Analysis of Yield Variation in Soybean Genotypes Focused On the Biomass Production of Source and Sink Organs.

Identification of important plant traits involved in genotypic difference in yield is essential for understanding of yield determination process and conducting efficient selection for high yield. Crop growth and yield attributes were determined in a high productive field condition for total of 20 soybean genotypes, including Japanese and US commercial cultivars and recombinant inbred lines from a cross between cv. Stressland and cv. Tachinagaha. The seed yield variation was observed to range from 2.7 t ha-1 of cv. Norin 1 to 4.8 t ha-1 of cv. Hutcheson. Crop leaf dry weight at the beginning of seed filling (LW) did not closely correlate with yield. Pod-wall dry weight at maturity (PWW) also correlated neither with LW or yield, with a relatively limited variation among genotypes. Compared with LW and PWW per se, the ratio of seed dry weight to PWW (SW/PWW) showed a notably close correlation with yield. These results indicate that most of yield variation was occurred after the pod formation in this study, when it was assumed that the change of pod dry weight was small after maximum pod elongation. The genotype with small ratio of PWW to LW, which maintains enough sources, had relatively large value of SW/PWW but the relation was weak, so the existence of complementary relationship between these two traits was not obvious. We also found a relatively consistent tendency between the crop- and plant-base measurements for the cultivar difference in SW/PWW. The SW/PWW may be an effective criterion in selection for higher seed yield, if the stability is fully confirmed.