Isolation and Evaluation of Rock Phosphate Solubilizing Fungi as Potential Biofertilizer

Abstract

RP solubilizing fungi were isolated from rhizosphere soil of crop fields using the dilution plate method. Soil sample (10 g) was mixed with 90 mL sterile distilled water. It was vigorously shaken and left to stand for 5 min. Homogeneous soil solution was serially diluted using normal saline. Dilutions from 10 -4 , 10 -5 and 10 -6 were plated on PDA and incubated at 28 ± 2 ° C for 3 days. Isolated fungal strains were maintained on PDA slants until use. Phosphate solubilizing ability of the isolates was confirmed by incubating them on PVK medium incorporated with 5% Senegal RP at 28 ± 2 ° C for 7 days. Diameter of clearance zone was measured successively after 24 h, up to 7 days. The Solubilization Index (SI) is the ratio of total diameter i.e. clearance zone including fungal growth and the colony diameter. All the observations were recorded in triplicate. RP Solubilisation in liquid culture Microorganisms were tested in liquid media to assess their capability of releasing P from insoluble sources. Modified PVK broth (100 mL with 5% Senegal RP) was distributed into 500 mL Erlenmeyer flasks and the pH was adjusted to 7.0. After sterilisation and cooling, 1mL mycelia suspensions were used to inoculate flasks in triplicate. Non-inoculated flasks supplemented with RP served as controls. Incubation was made at 28 ± 2 ° C, 150 rpm for 30 days with intermittent sample withdrawal (centrifuged at 17250 g for 10 min) for P solubilization, pH measurement and organic acid analysis on 7 th , 14 th and 21 st day. The quantitative estimation of solubilized P was done by the Vanadomolybdophosphoric yellow color method [16].