Biological control of three phytopathogenic fungi by Pseudomonas fluorescens isolated from rhizosphere.

Plant protection is an important area which needs attention since most of the hazardous inputs added into the agricultural system are in the form of plant protection chemicals. Pseudomonas fluorescens possess a variety of promising properties which make it a better biocontrol agent. The objectives of the present study were to isolate P.fluorescens from soil, to check its antagonistic activity and effect of its secondary metabolites on three fungal plant pathogens by in vitro techniques. P.fluorscens was isolated from rhizosphere soil on King’s B medium and its antagonistic effect on three fungal plant pathogens was studied in vitro. Its antagonistic activity was checked by co-inoculation with the fungal isolates. In pour plate method, P.fluorescens on coinoculation with fugal pathogens decreased their growth rate. Maximum inhibition was observed in Pythium ultimim (80%) followed by Macrophomina phaseolina (70%) and Pyricularia oryzae (50%). Effect of the separated secondary metabolites on the fungal growth by broth dilution technique and antifungal activity by agar well diffusion technique was studied. P.fluorescens produces a broad-spectrum antifungal compound, which inhibits a variety of plant Pathogenic fungi and inhibits Pythium ultimim more when compared to other plant pathogens in the present study. Further investigations on the type of antifungal components and in vivo experiments will make P.fluorescens as one of the most suitable biocontrol agent in suppressing the phytopathogenic fungi and replace chemical fungicides.