Protective Rhizobacterial Strains Against Black Shoot Blight Caused by Erwinia pyrifoliae on Apple Plants

Disease suppression against black shoot blight caused by Erwinia pyrifoliae was evaluated using rhizobacterial strains isolated from Jeju Island in apple plants. Total 81 rhizobacterial strains were isolated from plant rhizospheres collected on Jeju Island. Among them, three isolates DR1-6, DR2-3, and DRB1-1 exhibiting antibacterial activity on artificial media were selected for further evaluation. In inoculation bioassays, disease severity on apple leaves was significantly reduced following treatment with mixtures of E. pyrifoliae and the rhizobacterial strains. Notably, DRB1-1 and DR2-3 reduced disease severity to levels comparable to antibiotic treatment, while DR1-6 showed only moderate suppression despite strong in vitro antibacterial activity. Quantitative analysis using qPCR revealed significant reductions in E. pyrifoliae populations on treated leaves, consistent with disease suppression. Based on 16S rRNA gene sequence analysis and scanning electron microscopy, strains DR1-6, DR2-3, and DRB1-1 were identified as Pseudomonas fluorescens, Serratia nematodiphila, and Paenibacillus polymyxa, respectively. These results indicate that the selected rhizobacterial strains have potential as biocontrol agents for managing black shoot blight in crop plants, including apple.