In-vitro antagonistic potential of pseudomonas fluorescens isolates and their metabolites against rice sheath blight pathogen, rhizoctonia solani.

Sheath blight of rice caused by Rhizoctonia solani is an economically important disease affecting rice production. Eight Pseudomonas fluorescens strains were isolated from rhizosphere of rice seedlings collected from Andhra Pradesh and Tamilnadu. These strains were characterized with PCR based RAPD technique and tested for their in-vitro antagonistic activity against R. solani. Crude metabolites from one particular isolate of P. fluorescens (P. f 003) were extracted with organic solvents such as ethyl acetate and petroleum ether and these were tested against R. solani. Commonly used fungicides in rice sheath blight disease management such as hexaconazole, carbendazim, copper oxy chloride and mancozeb at 150 ppm were screened against mycelial growth of R. solani using poisoned food technique. All the strains tested were exhibited antagonistic activity against R. solani. One isolate, P.f 003 gave 78% inhibition compared to control. All the fungicides and crude extracts of P.f.003 inhibited the mycelial growth of R. solani. Highest inhibition was recorded with hexaconazole and ethyl acetate crude metabolite extract. The results offer a scope for integrating P. fluorescens with chemical fungicides for control of sheath blight of rice.