Phenotypic and Phylogenetic Characterization of Micro-symbionts Nodulating Winged Bean Landraces

Winged bean (Psophocarpus tetragonolobus L.) is a potential source of protein for the tropics and almost equivalent to protein content of soybean. However, information on winged bean-bacteria association is still limited. This study was conducted to assess phenotypic and genetic characterization of micro-symbionts that could effectively nodulate winged beans. The greenhouse experiment was performed in a completely randomized design with five accessions of winged bean and five replicates. The micro-symbionts were isolated from the root nodules and subjected to nodulation test on host plants. The effective nodulating isolates were characterized by phenotypic characteristics and 16S rRNA gene sequencing technique. The strains were also assayed for plant growth promotion traits. Thirty micro-symbionts were isolated from root nodules of winged bean plants but only twelve (40.0%) effectively nodulated their host plants. All the effective micro-symbionts were Gram negative, rod-shaped bacteria. Six of the effective rhizobia isolates were slow growers while others were fast growers. The results further showed that four of the isolates could produce ammonia and indole acetic acid, as well as solubilizing phosphate. The phylogenetic analysis revealed that the micro-symbionts were similar to strains of Rhizobium, Bradyrhizobium and Mesorhizobium. The study therefore showed the potential of these micro-symbiont strains in nodulating winged bean.