Antibacterial agents to control of pathogenic Xanthomonas arboricola pv. juglandis on walnut fruits and plants by polygodial derivatives formulations

BACKGROUND Walnut bacterial blight, caused by Xanthomonas arboricola pv. juglandis (Xaj), leads to significant yield losses in walnut production, which is a key agricultural sector in Chile. Conventional control methods based on copper have limitations owing to environmental concerns, phytotoxicity, and bacterial resistance. Plant‐derived compounds such as polygodial offer a promising alternative as a result of their potent antibacterial properties. This study aimed to develop and evaluate the antimicrobial efficacy of nanoemulsions containing drimanic compounds, specifically polygodial ( 1 ) and epi‐polygodial ( 2 ), as a sustainable strategy to control Xaj. RESULTS Both polygodial ( 1 ) and epi‐polygodial ( 2 ) demonstrated significant antibacterial activity against Xaj strains in vitro and in planta . In assays with immature walnut fruits, the nanoemulsion with compound 1 at 125 ppm reduced disease severity by 40%, an efficacy level intermediate between the negative control and the commercial chemical treatment (65% reduction). The nanoformulations effectively suppressed infections on leaves and shoots, and importantly, no phytotoxic effects were observed on either fruits or plants. CONCLUSION Polygodial and epi‐polygodial are potent antibacterial agents against Xaj, making them excellent candidates for new biopesticides. This study successfully formulated these drimanic compounds into stable nanoemulsions that effectively control walnut bacterial blight without causing phytotoxicity. The development of these nanoformulations represents a significant advancement towards sustainable and effective disease management in the walnut industry, offering a viable alternative to conventional copper‐based bactericides.