Screening of phosphate-solubilizing microorganisms in rhizosphere and rhizoplane of adverse soil-adapting plants in Southern Thailand

Various adverse soils; peat, podzolic sandy, acid sulfate and salted-affected acid sulfate soils were widely distributed throughout Southern Thailand. These soils were infertile and strongly acidic. Phosphorus fertility of these soils was low due to the low content of available phosphorus (0.31-3.70 mg kg-1) especially in podzolic sandy soil. Acid sulfate soil and salt-affected acid sulfate soil contain relatively high level of exchangeable Al (13.3 and 9.87 cmolc kg-1, respectively). However, some native plants; Melaleuca cajuputi, Melastoma malabathricum, Scleria sumatrensis and Oryza sativa grow well in these adverse soils. Since the adverse soils distributed there are phosphorus-unavailable soils. Hence, base on an idea that phosphate-solubilizing microorganism is a key factor for plant growth, such functional rhizospherous microorganisms were screened using modified Pikovskaya's media containing 5 mg l-1 P in different phosphate forms, Al-PO4, Fe-PO4 and Na-phytate, and adjusted pH 4.0. The number of microorganisms in the rhizosphere tended to be lower than in the rhizoplane. Twelve isolates showed remarkable growth performance on these solid media. Among these selected, 5 strains were obtained from acid sulfate soil, suggesting acid sulfate soil-adapting plant is a good source of the phosphate-solubilizing microorganism.