Seed Vigor Effects on Growth Characteristics Associated with Seed Yield and Diallel Analysis of Seed Vigor in Soybean

Disagreements in relationships between seed vigor and seed yield, and lack of information regarding the inheritance of seed vigor in soybean [Glycine max (L.) Merrill] prompted an agronomic and a genetic study in 1994 and 1995. Objectives of the agronomic study were to determine the relationships of seed vigor with reproductive growth characteristics and yield, and to examine the influence of growth characteristics on relationships between seed vigor, yield, and agronomic performance. The objective of the genetic study was to determine combining ability estimates for seed vigor and its related traits. In the agronomic study seed vigor was classified into high and low classes by accelerated aging (AA) and standard germination (SG) within the large- and smallseeded soybean genotypes. Reproductive characteristics and agronomic traits were recorded. Significant seed vigor effects were found for flowering period, seed filling, plant height, and seed weight (P::; 0.05), but not for seed yield. Significant seed size x seed vigor interactions were found for all reproductive periods and nearly all agronomic traits. Initial seed vigor was highly correlated with early plant population density (r = 0.90**). Initial seed vigor by AA test were correlated with early vegetative period (r = 0.55**), flowering period (r = 0.35*), and seed filling period (r = 0.34**). Visual seed quality ratings were significantly correlated with initial seed vigor (r = -0.63**). Within the high seed vigor class, seed vigor based on AA test was negatively correlated with seed yield (r = -0.50*). Large-seeded genotypes with high seed vigor produced higher seed yields than other genotypes in this study. In the genetic study, five high seed vigor and six low seed vigor soybean genotypes were crossed in a diallel. General combining ability (GCA) effects for seed vigor and seed yield were significant (P .S-0.0 1) and larger than specific combining ability (SCA) effects. Significant GCA and SCA effects were found for seed weight and visual seed quality, indicating that both additive and nonadditive genetic effects were involved in controlling these two traits. The ratios of mean squares [2GCA I (2GCA+SCA)] were 0.96 for seed vigor and 0.93 for seed yield, indicating that seed vigor and seed yield were mainly influenced by additive gene effects. Mean seed vigor (80.3 %) as determined by AA test and mean seed yield (2, 155 kg ha.1) in high vigor x high vigor crosses were higher than any other crosses. Mean percent AA germination rates in F2 populations were significantly related to midparent seed vigor (R2 = 0.52**) and midparent seed size (R2 = 0.31 **). These results indicated that seed vigor can be improved through breeding while maintaining high yields, because of the predominance of GCA effects in both seed vigor and seed yield