Verticillium wilt is considered the most important disease of cotton in the world, including Iran. Cultural practices and the use of resistant varieties are the most common strategies used to control Verticillium wilt of cotton. These strategies are not always available or effective. In recent years, biological control using fungal and bacterial antagonists, has been applied to control some cotton diseases including damping-off. In this study, we investigated the possibility of biological control of Verticillium wilt of cotton using bacterial antagonists. Suspension of eight bacterial strains of Pseudomonas fluorescens and Bacillus spp. isolated from different rhizospheric soils and plant roots in the Iranian cotton fields, were prepared with a concentration of 108 cfu/ml. Ten cotton seeds (cv Varamin) were then coated with each bacterial suspension and were planted in soil pre-inoculated with Verticillium dahliae microsclerotia. The efficacy of bacterial antagonists in reducing wilt disease was evaluated by determination of the disease index in different treatments. The results indicated that most isolates were effective in reducing disease (compared to the untreated control) 90 days after sowing. Isolates B5, B6, B2, B7, and B3 were the most effective, respectively, in reducing wilt index. In contrast, isolates B1, B4, and B8 did not significantly reduce the disease. In general, P. fluorescens isolates were more effective than Bacillus isolates. This study suggests that bacterial antagonists might be potential biological control agents of cotton.
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