Design, Synthesis, Antibacterial Evaluation, and Mechanistic Insights of Garlic-Derived Disulfides against Erwinia amylovora.

Erwinia amylovora, the causal agent of fire blight, poses a severe and ongoing threat to the global production of Rosaceous crops. We synthesized 54 garlic-derived disulfides and identified compound b as the most potent candidate (EC50 = 2.85 μg/mL), which significantly surpassed allicin and zhongshengmycin (ZSM). In planta assays on Cuiguan pear demonstrated that b provided exceptional curative and protective efficacy, effectively suppressing fire blight infections in flowers, leaves, shoots, and fruits. Mechanistically, b triggered lethal ROS accumulation by inhibiting catalase (CAT) and superoxide dismutase (SOD) activities, leading to compromised cell envelope and ultrastructural damage in E. amylovora. Notably, b attenuated bacterial virulence by suppressing swimming and swarming motility, reducing biofilm formation, and decreasing extracellular cellulase activity, while also inhibiting DNA and protein biosynthesis. Additionally, b exhibited minimal toxicity toward nontarget organisms, such as silkworms (Bombyx mori) and earthworms (Eisenia fetida), highlighting its environmental safety. These findings establish compound b as a highly effective, safe, and eco-friendly candidate for sustainable fire blight management.