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

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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 Seed 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. International rules for seed testing.International Seed Testing Association. Rules 1985. Annexesto chapter 3. Seed 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 ofSeeds. Chapman and Hall, London.3. Barnard, C. 1972. Register of Australian Herbage 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. Seed 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.)Seed Production. Butterworths, London.6. Hopkinson, J.M., and B.H. English. 1982a. Spikelet populationdynamics in seed crops of Panicum maximum'Gatton'. Seed 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 Seeds.Chapman and Hall, London.
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