Phage typing of indigenous soybean-rhizobia and relationship of a phage group strains for their asymbiotic and symbiotic nitrogen fixation

A total of 354 indigenous bradyrhizobia were isolated from soybean nodules collected from five major crop grown regions. Host-specific 12 phages, each active on particular strains were selected. Factors, which influence the interaction between the host and phage, were examined. Four different types of plaques were detected. Nearly 17% of isolates were found resistant to all phages. Phage sensitivity patterns revealed a total of 32 distinct phage genotype groups. Different set of phage combinations expressed variation in specificity for parasitizing against particular group of rhizobia. Distributions of isolates in each phage types differed markedly between regions. Interestingly, nine strains belonging to phage group 16 exhibited high ex planta nitrogenase activity in culture. However, no correlation could be established between high ex planta nitrogenase activity and their symbiotic effectiveness with soybean cultivars. Soybean cv. JS335 showed relatively superior performance than Bragg and Lee with indigenous bradyrhizobial strains. Phage typing revealed the existence of large genetic diversity among native rhizobia and selection of the superior bradyrhizobial strains can also be possible for a given soil-climate-cultivar complex.