing of nitrogenapplication. J. Br. Grassl. Soc. 33:159-166.19. Hebblethwaite, P.D., D. Wright, and A. Noble. 1980. Somephysiological aspects of seed yield in Lolium perenne L.(Perenial Ryegrass). pp. 71-90 In P.D. Hebblethwaite (ed.)<strong>Seed</strong> production. Butterworths, London.20. Hill, M.J. 1980. Temperate pasture grass-seed crops: formativefactors. pp. 137-149. In P.D. Hebblethwaite (ed.). <strong>Seed</strong>production. Butterworths, London.21. Hill, M.J., and B.R. Watkin. 1975. <strong>Seed</strong> production studieson perennial ryegrass, timothy and prairie grass. I. Effect oftiller age on tiller survival, ear emergence and seedheadcomponents. J. Br. Grassl. Soc. 30:63-71.22. Langer, R.H.M. 1979. How Grasses Grow. (2nd ed.).Edward Arnold, London.23. Ong, C.K., K.E. Colvill, and C. Marshall. 1978a. Assimilationof 14CQ 2by the inflorescence of Poa annua L. andLatium perenne L. Ann. Bot. 42:855-862.24. Ong, C.K. and C. Marshall. 1975. Assimilate distribution inPoa annuaL. Ann. Bot. 39:413-421.25. Ong, C.K., C. Marshall, and G.R. Sagar. 1978b. Thephysiology of tiller death in grasses. 2. Causes of tiller deathin a grass sward. J. Br. Grassl. Soc. 33: 205-211.26. Ong, C.K., C. Marshall, and G.R. Sagar. 1978c. The effectsof nutrient supply on flowering and seed production in PoaannuaL. J. Br. Grassl. Soc. 33:117-121.27. Pollock, C.J. 1981. Environmental effects on reserve carbohydratemetabolism in Phleum pratense. pp. 115-118. In C.E.Wright (ed.) Plant physiology and herbage production. Br.Grassl. Soc., Maidenhead.28. Pollock, C.J., and T. Jones. 1979. Seasonal patterns offructan metabolism in forage grasses. New Phytologist 83:9-15.29. Ryle, G .J .A. 1964. The influence of date of origin of the shootand level of nitrogen on ear size in three perennial grasses.Ann. Appl. Bioi. 53:311-323.30. Ryle, G.J.A. 1966. Physiological aspects of seed yield ingrasses. pp. 106-118. In F.L. Milthorpe and J.D. Ivins (eds.).The growth of cereals and grasses. Butterworths, London.31. Ryle, G.J.A. 1967. Effects of shading on inflorescence sizeand development in perennial grasses. Ann. Appl. Bioi.59:297-308.32. Silvertown, J.W. 1982. Introduction to Plant PopulationEcology. Longman, London.33. Spiertz, J.H.J., and J. Ellen. 1972. The effect of lightintensity on some morphological and physiological aspects ofthe crop perennial ryegrass (Latium perenne L. var. 'cropper')and its effect on seed production. Netherlands J. Agric. Sci.20:232-246.34. Wardlaw, I.F. 1975. The physiology and development oftemperate cereals. pp. 58-98. In A. Lazenby and E.M. Matheson(eds.) Australian field crops I. Angus and Robertson, Sydney.35. Wareing, P.F. 1977. Growth substances and integration in thewhole plant. pp. 337-365. In D.H. Jennings (ed.) Integra-tionof activity in the higher plant. Cambridge University Press.36. Wareing, P.F. 1979. Growth regulators and assimilate partition.pp. 309-317. In T.K. Scott (ed.) Plant regulation andworld agriculture. Plenum Press, New York.37. Wright, D., and P.D. Hebblethwaite. 1979. Lodging studiesin Lolium perenne grown for seed. 3. Chemical control oflodging. J. Agric. Sci., Cambridge 93:669-679.
Floret Site Utilization in Grasses: Definitions, Breeding Perspectivesand MethodologytA. ElgersmaABSTRACTThe seed yield of grasses needs improvement, and seed yieldshould become a more important selection criterion in grassbreeding. <strong>Seed</strong> yield depends largely on the degree of floret siteutilization (FSU). This term is extensively discussed in this paperand several definitions are reviewed. A distinction is made betweenbiological and economical FSU. Causes of variation inFSU and various determination methods are discussed. Suggestionfor breeding for increased FSU are also given.Additional index words: <strong>Seed</strong> yield, pollination, fertilization,seed set, seed development, seed harvest, abortion, shattering,harvest losses.INTRODUCTIONThe success of a herbage cultivar in commercial productionnot only depends on its forage attributes, but also on itsability to produce seed. In forage varieties, characteristicssuch as high vegetative production, persistency and qualityare of importance to the farmer. The seed producer, however,desires high seed yields of good quality.There are two alternatives for maximizing seed yields:1. Cultural manipulation of the grass seed crop to maximizedevelopment of flowering stems and fertileflorets.2. Breeding for improved seed production jointly withforage production when developing new varieties.Breeding perspectives for higher seed production are thefocus of this paper.Floret Site Utilization (FSU), Definitions and ComponentsGrass seed crops have a high yield potential, but thispotential is never fully realized. Griffiths et al. (1973),Hebblethwaite (1977) and Burbidge et al. (1978) found realizedyields to be much lower. Based on seed yield components,the theoretical production or potential yield can becalculated as inflorescences m-z x spikelets/inflorescence xflorets/spikelet x FSU x average seed weight. Owing to the'Elgersma, A. Foundation for Agricultural Plant Breeding, P.O.Box 117, 6700 AC Wageningen, the Netherlands. Received forpublication 4 November 1985.negative feedback on forage production, it is not desirable toincrease the size of the reproductive system, i.e. florets m-z.Instead, the efficiency should be increased (Bean, 1972),which can be achieved by improving the FSU. The meaningof this term, however, is not clearly defined. Bean (1972)defines efficiency of the reproductive system as the percentageof flowers which produce seed, and the size to whichthese seeds develop. Several other terms have been used todescribe FSU. For example, seed set, floret fertility or fertilityindex have been used. However, some of these last terms arealready used for other traits, being components of the total''floret site utilization''. For a full understanding ofFSU it isnecessary to analyze which processes occur from the time ofanthesis until determination of the final seed yield. It isimportant to know how these processes are influenced byenvironmental and genetic factors, and by genotype x environmentinteractions.In a biological sense, FSU can be defined as the percentageof florets, present at anthesis, resulting in a viable seed.For seed growers, the percentage and quality of the seeds thatcan be harvested is of interest. After harvesting and cleaning,the commercial seed yield can be expressed as a percentageof the potential seed yield. In an economical sense, FSU canbe defined as the percentage of florets present at anthesiswhich contribute to the harvested seed. Economical FSUresults from the following processes: pollination, fertilization,seed set, seed development, harvesting and cleaning. Duringeach of these processes losses may occur (Table 1).PollinationThe term 'pollination' is used to describe processes occurringfrom the time of anther dehiscence until the pollenreaches the stigma. Pollen grains on the stigma have a mutuallystimulating effect on pollen germination. Reduction ofthe number of pollen grains on the stigma may reduce fertilization.Early lodging limits pollen transport and successfulpollination. On the other hand, uniform flowering and highpollen production favor pollination. Pollination is influencedby environmental factors.FertilizationIn the progamic phase of fertilization, seed set may bereduced due to non-viability of pollen grains or incompatibility.Non-viable egg cells may also reduce FSU.Pollen grains of grasses have a low retention of viability,especially at low humidity. Jones and Brown (1951) stated50
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 51Table 1. Processes occurring after an thesis and associated lossesthat reduce floret site utilization.Florets at anthesisPollination------------------------------------------Fertilization -----------------------------------------<strong>Seed</strong> set----------------------------------------------LossesEmpty floretsEmpty floretsEmpty floretsEarly abortion<strong>Seed</strong> development- Early growth stage------------------------------- Abortion- Food reserve accumulation stage-------------- DiseasesAbortion- Ripening stage------------------------------------ DiseasesShatteringHarvesting------------------------------------------- ShatteringDamageCleaning--------------------------------------------- Empty floretsLight seedsHeavy seeds<strong>Seed</strong> yieldthat the poor seed set observed in some grass species may bedue to the susceptibility of stigmas to damage under hightemperatures and to desiccation of the pollen. Stigma witheringin grasses begins a few hours after pollination. On thestigma, about 60-80% of the grass pollen germinates. Thegermination percentage increased with greater maturity ofpollen and stigma (Watanabe, 1961). Hebblethwaite andHampton (1981) mentioned that possibly not all florets arepotentially fertile, either because of pest damage (Johnston,1960) or because they are morphologically sterile and incapableof developing seed (Johnston, 1960; Hill, 1980).Johnston (1960) found up to 10% morphological sterility inflowers of Dactylis glomerata. Part of the 'sterility' inBromus inermis and Agropyron spp. is genetically determined;the environment also strongly influences the percentage offlowers that set seed (Knowles and Baenziger, 1962).Fertilization may be reduced due to self-incompatibility,which is quite common in grasses. In ryegrass, for example,there is a 2 loci gametophytic system, but under certainconditions some self-fertilization can occur. Probably theabsence of other pollen favors self-fertilization. Poor seed setmight occur when synthetic varieties are based on a fewclones.