Chemical Composition of Essential Oils and Their Antifungal Activity in Controlling Ascochyta rabiei

Investigation for developing natural plant protection products as an alternative to synthetic fungicides has become important regarding the environmental impact. In this study, the chemical composition and the antifungal activity of five Moroccan aromatic plants, namely, oregano (Origanum compactum), thyme (Thymus vulgaris), Eucalyptus (Eucalyptus camaldulensis), mint (Mentha pulegium L) and myrtle (Myrtus communis) was explored for controlling Ascochyta rabiei, in vitro. The pathogen is a seed-borne causal agent of Ascochyta blight and it is considered the most economically damaging disease of chickpea. The radial growth of A. rabiei was completely inhibited by oregano, mint, thyme and myrtle at low concentrations (0.15-5 μL mL-1). The most important effect was obtained with oregano (Minimum Inhibitory Concentration, MIC- 0.15 μL mL-1), followed by Thyme (MIC- 0.5 μL mL-1). The phytotoxicity test of these essential oils on chickpea germination showed that oregano and Thyme oils do not have phytotoxic effects at MIC concentrations, whereas mint and myrtle oils can have an effect on reducing germination percentage of chickpea seeds. The chemical composition of tested essential oils was analyzed using Gas Chromatography-Mass Spectrometry (GC-MS analysis). The analysis revealed the dominance of two compounds (Thymol and Carvacrol) in the most effective oils and can represent the principal active ingredient in the pathogen control. Therefore, the essential oils of oregano and Thyme or their major compounds could be investigated for seed or foliar treatment of chickpea against Ascochyta blight infection.