Origanum vulgare ssp. viridulum and ssp. vulgare essential oils against agronomically critical fungal and bacterial pathogens

Fungal and bacterial phytopathogens cause substantial agricultural losses, motivating development of natural antimicrobial alternatives to synthetic pesticides. This study evaluated the antimicrobial efficacy of essential oils (EOs) from two Origanum vulgare subspecies, ssp. viridulum (Behshahr, Iran) and ssp. vulgare (Chalus, Iran), against five fungal and five gram-negative bacterial phytopathogens. GC-MS profiling delineated two chemotypes: a thymol chemotype (ssp. viridulum: thymol ۲۹.۹%, γ-terpinene ۱۳.۰%, β-pinene ۱۱.۳%; ۰.۴۰% v/w yield) and a linalyl acetate chemotype (ssp. vulgare: linalyl acetate ۲۷.۲%, γ-terpinene ۱۶.۵%, ۳-octanone ۱۰.۹%; ۰.۱۰% v/w yield). Factorial bioassays (disc and well diffusion, three concentrations) demonstrated that ssp. viridulum exhibited superior overall efficacy (۵۰.۰۷% mean inhibition) compared to ssp. vulgare (۳۰.۲۲%). Strong fungal selectivity was observed (۶۴.۴۹% mean inhibition) relative to bacterial pathogens (۱۵.۷۵%), a ۴.۱-fold difference attributable to the Gram-negative outer membrane permeability barrier. Sclerotinia sclerotiorum was the most susceptible pathogen (۹۰.۲۴% mean inhibition; ۱۰۰% at ۵ µl), while Pseudomonas syringae was the least responsive (۱۲.۸۱%). These results established ssp. viridulum EO as a candidate natural antifungal for post-harvest and protected-cultivation applications, contingent on in vivo and formulation validation. Bacterial disease management requires complementary strategies. The findings linked subspecies-level chemotypic variation to differential biocontrol efficacy, supporting chemotype-based EO standardization for targeted crop protection.

کلیدواژه ها:

Essential oil profiling ، Oregano ، Phytopathogen biocontrol ، Subspecific differentiation ، Thymol chemotype