<strong>Seed</strong> SetAccording to Hill (1980), the term 'seed set' describes theearly growth of the embryo and endosperm. "Set" is indicatedby the presence of cell division following successfulfertilization.As shown by Hill (1971) and Burbidge et al. (1978),approximately 60% of all florets are capable of being fertilized.The position of a floret in the inflorescence influences theprobability of seed set (Anslow, 1964). In rye grass, abortionmay occur after fertilization up to approximately 21 daysafter anthesis. Soon after fertilization, cell division can bedisrupted resulting in a misshapen ovary. At a later stage,seed development is often resumed. In other cases, cellsdisintegrate and the entire ovule collapses (Hill, 1980).It is not clear whether abortion occurs more often afterself-fertilization. Burbidge et al. (1978) noticed in Loliumperenne that many more seeds were set than were harvested,even when the crop was not lodged. They mentioned twopossible reasons for abortion of developing seeds: hormonalinhibition of seed growth and competition for assimilates.<strong>Seed</strong> DevelopmentHyde et al., (1959) distinguished three stages in seeddevelopment in ryegrasses:Stage 1: the growth stage, duration 10days after pollination.Characteristics: rapid increase in seed weight,high seed moisture content and non-viability.Stage 2: the food reserve accumulation stage, duration afurther 10-14 days. Characteristics: a threefoldincrease in seed dry weight. <strong>Seed</strong>s attain full viability.Stage 3: the ripening stage, duration 3-7 days. Characteristics:dry weight remains approximately constant,but moisture content falls from about 10% to equilibriumwith the atmosphere.The stage of seed development affects three importantaspects of seed quality: viability, seedling vigor and storagelife (Hyde, 1950). Perennial ryegrass seed harvested 14 daysafter pollination would be viable, but would give rise toseedlings with poor vigor as high seedling vigor is not presentuntil about 24 days after pollination. Immature seeds deterioraterapidly in storage.A study by Hill (1971) with perennial ryegrass has shownthat different genotypes may have different patterns of embryomaturation. Furthermore, genotypes differ with respectto dehydration and the time taken to attain harvest ripeness(Hill, 1980). Cultural practices have a major effect on seeddevelopment.During seed development, shedding losses occur. Besidestrying to increase seed set, loss of viable seed can also bereduced. Burbidge et al. (1978) did not consider shedding tobe a major factor, which contrasts with the results of Stoddart(1964). According to Stoddart (1964), one of the principalsources of yield loss in grass seed crops is the amount of seedshed from the inflorescence. Environmental factors, such asheavy winds, affect shedding. Spread in ripening time alsopromotes shattering. In Lolium multiflorum, genetic variationfor seed retention was found between populations (Harun andBean, 1979). Several authors reported improved seed retentionresulting from breeding for this character (McWilliam,1980; Phalaris aquatica (syn. tuberosa); Bean, 1969; Phleumpratense; Falcinelli et al., 1984; Dactylis glomerata).<strong>Seed</strong> retention does not affect forage qualities and seems tobe a very desirable character in grass seed crops. Whengrowth regulators are introduced into commercial seed production,seed retention will become even more significant.
52 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985HarvestingNot all seed that is produced can be harvested because ofspread in ripeness, lodging and harvest losses. Within a seedcrop, differences in ripeness exist within and between spikelets,between inflorescences and between plants. The apicalflorets in the spikelet, the apical part of an inflorescence andthe oldest inflorescences ripen fast. The harvest time is acompromise between seed yield and quality. When the cropis harvested too early, many immature seeds are harvested,resulting in:-drying costs-increased risk of damage-cleaning losses (light seed)-loss of quality (light seed with low seedling vigor)If harvest is late, many seeds are lost through shedding. Atfirst, apical seeds will shatter which contain light seed. Then,the oldest inflorescences which carry the heaviest and thegreatest number of seeds also start to shed. Bonin and Goplen(1963) found that within clones of Phalaris arundinaceashattered seeds were heavier than non-shattered seeds. Jensen(1976) found that shed seeds had a lower moisture contentthan non-shattered seeds. As the time of harvesting differsmore from the mean ripeness date, the risk of genetic shiftalso increases (Davies, 1954).A lodged crop is difficult to harvest. Morover, new vegetativetillers may grow through the lodged inflorescencesand hamper harvesting. <strong>Seed</strong> quality decreases when theseeds are attacked by fungi. In a lodged crop, shattering isreduced. The harvest method, i.e. combining or swathing,affects seed yield losses. <strong>Seed</strong>s can be damaged, resulting indecreased quality. Harvest losses are greatly influenced byweather conditions.CleaningAfter harvesting and drying, the seed is cleaned. Normalor "heavy" seed is separated from dust, sand, stalks, entirespikelets, empty florets, light seed and weeds. The cleanedseed is weighed, providing the final (economical) seed yield.The number of clean seeds can be calculated from the thousandseed weight (TSW).BREEDING PERSPECTIVESPossible breeding perspectives for improved FSU, indicatedin the above review, are presented in Table 2. Moreresearch is needed to investigate which process has the highestcorrelation with grass seed yield, which characteristic hasthe largest genetic variation and which trait has the highestheritability.It is interesting to note that several authors (Knowles andBaenziger, 1962; Ross and Adams, 1955; Lowe and Murphy,1955; Raeber and Kalton, 1956; Nielson and Kalton, 1959;Ibrahim and Frakes, 1984; Slinkard, 1965 and Davies, 1954)reported FSU to be a fairly stable and highly heritable character.Others, (Mackay, 1960; Bean, 1969; and Bugge,1981), mentioned large environmental effects on FSU.A good relationship between ''seed set'' or ''fertility index''and seed production is reported by Knowles and Baenziger(1962), Ross and Adams (1955), Nielsen and Kalton (1959),Slinkard (1965), Davies (1954), Dewey and Lu (1959) andHearn and Holt (1969). However, the determination methodof FSU influences the correlation between FSU and seedyield.METHODOLOGYSeveral studies have been made ofFSU, "fertility index"or "seed set" in grasses. The results however, cannot easilybe compared, because different characters appear to havebeen determined in various ways. Three aspects of determiningFSU should be taken into account: time of determination,determination method and sampling technique.The time of determining the number of florets for calculatingthe potential yield is important. If florets are counted atanthesis, the estimated potential yield is much higher thanwhen counted after the harvest, because florets are lost duringdevelopment and harvest. The time of determining the numberof seeds for calculating the realized yield is also important.If seeds are counted before ripening, realized yield ismuch higher than when they are counted after harvest, becauseseeds are shed and lost during ripening, harvesting andcleaning.Several determination methods have been described previously:1. Number ratio between filled and total florets. Thismethod has been applied quite often to uncleaned seedharvested just prior to ripeness. (Bean, 1969; Davies,1954; Knowles and Baenziger, 1962). Empty and filledflorets were separated by feeling, pressing or by examinationover illuminated glass. Developing seeds are includedin the seed fraction so this method gives a measure ofbiological FSU.Table 2. Prospects of breeding for improved floret site utilizationin grasses.Process:PollinationFertilizationand seed set<strong>Seed</strong> developmentSelection for:- High pollen production- Uniform flowering (heading)- Lodging resistance- Pollen viability- Ovule viability- Retention of pollen andovule viability- Disease resistance- Lodging resistance- Compatibility- Disease resistance- Lodging resistance- Reduced embryo abortion- Uniform ripening- <strong>Seed</strong> retention
