Biochemical, functional and molecular characterization of pigeon pea rhizobia isolated from semi-arid regions of India.

Pigeon pea (Cajanus cajan (L.) Millspaugh) is among the top ten legumes grown globally not only having high tolerance to environmental stresses along, but also has the high biomass and productivity with optimal nutritional profiles. In the present study, 55 isolates of rhizobia were identified from 22 nodule samples of pigeon pea collected from semi-arid regions of India on the basis of morphological, biochemical, plant growth promoting activities and their ability to tolerate the stress conditions viz. pH, salt, temperature and drought stress. Amongst all the 55 isolates, 37 isolates showed effective nodulation under in vitro conditions in pigeon pea. Further, five isolates having multiple PGP activities and high in vitro symbiotic efficiency were subjected to 16S rRNA sequencing and confirmed their identities as Rhizobium, Mesorhizobium, Sinorhizobium sp. Further these 37 isolates were characterized at molecular level using ARDRA and revealed significant molecular diversity. Based on UPGMA clustering analysis, these isolates showed significant molecular diversity. The high degree of molecular diversity is due to mixed cropping of legumes in the region. The assessment of genetic diversity and molecular characterization of novel strains is a very important tool for the replacement of ineffective rhizobial strains with the efficient strains for the improvement in the nodulation and pigeon pea quality. The pigeon pea isolates with multiple PGPR activities could be further used for commercial production.