Solubilization of inorganic phosphate and plant growth promotion by cold tolerant mutants of Pseudomonasfluorescens.

A study for screening and selection of cold tolerant mutants of Pseudomonas fluorescens strains GRS1, PRS9 and ATCC13525 based on 'P' solubilization ability and subsequent effect on plant growth promotion under in vitro and in situ conditions was conducted. Of all the mutants tested, two were selected, as there was a 21-fold increase in CRPF, (GRS, mutant) and a 10-fold decrease in CRPF7 (PRS9 mutant) over their respective wild types. Under in vitro conditions at 10 degrees C, these cold tolerant mutants exhibited increased plant growth indicating their functionality at low temperature. Subsequently, greenhouse trials using soil-plant microcosms were conducted which revealed that CRPF, (high 'P' solubilizer) was a good rhizosphere colonizer showing a significant increase in root (30 and 20%) and shoot length (20 and 24%) of mung bean, both in sterilized and unsterilized soil, respectively. On the contrary, CRPF, (low 'P' solubilizer) did not stimulate plant growth. Furthermore, sand experiments indicated that tricalcium phosphate served as better phosphorus source for CRPF2 treated mung bean seeds.