Biocontrol potential of Paenibacillus polymyxa against Verticillium dahliae infecting cotton plants

Abstract Verticillium wilt of cotton is an economically important disease caused by V. dahliae throughout the world. To control this disease, five bacterial strains from cotton-growing fields were screened for their antagonistic activity against V. dahliae . Interestingly, they were all identified as Paenibacillus polymyxa by testing morphological and ultrastructural characteristics as well as 16S rRNA sequences and fatty acid composition analysis. The observation of sporulation process revealed that the structure of the endospore coat was composed of three layers including outer, middle and inner spore coats. Among five strains, ShX301 showed highest antagonistic activity against spore germination and mycelial growth of V. dahliae . In addition, in vitro experiments showed that ShX301 had a broad-spectrum antifungal activity against other plant pathogens. The experiments for controlling Verticillium wilt of cotton in greenhouse demonstrated that inoculation by strain ShX301 reduced disease incidence and severity by 71.4% and 40.3%, respectively. Moreover, ShX301 significantly promoted the growth of cotton seedling. Assessment of plant growth promotion showed that inoculation by ShX301 promoted cotton plant growth enhancing aboveground seedling biomass by 45.5% as well as underground root length and biomass by 38.0% and 38.5%, respectively. This is the first report of P. polymyxa application to control Verticillium wilt of cotton and promoting cotton seedling growth. This study revealed that P. polymyxa ShX301 had high potential to be used as biocontrol agent and/or plant growth-promoting bacterium in agriculture.