Evaluation of phosphate solubilisation by Burkholderia sp. isolated from the rhizosphere of different crops

The ability of a few soil microorganisms to convert insoluble forms of phosphorus to an accessible form is an important trait in plant growth-promoting bacteria. The use of phosphate solubilizing bacteria (PSB) as inoculants, increases the P uptake by plants. In this study, a total of 15 PSB isolates from rhizosphere of maize, sunflower, sugarcane, rice, Mimosa, bhendi, cluster bean, sunhemp and lemon were tested for the mineral phosphate solubilizing (MPS) activities in Hydroxy Apatite (HAP) broth, by analyzing the soluble-P content, after 72 h of incubation at 30°C. The optimum conditions for maximum P solubilisation were: pH 7, temperature 30 ºC and 3% sugar. The ‘P’ solubilising ability of Burkholderia sp., isolated from bhendi rhizosphere soil was found to be 24.5 mg 100 mL. P-solubilizing activity of these strains was associated with the release of the organic acids and a drop in the pH of the medium. An inverse relationship between pH and P solubilised was apparent, from this study. Based on the morphological properties, the isolates were tentatively identified as Burkholderia sp.