Relationships among photosynthetic rate, bean yield and other characters in field-grown cultivars of soybean

In field experiments with young spaced plants of 48 soybean (Glycine max (L.) Merr.) cultivars, derived lines tended to have higher rates of apparent photosynthesis (P A ) than their parent lines over 3 yr of tests using the 14 CO 2 method. For 2 yr in which chlorophyll and specific leaf weight (SLW) were also measured, a significant number of derived lines had higher P A , chlorophyll and SLW than their parent lines. With 12 cultivars of similar maturity, grown as row-crop tests for 4 yr, P A and leaf percent N were correlated with each other during August (pod-filling period) but not during July (flowering period). August P A and leaf percent N were correlated with bean yield, but July values were not. Chlorophyll and SLW were correlated with each other in July and in August; each was correlated with P A in July but not in August. Although July measurements of leaf characters were not correlated with bean yield, July and August values were correlated for P A and for chlorophyll. The correlations observed among the characters in different sampling periods are discussed in relation to possibilities for selection.