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 532. Germination percentage. This method is similar tomethod 1 in that developing, viable seeds are included.Very young seeds in the early growth stage which do notgerminate are not included, however. Biological FSUmeasured in this way will therefore be lower than FSU asestimated by method 1 (Lewis, 1966; van Wijk, 1985).3. Weight ratio between cleaned and uncleaned seed. Thismethod is easy to apply, but does not give relevant informationabout FSU. After threshing, seeds are separatedfrom empty florets and light seeds with a wind blower.Cleaned seed is much heavier than light and empty seed,so the percentage of cleaned seed is very high. This resultsautomatically in a high, significant correlation betweenestimates of FSU and final seed yield (van Wijk, 1985;Raeber and Kalton, 1956).4. Volume ratio between cleaned and uncleaned seed.This method gives a better estimation of the percentage ofwell-developed seeds than method 3 because seeds andempty florets differ less in volume than in weight (Hearnand Holt, 1969).5. Number ratio between cleaned and uncleaned seed.This method is more precise than the fourth, but is verylaborious. After threshing, all potential seeds are counted.<strong>Seed</strong>s are separated from empty florets and light seedswith a wind blower. Cleaned seeds are counted. Likemethods 3 and 4, method 5 underestimates potential seedyield, i.e. the number of floret sites, because losses offloret sites are not included. Estimated FSU based onthese methods will, therefore, be too high. Because onlycleaned seeds are counted, a measure of economical FSUis given.(Lewis, 1966; Johnston, 1960).6. Calculated ratio between realized and potential seedyield: FSU =yield m-2/(inflorescences m-2 x TSW /1000 xflorets/inflorescence). This method calculates economicalFSU. Number of inflorescences m-2 and florets/inflorescence are determined at anthesis to obtain a ''realistic"potential yield. FSU-values calculated in this wayare much lower than values obtained with the other methods(Meijer, pers. comm.).Method 1 seems most suitable for determining biologicalFSU. Shattering losses are not measured when applyingthese methods. For determination of biological FSU, however,shed seed should also be taken into account. For determinationof economical FSU, method 6 seems the best.The sampling technique for FSU should depend on thepurpose. If the aim is to determine the FSU of a crop,inflorescences must be taken at random. If the aim is to detectgenetic differences in FSU between genotypes or populations,variation due to age, developmental stage or size ofthe inflorescence should be reduced. Therefore, spikeletsshould be taken from similar positions in the infloresencesand florets from the same positions in the spikelets.SUMMARYThe seed yield of grasses needs improvement. <strong>Seed</strong> yieldshould become a more important selection criterion in grassbreeding. The yield potential, i.e. florets m-2 is much higherthan the realized yields. <strong>Seed</strong> yield depends largely on thedegree of floret site utilization (FSU). This term is not clearlydefined. A distinction should be made between biologicaland economical FSU. Biological FSU can be defined as thepercentage of florets resulting in a viable seed. This characteristicresults from several processes, i.e. pollination, fertilization,seed set and seed development. Economical FSUcan be defined as the percentage of florets resulting in aharvested seed. This characteristic results from biologicalFSU, harvesting and cleaning.In this paper the processes composing FSU in grasses arediscussed. During each process losses may occur, resultingin decreased FSU. For several traits, genetic variation hasbeen found which might offer perspectives when breedingfor improved seed yield in grasses.There is no agreement on heritability of FSU. However,results can hardly be compared among experiments becauseseveral definitions ofFSU and various determination methodshave been used. In this paper, three aspects of the methodologyof FSU are discussed: time, method and samplingtechnique. FSU should be determined in a proper way, andmethods and terms should be standardized. More research isneeded on FSU in grasses to develop better selection criteriafor improved seed yields.ACKNOWLEDGEMENTSFinancial support from the Commodity Board for ArableProducts is gratefully acknowledged.REFERENCES1. Anslow, R.C. 1964. <strong>Seed</strong> formation in perennial ryegrass II.Maturation of seed. J. Br. Grassl. Soc. 19:349-357.2. Bean, E.W. 1969. 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In EuropeanGrassland Conference. OEEC.8. Dewey, D.R., and K.H. Lu. 1959. A correlation and pathcoefficientanalysis of components of crested wheatgrass seedproduction. Agron. J. 51:515-518.9. Falcinelli, M., F. Veronesi, and V. Negri. 1984. <strong>Seed</strong> dispersalof Italian ecotypes of cocksfoot (Dactylis glomerataL.). J. Appl. <strong>Seed</strong>. Prod. 2:13-17.
54 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 198510. Griffiths, D.J., H.M. Roberts, and J. Lewis. 1973. The seedyield potential of grasses. Welsh Plant Breeding Station, AnnualReport, 1973. pp. 117-123.11. Harun, R.M.R., and E.W. Bean. 1979. <strong>Seed</strong> developmentand seed shedding in North Italian ecotypes of Lolium multijlorum.Grass and Forage Science 34:215-220.12. Hearn, C.J., and E. C. Holt. 1969. Variability in componentsof seed production in Panicum coloratum L. Crop Sci. 9:38-40.13. Hebblethwaite, P.D. 1977. Irrigation and nitrogen studies inS.23 ryegrass grown for seed. 1. Growth, development, seedyield components and seed yield. J. Agric. Sci., Camb.88:605-614.14. Hebblethwaite, P.D., and J.G. Hampton. 1981. Physiologicalaspects of seed production in perennial ryegrass. pp.17-32. In Breeding high yielding forage varieties combinedwith high seed yield. Report of the meeting of the FodderCrops Section of Eucarpia in Merelbeke (Belgium), 8-10September 1981.15. Hill, M.J. 1971. A study of seed production in 'GrasslandsRauanui' perennial ryegrass (Lolium perenne), 'GrasslandsKahu' Timothy (Phleum pratense L.) and prairie grass(Bromus unilodes H.B.K.). Ph.D. thesis, Massey University,Palmetston North.16. Hill, M.J. 1980. Temperate pasture grass-seed crops: formativefactors. pp. 137-150 In P.D. Hebblethwaite (ed.). <strong>Seed</strong>production. Butterworths, London.17. Hyde, E.O.C. 1950. Studies on the development of whiteclover seed. pp. 12:101-107. In Proc. N.Z. Grassl. Assoc.18. Hyde, E.O.C., M.A. McLeavy, and G.S. Harris. 1959. <strong>Seed</strong>development in rye grass and in red and white clover. N .Z.J. ofAgric. Res. 2:947-952.19. Ibrahim, A.E.S., and R.V. Frakes. 1984. Variability andinterrelations of seed yield components in tall fescue (F.arundinacea Schreb.) Genet. Agr. 38:387-398.20. Jensen, H. A. 1976. Investigation of anthesis, length of caryapsis,moisture content, seed weight, seed shedding and strippingripeness during development and ripening of a F estucapratensis seed crop. Acta Agric. Scandinavica 26:264-268.21. Johnston, M.E.H. 1960. Investigations into seed setting incocksfoot seed crops in New Zealand. N.Z.J. Agric. Res.3:345-357.22. Jones, M.D., and J.G. Brown. 1951. Pollination cycles ofsome grasses in Oklahoma. Agron. J. 43:218-222.23. Knowles, R.P., and H. Baenziger. 1962. Fertility indices incross-pollinated grasses. Can. J. Pl. Sci. 42:460-471.24. Lewis, J. 1966. The relationship between seed yield andassociated characters in meadow fescue (Festuca pratensis).J. Agric. Sci., Camb. 67:243-248.25. Lowe, C.C., and R.P. Murphy. 1955. Open-pollinated seedsetting among self sterile clones of smooth bromegrass.Agron. J. 221-224.26. Mackay, K.H. 1960. Variations in cross-fertility in two xenogamousgrasses, Bromus inermis Leyss. and Phleum pratenseL. Doctoral thesis, Univ. Wisconsin.27. McWilliam, J.R. 1980. The development and significance ofseed retention in grasses. pp. 51-60. In P.D. Hebblethwaite(ed.). <strong>Seed</strong> Production. Butterworths, London.28. Nielson, A.K., and R.R. Kalton. 1959. Combining ability forseed characteristics in Bromus inermis Leyss. Agron. J.51:178-181.29. Raeber, J.G., and R.R. Kalton. 1956. Variation and inheritanceof fertility and its components inBromus inermis Leyss.Agron. J. 48:212-216.30. Ross, J. G. , and M. W. Adams. 1955. The influence of heredityon seed and forage production in smooth bromegrass. Proc.S. Dakota Acad. Sci. 34:16-20.31. Slinkard, A.E. 1965. Fertility in intermediate wheatgrassAgropyron intermedium (Host) Beauv. Crop Sci. 5:363-365.32. Stoddart, J.L. 1964. <strong>Seed</strong> ripening in grasses. I. Changes incarbohydrate content. J. Agric. Sci. 62:67-72.33. Wantanabe, K. 1961. Studies on the germination of grasspollen. II. Germination capacity of pollen in relation to maturityof pollen and stigma. Bot. Mag., Tokyo 74:131-137.34. Wijk, A.J.P., van 1985. Factors affecting seed yield in breedingmaterial of Kentucky bluegrass (Poa pratensis L.) J. Appl.<strong>Seed</strong> Prod. (in press).
