Analysis of Differences in Sink Activity among Soybean Genotypes Based on Dry Matter Accumulation Rates per Unit Seedcoat Area
This study tested the hypothesis that genetic differences for sink activity, a component of sink strength, affect assimilate flux to seeds in soybean [Glycine max (L.) Merr.]. Dry matter accumulation rate per unit seedcoat area (SDMAR) was selected to investigate sink activity. The capacity to maintain high SDMAR under limiting and nonlimiting assimilate availability was used to identify those genotypes having high sink activity. The ellipsoid served as the model to determine seedcoat area and seed volume. Four soybean genotypes differing in accumulation rates and 24 genotypes reflecting divergent selection for seed yield were evaluated in the greenhouse under three treatments: control, side leaflets removed, and pods removed except for selected pods. Highly significant mean squares for SDMAR were found for genotypes and for the genotype-by-treatment interaction. The SDMARs for genotypes with high and with low SDMAR were proportionately affected under treatments that decreased or increased SDMAR. High SDMAR imparted no advantage for maintaining assimilate utilization under limiting assimilates. Further, genotypes selected for high and for low seed yields had similar SDMARs. The results do not support the concept of major differences in sink activity among genotypes. The pod-removed treatment increased SDMAR 16% and reduced the increase in seed dry weight per unit volume associated with maturation, or it delayed the maturation process. High yielding genotypes had lower dry weight per seed volume than low yielding genotypes. The capacity to maintain sink activity may be a component for high seed yield.
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