Volume 15, No. 1, 1991

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(pp. 1-11)
Using Indicator Seeds to Test for Seed Lot Heterogeneity1
Dan Niffenegger2
Cost-effective and timely procedures to determine heterogeneity level in batch-mixed  commercial seed lots are not available. This is a concept paper describing a procedure  which can fill the void. The principal change from present practice is to incorporate known numbers of indicator seeds (seeds marked for easy detection) into a seed lot as it is being mixed and then to test for random distribution of the indicator seeds within the lot.

The procedure is illustrated with examples for a blend of two alfalfa (Medicago sativa L.) seed lots, a direct-harvest alfalfa seed lot, and a lawngrass seed mixture. Key steps are (1) determine amount of indicator seed needed, (2) obtain and mark the indicator seeds, (3) mix the seed lot, incorporating the indicator seeds as additional components of the lot, (4) draw samples, (5) count and record numbers of indicator seeds in samples, and (6) analyze results. The test requires no specialized equipment, and can be run by conditioning plant employees. Calculations can be made with the aid of a hand calculator. The test can be especially useful for testing the effectiveness of seed mixing systems (equipment, mixing time, warehouse procedures, etc.). Benefits of using the test could include gaining approval for an increase in size of some U.S. seed lots entering international seed markets; reduced numbers of "stop sales" in intra- and interstate commerce; reduction in the occurrence of under-mixing and concurrent heterogeneity; reduction of over-mixing and concurrent unnecessary seed damage; and a higher quality product for consumers.
Additional Index Words: Homogeneity, Bagging, Tolerances, Seed statistics, Mixing, Marketing, Sampling, Blending .
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(pp. 12-21)
Effect of Drought Stress on Soybean Seed Germination and Vigor1
R.D. Vieira, D.M. TeKrony and D.B. Egli2
Environmental stress during seed development may influence soybean [Glycine max (L.) Merrill] seed quality. Two greenhouse experiments were conducted to study the effect of drought stress on soybean (cv. 'McCall') seed germination and vigor. Two stress treatments (moderate and severe) were imposed at growth stages R5 and R6 and compared with well watered plants.

Drought stress significantly reduced weight per seed and yield per plant and increased stomatal resistance. It had little effect on seed shape; however, and few shrunken or wrinkled seed were produced. Drought stress had no effect on seed germination and little effect on seed vigor as measured by the accelerated aging, conductivity and cold tests. In one experiment, drought stress increased the proportion of hard seed (especially in the smaller seed size fraction) which lowered 3-day germination, but did not affect final germination or vigor. Although the most severe drought stress treatment reduced seed weight and yield substantially (34% and 38%, respectively) it had little or no effect on seed quality.
Additional  Index Words: Glycine max (L.) Merrill, yield, seed size, accelerated aging, conductivity.
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(pp. 22-28)
Scarification of Hardseeded Soybeans by Combine Harvesting1
S.H. Moore and E.A. Drummond2
Soybean [Glycine max (L.) Merr] cultivars with water-impermeable seed coats have superior resistance to seed deterioration caused by late-season rains that may delay harvest. The purpose of this study was to determine if a cultivar with a high percentage of hard seed may be sufficiently scarified by mechanical harvest to permit rapid imbibition and germination. A hardseeded strain, 'D86-4510,' was harvested in 1988 and 1989 with a Massey Super 35 combine at recommended and increased cylinder speeds in factorial combination with recommended and reduced concave spacings.

