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

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 Seed 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 Seed 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. Seedat 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-