Synthesis and biological characterization of formononetin derivatives against phytopathogenic oomycete and bacteria: preliminary mechanisms, theoretical predictions, and biosafety evaluation

Background The increasing prevalence of phytopathogenic oomycetes and bacteria, particularly Phytophthora capsici ( Pc ) and Xanthomonas oryzae pv. oryzae ( Xoo ), poses severe threats to global agricultural production. Developing novel antimicrobial agents with dual antimicrobial activities, multiple mechanisms of action, and favorable biosafety profiles is urgently needed. Results This study aims to design, synthesize, and evaluate formononetin derivatives as dual‐action antimicrobial agents against these pathogens, preliminarily elucidating their mechanisms and biosafety. Among the tested compounds, B14 showed the most potent inhibitory effects, with half‐maximal effective concentrations of 4.99 μg/mL against Pc and 2.26 μg/mL against Xoo . In in vivo experiments, B14 displayed remarkable therapeutic activity. At 200 and 100 μg/mL against Pc on eggplant fruits (76.9–84.0%), chili leaves (77.0–78.5%), and chili fruits (80.1–80.2%), and against bacterial leaf blight on rice (56.1–58.1%), significantly outperforming the commercial controls azoxystrobin and thiodiazole copper. Preliminary mechanistic studies revealed that B14 disrupted Pc membrane integrity and induced reactive oxygen species accumulation, while suppressing bacterial virulence factors and defense enzyme activities. Theoretical predictions supported the observed structure–activity relationships. B14 showed no significant phytotoxicity or developmental toxicity in seed germination and zebrafish embryo assays. Conclusion Formononetin derivative B14 is a promising dual‐action antimicrobial candidate with distinct mechanisms against oomycetes and bacteria, offering a sustainable strategy for managing phytopathogens.