Diversity Of Nitrogen-Fixing Symbiotic Rhizobia With Special Reference To Indian Thar Desert

The symbiotic nitrogen-fixing bacteria are found in diverse climatic conditions and are ecologically important. The classification of rhizobia has always been fascinating; with the advent of polyphasic approaches, it is continuously changing by addition of new genera and species and the reclassification and discovery of nontraditional rhizobia. In comparison with crop legumes, the study of symbiotic associations in wild/native legumes has led to the discovery of several genetically diverse rhizobia. In the era of global climate change, increasing desertification, and for food security, the identification and characterization of rhizobia adapted to arid and hot climatic conditions are important. With this aim desert rhizobia associated with several native legumes belonging to different tribes have been broadly studied from less-explored regions of Indian Thar Desert. The diverse legumes in alkaline soils of the Thar Desert are found to be nodulated by traditional rhizobial genera, Ensifer and Bradyrhizobium. On the basis of core gene phylogeny, the Ensifer strains affiliated to mimosoid, cesalpinioid, and papilionoid legumes clustered into novel clades and lineages. Bradyrhizobium strains phylogenetically diversified from the B. yuanmingense type strain are microsymbiont of species of Tephrosia, Alysicarpus, Crotalaria, and Chamaecrista in addition to strains of Ensifer. The tree rhizobia (isolated from Vachellia, Senegalia, Prosopis, Mimosa) have host range restricted to tree species and therefore could be used as an inoculum in forestry practices. The other native rhizobia isolated from wild legumes (Tephrosia and Chamaecrista) are compatible with crop legumes (Vigna, Cyamopsis, Glycine max) and can be useful in preparation of consortia for extension of agricultural practices.