Essential oils as natural alternatives against phytopathogenic Xanthomonas campestris

Black rot represents an important bacterial disease impacting major Brassicaceae crops, including cabbage, broccoli, and turnip. It is caused by the gram-negative phytopathogen Xanthomonas campestris - known for the industrial production of the exopolysaccharide xanthan – that invades host tissues through natural openings or wounds. Infection leads to colonization of the vascular system and parenchyma, resulting in characteristic V-shaped chlorotic lesions and degradation of plant vasculature. Traditional control strategies depend primarily on copper-based compounds; however, their effectiveness is often limited, and prolonged application promotes the emergence of resistant strains. In this context, essential oils (EO) have gained attention as biodegradable and environmentally compatible alternatives rich in natural antimicrobial compounds. This study assessed the bactericidal activity of Cymbopogon citratus, Eucalyptus globulus, Foeniculum vulgare, Origanum vulgare, Rosmarinus officinalis, and Satureja montana EOs against a highly virulent X. campestris isolate (CPBF 278) using the spectrophotometric Alamar Blue cell viability assay. At a concentration of 1 µL.mL^-1, the carvacrol rich S. montana essential oil achieved complete inhibition (100 ± 0.0%), while O. vulgare oil demonstrated a strong activity (88.8 ± 4.1%), with the former exhibiting a rapid action within 15–30 minutes of contact. These results indicate that selected EOs can offer promising sustainable alternatives for black rot management. Their development as potential phytosanitary products could lead to reduced dependence on copper bactericides, minimize resistance development, and support environmentally responsible crop protection, thereby advancing resilient and ecologically balanced crop production systems.