Survival and Phosphate Solubilizing Ability of Bacillus megaterium in Liquid Inoculants under High Temperature and Desiccation Stress

Inoculation of phosphate-solubilizing microorganisms along with rock phosphate is known to enhance the available P from soil. The success of such solubilization is largely dependent on the ability of the inoculant strain to survive under adverse environmental conditions. In this context, liquid inoculants are gaining importance and are becoming popular with longer shelf-life. In the present investigation, a preliminary study was conducted to determine the survival of Bacillus megaterium in liquid formulations supplemented with osmo/cell-protectants under the influence of high temperature, desiccation stress and their subsequent influence on P-uptake by cowpea plants. Liquid inoculant-2 containing osmoprotectants viz., polyvinyl pyrrolidone (PVP), high quantity of glycerol (12 ml L-1) and glucose supported higher viable population up to a storage period of four weeks at 48ºC (log10 10.62 CFU ml-1) and desiccation stress (log10 10.04 CFU ml-1) as compared to liquid inoculant-1 containing osmoprotectants viz., PVP, low quantity of glycerol (1 ml L-1), trehalose, arabinose and FeEDTA; and nutrient glucose broth without any osmoprotectants. Liquid inoculant-2 also enhanced the P-uptake of cowpea plants significantly.