Biological control of tomato bacterial wilt and apple fire blight using n-docosane, a plant resistance inducer from...

Streptomyces sp. JCK-8055 effectively controls major bacterial plant diseases, such as apple fire blight and tomato bacterial wilt, caused by Erwinia amylovora and Ralstonia solanacearum, mainly by inducing plant defense responses. However, the specific metabolite responsible for this resistance-inducing activity had not been previously identified. This study aims to identify and evaluate the resistance-inducing metabolites of JCK-8055 and their effects on defense signaling against tomato bacterial wilt and apple fire blight. In this study, docosane was identified as the active metabolite using a combination of solvent partitioning, thin-layer chromatography, Arabidopsis thaliana pathogenesis-related 1::β-glucuronidase (GUS) bioassays, in vivo tomato bacterial wilt assays, and gas chromatography-mass spectrometry. At concentrations of 0.6-600 ng/mL, docosane demonstrated positive responses in the GUS assay. While docosane within this concentration range did not directly inhibit the growth of E. amylovora or R. solanacearum in vitro, it effectively suppressed tomato bacterial wilt in planta. Its disease control efficacy against tomato bacterial wilt was similar in a 0.6-60 ng/mL range but decreased significantly at 600 ng/mL. Among the tested concentrations, 6 ng/mL provided the most consistent disease control with the lowest variability. Gene expression analysis further revealed that docosane simultaneously and synergistically upregulated key defense-related genes associated with salicylic acid, jasmonic acid, and ethylene signaling pathways. In conclusion, these findings reveal docosane as a resistance-inducing metabolite produced by Streptomyces sp. JCK-8055 and highlight its strong potential as a biocontrol agent for managing bacterial plant disease, even at the low concentration of 6 ng/mL.