Discovery of natural Nopol as promising antibacterial alternative with the capacity to suppress bacterial virulence and enhance plant immunity.

Outbreaks of plant diseases pose a severe threat to crop production and global food security. The extensive and prolonged use of conventional chemical bactericides has exacerbated pathogen resistance, creating an urgent demand for novel antibacterial agents with high biosafety profiles. This study screened a series of cyclic terpenoids against three phytopathogenic bacteria: Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa), with Nopol showing the strongest inhibitory activity against Xoo (EC50 = 8.86 mg·L-1). Mechanistic investigations furthermore revealed that Nopol significantly suppressed various crucial bacterial virulence factors, thereby disrupting the bacterial infection process. Pot experiments showed Nopol's curative (45.1%) and protective (52.8%) efficacies against Xoo, outperforming thiodiazole copper and comparable to zinc thiazole. Its potent protective activity may relate to jasmonic acid-mediated plant defense pathway. Collectively, our findings robustly establish Nopol as a highly promising botanical bactericide and a valuable lead compound for the rational design and development of innovative, eco-friendly bactericidal agents for sustainable plant bacterial disease management.