Abstract: The analysis of major-minor locus groups of diallel crosses based on major gene plus polygene mixed inheritance model provides a way to explore the genetic structure of hybrids among a group of materials. Eight soybean parental materials, seven from Huang-Huai region in China and one from the US with maturity group II–IV were used to develop a set of 36 diallel crosses (including 28 F₁ crosses and eight parents) according to the Griffing II pattern. The materials were tested in 2003-2005. From the analysis of major-minor locus groups of the 36 materials, the results showed that six major locus groups plus minor locus groups were detected to explain 75.98% and 10.81% of the phenotypic yield variation, respectively. Which indicated that major locus groups were the major source of genetic variation among the materials with their additive effects (a_J) of 140.10, 259.65, 1.95, 151.35, –32.70, and 45.00 kg ha^–1 and dominance effects (d_J) of 177.15, 314.25, 105.75, 75.90, 242.85, and 171.00 kg ha^–1, respectively, while the minor locus groups were a supplement source in the genetic system. The genetic constitutions of the hybrids were composed of heterozygous dominance effects of major locus groups, homozygous additive effects of major locus groups, heterozygous dominance effects of minor locus groups and homozygous additive effects of minor locus groups, with their relative importance in a descending order. The dissection of the relative importance of the genetic effects of major-minor locus groups helps to explain the genetic characteristics of the hybrids among the parents and provides the genetic basis for further mining the genetic potential of parental materials in the improvement of hybrids.

Key words: Soybean, Yield, Heterosis, Major-minor locus groups, Additive effects, Dominance effects