Screening soybean genotypes for promiscuous symbiotic association with Bradyrhizobium strains

The current low soybean (Glycine max L. Merrill) yields in Sub-Saharan Africa can be alleviated by developing promiscuous genotypes. The research trend in Africa is towards developing promiscuous varieties for less labour and high yields in soybean production. A greenhouse experiment was conducted at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) with the aim of screening of soybean germplasm for promiscuous symbiotic association with Bradyrhizobium sp. in order to identify genotypes with potential to be used as parents to initiate a breeding programme focusing on promiscuous nodulation. The response of 65 soybean genotypes from different origins to cowpea-type inoculant, Bradyrhizobium sp. strain USDA 3456 were evaluated. Soybean seeds inoculated with both Bradyrhizobium sp. strain USDA 3456 and Bradyrhizobium japonicum strain USDA 110 were planted in buckets filled with steam-sterilised soil. Significant differences in the number of nodules, effective nodules, fresh and dry weight of nodules were observed among genotypes (P<0.001). Twelve of the 65 genotypes were highly responsive to Bradyrhizobium sp., with over 10 nodules per plant, over 50 mg dry weight of nodules, and 50% effective nodules. A highly positive correlation was shown between dry weight of nodules and nodule number. This study proposes the soybean genotypes NamII, WonderSoya, Bulindi 48C, NamSoy 4M, MakSoy 3N, NamSoy 3, K-Local, Kabanyolo 1, UG 5, Soprano, MakSoy 2N, and MakSoy 5N as potential parental materials for subsequent breeding work.