Phylogenetically diverseBradyrhizobiumgenospecies nodulate Bambara groundnut (Vigna subterraneaL. Verdc) and soybean (Glycine maxL. Merril) in the northern savanna zones of Ghana

A total of 102 bacterial strains isolated from nodules of three Bambara groundnut and one soybean cultivars grown in ninteen soil samples collected from northern Ghana were characterized using multi-locus gene sequence analysis. Based on a concatenated sequence analysis (glnII-rpoB-recA-gyrB-atpD-dnaK), 54 representative strains were distributed in twelve distinct lineages, many of which were placed mainly in the Bradyrhizobium japonicum and Bradyrhizobium elkanii supergroups. Twenty four of the 54 representative strains belonged to seven putative novel species, while thirty were conspecific with four recognized Bradyrhizobium species. The nodA phylogeny placed all the representative strains in the cosmopolitan nodA clade III. The strains were further separated in seven nodA sub-clusters with reference strains mainly of African origin. The nifH phylogeny was somewhat congruent with the nodA phylogeny but both symbiotic genes were mostly incongruent with the core housekeeping gene phylogeny indicating that the strains acquired their symbiotic genes horizontally from distantly related Bradyrhizobium species. Using Redundancy Analysis, the distribution of genospecies was found to be influenced by the edaphic factors of the respective sampling sites. In general, these results mainly underscore the high genetic diversity of Bambara groundnut-nodulating bradyrhizobia in Ghanaian soils and suggest a possible vast resource of adapted inoculant strains.