Selection based on canopy‐apparent photosynthesis (CAP) may be a means of improving the effectiveness of selection for seed yield in soybeans [ Glycine max (L.) Merr.]. The present study was undertaken to determine the heritability of CAP and to determine the relationship of CAP to seed yield in F 3 ‐derived lines from two soybean crosses. In 1977 and 1978, 34 F 3 ‐derived soybean lines from each of the crosses, ‘Dare’ × ‘Forrest’ (Cross V) and ‘Tracy’ × ‘Davis’ (Cross VI), were planted in a randomized complete block design with three replications. Two CAP determinations/plot were made during the period of pod and seed development. Significant genotypic variation and transgressive segregation for CAP occurred at each measurement for both crosses. Heritabilities based on variance component estimates were 41% for CAP and 28% for seed yield in Cross V and 65 and 14% for Cross VI. Seed yield and CAP were significantly related (r=0.55 and 0.54) in both crosses. The average yield improvement over the 2 years of indirect selection based on CAP rate, using a 15% selection intensity, was 79% of direct selection for yield in Cross V and 146% in Cross VI. Based on the 2‐year means, 6 of the 10 highest yielding lines in Cross VI were among the 10 lines with the highest CAP rates. With the techniques used in our experiment, the cost and time of measuring CAP greatly exceeded that for measuring yield. The value of selecting for increased CAP to increase seed yield will be determined by the adaptability of current and future technology to determine CAP on fieldgrown soybeans.
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Harrison et al. (1981) studied this question.