Xanthomonas campestris is a phytopathogenic Gram-negative bacterium responsible for black rot in economically vital cruciferous crops, such as cabbage, broccoli, and cauliflower. Conventional management strategies rely heavily on copper-based chemical treatments; however, their efficacy is limited and prolonged use drives the development of resistant strains. Consequently, plant-derived essential oils (EOs) have emerged as viable, eco-friendly alternatives, offering biodegradable and structurally diverse sources of natural antimicrobials. The unique edaphoclimatic conditions of the Azores archipelago - characterized by volcanic soils, minimal anthropogenic pollution, and a hyper-humid temperate climate - creates distinct conditions for the production of chemically distinct EO profiles. In this study, EOs extracted via steam distillation of branches and leaves of Cryptomeria japonica (4 h), Cupressus leylandii (3.5 h), Eucalyptus globulus (2 h), and Laurus sp. (3 h) were screened for their microbiocidal potential against a highly virulent X. campestris isolate (CPBF 278). Antibacterial efficacy was quantified using the spectrophotometric Alamar Blue cell viability assay. At a standardized concentration of 1 µL/mL, the EOs demonstrated divergent inhibitory profiles. The most potent antibacterial efficacy was exhibited by Laurus sp. EO (92.4% inhibition), extracted from foliar and floral branches, followed closely by the biomass-derived shoots of C. japonica (90.8% inhibition). While E. globulus EO also displayed pronounced inhibitory activity (86.4% inhibition), C. leylandii shoot EO proved largely ineffective (6.9% inhibition). These findings highlight that turning waste products from the exploitation of agroforestry systems into botanical phytopharmaceuticals can offer a cost-effective, circular-economy strategy to control critical crop pathogens and foster sustainable agricultural ecosystems.

Acknowledgements: Thanks to Alicja Surowiak (Wrocław University of Science and Technology), to FCT structural funding for GreenIt (UID/04551/2025) and BioISI (UID/04046/2025) research centers.