Isolation of bacterial strains possessing nitrogen-fixation, phosphate and potassium-solubilization and their inoculation effects on sugarcane.

Inorganic nitrogen (N), phosphate (P) and potash (K) are the most influencing macro-nutrients for plant growth and microbial supplementation of these minerals through N2-fixation, P- and K-solubilization is gaining importance. In the present study, a macronutrient deficient (MD), N-free novel medium, supplemented with tri calcium phosphate (TCP as P- source) and Mica (as K- source) was used for isolation of microbes possessing nitrogen fixing, P- & K solubilizing abilities. Samples of rhizosphere and non-rhizosphere soils, roots and leaves of sugarcane varieties (viz., Co 6304, Co 86032 and CoC 671) collected from Tamil Nadu, India were used for isolation. Totally, 8 individual nitrogen-fixing, phosphate- and potash-solubilizing bacterial strains were obtained. Nitrogen-fixing abilities of these isolates were confirmed by analyzing acetylene reduction (AR) activity and the presence of nif genes. P- and K- solubilizing activities were confirmed by cultivating these isolates in solid/liquid medium supplemented with insoluble forms of P and K. These isolates which produced growth hormone IAA, were in two groups as Roseateles terrae and Burkholderia gladioli, respectively based on the morphological, physiological, biochemical and 16S rDNA gene sequence analysis. Association between diazotrophic, P- and K-solubilizing R. terrae and B. gladioli with sugarcane has not been reported earlier. These isolates were tested for their growth-promoting abilities in sugarcane cultivated in pots, and the results showed that these isolates were able to increase the leaf chlorophyll, N content and total biomass. This study may encourage farmers to use single microbe for microbial supplementation of N, P and K instead of consortium of microbes wherein the compatibility between different microbes is often compromised.