The Effect of Uneven Ripening on Floret Site Utilizationin Perennial Ryegrass <strong>Seed</strong> CropsW.J.M. Meijer'ABSTRACTPrior to harvest of perennial ryegrass seed crops much higherseed numbers are observed than are recovered after threshingand cleaning. A considerable amount of light seeds must be lostduring threshing and cleaning. In recent literature most of theselosses are attributed to assimilate shortage and abortion of developingseeds. The significance of uneven ripening is discussed asanother major factor contributing to the poor utilization of yieldpotential.Additional index words: seed set, grass seed, seed abortion,Lolium perenne L.INTRODUCTIONSome weeks after anthesis in seed crops of perennialryegrass the maximum number of developing seeds are recorded(Burbidge et al., 1978; Hampton and Hebblethwaite,1985). During the seed filling stage the number of seedsdecreases as a result of abortion and seed shedding. Abortionthat occurs soon after fertilization is difficult to detect. Cytologicalmethods are required to distinguish between unfertilizedand early aborted florets. Abortion later in the seedfilling stage results in an increased fraction of light seeds.These florets appear as early maturing seeds. It depends onhow abortion is defined whether this late abortion decreasesseed set. A second important reduction in seed number occursduring harvest and cleaning. Not all of these losses canbe attributed to abortion, or shedding at harvest. This papersuggests that the uneven development of ears and unevenripening within ears substantially contribute to the fraction oflight seeds which is lost during the cleaning procedures.DISCUSSIONObserved and Calculated Floret Site UtilizationOften percentage seed set just prior to harvest is assessedby recording the presence or absence of a developing seed foreach floret position in a number of inflorescences. Even inlodged crops, initially 50-80% seed set is observed (Anslow,1963; Akpan and Bean, 1977; Hampton and Hebblethwaite,1985). Calculation of seed set from cleaned seed yield, seedweight and the floret numbers (assessed before harvest),often results in values approximately half of the observedseed set (Wright and Hebblethwaite, 1979; Hampton et al.,1983; Hampton and Hebblethwaite, 1984).Burbidge et al.(1978) observed a maximum seed set ofabout 60% 3 weeks after peak anthesis. However, during the6-13 days before harvest, seed set decreased to 20-30%.From this decline it was concluded that abortion of developingseed reduces the number of seed harvested. Not mentionedby Burbidge et al. (1978), however, is how abortion wasdefined. Abortion of developing seed late in the filling periodmay give rise to an increased proportion of light seed. However,in recording presence or absence, these light seeds maybe scored as present. Hampton and Hebblethwaite (1985)reported a small decrease in seed set until shedding of matureseed became important. Anslow (1963) observed an increasein seed set of 59% just after last anthesis to 69% at ripeness.This increase was attributed to shedding of predominantlyempty florets during the early stages of maturity.In some of our experiments with perennial ryegrass (treatedwith nitrogen fertilizer and growth retardant), floret numberswere recorded at the end of an thesis and prior to harvest.Shedding considerably decreased floret number. Often twodistal florets per spikelet were shed. Probably many of theseflorets are morphologically incomplete.During the second half of the seed filling period someyellowing, early maturing seeds were observed in otherwisegreen inflorescences. However these apparently late abortedseeds never exceeded 3% of the total. From the seed numberobserved at harvest, 40-70% was recovered after cleaning(Table 1, 2). Shedding at harvest can explain only a minorpart of this seed loss. Minimum losses at harvest of 5-10%Table 1. Losses of floret and seed number during seed fillingand at harvest observed in a nitrogen application experimentin perennial ryegrass (cv. Barlenna, 1981).no. florets ear -1 no. seeds ear -ISpring Nitrogenkg N ha-l End of Prior to Prior to Calculatedan thesis harvest harvest from yield'Research Station for Arable Farming and Field Production ofVegetables (PAGV), P.O. Box 430, 8200 AK Lelystad, TheNetherlands.60 115 81 55 32120 110 81 46 29210 108 76 41 2955
56 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 2. <strong>Seed</strong> yield components in two experiments on a growth retardant in perennial ryegrass. Observed ear, floret and seed numberjust prior to harvest. Calculated seed number from seed yield (cv. Pablo, 1982 and 1983).Paclobutrazol Florets m-2 No. seeds m-2 10 -3 %seed set %(kg ha-l) Ears m-2 10-3Observed Calculated Observed Calculated Recovery19820 2260 312 2000.75 2880 400 26819830 1980 386 2080.50 2570 506 253118 64 38 59131 67 33 4999 54 25 4896 50are recorded (Madsen, 1972; Andersen and Andersen 197 5).Probably the light seed was removed with the empty floretswhile cleaning.Poor seed filling can result from reduced assimilate productionin lodged crops (Burbidge et al., 1978) or earlysenescence of photosynthetic tissue (Hampton andHebblethwaite, 1984). Also, competition for assimilatesfrom the enlongating stem (Clemence, 1982) and from vegetativetillers (Hampton, 1983) can impede seed filling.Uneven RipeningAlso uneven ripening can explain a great deal of the lowrecovery from the potential yield observed before harvest.With perennial ryegrass, ears can be produced by tillersemerging from the previous autumn and until late spring.However, this flexibility may increase unevenness. Anslow( 1963, 1964) assessed variation in an thesis and ripening in anearly-sown, low-fertilized and therefore relatively uniformryegrass crop. At optimum harvest time, mean seed weightof the earliest heads to flower was 2 mg and of intermediateflowering ears was 1.6 mg. About 40% of the fertile tillersemerged late. These late heads produced 27% of seed numbers,their mean seed weight was 1. 2 mg. Within each head,even greater variation in seed weight was recorded.The importance of even ripening was also detectable insome of our trials with application of the growth retardantpaclobutrazol in perennial ryegrass (Table 2). Lodging wasdelayed and less severe and in both years higher ear numberswere recorded compared with untreated crops. Probably thebetter light penetration in the treated crops explains thesegreater numbers. In the early-lodging, untreated crops, fewerof the late emerging and late elongating fertile tillers wouldhave survived. This increase in ear number resulted in ahigher floret and seed number at harvest. All crops wereharvested when shedding of full seeds became significant.Although in the treated crops the potential yield was muchgreater, recovery was considerably lower. It seems likelythat at harvest many seeds of the late ears were only poorlyfilled and subsequently lost in cleaning. Probably adaptationof harvest method and time is needed after growth retardantapplications (Hampton and Hebblethwaite, 1985) howeverthese results suggest that a higher potential has to be combinedwith more even ripening.Implications for Agricultural ResearchThe low percentage recovery clearly demonstrates theneed to aim at even ripening. Early establishment of rye grasscrops allows for adequate tillering which results in a uniformseed head population, (Foster, 1969). This gives some possibilityto improve crop evenness for growers. However,improvement in uniformity of ripening by breeders is to berecommended. In cross-pollinating cultivars, variation inperiod of anthesis and maturity is always evident. Thesedifferences seem even more pronounced in years of adverseflowering conditions. Strong selection for even ripeningshould be given high priority by plant breeders.Another means to increase recovery would be to improveseed retention. Better seed retention would allow harvest tobe delayed until late-emerging heads have fully ripened.REFERENCESI. Akpan, E.E.J., and E.W. Bean. 1977. The effects of temperatureupon seed development in three species of foragegrasses. Ann of Bot. 41:689-695.2. Andersen, S., and S. Andersen. 1975. Hosttidsforsog medfrograss. Tidsskrift for Froavl 63(754):176-184.3. Anslow, R.C. 1963. <strong>Seed</strong>formationinperennialryegrass. 1.Anther exertion and seed set. J. Br. Grassl. Soc. 18:90-96.4. Anslow, R.C. 1964. <strong>Seed</strong> formation in perennial ryegrass. 2.Maturation of seed. J. Br. Grassl. Soc. 19:349-357.5. Burbidge, A., P.D. Hebblethwaite, and J.D. Ivins. 1978.Lodging studies in Lolium perenne grown for seed. 2. Floretsite utilization. J. Agric. Sci., Camb. 90:269-274.6. Clemence, T.G.A. 1982. <strong>Seed</strong> production by amenity ryegrassLolium perenne. Ph.D. thesis, University of Nottingham.7. Foster, C.A. 1969. The influence of planting date on theseed-bearing capacity of tillers of perennial ryegrass spacedplants grown for seed. J. Br. Grassl. Soc. 24:271-276.8. Hampton, J.G. 1983. Chemical manipulation of Loliumperenne grown for seed production. Ph.D. thesis, Universityof Nottingham.9. Hampton, J.G. and P.D. Hebblethwaite. 1984. The effect offungicide application on seed yield in perennial rye grass cv. S24. Ann. Appl. Bioi. 104:231-239.10. Hampton, J.G. and P.D. Hebblethwaite. 1985. The effect ofgrowth retardant application on floret site utilization and assimilatedistribution in ears of perennial ryegrass cv. S 24.Ann. Appl. Bioi. 107:127-136.11. Hampton, J.G., T.G.A. Clemence and P.D. Hebblethwaite.
