Isolation and characterisation of phosphate solubilising bacteria from rhizospheric soil of orange trees of darjeeling hills, india

Plant growth promoting rhizobacteria (PGPR) influence the plant growth by improvement in the nutrient mobilisation, solubilisation and production of plant growth promoting substances. The Rhizospheric soil samples of orange (Citrus reticulata Blanco) trees growing in Mangwa Busty, Darjeeling district was screened for the presence of solubilisation of tricalcium phosphate (TCP) in Pikovskaya’s (PKV) agar and two bacterial isolates showing clearing zone around their colonies were selected and subjected to characterisation. The isolates were designated as GCM1 and GCM2. They were further analysed for their capacity to solubilise tricalcium phosphate (TCP) in PKV broth. Phosphate solubilisation was accompanied with a reduction in the pH of the medium from 7.2 to 5.22 (GCM1) after 7 days of incubation. Furthermore these isolates were capable of producing plant growth promoting substance, indole acetic acid (IAA). These isolates (GCM1 & GCM2) were further grown at different glucose concentrations of 5g/l, 10g/l, 15g/l and 20g/l. It was observed that higher concentration of glucose yielded the higher amount of soluble phosphate in the medium. Isolate GCM2 solubilised 200.18 ppm phosphate at 20g/l glucose concentration and pH was reduced to 4.94. Further their survivality were tested at different pH of 5, 7 and 9 and it was found that they could survive well at acidic pH of 5 upto 7 days of incubation. These two isolates GCM1 and GCM2 were identified as Bacillus sp. and Pseudomonas sp. at IMTECH (MTCC), Chandigarh, India. Both the isolates were found to increase the growth of orange seedlings in greenhouse condition. These isolates may be used as field inoculants in the orange plantation and other agricultural systems preceded by detailed agronomical evaluation.