Biological control of bacterial blight of cotton caused by Xanthomonas axonopodis pv. malvacearum with Pseudomonas fluorescens

In vitro antagonistic activities of seven strains of Pseudomonas fluorescens isolated from the rhizosphere of cotton were tested against Xanthomnas axonopodis pv. malvacearum (Xam), the causal agent of bacterial blight of cotton. Among them P. fluorescens strains MMP and Pf1 showed a high level of inhibition of Xam in vitro. Talc-based formulation of theses two isolates (MMP and Pf1) with the best efficacy in inhibiting the growth of Xam were prepared for further experiments. Wet seed treatment with P. fluorescens Pf1 significantly increased the seed germination and seedling vigour of cotton. Seed treatment followed by foliar application of Pf1 significantly reduced the incidence of bacterial blight and recorded the percent disease index of 14.5 as against 43.8 in control. Peroxidase (PO) isozyme analysis indicated that application of P. fluorescens MMP and Pf1 and inoculation with Xam resulted in induction of a new peroxidase (PO5).