Growth-promoting and disease-suppressing effects of Paenibacillus polymyxa strain YCP16-23 on pepper (Capsicum annuum) plants

Phytophthora blight is the most devastating disease for pepper (Capsicum annuum L.) production and is caused by Phytophthora capsici. Current management strategies are not effective. Our study assessed the multi-trait effects of Paenibacillus polymyxa, which suppresses Phytophthora blight and promotes plant growth in pepper plants. A total of 82 bacterial strains isolated from rhizosphere soil of pepper plants were screened for in vitro inhibition of P. capsici growth. The results revealed that only six strains showed strong antagonistic activity against P. capsici. These six strains were used for controlling Phytophthora blight in pepper by seedling assays under greenhouse conditions. Three strains showed a lower incidence of Phytophthora blight and were used in further growth-promoting and biocontrol studies under greenhouse conditions. Strain YCP16-23 showed >60.0% suppression of P. capsici and significantly promoted growth of pepper plants compared to the untreated control. Based on cultural and morphological characterization and 16S rRNA gene sequencing, strain YCP16-23 was identified as Paenibacillus polymyxa. Strain YCP16-23 demonstrated many characteristics that are beneficial for plants, such as production of α-amylase, ammonia, cellulase, indole-3-acetic acid, pectinase, siderophores, and protease, as well as solubilization of phosphate. In a two-year field trial, strain YCP16-23 exhibited remarkable disease suppressing effect by controlling Phytophthora blight (76.24% and 38.09% in years 2017 and 2018, respectively) compared with the untreated control. Strain YCP16-23 caused disease suppression comparable to the microbial fungicides ‘Cike’ (72.04% and 15.41%) and Fluazinam (80.47% and 5.24%). Overall, the results suggest that strain YCP16-23 could provide protection against Phytophthora blight via direct and indirect modes of action and can be used as a biocontrol agent.