Selection in heterogeneous soybean populations: 1. Variation sources

Soybean seed yield variation complex was studied in order to define further research directions aimed at minimizing of variation components useless for breeding. Individual plant seed yield variation was studied on model populations consisting of 000-00 maturity group cultivars and simulating diversity in real hybrid populations, at two plant populations of 40 and 20 plants per sq. m. Heritability was equal to 10-13%; thus, direct selection for seed yield is ineffective. Genotype ranks changed in heterogeneous populations compared to the same cultivars grown in pure line populations due to genotypic competition; interaction variance was equal to 14-17%. Ecological competition reaching 70-76% contributed most into the overall variance. In low plant population, genetically useful and genotypic competitive variances were increased a little while ecological competitive variance decreased. Thus, decreasing of the main variance component useless for breeding, i.e. intragenotypic variance, should be more effective at low plant population; however, analysis of intergenotypic competition is required.