The objective of this study was to investigate the chemical composition and in vitro antifungal activity of Mentha × Piperita L. (peppermint) essential oil (EO) against some plant pathogenic fungi (Alternaria alternata, Penicillium expansum, Rhizoctonia solani, and Rhizopus stolonifer). Antifungal activity of EO against the selected fungi was conducted using the agar diffusion method by adding peppermint EO concentrations (0, 250, 500, 750, 1000, and 2000 ppm). The Gas chromatography/mass spectrometry (GC/MS) analysis of peppermint EO showed that the main constituent was Menthol (36.4%), followed by Menthone (27.7%) and Menthyl acetate (11.2%). The mycelium growth of the selected fungi was significantly inhibited by peppermint EO. Light and electron microscopy studies showed that mycelium morphology was seriously changed after treatment with peppermint essential oil. The level of malondialdehyde illustrated that peppermint EO led to lipid peroxidation in the fungal pathogens. Therefore, due to its antifungal properties, peppermint EO can be used as an additive in the food industry and as an active substance in pharmaceuticals.

Keywords