EFFECT OF PLANT-GROWTH PROMOTING RHIZOBACTERIA ON COMPETITIVE ABILITYOF INTRODUCED BRADYRHIZOBIUM SP. (VIGNA) FOR NODULATION

Four plant growth promoting rhizobacterial (PGPR) isolates belonging t o genera Bacillus and Enterobacter and two Bra-dyrhizobium 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 Bradyrhizobium 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 Brady rhizobium strain S 24, after 50 and 80 days of plant growth. Single in oculations of PGPR isolates significantly increased grain yield over u ninoculated control. The influence of PGPR isolates on the ability of Bradyrhizobium strains to compete with indigenous population of bradyr hizobia was studied in terms of nodule occupancy. Bradyrhizobium strai ns were genetically marked by studying their intrinsic Antibiotic Resi stance pattern. The nodule occupancy of Bradyrhizobium strain S 24 inc reased from 60% (treatment with single inoculation of S 24) to 81% in presence of an Enterobacter isolate EG-ER-2. Another Enterobacter isol ate KG-ER-1 increased nodule occupancy of bradyrhizobial strain Cog 15 from 77% (treatment with single inoculation of Cog 15) to 88%.