Molecular diversity of stress-tolerant PGPR rhizobia nodulating clusterbean (Cyamopsis tetragonoloba L.) grown in hyper-arid zone of Rajasthan

A total of 81 rhizobia were retrieved from nodules of clusterbean grown in hyper-arid zone of Rajasthan. Twenty one rhizobial isolates showed combined drought tolerance of 40% concentration of polyethylene glycol 6000 and temperature tolerance at 45°C. All the stress-tolerant rhizobia were authenticated by plant infectivity test and further showed the presence of nitrogen fixation nifH gene. Most of the stress-tolerant rhizobia harbour multiple PGPR traits. The molecular diversity among stress-tolerant rhizobia was accomplished through RFLP of 16S rDNA using restriction enzymes MspI and HaeIII. Dendrogram data showed that all 21 isolates were distributed into two major clusters. Total of 20 genotypes were formed but 13 biotypes were constituted at 80% level of similarity. Out of these, biotype 10 was found to be the most prevalent biotype of hyper-arid zone. Moreover, isolates from same nodule were not 100% similar. It indicated that vast diversity was present among stress-tolerant clusterbean rhizobial isolates.