PLANT GROWTH PROMOTING RHIZOBACTERIA INDUCED MODULATION OF PHYSIOLOGICAL RESPONSES IN RICE UNDER SALT AND DROUGHT STRESSES

Effects of Pseudomonas sp. on physiology of Oryza sativa (L.) var. KS -282 were evaluated under induced drought stress and salinity stress conditions. For seed inoculation, sterilized seeds were immersed in Pseudomonas broth culture for 2 to 4 hours, whereas control seeds were soaked in distilled water for the same time period before being sowed in autoclaved, sand -soil mixture. Drought stress was induced by withholding water supply for 10 days, while salinity stress was induced by irrigating with 200 mM NaCl. Plants were harvested at the vegetative stage. Both the stresses significantly decreased the relative water content of leaves, root area, total soluble leaf proteins, chlorophyll content of leaves, osmotic potential of leaves whereaas electrolyte leakage, proline content of leaves and superoxide dismutase activity were significantly increased. The decrease in moisture content of the rhizosphere soil was much less marked in salt -stressed plants. The PGPR ameliorated the adverse effects of drought and salt stress on all parameters but at different magnitude. Generally, PGPR were more effective under drought stress. The percentage decrease in soil moisture content and relative water content (RWC) were higher under drought stress. The drought stress induced a decrease in protein production, and an increase in proline was similar under both stresses however, the PGPR induced production of protein was 50% lower in saline condition but was equally effective for proline production. The antioxidant enzyme superoxide dismutase (SOD) activity was higher under drought stress than that under salt stress, and PGPR further augmented it. It is inferred from the present finding that the effect of drought is more pronounced in rice and that the ameliorative effectiveness of PGPR used as bioinoculant differs under different stresses for a plant grown under similar condition.