Comparative investigation of the effects of antifungal activities of some essential oils on Alternaria alternata fungus as a causal agent of tomato early blight disease

Tomato early blight disease, caused by the fungus Alternaria alternata, is one of the most devastating diseases for the crop in Iran and worldwide. Recent studies have shown that some secondary metabolites of medicinal plants are effective in preventing the growth of fungi and are a good alternative to the use of chemical pesticides. In the present study, ten medicinal plants including Eucalyptus sp., Thymus vulgaris, Mentha piperita, Mentha longifolia, Mentha aquatica, Satureja hortensis, Achillea millefolium, Foeniculum vulgare, Anethum graveolens, and Trachyspermum copticum were collected during 2016-2017. Their essential oils were extracted using Clevenger apparatus, and GC-MS device was used to identify the essential oil compounds. Antifungal activity of essential oils was assayed through the inhibition of fungal colony growth at five concentrations of 0, 200, 400, 800, and 1200 ppm in mixing with potato dextrose agar medium with three replicates. The findings revealed that fungus colony growth was inhibited with increases in essential oils concentrations, and there were significant differences among different essential oils. Essential oils of Satureja hortensis, Trachyspermum copticum and Thymus vulgaris in 800 and 1200 ppm and Anethum graveolens in 1200 ppm demonstrated the highest effect on fungus colony growth. This study found that Carvacrol, Thymol, Para-cymene, and Gamma-terpinene ingredients tend to have the highest antifungal effects.