Exploring the Antifungal Efficacy of Essential Oils against Alternaria solani, the Causative Pathogen of Early Leaf Blight in Tomato Plants

Alternaria solani is an important necrotrophic fungus that is responsible for the early blight disease which is a common disease in tomato fields. In this research, the antifungal activity of essential oils extracted from Satureja hortensis, Thymbra spicata, Thymus sipyleus, Origanum majorana, O. syriacium, O. onites, O. vulgar, Artemisia absinthium, A. santonicum and A. spicigera were tested against Alternaria solani the causative agent of Tomato early blight disease. The study was carried out in two different ways, in vitro and in vivo. In vitro studies were conducted on media mixed with essential oils, and different concentrations of oils were examined on fungal growth in petri dishes. In in vivo studies, the effects of essential oils on the development of disease lesions were evaluated by infecting healthy tomato fruits. The concentrations used in the study were 140, 280, 560 and 1000 µl/L in the in vitro and 2.5, 5, 10 and 20 µl/fruit under in vivo conditions. Among the in vitro trials, the essential oils extracted from Thymus sipyleus and O. onites exhibited the most pronounced antifungal efficacy, achieving complete growth inhibition of the fungal pathogen across all concentrations whereas the essential oils from Artemisia spicigera and A. santonicum displayed relatively lower efficacy compared to the other oils. Conversely, under in vivo conditions, the essential oils derived from O. majorana and A. absinthium demonstrated the greatest capacity to impede the development of disease lesions on the fruit, yielding inhibition rates of 84% and 64% at 2.5 µl per fruit concentrations, respectively. In contrast the essential oils from Artemisia spicigera and A. santonicum had the least effect on the development of the disease, as there was disease lesions appeared even on the fruits that were applied at 20µl/fruit doses. Although most of the essential oils had some degree of antifungal action, still much effort is needed to put on both in vitro and in vivo trials to strength the reliability and consistency of the future related researches.