Chemical profile and bioactivity of essential oils from five Turkish thyme species against white mold fungal disease agent Sclerotinia sclerotiorum

This study investigated the phytochemical profile, antioxidant properties, and antifungal activity of essential oils (EOs) from five thyme species growing wild in Turkey: 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 essential oils (EOs) were extracted using the hydro distillation technique. Gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds contained in the oils. The antioxidant potential of each sample was determined by its ability to scavenge DPPH free radicals, while the total phenolic content was quantified using the Folin-Ciocalteu assay. The antifungal potential of the oils against Sclerotinia sclerotiorum (Lib.) de Bary, a soil-borne plant pathogen, was evaluated through vapour-phase exposure at different concentrations. GC-MS results showed that the predominant constituents of the essential oils were phenolic monoterpenes, in particular carvacrol and thymol. Among the species analyzed, O. vulgare subsp. hirtum had the highest carvacrol content, reaching 88.12%. Among the oils tested, T. spicata L. var. spicata showed the highest antioxidant capacity, as shown by its low IC₅₀ value of 10.698 mg L^-1, and was also rich in phenolic compounds, containing 4.771 µg mg^-1. In addition, the EOs of S. cilicica and T. spicata L. var. spicata completely inhibited the growth of fungal mycelia at a dose of 1.0 µL/Petri dish, indicating strong antifungal activity. The EC₅₀ values were between 0.14 and 1.90 µL/Petri dish, with T. spicata L. var. spicata showing the greatest efficacy. In summary, the results emphasise the potential of thyme-derived EOs especially those rich in carvacrol as an environmentally friendly and natural substitute for chemical fungicides in the control of fungal infections in plants.