1988 Volume 57 Issue 4 Pages 743-748
In a field experiment using 17 soybean cultivars and lines with a diverse variation of seed yield within each maturity group (early, middle and late), the association of apparent photosynthetic rates per leaf area (AP) with seed yields was examined. AP was measured of intact leaves of most actively working at three growth stages :vegetative (VT), pod formation (PF), and seed development (SD). Significant cultivar differences in AP within maturity groups were observed at VT and PF of early maturing, at all the three stages of middle maturing, and at SD of late maturing cultivars, respectively. AP tended to increase with growth stage, being accompanied by a variation of' cultivar ranking. Across cultivars and lines in each group, AP tended to be correlated negatively with single leaf area, and positively with specific leaf weight (SLW) and chlorophyll content at VT, but the tendency became ambiguous at later stages. APs measured at VT and PF did not bear significant correlations with crop growth rates (CGR) or net assimilation rates (NAR) determined between the two stages. Seed yields were positively correlated with APs measured at SD in the late maturing group, but no significant correlations between them were observed at other growth stages, or in the early and middle maturing groups. We presumed that greater sink demand by high-yielding cultivars were responsible for a higher AP, not that a higher AP contributed to an increased seed yield.
