Keywords: Osmotic stress, Endophytic bacteria, IAA production, GA production, PEG 6000, Exo-polysaccharide, Bacillus casamancensis, Bacillus aryabhattai
The present investigation was conducted to determined the effect of osmotic stress on plant growth promoting activities of the osmotolerant endophytic bacteria. Osmotic stress led to a decrease in growth of both the endophytic Bacillus aryabhattai strain NSRSSS-1 and Bacillus casamancensis strain MKS 6. However, supplementation of the medium with 40% PEG 6000 led to drastic reduction in growth of both the cultures. Both endophytic bacterial strains were found to improve seed germination, plumule and radicle length under severe stress conditions. Effect of osmotic stress on plant growth promoting activities of the selected osmotolerant endophytic strains were determined. Both strains were found to possess multiple plant growth promoting activities such as P-solubilization and phytohormone production traits. Osmotic stress had a beneficial effect on P-solubilization, Indole acitic acid and exopolysaccharides production ability of both of the cultures. Osmotic stress had an inhibitory effect on GA production ability of both the cultures.
During plant-endophyte association, in vitro conditions, there was an associated decrease in ethylene production by the plant under osmotic stress conditions while IAA, GA and exopolysaccharide production during the plant-endophyte association was significantly enhanced under severe water stress conditions. On the basis of growth at higher PEG concentration, seed germination percentage, plant growth promoting traits and exopolysaccharide production two most promising strains were identified, which can be used as biofertilizers to improve productivity of Cluster bean in arid and semi arid regions of the country.
First author is thankful to Indian Agricultural Research Institute, New Delhi and Division of Microbiology for providing the necessary infrastructure facilities.