Delineation of Phosphate Solubilizing Bacteria from Rhizospheres of Different Crops of Assam

Study was undertaken to harness prospective phosphate solubilizing bacteria (PSB) from rhizosphere of different crops of Assam. Twenty-nine PSB isolates representing rhizosphere samples were isolated, screened and evaluated on Pikovskaya's solid as well as in liquid media. Thirteen isolates were further screened out on the basis of maximum clear zone formation for elaborate study to differentiate variation, if any, among cultures. Thus, the isolates were subjected to series of tests including quantification of P-solubilization followed by biochemical and intrinsic antibiotic resistance characterization. The maximum (10.33 x 10⁶ cfu g⁻¹) PSB were noted in wheat rhizosphere (PSB₂₈). The organic carbon (OC) of rhizospheres appeared strongest factor (r=0.880*) causing variation in PSB population across rhizospheres. The degree of tri-calcium phosphate (TCP) solubilization ranged from 7.33 to 59.66% among individual cultures. The isolate PSB₆₃ from rice rhizosphere and PSB_5W from toria rhizosphere were regarded as excellent P-solubilizer that recorded as high as 59.66% coupled with maximum drop of pH to 3.98 and 4.86, respectively from neutral. However, no significant correlation (r=0.124) was observed between pH drop and extent of P-solubilization among isolates. Five isolates showing maximum P-solubilization were further evaluated for biochemical traits and intrinsic antibiotic resistance (IAR) potentials. The isolates differed specifically in assimilating different carbohydrates and IAR profiles. However, the entire test isolates showed decarboxylase activity and could ferment citrate as sole carbon source and therefore established high activity in the rhizosphere.