Non-polar compound profile and preliminary assessment of the antifungal activity of Foeniculum vulgare and Thymus vulgaris

Foeniculum vulgare and Thymus vulgaris are common medicinal and aromatic plants that have been shown to have broad-spectrum antifungal and antibacterial effects. However, most of the effects have been prescribed to the compounds in their essential oils and few studies have considered the non-polar solvent extracts. In this study, we characterized the chemical composition of dichloromethane extracts of the two plants by GC-MS and conducted a preliminary assessment of the antifungal activity of these extracts against Alternaria solani, Botrytis cinerea, Colletotrichum coccodes and Fusarium graminearum. These pathogens were chosen because they are some of the causal agents of fungal diseases in potatoes, tomatoes and wheat which are some of the major crops in Africa and around the world. We also assessed the effect of thymol, one of the major compounds in both extracts on the same pathogens. γ-asarone and thymol were identified as the major compounds in F. vulgare whereas thymol, tetracosanol and p-cymene-2,5-diol were the major compounds in T. vulgaris. Some of the compounds were found to be common to both plants while others were exclusive to each plant. In the preliminary antifungal tests, none of the extracts were found to have an inhibitory effect on any of the pathogens at the tested concentration. Thymol showed inhibitory effect against C. coccodes but not on the other three pathogens. We hypothesize the observed inactivity of the extracts to be possibly partly due to generally decreased proportions of bioactive volatile compounds in the extracts which could have occurred during post-harvest handling and storage of the plant material prior to extraction and assay. The absence in the extract of other antifungal compounds prevalent in essential oils also potentially contributes to the observed inactivity. Nevertheless, F. vulgare and T. vulgaris can be used as potential sources of known bioprotectant compounds for instance thymol.