Non-Rhizobial Nodule Associated Bacteria (NAB) From Blackgram (Vigna mungo L.) and their possible role in plant growth promotion


                                Rhizosphere engineering is one of the means to increase the competitive survivability of rhizobial bio-inoculants. This can be achieved by altering the rhizospheric community structure with a co-compatible and co-operative microbial partner. There exists a proto-cooperative mode of interaction between the non-rhizobial endophytes (NRE) and the endosymbiont Rhizobium, which can be unraveled to enhance their competitive survivability. In the present investigation, 8 isolates of nodule associated bacteria (NAB) and 1 rhizobial species were isolated from the root nodules of black gram (Vigna mungo L.,) cultivar VBN6. Among the NAB isolates, 75% were gram positive bacilli belonging to the phylum firmicutes. The promising NABs that showed maximum PGP features were phylogenetically affiliated as Bacillus subtilis NANEB1 and Paenibacillus taichungensis TNEB6. Among them, P.taichungensis TNEB6 registered significant IAA production (15.39µg.ml1), siderophore (10.7%), ammonia, HCN and also ACC deaminase activity (94.3 mg-1 hr-1). Interestingly, 75 % of the NAB isolates could solubilize phosphorous. Furthermore, P.taichungensis TNEB6, when co-inoculated with Rhizobium sp showed significant plant growth promotion with respect to enhanced root and shoot length. The vigor index was also maximum in the treatment that received co-inoculation of Rhizobium sp and P.taichungensis (1812) Hence, the study suggests the scope of enhancing the yield potential and fitness of blackgram using a compatible co-inoculant, comprising a multifunctional NAB, P.taichungensis TNEB6, and Rhizobium sp

Key words : nodules, nodule-associated bacteria, Blackgram, Paenibacillus, Rhizobium, Co-inoculant.