Abstract

Many phosphate solubilizing fungi (PSF) are found in soil and their introduction in the rhizosphere of crops not only increases the availability of phosphorus from insoluble sources of phosphate but also increases the efficiency of phosphate fertilizers such as superphosphate and rock phosphate. Studies on 2 strains belonging to Aspergillus niger, and 1 strain each of Aspergillus flavus, Penicillium aurantiogriseum and Penicillium claviformis with special reference to phosphate solubilization were performed in this communication. All the fungal strains showed halo zone around them on Pikovskaya plates. Quantitative estimation of 3 indigenous strains along with the other 2 non-indigenous strains taken as reference strains was done in two nutrient broths namely: Czapek’s Dox and Pikovskaya containing dicalcium phosphate (DCP) as insoluble source of phosphorus. Out of the two media selected for the study, Pikovskaya broth supported better solubilization. The insoluble phosphates DCP, TCP (tricalcium phosphate) and hypt (hydroxyapatite) were tested, DCP was least solubilized by all strains but there was no significant difference in solubilization of TCP and hydroxyapatite. There was significant negative correlation between pH and phosphate solubilized in all forms of insoluble phosphates. Types of nitrogen sources and metal ions were also screened during the study. (Na₄)₂SO₄ supported more solubilization than NaNO₃, whereas phosphate solubilizing activity decreased (except in A. niger ATCC 282) in presence of Mn⁺² and Fe⁺³ but presence of Al⁺³ did not have statistically significant effect on solubilization. Though various species of Penicillium have been reported for phosphate solubilization in literature but to the best of our knowledge this is first report of phosphate solubilization by P. claviformis.

Key words: Aspergillus, Penicillium, phosphate solubilisation, dicalcium phosphate, tricalcium phosphate, hydroxyapatite.