Assessing promiscuous traits in soybean genotypes at Bako, Western Ethiopia

Soil acidity challenges specific Bradyrhizobium japonicum bacteria that soybean [Glycine max L. (Merrill)] varieties require for effective nodulation and nitrogen fixation. Thus, promiscuous soybean varieties or genotypes that can form root nodules with a wide range of indigenous rhizobial bacteria are essential in areas where specific Bradyrhizobium japonicum inoculants may not be readily available. Therefore, this study was conducted to evaluate promiscuous soybean genotypes for effective nodulation, yield, and yield-related traits as potential materials for subsequent breeding work in Bako, Western Ethiopia. One hundred ninety-six promiscuous soybean genotypes were laid out in a partially balanced (simple lattice) design with two replications. The results showed that days to 50% flowering, days to maturity, nodule number, plant height, number of primary branches per plant, number of pods per plant, number of seeds per pod, hundred seed weight, grain yield, bacterial blight, bacterial pustule, and frog eye leaf spot (p < 0.01) varied significantly among the evaluated soybean genotypes. The grain yield of the evaluated soybean genotypes ranged from 1141.8 to 4235.1 kg ha⁻¹. These variable yield responses observed are due to differences in genetic potential, physiological characteristics, growth habits, and maturity differences of the evaluated soybean genotypes. Principal component analysis revealed that plant height, the number of primary branches, the number of nodules, the number of pods per plant, and grain yield are correlated parameters. K-means clustering was used to identify genotypes with similar characteristics. Therefore, 60 promiscuous soybean genotypes were selected and promoted to the next breeding stage based on their nodulation characteristics and yield potential. Thus, from this study, it can be concluded that selecting and promoting soybean genotypes based on their promiscuous nature is one strategy to improve soybean yield, especially where an effective Bradyrhizobium japonicum strain is not available to the farmers.