Evaluation of Paenibacillus polymyxa strain SC09-21 for biocontrol of Phytophthora blight and growth stimulation in pepper plants

We assessed the efficacy of Paenibacillus polymyxa strain SC09-21 for reducing Phytophthora blight (caused by Phytophthora capsici) in pepper plants, and its ability to enhance plant growth. The results of in vitro studies indicated that SC09-21 effectively reduced the radial growth of eight plant pathogens in dual culture, and exerted the maximum antifungal activity against P. capsici. SC09-21 produced ammonia, cellulase, indole-3-acetic acid, protease, and siderophores, and solubilized calcium phosphate. Compared to the control, SC09-21 significantly (P = 0.05) reduced Phytophthora blight severity in pepper plants. After treatment with SC09-21, pepper leaves showed an increase in phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenol oxidase (PPO), and superoxide dismutase (SOD) activities. PAL, PPO, PO, and SOD activities were higher in treated seedlings than in untreated control. In addition, SC09-21 treatment enhanced pathogenesis-related (PR) protein gene expression in pepper plants, including those of CaPR4 and CaChi2, in the absence of P. capsici. Thus, SC09-21 enhanced different growth parameters. These results indicate that SC09-21 induces a defensive response against P. capsici and promotes growth in pepper plants. Therefore, it could be used as a potential agent for the biological control and growth promotion of plants.