Multitarget Mechanisms and Biocontrol Potential of Iturin A Against Ralstonia solanacearum in Tomato

Tomato bacterial wilt, caused by Ralstonia solanacearum, poses a severe threat to both tomato yield and quality, and therefore, there is an urgent need for environmentally friendly control measures.. In this study, the cyclic lipopeptide Iturin A was purified from the fermentation broth of Bacillus amyloliquefaciens and its antibacterial activity against R. solanacearum and other pathogenic bacteria was assessed. Iturin A could effectively inhibit the growth of R. solanacearum in vitro and significantly reduced disease incidence in pot experiments. Microscopic observations revealed that Iturin A induced severe morphological damage, including membrane disruption and cytoplasmic leakage, while crystal violet staining confirmed a strong inhibition of biofilm formation. Additionally, Iturin A treatment resulted in the accumulation of intracellular reactive oxygen species (ROS), a decrease in succinate dehydrogenase (SDH) activity, and reductions in NAD+ and NADH content, while altering cytochrome c oxidase (CcO) staining, indicating disruption of the electron transport chain and energy metabolism. Transcriptome analysis further revealed downregulation of genes related to the cell membrane and type III secretion system (T3SS). These results suggest that Iturin A targets multiple pathways to impair cell integrity, biofilm formation, energy metabolism, and virulence, effectively controlling tomato bacterial wilt and highlighting its potential as a green biopesticide.