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

Selecting for increased weight per seed among male-sterile soybean pla nts [Glycine mar (L.) Merr.] increased seed weight and seed yield for male-fertile progeny but had minimal effects on seed number per ha. As similate availability to the seed during selection was essentially non limiting for an extended period, since male-sterile plants have few se eds per plant. For the observed range, seed weight has shown no associ ation with Seed yield potential. This study tested two alternate hypot heses to explain the increased seed yield potential: (i) selection ide ntified 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 un it seed coat area, and rate of increase in seed density were determine d for greenhouse-grown plants using a 7-d period during mid seed devel opment. The following observations led to the acceptance of the reduce d seed maturation rate hypothesis: (i) When assimilates were made esse ntially nonlimiting to the seed by partial pod removal, selected and n onselected populations had similar DMAR per unit seed coat area and pe r unit seed dry weight. (ii) Selection for seed weight on male-sterile plants reduced the rate of increase in seed density. (iii) DMAR per u nit seed coat area did not increase with selection. Selected and nonse lected populations, had similar DMAR per unit seed dry weight. Apparen tly, selection had occurred against the reduction in rate of dry matte r uptake by the seed. This reduction is normally associated with reduc ed seed maturation rate. Selection for seed weight on male-sterile pla nts can be completed during the early generations of a breeding progra m and used to identify genotypes that have longer seed filling duratio ns and more efficient systems for assimilate utilization.