Deterioration of soybean seed in storage

Abstract

Hand harvested Lee 68 soybean seed were rapidly to produce six sublots differing in physiological quality. The deterioration of these sublots under moderately adverse storage conditions was then characterized in terms ol the sequence, degree and direction of change in selected physiological parameters. Deterioration was first manifested in an increased sensitivity or susceptibility of the seed to environment stress (accelerated aging, high and low temperatures). Later during the storage period, rate of germination decreased and RQ in creased. Finally, germination percentage, rate of seedling growth, and CL con sumption decreased in that order. In a parallel study, it was demonstrated that permeability of the seed to TTC increased with degree of deterioration, but formazan production decreased when the permeability factor was eliminated. Accelerated aging, cold test, and hot water treatment responses were most closely associated with longevity of the seed in storage. Additional index words: Accelerated aging, cold test, growth rate, longevity, respiration, vigor Introduction Seedsmen usually do not attempt to carry-over soybean seed from one plant ing season to the next because of their relatively short storage life. This situation contributes to many problems in the seed industry. It is often a very good practice to carry-over 10-20% of the seed of each crop to hedge against a crop failure the following season. More importantly, basic soybean seed stocks (foundation and registered seed) are high priced and sale of these seeds to the oil mill results in a large financial loss as well as loss of valuable seed reserves. One solution to the problem of soybean deterioration in storage would be to select soybean seed lots with high storage potential. Presently, the laboratory germination test is the only widely accepted method for measuring the physio logical quality of seed, and the inadequacies of this test for measuring the per formance of seed lots under various storage environments and less than optimum field conditions have been emphasized by several investigators (6, 8, 10, 15, 19, 26). Deterioration can progress during storage to the extent that the seed are essentially worthless for planting purposes although germination percentage re mains relatively high (16, 20). During the past decade attention has been directed toward investigating the physical (10, 16), physiological (7, 9, 13, 17, 22, 23, 27), and biochemical (1, 2, 3, ijournal Paper No. 2193 of the Mississippi Agricultural and Forestry Experiment Station, State College. Mississippi. -Former Assistant Agronomist, Seed Technology Laboratory, Agronomy Department, MSU, and Agronomist, respectively. 41 This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 07:30:49 UTC All use subject to http://about.jstor.org/terms 42 I'ROC. ASSOCIATION OF OFFICIAL SEED ANALYSTS 4, 18) changes associated with the process of seed deterioration. Seed deterioration is now believed to be closely related to many of the unsolved seed quality prob lems in the seed industry, such as accurate assessment of the planting value of seed (10, 16, 20, 26), evaluation of the storage potential of the various seed lots of a specific kind (12, 14, 19), determination of the degree of deterioration that seed can sustain without being detrimental to field performance (6, 17, 22, 23, 25), and formulation of a satisfactory definition of seed quality (10, 16, 21, 26). The objectives of the present study were: (1) To study the rate and progress of deterioration in soybean seed under different storage environments; (2) To evaluate different methods for determining the extent and progress of deteriora tion during storage; and (3) To evaluate different methods of predicting seed storability. Materials and Methods Foundation Lee-68 soybean seed of the 1968 crop were hand harvested on the North Agronomy Farm, State College, Mississippi. All seeds were cleaned with hand screens and a laboratory aspirator. Approximately 200 lbs of the seed were adjusted to a seed moisture content of 12.3% in a controlled environment room set at 20°C-90% RH. The seed were then subdivided into eight sublots, sealed in glass containers, and aged at 38°C for 0, 5, 10, 15, 20, 25, 28 and 34 days. Seed from the 28 and 34 day aging periods were used only for the dehydrogenase evaluations, while those from the other six aging treatments (periods) were stored at 30°C-50% RH and 20°C 75% RH. Samples were placed in storage at monthly intervals for a period of nine months so that all storage periods terminated on the same date. During the interval from completion of aging treatments to placement in storage, the seed were kept in a refrigerated storeroom at 5°C-40% RH. Non-aged seed served as the control in all instances. The extent and progress of deterioration during storage were determined by the following laboratory evaluations: standard germination, first count germina tion, rate of radicle-hypocotyl growth, accelerated aging response, cold test per formance, hot water treatment response, rate of respiration, and dehydrogenase activity. The procedures and methods used for these evaluations are described below. Standard Germination and First Count Germination—Standard procedures as described in the Rules for Testing Seeds (5) were used for laboratory germina tion tests. However, first counts were made four days after planting in an attempt to more accurately identify differences in performance among the samples. Final counts were made eight days after planting. Four replications of 50 seeds each were germinated in rolled paper towels at an alternating temperature of 20-30°C. Radicle-Hypocotyl Length—Ninety seeds from each sample were planted in six replications of 15 seeds each in a straight line about three inches from the top of two moist paper germination towels. A third towel was used as a cover. The towels were then folded, placed on a tray and positioned at a 45° inclination with radicle ends downward in a constant 25°C dark germinator. Root lengths were This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 07:30:49 UTC All use subject to http://about.jstor.org/terms