Seed were also threshed by hand, for comparison. Harvested seed were analyzed using 24-h soak, standard germination, and accelerated aging tests. Combine harvesting reduced the percentage of hard seed in both years. Reduction in concave spacing had no affect in 1988, but lowered hard seed by 60% in 1989. Increasing cylinder speed from 700 to 1050 rpm reduced hard seed by 9% in both years. Although machine-harvest treatments reduced hard seed, 47% and 63% of seed from D86-4510 remained hard in 1988 and 1989, respectively, when harvested at the highest cylinder speed and closest concave spacing. A 24-h soak test conducted 210 d after the 1989 harvest revealed no appreciable changes in hardseededness. Since 47% or more of the seed from D86-4510 remained hard after machine harvest each year, it seems apparent that seed from similar cultivars now being developed will require specific post-harvest scarification prior to planting. Additional index words: Glycine max (L.) Merr, lmbibition, Accelerated aging, Germination.
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(pp. 29-41)
Influence of accelerated Aging on Fatty Acid Composition of Slash Pine (Pinus elliottii Engelm. var. elliottii) Seeds1
A Marquez-Millano, W.W. Elam, and C.A. Blanche2
Seeds of slash pine (Pinus elliottii Engelm. var. elliottii) were aged at 41 and 45o C. for periods ranging from O to 288 h, and their fatty acid composition during accelerated aging (AA) was analyzed to determine if a relationship existed between fatty acid changes and loss of seed germinability.

Myristic, palmitic, stearic, oleic, linoleic, linolenic, arachidic, cis-eicosenoic, and eicosadienoic fatty acids were found in slash pine seeds subjected to AA at 41o C.  These same fatty acids, with the exception of myristic acid, were present in seeds aged at 45o C. Two unknown fatty acids were detected at both temperatures. The saturated fatty acids fluctuated with no definite trend over time during AA at 41o C., while linoleic and linolenic acids decreased with increasing period of AA. At 45o C. AA, saturated and unsaturated fatty acids significantly declined after 192 h. Loss of vigor as determined by percent germination preceded declines in fatty acids at 45o C. AA, while, at 41o C., decline in fatty acids was accompanied by loss of vigor. Correlation analysis showed significant relationship of percent germination with total saturated and total unsaturated fatty acids after 48 and 96 h of AA at 41o C.
Additional index words: Seed vigor, Electrolyte leakage.
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(pp. 42-57)
Scanning Electron Microscopy of High Quality and Low Quality Sorghum Seeds1
S. Paliwal, C. Baskin, and J.C. Delouche2
Comparison of the anatomical structures of high density seeds with low density seeds and early germinating with late germinating seeds of sorghum [Sorghum bicolor (L.)] were made using scanning electron microscopy. The differences in anatomical structures of high and low density seeds and early and late germinating seeds were primarily due to differences in maturity.

High density seed had a thinner pericarp, were better filled in the endosperm and had a better developed embryonic axis than the low density seed. Differences in early germinating and late germinating seed between 1.17 and 1.30 specific gravity were not as pronounced as in the low density seeds and late vs. early germinating seed from the ungraded sample. There were no obvious differences in pericarp thickness, celeoptile and plumule development. Differences were evident in the radicle area where structures were not as well organized.
Additional Index Words: Seed quality, Seed density, Seed morphology.
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(pp. 58-66)
Estimation of Some Major Costs for Commercial Freeze-thaw Scarification of Alfalfa Seed
D.G. Stout and J. Langton1
Freeze-thawing has been established as an effective method to decrease hard-seededness and increase germination of alfalfa (Medicago sativa L.), but has not been adopted commercially. Since this technique appears to offer technical advantages compared to many other methods of scarifying alfalfa seed, this study evaluates the major costs involved in it's commercial application.

An experiment with two cultivars (Apica and Barrier) and different numbers of freeze-thaw cycles indicated that maximum germination occurred following two freeze-thaw cycles. A freeze-temperature experiment with the two cultivars indicated that -61o C. was as effective at increasing germination as -80o C. following one freeze thaw cycle and nearly as effective following three freeze­ thaw cycles. A freeze temperature of -61o C. has an advantage over -80o C., as liquid carbon dioxide can be used to obtain this freezing temperature. Freezing equipment exists that can use either liquid carbon dioxide or liquid nitrogen and this could be incorporated as an additional step into a process where seed is being moved about on conveyors. For liquid carbon dioxide, the carbon dioxide represents about 73% of the cost while the capital cost and maintenance of equipment represents about 27% of the cost. The greater the quantity of seed scarified, the lower is the unit cost of scarification. Our estimates of cost suggest that treatment of 1,000,000 kg of seed or more annually would result in an increase of about 1% in the retail value of the seed.
Additional Index Words: Medicago, Germination, Seed coat, Hard­seededness, Impermeable seed
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