Effect of plant growth promoting rhizobacteria on competitive ability of introduced Bradyrhizobium sp. ( Vigna) for nodulation

Abstract

Four plant growth promoting rhizobacterial (PGPR) isolates belonging to genera Bacillus and Enterobacter and two Bradyrhizobium spp. ( Vigna) strains Cog 15 and S 24 were selected for competition studies. PGPR isolates did not antagonize Bradyrhizobium strains Cog 15 and S 24 on plates. In unsterile soil, co-inoculations of PGPR and Bradyrhizohium strains failed to show any conclusive influence on nodulation and ARA at 50 days of plant growth. PGPR isolates had a direct effect on shoot biomass development, N content and grain yield when tested with Bradyrhizohium strain S 24, after 50 and 80 days of plant growth. Single inoculations of PGPR isolates significantly increased grain yield over uninoculated control. The influence of PGPR isolates on the ability of Bradyrhizohium strains to compete with indigenous population of bradyrhizobia was studied in terms of nodule occupancy. Bradyrhizobium strains were genetically marked by studying their intrinsic Antibiotic Resistance pattern. The nodule occupancy of Bradyrhizobium strainS 24 increased from 60% (treatment with single inoculation of S 24) to 81% in presence of an Enterobacter isolate EG-ER-2. Another Enterobacter isolate KG-ER-1 increased nodule occupancy of bradyrhizobial strain Cog 15 from 77% (treatment with single inoculation of Cog 15) to 88%.