Assessing essential oils from Macaronesia: a study on their efficacy against phytopathogenic and obligate biotrophic fungi.

BACKGROUND Essential oils (EOs) extracted from eight culinary herbs and spices, some endemic to Macaronesia flora (Cedronella canariensis, Clinopodium ascendens and Laurus novocanariensis) and others common in Mediterranean cuisine (Cinnamomum burmannii, Ocimum gratissimum, Origanum vulgare subsp. virens, Syzygium aromaticum and Thymus vulgaris) were evaluated via direct-contact bioassays, both in vitro and in vivo, against three species of phytopathogenic fungi (Alternaria alternata, Botrytis cinerea, and Fusarium oxysporum) and the obligatory biotrophic fungus Oidium farinosum. Carvacrol-rich Origanum vulgare was selected to study the influence of isomerism on bioactivity, because Thymus vulgaris is rich in thymol, a structural isomer of carvacrol. RESULTS Five EOs exhibited strong to moderate antifungal activity and were further screened at lower concentrations to assess their toxicity and growth inhibition thresholds. Cedronella canariensis showed no antifungal activity, whereas Laurus novocanariensis demonstrated only weak activity against Botrytis cinerea. This fungus was more susceptible to the tested EO than the other phytopathogenic fungi. Origanum vulgare was slightly more effective than Thymus vulgaris, for all three phytopathogenic fungi. Ocimum gratissimum, Syzygium aromaticum, and Cinnamomum burmannii significantly reduced powdery mildew severity, whereas Origanum vulgare and Thymus vulgaris showed moderate activity. CONCLUSION Phenylpropanoid-rich EOs, such as Cinnamomum burmannii, Ocimum gratissimum, and S. aromaticum, exhibited the strongest antifungal activity in both bioassays with phytopathogenic and obligate biotrophic fungi. Our results confirm the higher antifungal activity of the phenylpropanoid class of EOs. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.