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

摘要

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. Introduction Research on a more sustainable and environmental friendly agriculture system is the need of the hour, as there is a growing concern on the deteriorating quality of the environment as a result of the intensive agriculture. Despite the many achievements of modern agriculture, certain cultural practices have actually enhanced the destructive potential of diseases. It is true that a huge number of fungal diseases plague the crop plants throughout the year when a farmer fails to take proper preventative measures. Plant disease control, therefore has become heavily dependent on fungicides to combat the wide variety of fungal diseases. A land mark study published by the us environment protection agency indicates that in the US alone 3000-6000 cancer cases are induced annually by pesticide residues on foods and another 50-150 by exposure to pesticides during application (Goud, 2004).This type of findings have made the governments of many countries increasingly aware of the drawbacks of many chemical pesticides in terms of their effect on the environment, as well as on the grower and consumer of agriculture products. 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. Studies aimed at replacing pesticides with environmentally safer methods are currently being conducted at many research centers. Biological control of plant diseases assumes a greater importance at this juncture. The efficient use of rhizosphere microorganisms to control plant pathogens has been reported worldwide in different plants. Soil pseudomonads possess a variety of promising properties, which make them better biocontrol agents (Cook,1993). In the last two decades endophytic bacteria especially Pseudomonas fluorescens have received considerable attention as potential biocontrol agent of a number of soil borne pathogens. Unfortunately, the seemingly inherent variable performance of most biocontrol strains between field locations and cropping seasons has hampered commercial development, and relatively few biological agents are registered for use in production agriculture (Cook,1996).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. Material And Methods