Gene action and heritability of leaf and reproductive characteristics in soybean [Glycine max]

Soybean [Glycine max (L.) Merr.] cultivars with smaller area and lanceolate leaves have shown better light distribution through their canopy and a higher photosynthetic rate than those with larger leaf area and oval leaf shape. However, very little information has been published about leaf characteristics in relation to yield potential and inheritance which would assist breeding effects to develop new cultivars with optimum leaf area and leaf shape. Gene action and heritability for leaf area, leaf shape, and other reproductive characteristics were studied in a diallel cross including nine parents with large, medium, and small leaf area. Most progenies from crosses among parents with different leaf areas had larger mean leaf area, longer flowering, and later maturity than the midparent and both parents, suggesting transgressive segregation for these traits. General combining ability (GCA) and specific combining ability (SCA) for leaf area and leaf shape were significant in populations. Ratios of GCA to SCA were 0.96 for leaf shape and 0.89 for leaf area, indicating that GCA effects were more important than SCA. Genetic gain for leaf area and shape may be possible through selections. Narrow sense heritability estimated on the basis of variance components was 43.4% for leaf area, 63.2% for leaf shape, and 29.1% for maturity, which were lower than days to flowering and flowering period due to large error variances (sigma2E) caused by field environmental factors. This study indicated that it is possible to optimize leaf area and leaf shape related to photosynthetic rate and subsequently yield, because of relatively large and significant GCA effects for these traits. The predominance of additive effects should improve the effectiveness of selection based on performance of individual cultivars