Genetic characterization and diversity of rhizobia isolated from root nodules of green gram (Vigna radiata L.) found in central plateau of India

Plant growth promoting rhizobia play an important in agricultural ecosystem through symbiotic association with a wide range of leguminous plants. Legume-rhizobia association is a host specific symbiosis hence the need to identify the strains and the diversity of rhizobia associated with specific type of legume for better bio-prospecting of the associated benefits. A wide range of variation is present among the distribution of rhizobia and greatly affected by geographical locality, edaphic factors and environmental variation with time and space. Molecular techniques have been developed to aid the traditional phenotypic and morpho-cultural techniques in distinguishing the different microbial genera, species and strains. The present study aimed at isolation and morphomolecular characterization of rhizobia from root nodule of green gram cultivated in central part of India.

In the field-laboratory investigation during 2018-2019, various locations of central India with contrasting agro climatic conditions were surveyed and rhizobia trapping done. A total of 40 rhizobia were retrieved from nodules of green gram and characterized in laboratory based on morphological, biochemical and molecular techniques and results validated for taxonomic identification.

In our investigation all forty isolated rhizobia were found phosphate solubilizers, 38 IAA producers and 37 ammonia excretors and grew well at 28°C and 37°C. In carbohydrate fermentation test 34 isolates changed the broth colour from red to yellow with gas formation in durum tubes. Twenty diverse rhizobia isolates were selected with respect to their multifunctional properties and studied for molecular characterization. Based on 16S rRNA gene sequencing, these bacterial strains were identified under two genera: Rhizobium and Brady Rhizobium. Phylogenetic analysis divided 20 rhizobia isolates into two clusters. Major group included 12 strains and minor group included 8 strains.