Isolation of phosphate solubilising rhizobacteria and endorhizobacteria from medicinal plant Picrorhiza kurroa and their optimization for tricalcium phosphate solubilization

Phosphate solubilizing microorganisms play an important role in supplementing phosphorus to the plants by several mechanisms like lowering of pH by acid production and ion chelation and thus benefit plant growth and development. Therefore, the aim of this study was to determine the phosphate solubilizing potential of plant growth promoting rhizobacteria (PGPR) isolated from Picrorhiza kurroa. Forty bacterial isolates were selected (by modified replica plating technique) as the representative of the total plated population from the rhizosphere soil and rhizome/roots of the Picrorhiza kurroa from two locations of Chamba district. All the bacterial isolates were able to show P- solubilization on Pikovskaya’s, solid medium and were also grown on liquid Pikovskaya’s medium for estimating their P- solubilizing potential. out of the forty isolates five isolates (PkR (7a)*,Pk7(B),Pk14(b), Pk12(d) and PC4) showed maximum P- solubilization, solubilizing 320.00 mg/l, 120.00 mg/l, 205.00 mg/l,100.00 mg/l and 180.00 mg/l respectively. These five isolates were selected for their ability to solubilize tricalcium phosphate(TCP). in four different media viz., Pikovskaya’s Broth, Luria Bertani Broth, Nutrient Broth, National Botanical Research Institute Phosphate Growth Media and Pikovskaya’s Broth was found to be the best medium for growth and P-solubilization. Further two isolates PkR (7a)*and and PC4 were selected for optimization of various parameters like effect of incubation period, temperature, pH, age of inoculum, size of inoculums, higher concentration of tricalcium phosphate on tricalcium phosphate solubilization and it was found that the isolate PkR (7a)* showed maximum P- solubilization of 320.00 mg/l at pH 7.0, 0.5 per cent TCP concentration, 10% of inoculum size and 24 h old culture after 72 h of incubation at 35 0C in PVK broth. This isolate was identified as Bacillus subtilis by 16S rDNA sequencing.