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 571983. Nitrogen studies in Lolium perenne grown for seed.Grass and Forage Sci. 38:97-105.12. Madsen, N.P. 1972. Combine harvesting of grass seed fromthe standing crop. Dansk Landbrug 3:(7)24-27.13. Wright, D. and P.D. Hebblethwaite. 1979. Lodging studies inLolium perenne grown for seed. 3. Chemical control of lodging.J. Agric. Sci., Camb. 93:669-679.The Influence of Environmental and Agronomic Factors on Floret Site Utilizationin Perennial RyegrassP.D. HebblethwaitetABSTRACTThis paper reviews some of the work carried out at theUniversity of Nottingham on environmental and agronomicfactors which affect floret site utilization in the ryegrass seedcrop. Low average temperature at anthesis was shown todecrease floret site utilization. Level, timing of nitrogen applicationand lodging influenced floret site utilization. The use ofgrowth regulators increased floret site utilization and yield. Thefuture role of chemical manipulation and its influence on floretsite utilization is discussed.Additional index words: florets, seed set, t4C-assimilate, growthregulators, macro-environment, nitrogen, water.INTRODUCTIONMuch work has been carried out on the development ofpotential yield in ryegrass seed crops (Anslow, 1963; Ryle,1964; 1966; Hebblethwaite, Wright and Noble, 1980;Hampton, 1983) but little on the utilization of that potential(Hill, 1980). Most ryegrass seed crops produce largenumbers of floret sites per unit area and therefore potentialyields. Estimates indicate that if all floret sites are utilizedyields of around 8 t ha-I would be achieved in most crops(Hebblethwaite et al., 1980; Hampton, 1983). Actual percentagefloret site utilization under farm conditions isusually only about 10% which results in yields of well under1 tha-t.Consequently this paper deals with environmental andagronomic factors affecting floret site utilization and notfloret production.ENVIRONMENTAL FACTORSAt the University of Nottingham an examination ofmacro-environmental factors during anthesis and its relationshipto yield of the perennial ryegrass seed crop ( cv.S.24) was carried out using data collected over a ten yearperiod (Hampton and Hebblethwaite, 1983). Minimumscreen temperature during the month of June, during theweek of anthesis and during the week after anthesis wassignificantly related to seed numbers and yield. This factoraccounted for over 70% of the variance in seed numbersrecorded. Although measurement of the macro-environmentis crude compared to micro-environmental measurementswithin the crop this finding which takes 10 differing seasonsinto account agrees well with micro-environmental responsesreported by others (Jones and Brown, 1951; Hill, 1971;1980). Consequently it must be assumed that low averagetemperatures at anthesis (i.e. below 8 C) are likely todecrease floret site utilization. Little is known why thisshould be the case and what sort of damage occurs. Furtherwork into the effects of low temperature on floret siteutilization needs to be carried out.The only other weather factor related to seed numberswas wind velocity in the week following anthesis where areduction was recorded with increasing velocity. Rainfall,radiation, and relative humidity had no significant influenceon seed numbers (Hampton and Hebblethwaite, 1983).Irriga-tion experiments have also indicated that water stressequivalent to a profile soil water deficit of 90-100 mm willhave little effect on floret site utilization (Hebblethwaite,1977). Excess water during the period of seed set anddevelopment can increase secondary tillering and this couldbe at the expense of seed fill and consequently decreaseyield.AGRONOMIC FACTORS1Reader in Agronomy, University of Nottingham, School ofAgriculture, Sutton Bonington, Loughborough, Leics. U.K. Receivedfor publication 3 December 1985.Nitrogen experiments have shown that increasing theamount of spring applied nitrogen can increase the numberof florets per unit area but percentage seed set can be
58 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985decreased (Hebblethwaite, et al., 1980). This may be aresult of earlier and more severe lodging, or to increasedcompetition for assimilates between floret site and secondaryvegetative tillering (Hebblethwaite et al., 1980; Hampton,1983; Clemence and Hebblethwaite, 1984). Vegetativetillers subtending developing fertile tillers compete forassimilates with the growing seed (Hampton, 1983; Clemenceand Hebblethwaite, 1984). In a lodged crop (cv. S.24)assimilate movement from the flag and penultimate leaveswas mostly down the plant to the subtending vegetativetillers. This was confirmed by Clemence and Hebblethwaite(1984) who also showed that during stem elongation, theear was a net exporter of assimilate and that up to 10% ofthis assimilate was recovered from subtending vegetativetillers. Transfer of assimilates from vegetative to parenttillers was found to be low as only about seven percent ofthe t4C they fixed was exported (Hampton, 1983).Delaying the application of nitrogen to ear emergencedecreases the number of florets per unit area but increasesseed set. This can be attributed to a reduction in the severityof lodging at anthesis, or a reduction in the number ofpotential seed sites per ear resulting in less competitionbetween sites. However, this delay in nitrogen applicationdecreases yield in spite of the increased seed set because ofthe reduced yield potential (Hebblethwaite et al., 1980).Late nitrogen application can also result in excess secondarytillering (Nordestgaard, 1980) particularly in wet seasonsand this could result in further competition for assimilates.High levels of nitrogen increase the severity and bringforward the time of lodging (Hebblethwaite and Ivins,1977). Lodging decreases the proportion of florets that setseed (Burbidge et al., 1978). In S.24 the percentage offlorets which set seed decreased from the base to the apex ofthe ear in a lodged crop but was more uniformly distributedin an erect crop (Burbidge et al., 1978). In S. 24 thepercentage seed set for each floret position was also foundto be higher in erect crops (Burbidge et al., 1978). Lowerseed set in lodged crops have been attributed to suppressionor inhibition of anthesis (Burbidge, 1977) because of lessfavorable micro-environmental conditions (Hampton andHebblethwaite, 1983) and decreased pollen dispersal(Wright and Hebblethwaite, 1979).The above work on nitrogen and lodging indicated thatthe prevention of lodging by chemical means could significantlyincrease seed set and yield in ryegrass seed crops. In1981 and 1982 work using the chemical paclobutrazolsprayed at spikelet initiation showed that this treatmentsignificantly increased the number of seeds per spikeletpresent at final harvest by reducing the number of seedsaborted during seed development (Hampton andHebblethwaite, 1985a) and this resulted in substantialincreases in seed yield (Hampton and Hebblethwaite, 1985b).This increase due to paclobutrazol application was due to analteration in the distribution of florets and seeds per spikelet,as both the basal and penultimate spikelets contained moreflorets and seeds than did those of untreated plants (Hamptonand Hebblethwaite, 1985a).Further work indicated that in untreated plants, assimilaterecovery was lower from the terminal section of the ear,whereas in chemically treated plants, no differences werefound between basal, intermediate or terminal sections ofthe ear. Assimilate demand at all sections of the ear werealso increased when the ear and leaves were fed with t4C0 2in paclobutrazol treated plants (Hampton and Hebblethwaite,1985a). This work shows that abortion of developing seedsis an important factor in contribution to low number ofseeds harvested.As well as the above effects this chemical was highlysuccessful in preventing lodging by increasing stern basestrength, reducing stern internode length, increasing rootdry matter and leaf area duration. All these responsesenabled large increases in seed yield (Hampton andHebblethwaite, 1985b).In the short term there is little the breeder can do to selectfor higher seed yield in known varieties. The use of growthregulators therefore has a great potential for the future.Paclobutrazol (Parlay) has been released since 1985 on alimited basis for commercial use in U.K. and U.S.A.herbage seed crops. Results to date have been promising.Further work is also being carried out on other growthregulators and results have been good (Hebblethwaite,Barrett and McGilloway, 1985). However, these productscan result in upright crops which are highly susceptible toshedding prior to harvest under adverse conditions (Hampton,1983). In the long term it is therefore important thatchemical manipulation of seed shed is given researchpriority. Work started at the University of Nottingham in1985 in this area but with no success to date (Hebblethwaiteet al., 1985).In the long term the herbage seed grower may be lookingto multiple chemical use. Work at the University of Nottingham(Hampton and Hebblethwaite, 1984) has alreadyshown that a combination of GA 3 and paclobutrazol canreduce vegetative tillering prior to ear emergence, reducestem length and lodging with a possible increase in seed setand yield. The next stage is to look for a chemical whichwill substantially increase seed set, seed retention, andtransfer of assimilates to the seed. Added to this could be achemical which would prevent shedding in an upright crop.Perhaps all these functions may be found in one or twochemicals in the future. This approach is not too far distantfrom commercial reality. The speed at which such developmentswill take place will depend on the funding of researchin the future.REFERENCES1. Anslow, R. C. 1963 . <strong>Seed</strong> formation in perennial rye grass. IAnther exsertion and seed set. J. Br. Grassl. Soc. 18:90-96.2. Burbidge, A. 1977. Lodging and its controlin Latium perennegrown for seed. Ph.D. thesis, University of Nottingham.3. Burbidge, A., P.D. Hebblethwaite, and J.D. Ivins. 1978.Lodging studies in Lolium perenne grown for seed. 2. Floretsite utilization. J. Agric. Sci., Camb. 90:269-274.4. Clemence, T.G.A., and P.D. Hebblethwaite. 1984. An appraisalof ear, leaf, and stem t4C0 2assimilation, t4C assimilatedistribution and growth in a reproductive seed crop ofamenity Lolium perenne. Ann. Appl. Bioi. 105:319-327.5. Hampton, J.G. 1983. Chemical manipulation of Lolium per-
