JASP 3 -- 1985.pdf - International Herbage Seed Group

56 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985Table 2. Seed 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. Seedformationinperennialryegrass. 1.Anther exertion and seed set. J. Br. Grassl. Soc. 18:90-96.4. Anslow, R.C. 1964. Seed 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. Seed 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.