Phosphorus Solubilization and Plant Growth Promotion Ability of Rhizobacteria of R. communis L Growing in Assam, India

Abstract

Castor (Ricinus communis L) is the primary host plant of eri silkworm and its rhizosphere harbours diverse group of microbial community with biofertilizer potentiality. Phosphate solubilizing bacteria (PSB) render available phosphate (P) in agricultural soil by P mineralization process through enzyme mediated reaction. In search for PSB strains, 15 castor rhizobacteria were isolated and characterized for morphological and biochemical properties. The isolates were screened in vitro for P solubilization efficiency both qualitatively and quantitatively. Isolate MAJ PSB12 produced highest soluble P concentration (322.20 µmol/l) in National Botanical Research Institute Phosphate medium after 96 h of incubation with a maximum drop in pH to 5.4 from 7.0. Among the isolates, maximum content of IAA (24.6 mg/l) and GA3 (3.921 mg/l) was also found to be produced by the same strain. The most potential isolate was identified as Bacillus firmus MAJ PSB12 by 16S rRNA gene homology analysis and the sequence was submitted to National Centre for Biotechnology Information GenBank. Although many species belonging to the genus Bacillus are efficient P solubilizer, application of native rhizobacteria is easier for adaptation and succession during biofertilization process. B. firmus MAJ PSB12 can be utilized as potential biofertilizer to promote sustainable castor cultivation in sericulture for upliftment of rural livelihood.