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 59enne grown for seed production. Ph.D. thesis, University ofNottingham.6. Hampton, J.G., and P.D. Hebblethwaite. 1983. The effects ofthe environment at anthesis on the seed yield and yieldcomponents of perennial ryegrass (L. perenne) cv. S.24. J.Appl. <strong>Seed</strong> Prod. 1:21-22.7. Hampton, J.G., and P.D. Hebblethwaite. 1984. Experimentswith vegetative tiller manipulation in the perennial ryegrass(Lolium perenne L.) seed crop by the application of growthregulators. J. Appl. <strong>Seed</strong> Prod. 2:1-7.8. Hampton, J.G., and P.D. Hebblethwaite. l985a. The effect ofgrowth retardant application on floret site utilization andassimilate distribution in ears of perennial rye grass cv. S .24.Ann. Appl. Bioi. 107:127-136.9. Hampton, J.G., and P.D. Hebblethwaite. 1985b. The effect ofthe growth regulator paclobutrazol (PP333) on the growth,development and yield of Lolium perenne grown for seed.Grass and Forage Sci. 40:93-IOI.10. Hebblethwaite, P.D. 1977. Irrigation and nitrogen studies inS.23 ryegrass grown for seed. I. Growth, development, seedyield components and seed yield. J. Agric. Sci., Camb.88:605-614.II. Hebblethwaite, P.D., S. Barrett, and D. McGilloway. 1985.Ryegrass seed production research, Report No. 9. pp. l-5.University of Nottingham, Dept. of Agric. and Hort.12. Hebblethwaite, P.D., and J.D. Ivins. 1977. Nitrogen studiesin Lolium perenne grown for seed. I. Level of application. J.Br. Grassl. Soc. 32:195-204.13. Hebblethwaite, P.D., D. Wright, and A. Noble. 1980. Somephysiological aspects of seed yield in Lolium perenne L. pp.71-90. In P.D. Hebblethwaite (ed.) <strong>Seed</strong> production. Butterworths,London.14. Hill, M.J. 1971. A study of seed production in perennialryegrass, timothy and prairie grass. Ph.D. thesis, MasseyUniversity, New Zealand.15. Hill, M.J. 1980. Temperate pasture grass-seed crops: formativefactors. pp. 137-149. In P.D. Hebblethwaite (ed.) <strong>Seed</strong>production. Butterworths, London.16. Jones, M.D., and J.G. Brown. 1951. Pollination cycles ofsome grasses in Oklahoma. Agron. J. 43:218-222.17. Nordestgaard, A. 1980. The effect of quantity of nitrogen,date of application and the influence of autumn treatment onthe seed yield of grasses. pp. 105-119. In P.D. Hebblethwaite(ed.) <strong>Seed</strong> production. Butterworths, London.18. Ryle, G .J .A. 1964. The influence of date of origin of the shootand level of nitrogen on ear size in three perennial grasses.Ann. Appl. Bioi. 53:311-323.19. Ryle, G.J.A. 1966. Physiological aspects of seed yield ingrasses. pp. 106-120. In F.L. Milthorpe and J.D. Ivins (eds.)Growth of cereals and grasses. Butterworths, London.20. Wright, D., and P.D. Hebblethwaite. 1979. Lodging studiesin Lolium perenne grown for seed. 3. Chemical control oflodging. J. Agric. Sci., Camb. 93:669-679.Factors Affecting <strong>Seed</strong> Yield in Breeding Material ofKentucky bluegrass (Poa pratensis L.)A.J.P. van Wijk1ABSTRACTFactors affecting seed yield, including seed yield components,were determined in two breeding populations of Kentucky bluegrass(Poa pratensis L. ). In both populations a higher number ofinflorescences and spikelets had a positive effect on seed yield,but their effect was reduced by a smaller seed weight. It wasconcluded that the seed yield per plant could be used as abreeding objective when selecting for seed yield.Additional index words: seed yield components, path coefficients,multiple regression.ID.J. van der Have B.V., P.O. Box 1, 4410 AA Rilland, theNetherlands.INTRODUCTIONKentucky bluegrass (Poa pratensis L.) is widely used as aturf grass in temperate areas and possesses favorable turfcharacteristics. However good the turf quality is, the ultimatecommercial success of a cultivar will be determined by theeconomics of its seed production. Numerous cultivars havebeen developed that excelled in turf quality but were nevermarketed because of their inability to produce seed in largeenough quantities. Examples are also known of cultivars thatare high in seed production but poor in turf quality.The breeder, therefore, is challenged to combine both turfquality and seed productivity in one and the same cultivar -two characteristics that act adversely on each other.Various studies have been undertaken to define the componentsdetermining seed yield and therefore should be theobjectives in a selection program for higher seed yield (Deweyand Lu, 1959; Lewis, 1966; Knowles et al., 1970; Bugge,1981; Wilson et al., 1981; Nguyen and Sieper, 1983). Oftensuch studies have been based on a limited number of plants
60 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985and on refined observations. In a large scale breedingprogram however, thousands of plants have to be screenedfor seed productivity and simple screening characteristicsare required in order to cope with these numbers.The present study was set up to defme the factors affectingseed yield which could be determined for a large number ofplants.MATERIALS AND METHODSThe bluegrass material studied originated from two hybridizationprograms between cultivars, that were crossed in1976 and 1977 respectively as described by Hintzen and vanWijk (I985).The PI-plants that deviated positively (i.e. vigorous andhealthy growth with an adequate number of inflorescences)from the mother plant were selected. In 1979 2.9% of theFl-plants were selected; in 1980 this percentage was 1.2%.The origin and number of the selected plants is given in Table1.The selected plants were multiplied vegetatively. Of theTable 1. Origin and number of plants studied.Origin1979ParadeParadeParadeParadeFylkingContinentalAquila1980PionPionPionEn topperEntopperEntopperParadeParadeParadeParadeAquilaAquilaAquilaAquilaAquilaMentorMentorMentorMentorEnwartoBaron*Continental*Aquila*En topper*Baron*Aquila*Parade*Parade*Mentor*Aquila*Parade*Mentor*Aquila*Parade*Entopper*Pion*Mentor*Aquila*Bristol*Baron*Parade*Enwarto*En topper*Bristol*Baron*En topper*Pion*Pion*MentorNo.2492495534332222I32clones selected in 1979, 15 plants per clone were planted at adistance of 30 x 30 em on 9 August I979. Of the 1980-selected clones, 20 plants per clone were planted at the samedistance on 19 August 1980. The distance between plots was90 em. At time of planting in 1979, 100 kgN ha-t was appliedas calcium ammonium nitrate, while the 1980 planting received40 kg N ha-t at time of planting and 40 kg N ha-t on 20October 1980. The grass was not cut during autumn. On 28February 1980 and 19 February 1981 respectively, 60 kg Nha-t was applied.In the 1979- and 1980- program 50 and 45 F1-plants werechosen at random for making the observations describedbelow. The cultivars Aquila, Continental, Fylking and Paradewere included as standards in the 1979- program; Aquila,Baron, Birka, Entopper, Enwarto, Parade and Pion for the1980-program. The standard cultivars were planted as thePI-plants were. Observations made in I980 and 1981 arelisted in Table 2.One week before harvesting, an area of 30 x 30 em of thetreated plants in the vegetative stage was cut at ground level.Observations made on the material harvested are listed inTable 2.The remaining I4 (1980) or 19 plants (1981) were harvestedwhen the seed was ripe. After threshing and cleaning, thefollowing was determined or calculated: seed yield per plant,seed yield per inflorescence, and 1000 grain weight.The measured and calculated characteristics were subjectedto a regression analysis. Path coefficients were calculatedaccording to Dewey and Lu (1959) between number of inflorescences,number of florets, 1000 grain weight and floretutilization (1980), or number of germinating seeds (1981)with seed yield per plant and seed yield per inflorescence asdependent variables (excluding number of inflorescences forthe latter). The variables with the highest predictability of thedependent variables were selected according to Daniel andWood (1971), as described by van Wijk (1977). Of eachcharacteristic, the relative influence on the dependent variablewas calculated. The relative influence describes thefraction of the total change in the dependent variable that canbe accounted for by the accompanying total change in the ithindependent variable and is defined as: relative influence =( jbi jwJjwy in whichbi= the partial regression coefficient of the ithindependent variable xwi = the range of the ith independent variable xwy= the range of the dependent variable yRESULTSThough the plants studied were selected for high growthvigor and number of inflorescences, a wide variation in themeasured characteristics still occurred. In Table 3 the means,the coefficients of variation and the ranges of the measuredcharacteristics are presented (standard cultivars are included).In spite of their different genetic background, the 1979-and 1980- plants showed a fair agreement in these values.In both years, plant height and 1000-grain weight had thelowest coefficients of variation, while increase in culm num-
