Management of bacterial blight of cotton using a mixture of Pseudomonas fluorescens and Bacillus subtilis

The potential of antagonistic rhizobacteria in the management of bacterial blight of cotton caused by Xanthomonas axonopodis pv. malvacearum (Xam) was evaluated under greenhouse and field conditions. In this study, 93 bacterial isolates from the rhizosphere of cotton were screened for their efficacy in inhibiting the growth of Xam in vitro. Among them, 21 isolates were found to inhibit the in vitro growth of Xam. These isolates were identified as Pseudomonas fluorescens and Bacillus subtilis based on phenotypic characteristics, biochemical properties and using 16S-23S intergenic transcribed spacer-Polymerase Chain Reaction (PCR). Among the 21 isolates, the isolates P. fluorescens Pf32 and P. fluorescens Pf93 and B. subtilis B49 exhibited the maximum inhibitory activity against Xam. Talc-based powder formulations of the effective antagonistic isolates of P. fluorescens (Pf32, Pf93) and B. subtilis (B49) were developed and evaluated individually and in combination for their efficacy in the management of bacterial blight of cotton under greenhouse and field conditions. The P. fluorescens isolates Pf32 and Pf93 and Bacillus subtilis isolate B49 survived well in the talc-based formulation for more than 90 days. The application of a mixture of Pf32, Pf93 and B49 to seed, soil and foliage significantly reduced the bacterial blight incidence and increased the plant height, number of branches and number of bolls under field conditions. The plots treated with a mixture of Pf32, Pf93 and B49 recorded the maximum yield of 1915 kg/ha and 1512 kg/ha in trial I and trial II compared to 1210 kg/ha and 987 kg/ha in the untreated control, respectively.