Plant growth promotion in Oryza sativa by Bradyrhizobium sp. isolated from the rhizosphere of Aeschynomene indica.

Aeschynomene indica is traditionally used as green manure in Tamil Nadu, India, to cultivate Oryza sativa. This plant contains Bradyrhizobium sp. in its root and stem nodules as PGPR. In this work, we isolated Bradyrhizobium sp. from the root nodules of A. indica using a selective medium and used it as a biofertilizer for O. sativa. The isolated microorganism was confirmed by various biochemical tests of Bergeys Manual. Plant growth activity was measured in terms of plant height, plant diameter, leaf width, leaf length, grain weight, soil nitrogen fixation and nutritional value of the grains. Growth promotion of isolated Bradyrhizobium sp. was compared with commercial NPK fertilizers and commercial Rhizobium liquid fertilizer. Plants treated with Bradyrhizobium sp. provided a yield of 37.2 grams with average weight of 0.0182 g/grain while NPK treated plants had 38.4 g with average weight of 0.0175 g/grain. Total nitrogen fixed by Bradyrhizobium sp. (192 kb/ha) is almost similar to that of commercial NPK fertilizer (196 kg/ha). The nutritional value of the grains produced by Bradyrhizobium treatment (302 kcal) is higher than that of NPK fertilizer (286.12 kcal). Thus, free-living Bradyrhizobium sp. can be used as a biofertilizer for crops which does not have nodulation capability.