Abstract
Fourteen plant growth promoting rhizobacteria (PGPR) isolated from rhizotic zones of field-grown green gram [Vigna radiata (L.) Wilczek] plants were examined for their growth-promoting attributes and ability to affect the growth in vitro of 10 strains of Bradyrhizobium sp. (Vigna). None of the rhizosphere bacteria was found to repress or stimulate the growth of any of the Bradyrhizobium strains tested. However, they produced antibiotics and siderophores and plant growth promoting substances. Ex planta and plant nitrogen fixation and phosphate solubilization was not detected by any of the isolates. Under in-vitro conditions, nine isolates inhibited growth of soil-borne fungal pathogens; one of them identified as Bacillus sp. antagonized all the fungi tested on two different media. All PGPR isolates were tested both in sterile and unsterile soil for their ability to promote nodulation, nitrogen fixation, growth, and yield of green gram in the presence of two Bradyrhizobium sp. (Vigna) strains S 24 and Cog 15. In sterile soil, all PGPR isolates had a positive effect on shoot biomass development, acetylene reduction assay (ARA), and N content when co-inoculated with Bradyrhizobium strain Cog 15, but could influence only shoot biomass development in the presence of strain S 24. In unsterile soil, PGPR isolates had a nodule-stimulatory effect on strain Cog 15 and a plant growth promoting effect on strain S 24, after 50 and 90 days of plant growth. Five isolates EG-RS-3, EG-RS-4, and NG-ER-7 (Bacillus spp), and KG-ER-1 and EG-ER-2 (Enterobacter spp) significantly increased yield of green gram in unsterile soil.