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 198561Table 2. Observations during plant development and at harvest.Growth StageVegetative stage-tiller number-growth stage-lodging-mildew-increase in numberof inflorescences-plant heightObservationsthe number of tillers in an area of 30 x 30 em around one plant1 =vegetative, 9=fully emerged inflorescencel=none, 9=heavy1 =none, 9=presentthe number of inflorescences was determined every 4 days till itremained constant - the regression coefficient between time andnumber of inflorescences was a measure for theincreasemeasured on the longest culm at full head emergenceDate1980 198J19/3 21/312/51/63/63/6 3/6Reproductive stage-number of inflorescences-number of spikeletsper culm-% vegetative tillers-% generative tillers-% floret utilizationin 1980-number of germinatingseeds perinflorescencein 1981determined on 10 culms (1980) and 5 culms (1981) respectivelythe number of tillers that had not produced an inflorescence was expressedas a percentage of the total number of harvested tillersthe percentage tillers, present on 19/3/1980 or 21/3/1981 that producedinflorescencesthe weight of filled florets, as determined with a seed blower, was expressed asa percentage of the weight of all florets15 inflorescences were laid out for germination (7 months after harvesting) andthe number of germinating seeds was countedher, seed yield per plant and per inflorescence had the highest.The percentage generative tillers was in some cases higherthan 100, which meant that more tillers than the ones countedin March produced inflorescences. This was partly caused byinaccuracies at counting and by the fact that later developedtillers became generative as well.Table 3. Means, coefficients of variation and ranges of the measured characteristics.The determination of floret utilization and number of germinatingseeds per culm showed diverging results. The variationin floret utilization as determined by the weights of thefilled and non-filled florets was much smaller than the numberof germinating seeds per culm, which was a measure offloret utilization as well.1980 1981Characteristic Mean CV% Range Mean CV% RangeNumber of tillers 189 42 40-379 184 33 60-345Growth stage 4.2 43 1-7Lodging 2.3 92 1-9Mildew 5.5 51 1-9Increase 8.4 46 2.3-16.3 10.0 47 2.5-22.9Plant height (em) 60 17 40-90 74 16 46-98Nb. of inflorescences 131 38 40-262 177 42 52-364Nb. of spikelets/infl. 170 22 105-283 139 25 76-220% Vegetative tillers 40 36 13-74 38 45 4-80% Generative tillers 75 37 31-159 105 13 84-170% Floret utilization 86 9 64-94Nb. germ. seeds/infl. 56 72 7-2121000-grain weight (mg) 470 17 290-730 479 21 230-710<strong>Seed</strong> yield/plant (g) 8.8 45 1.8-20.0 6.7 49 1.0-16.2<strong>Seed</strong> yield/infl. (mg) 74 45 18-158 42 54 7-102
62 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 4. Correlation coefficients between characteristics.TillernwnberGrowth stage1 =vegetative9=generativeLodging Mildew Increasel=none l=none in inflo-9~lodged 9=present rescencenbPlantheightNb of inflo- Nb of spike- % Veg. %Gen. <strong>Seed</strong>set- 1000 Grain <strong>Seed</strong> <strong>Seed</strong>rescences lets/culm tillers tillers Nb. of germ. weight yield/ yield/seeds plant infl.Tillernumber0.343*0.364** 0.521**0.237 0.757**0.1250.1350.597**0.711**0.033 0.047 -0.526** -0.211 -0.300* 0.003 -0.353**-0.002 -0.161 -0.381** -0.048 -0.333* 0.154 -0.368**Growthstage0.163 0.592**0.0250.365**0.151 -0.501 ** -0.349** -0.156 -0.233 0.083 -0.214Lodging0.0780.394**-0.0230.283* -0.103 -0.312* -0.124 -0.122 0.373** 0.276**Mildew0.0790.326*0.1140.083 0.108 -0.254 -0.198 -0.186 -0.011 -0.042Increase ininflorescence nb0.0540.035-0.218 -0.316* -0.002 -0.032 -0.153 0.198 -0.1710.111 -0.457** -0.405** 0.004 -0.373** 0.122 -0.459**Plantheight0.0120.0460.333* -0.065 -0.134 -0.020 0.029 0.182 0.1660.226 -0.250 -0.354** -0.226 -0.028 0.355** 0.396**Nb ofinflorescences-0.061 -0.340* 0.284* -0.152 -0.292* 0.2300.024 -0.524** -0.252 0.033 -0.338* 0.228Nb of spikelets/culm0.003 -0.119 -0.255 ..0.276* 0.084 0.150-0.186 -0.014 0.195 -0.141 0.085 0.057% Veg.tiUers-0.448** 0.048 0.110 -0.277* -0.0090.232 0.122 0.139 -0.382** -0.012%Gen.tillers-0.097 -0.004 0.186 -0.1240.310* 0.164 -0.264 -0.048<strong>Seed</strong>set-Nbgerm. seeds0.505** 0.525** 0.546**0.257 0.080 0.035!000 Grainweight0.180 0.304*0.200 0.378*<strong>Seed</strong> yield/plant<strong>Seed</strong> yield/infl.first line: 1979 plantssecond line: 1980 plants**P < 0.01 *P < 0.05In Table 4 the correlation coefficients between the variouscharacteristics are presented. The only characteristic thatshowed a significant correlation with seed yield per plant inboth years was the percent vegetative tillers at harvest time.The more vegetative tillers were present, the lower the seedyield. Inflorescence number and percent vegetative tillerswere negatively correlated as can be expected. The correlationbetween inflorescence number and seed yield was positive,but not significant.The higher inflorescence number resulted in a lower 1000-grain weight as can be seen from the negative correlationbetween both characteristics. This contributed to the absenceof a significant relationship between inflorescence numberand seed yield.A high tiller number in spring was a good indication of thenumber of inflorescences that could be expected, as can beseen from the positive correlation between both characteristics.However, too many tillers, and consequently too manyculms, led to a low 1000-grain weight, adversely affectingseed yield per plant.For the 1979-plants the number of spikelets per culm had anegative significant correlation with 1 000-grain weight -- thesame trend existed for the 1980-plants though not significantly.Floret utilization as determined by the weight of the filledand non-filled florets had a positive correlation with 1000-grain weight and seed yield. These relatively high, significantcorrelations were partly a consequence of the method ofdetermination. The number of germinating seeds did notshow a significant relationship with 1000-grain weight orseed yield per plant.Plants that had lodged more, which were the tall plants,had a significantly higher seed yield than the not lodged,shorter plants as can be seen from the positive correlationsbetween these characteristics. The plants that showed heavierlodging also had less generative tillers developed ascompared to the March count. Also more mildew occurredon the densely tillering plants.In view of the negative correlations between tiller andculm number with 1000-grain weight it followed that seedyield per culm was negatively correlated with tiller number.In Table 5, the path coefficients between seed yield perplant and its components for both years are presented. Inspite of the fact that a large part of the variation observed inseed yield was not explained by the measured seed components(residual factors amounted to 0. 747 and 0.925 in 1980and 1981 respectively), similar trends existed in both years
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 63Table 5. Path coefficients between seed yield per plant and its components.1980 1981Number of inflorescencesDirect effect 0.355 0.344Indirect effect via 1000-grain weight -0.013 -0.117Indirect effect via spikelet number -0.017 0.003Indirect effect via floret uti!/ germ seeds -0.095 -0.002r=0.230r=0.228Number of spikeletsDirect effect 0.278 0.135Indirect effect via infl. number -0.022 0.008Indirect effect via 1000-grain weight -0.012 -0.049Indirect effect via floret uti!/ germ seeds -0.160 -0.009r=0.084r=0.0851000-grain weightDirect effect 0.043 0.347Indirect effect via infl. number -0.104 -0.116Indirect effect via spikelet number -0.076 -0.019Indirect effect via floret util/germ seeds 0.317 -0.012r=0.180r=0.200Floret utilization/number of germ seeds per infl.Direct effect 0.628 -0.047Indirect effect via infl. number -0.054 0.012Indirect effect via 1000-grain weight 0.022 0.089Indirect effect via spikelet number -0.071 0.026r=0.525r=0.080Unexplained 0.747 0.925Table 6. Path coefficients for seed yield per inflorescence and its components.1980 1981Number of spikeletsDirect effect 0.325 0.136Indirect effect via I 000-grain weight -0.028 -0.060Indirect effect via floret util/germ seeds -0.147 -0.019r=0.150r=0.0571000-Grain weightDirect effect 0.102 0.423Indirect effect via spikelet number -0.090 -0.019Indirect effect via floret util/ germ seeds 0.292 -0.026r=0.304r=0.378Floret utilization/Number of germinating seedsDirect effect 0.577 -0.100Indirect effect via spikelet number -0.083 0.026Indirect effect via 1000-grain weight 0.052 0.109r=0.546r=0.035Unexplained 0.778 0.914
