Antifungal activity of essential oils of Origanum majorana and Lavender angustifolia against Fusarium wilt and root rot disease of melon plants

The objective of this study was to evaluate the antifungal activity of essential oils of marjoram (Origanum majorana) and lavender (Lavender angustifolia) against eleven isolates of Fusarium oxysporum f. sp. melonis and ten isolates of Fusarium solani, the causal agents of Fusarium wilt and root rot disease of melon. The effect of essential oils on disease development under in vivo conditions was also tested. GC-MS analysis of marjoram essential oils showed that terpinen-4-ol (34.94%) is the major component, followed by γ-terpinene (24.66%), α-terpinene (13.22%), β-terpinene (5.84%), α-terpineol (3.98%), and β-phellandrene (3.16%). Chemical analysis of lavender essential oils showed that α-terpinene (48.76%) is the major component, followed by linalool (16.79%), γ-terpinene (7.00%), β-trans-ocimane (6.47%), β-caryophyllene (5.83%), and lavandulol (3.23%). All essential oils tested in vitro using the disk diffusion method revealed a significant antifungal effect against mycelium growth of all F. oxysporum f. sp. melonis and F. solani isolates. The volatile compounds of essential oils have completely inhibited spore germination of both pathogens. In vivo, the essential oils applied as biofumigant significantly reduced disease severity on melon plants 20 days post-incubation. Lavender essential oils significantly reduced disease severity by almost 60% as compared to control melon plants while Marjoram essential oils reduced disease severity by almost 23% under controlled conditions. These results showed that lavender essential oils may contribute to the development of new antifungal compounds to protect melon crops from Fusarium wilt and root rot disease.