Diversity and Phylogeny of Pigeonpea Rhizobia in Vertisols of Central India

Abstract

Pigeonpea (Cajanus cajan) is one of the important pulse crops of tropical countries and an important source of dietary protein. Biological nitrogen fixation is an ecologically and agriculturally important process performed by bacteria. Legumes possesses unique ability to establish symbiosis with nitrogen fixing bacteria of the family Rhizobiaceae from the genera Braidyrhizobum, Rhizobium, Allorhizobium, Mesorhizobium and Sinorhizobium which are collectively referred as rhizobia. The existence of diverse rhizobia helped the host legumes to adapt to many different habitats .The aim of this study is to characterize and evaluate the diversity of rhizobia isolated from the pigeon pea nodules. The rhizobia isolated were categorized into fast and slow growing rhizobia. Among the rhizobia tested for acid/alkali production, all the fast growers were acid producers (100%), whereas most of the slow growers (88.5%) were alkali producers. Alkali production can thus be inferred to be a characteristic feature of slow growing rhizobia. Different rhizobial strains show different degrees of susceptibility to antibiotics and intrinsic antibiotic resistance profiles may be used for identification and to assess diversity of the rhizobia. A larger proportion of the rhizobial strains were resistant to trimethoprim, penicillin and nalidixic acid (90%, 76% and 75%). Most of the slow growers were resistance to kanamycin (70%), nalidixic acid (66.6%) and tetracyclin (62.5%) whereas fast growers were resistance to Co-trimoxazole (83.3%), erythromycin (71%) and chloramphenicol (70%). On an average, the rhizobia are resistant to 36.72% of the antibiotics tested. Diversity of isolated strains was assessed using BOX PCR. Of The 51 isolates BOX PCR produced 40 distinct patterns, with sizes ranging from 3000 to 300 bp. Acid alkali production test, antibiotic resistance pattern and BOX PCR profile can be used as a simple means of assessing variability and grouping of similar isolates.