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In the present study rhizobial isolates from root nodules of various legumes were screened for phosphate
(P) solubilizing ability in both non-buffered and buffered media. Thirty five percent isolates showed P.
solubilizing ability in buffering conditions. There was reduction in pH of media with increase in P.
concentration up to 15 days. Isolate RASH6 selected on the bases of highest P. solubilizing ability in
buffering condition also showed IAA, siderophore, ammonia and HCN production. HPLC analysis
showed production of succinic and gluconic acids in the non-buffered culture medium.In buffered media
citric, succinic and gluconic acids were produced in higher concentrations in comparison to non-buffered
media, due to enhanced requirement of organic acids for reduction of pH in buffered condition. Pot study
showed that treatment with RASH6 had a significant effect on chickpea growth in soil amended with
tricalcium phosphate in comparison to without any amendment, indicating the role of P. solubilization
ability of rhizobia in plant growth enhancement. In treatment of soil amended with soluble phosphate
indicates that as soluble phosphate is already present in the soil, phosphate solubilization mechanism
may not be involved however other plant growth mechanism may be responsible for plant growth
promotion. There was enhancement in nodulation and nitrogenase on RASH6 treatment in soil amended
with phosphates indicated that improvement in P nutrition of the plant was responsible for increased
nodulation and N2-fixation. Rhizobial isolates having N2 fixing as well as high P solubilizing capability
can be of great value for sustainable yield enhancement.
Key words: Buffering condition, chickpea, organic acids, phosphate solubilizing microorganisms, rhizobia.