Chemical Profile and Bioactivity of Essential Oils from Five Turkish Thyme Species Against White Mold Fungal Disease Agent Sclerotinia sclerotiorum

This research examined the phytochemical profile, antioxidant properties, and antifungal efficacy of essential oils (EOs) derived from five thyme species growing wild in Türkiye: Origanum saccatum P.H. Davis, Origanum vulgare subsp. hirtum (link) Ietswaart, Satureja cilicica P.H. Davis, Thymbra spicata L. var. spicata L, and Thymus sipyleus subsp. sipyleus var. sipyleus . The extraction of essential oils was performed using the hydro distillation technique. To identify the volatile compounds, present in the oils, gas chromatography–mass spectrometry (GC–MS) was employed. The antioxidant potential of each sample was determined based on their ability to scavenge DPPH free radicals, while the total phenolic content was quantified utilizing the Folin–Ciocalteu assay. The antifungal potential of the oils against Sclerotinia sclerotiorum , a soil-borne plant pathogen, was evaluated through vapour-phase exposure at varying concentrations. GC-MS results showed that the predominant constituents of the essential oils were phenolic monoterpenes, particularly carvacrol and thymol. Among the analyzed species, O. vulgare subsp. hirtum exhibited the highest carvacrol content, reaching 88.12%. Among the tested oils, T. spicata var. spicata showed the highest antioxidant capacity, as indicated by its low IC₅₀ value of 10.698 mg/L, and was also rich in phenolic compounds, containing 4.771 µg/mg. Furthermore, the oils from S. cilicica and T. spicata var. spicata completely inhibited fungal mycelial growth at a dose of 1.0 µL/Petri dish, indicating strong antifungal efficacy. EC₅₀ values were found to range between 0.14 and 1.90 µL/Petri dish, with T. spicata var. spicata demonstrating the greatest effectiveness. In summary, the results emphasize the potential of thyme-derived EOs especially those rich in carvacrol as environmentally friendly and natural substitutes for chemical fungicides in controlling fungal infections in plants.