Phosphate solubilizing bacteria from the acidic soils of Eastern Himalayan region and their antagonistic effect on fungal pathogens

This study tries to identify the native population of phosphate solubilizing bacteria (PSB) in the rhizospheres of maize, rice, ginger and large cardamom grown in different regions of Sikkim (India). Out of 104 rhizospheric samples collected from three agroclimatic zones of the state, 42 number of PSBs were isolated. However, only 26 best performing PSB based upon their solubilization in solid media are reported in this paper. The highest number of PSB with greatest variants were found in the rhizosphere of rice.The population density of PSB varies between 2-36×106 cfu g−1. Based upon the morphological and 16S rRNA sequencing, the isolates were clustered under the genera Bacillus, Pseudomonas, Micrococcus, Staphylococcus, Microbacterium and Delftia. Phosphate solubilization efficiency of these isolates varied between 46 to 160% in solid medium and in the liquid Pikovskaya's medium phosphate solubilization capacity varied between 30.2 to 203.7 mg L−1. Though all of the isolates were able to solubilize aluminum and iron phosphate significantly however, they solubilized Ca3(PO4)2 to a greater extent than the other two with AlPO4 exhibiting comparatively poor solubilization among the three phosphate sources. Further, the in vitro antagonistic effect of the PSB isolates were studied with seven locally available fungal pathogens and it revealed that the Bacillus amyloliquefaciens PSB isolates showed higher antifungal activity against soil and root borne pathogens (Rhizoctonia sp., Pythium sp., Fusarium sp.) than the leaf pathogens.