CONTROL FOR RATE OF SEED DEVELOPMENT AND SEED YIELD POTENTIAL IN SOYBEAN

Selecting for increased weight per seed among male-sterile soybean plants [Glycine mar (L.) Merr.] increased seed weight and seed yield for male-fertile progeny but had minimal effects on seed number per ha. Assimilate availability to the seed during selection was essentially nonlimiting for an extended period, since male-sterile plants have few seeds per plant. For the observed range, seed weight has shown no association with Seed yield potential. This study tested two alternate hypotheses to explain the increased seed yield potential: (i) selection identified genotypes with increased seed sink activity per plant or (ii) selection identified genotypes with reduced seed maturation rates. Dry matter accumulation rate (DMAR) per unit seed dry weight, DMAR per unit seed coat area, and rate of increase in seed density were determined for greenhouse-grown plants using a 7-d period during mid seed development. The following observations led to the acceptance of the reduced seed maturation rate hypothesis: (i) When assimilates were made essentially nonlimiting to the seed by partial pod removal, selected and nonselected populations had similar DMAR per unit seed coat area and per unit seed dry weight. (ii) Selection for seed weight on male-sterile plants reduced the rate of increase in seed density. (iii) DMAR per unit seed coat area did not increase with selection. Selected and nonselected populations, had similar DMAR per unit seed dry weight. Apparently, selection had occurred against the reduction in rate of dry matter uptake by the seed. This reduction is normally associated with reduced seed maturation rate. Selection for seed weight on male-sterile plants can be completed during the early generations of a breeding program and used to identify genotypes that have longer seed filling durations and more efficient systems for assimilate utilization.