64 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985within the two (genetically different) populations.In 1980, the largest influence on seed yield was exerted byfloret utilization, but, as mentioned before, this might havebeen caused by its method of determination. Indirect effectsthrough the other components did not influence the directeffect a great deal, resulting in a high correlation betweenseed yield and floret utilization. The second highest effect in1980 came from inflorescence number, which was high in1981 as well. But contrary to 1980, the effect of inflorescencenumber in 1981 was reduced by a negative, indirecteffect via 1000-gmin weight, while the two other indirecteffects were negligible.The direct and indirect effects of the number of germinatingseeds per inflorescence in 1981 was very small givingevidence that this characteristic was in no way related to seedyield.The highest effect in 1981 was given by 1000-grain weight- an indirect negative effect via inflorescence number madethat the correlation between 1000-grain weight and seedyield was small. The same correlation in 1980 was largelycomposed of the indirect effect of floret utilization.Spikelet number had a relatively large influence in 1980,but the indirect effects via inflorescence number and floretutilization, made the correlation nil. The presence of manyspikelets had a positive effect on seed yield, but due to thelower weight of seeds, overall yield was smaller. A pathanalysis was also done for seed yield per inflorescence (Table6).In 1980, the largest direct effect on seed yield per inflorescencewas exerted by percent floret utilization. The secondlargest effect came from number of spikelets: a high numbercontributed towards a higher yield per inflorescence, but atthe same time seed weight and floret utilization were reducedas can be seen from the negative effects of these characteristics.Thousand-grain weight influenced seed yield positively.A larger influence than this effect was exerted by theindirect effect via percent floret utilization.Thousand-grain weight had the largest direct effect onseed yield per inflorescence in 1981. Spikelet number exertedsome influence. Though the influence of the number ofgerminating seeds per inflorescence was small, it is interestingto note that the direct, negative effect was compensatedby the indirect, positive effect via 1000-grain weight resultingin the absence of a clear correlation between both characteristics.Therefore, many germinating seeds per inflorescencedid not contribute to a higher seed yield per inflorescenceas these seeds had a low weight.The multiple regression of seed yield per plant is given inTable 7.Respectively 57 and 46% of the variation observed in seedyield per plant was explained by the independent variables,which was significant at P=O.Ol.In 1980, the largest relative influence was exerted bypercent generative tillers, percent floret utilization and tillernumber. These variables were not completely independentfrom each other. The squared multiple correlation coefficientwith the other 9 variables was 0.882, 0.446 and 0.916,respectively. Only subset equations with 7 independent vari-Table 7. Multiple regression with seed yield per plant as dependent variable.VariableTiller numberMildewGrowth stageIncrease infl. no.Plant heightLodgingInfl. number1000-grain weightSpikelet numberFloret util./germ. seeds% Veg. tillers% Gen. tillersConstantFR219801 20.318 1.80.123 0.70.126 0.90.243 0.5-0.258 1.10.009 0.20.348 2.74.077 5.8-0.029 0.90.996 2.4-44.6845.6 (10/43)0.56519813 1 2 30.59 0.020 0.2 0.040.05-0.001 0.0 0.000.10 -3.434 1.4 0.460.07 0.388 0.9 0.125.249 2.4 0.280.31 0.230 1.6 0.470.02 0.085 2.0 0.270.34 -0.046 0.4 0.040.67 0.139 1.2 0.190.10 -0.535 1.5 0.270.70 -0.465 1.3 0.2646.5783.1 (11/40)0.4611 = partial regression coefficient2 =!-value3 = relative influenceF-value- between brackets: degrees of freedomR 2 = squared multiple correlation coefficient
JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985 65abies could be selected that approached the fit of the data tothee ()_uation with all variables included. A smaller number ofvarialllbles increased bias and random error.Fc::x the 1981 data, increase in number of inflorescencesand :inflorescence number had the largest influence. TheirsquaJed multiple correlation coefficients were 0.889 and0.87 1, respectively. A subset equation was selected thatpred::i.cted the dependent variable with the same precision asthe tiii.Ill equation. The subset consisted of the variables lodging,inflorescence number, 1000-grain weight and percentvege 1ative tillers.DISCUSSION<strong>Seed</strong> yield in Kentucky bluegrass is a most unpredictablecharacteristic. Within one cultivar, yield levels between fieldsin the same year can vary to a great extent and differences upto 2010 - 300% can be obtained. Besides the genetical determin31!..tion, seed yield is largely affected by environmentalfact{)ol>rs, climate and management. In a survey on possiblefact{)ol>rs determining seed yield of two cultivars in two consecutiveyears with 87 and 107 growers respectively (vanWijk , unpublished data) no apparent factor could be definedexplaining the large yield differences. In general it was foundthat t:he high yielding fields were those that were given therecomended growing practices for bluegrass seed production.Tlae factors studied here were thought to affect seed yield.Observations were made on yield and its components and oncerta_:in characteristics (e.g. lodging and mildew) if clonessho\V'ed differences for the expression of these characteristics.Jncrease in inflorescence number was thought to reflectsynchonization of flowering and thus affect floret utilizationand :::seed yield. Floret utilization was determined in twodiffe.-ent ways in order to find a method that could be appliedon a large scale in relatively simple way.Tlae present study revealed information on the variation inthe s::ize of the reproductive system but failed to give someindic 4tion of its efficiency. This was largely caused by theabser1ce of a suitable method to determine floret utilization.In both years and for both populations, it was evident that ahigh~r number of inflorescences and spikelets had a positiveeffec 1: on seed yield but their effects were reduced by asmal.er 1000-grain weight.Tmus, it appears that selecting for a high inflorescencenumber will not indiscriminately increase seed yield becauseof a J!!llegative response in seed weight. The same trend wasobser-ved in seed yield trials with Kentucky bluegrass and redfescu_ e (F estuca rubra L.) sown at different times in the sameyear '(van Wijk, unpublished data). Sowing dates were midJune,_ mid July and mid August. The later sowing date reducedthe inflorescence number and increased 1000-grainweigatt. Hebblethwaite and Pierson (1983) also reported theeffec~ of sowing time on seed weight. A later sowing timeincre;;;;;ased 1000-grain weight and, floret utilization was less,givin .,g florets already utilized more chance to develop.In 1980 percent floret utilization was determined by separatingfilled and non-filled florets with a seed blower, whichwas c:::::alibrated for the actual amount of filled and non-filledfloret=s. However, percent floret utilization displayed such astron~ correlation with seed yield, that the method hasprobably separated heavy and light seeds. <strong>Seed</strong> cleaning,which was applied to determine the amount of seed perplant has the same effect. On the other hand, the method iseasy to apply and for that reason more research is neededwith a varying range of seed samples to assess itsapplicability.In 1981 the number of germinating seeds per inflorescencewas determined. This characteristic did not show any correlationwith seed yield and could not be used as a measure offloret utilization. <strong>Seed</strong> dormancy did not play a role as thedetermination was made seven months after harvest. A possiblecause for the low correlation between this characteristicand seed yield might have been that the seeds of the harvestedculms were immature as these were sampled one week beforeharvest in order not to lose any seeds. The number of germinatingseeds showed a positive correlation with 1000-grainweight, determined from mature seeds. The number of germinatingseeds per inflorescence showed a negative, thoughnot significant, correlation with lodging and plant height.Shorter plants that lodged less had more germinating seedsper inflorescence suggesting that those plants have a betterflower utilization.Based on these results, it is concluded that the yield perplant is the best determinant for seed yield, irrespective ofhow the components contribute to the resulting yield. Itcould be questioned whether there is an optimum betweennumber of inflorescences (number of spikelets and florets),seed weight and floret utilization. Can seed yield beincreased by improving floret utilization (either throughselection or management) or do correlated responsescounteract resulting in no improvement?Once single plants with a high seed yield have been selected,their yield capability in rows has to be investigated. Atrial set-up is therefore required that gives the closest correlationwith the actual field growing conditions.REFERENCES1. Bugge, G. 1981. Genetic variability in the components of seedyield of ryegrass species. Rep. Fodder Crops Section Eucarpia,Gent. pp. 37-41.2. Daniel, C., and F.S. Wood. 1971. Fitting equations to data.Wiley, New York.3. Dewey, D.R., and K.H. Lu. 1959. A correlation and pathcoefficientanalysis of components of crested wheatgrass seedproduction. Agron. J. 51:515-518.4. Hebblethwaite, P.D., and S.D. Pierson. 1983. The effects ofmethod and time of sowing on seed production in perennialrye grass. J. Appl. <strong>Seed</strong> Prod. 1:30-33.5. Hintzen, J.J., and A.J.P. van Wijk. 1985. Ecotype breedingand hybridization in Kentucky bluegrass (Poa pratensis L.).Proc. 5th Int. Turfgrass Cong., Avignon. pp. 213-219.6. Knowles, R.P., D.A. Cooke, and E. Buglass. 1970. Breedingfor seed yield and seed quality in smooth bromegrass, Bromusinermis Leyss. Crop Sci. 10:539-452.7. Lewis, D. 1966. The relationship between seed yield andas-sociated characters in meadow fescue (F estuca pratensis).J. Agric. Sci. 67:243-248.8. Nguyen H.T., and D.A. Sleper. 1983. Genetic variability ofseed yield and reproductive characters in tall fescue. Crop Sci.23:621-626.
66 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 19859. Wijk, A. J.P., van. 1977. An application of a multiple regressionmethod in tropical grass breeding. Neth. J. Agric. Sci.25:103-107.10. Wilson, A.M., R.L. Cuany, J.G. Fraser, and W.R. Oaks.1981. Relationships among components of seed yield in bluegrama. Agron. J. 73:1058-1062.
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