BIOFUNGICIDAL ACTIVITIES OF PLANT ESSENTIAL OILS AGAINST CUCUMBER ROOT AND STEM ROT DISEASE CAUSED BY FUSARIUM OXYSPORUM f sp RADICISCUCUMERINUM
E.M. Soylu, R. Incekara
The aim of this study was to investigate effects of essential oils of origanum (Origanum onites L.), lavender (Lavandula stoechas L. subsp. stoechas), fennel (Foeniculum vulgare Mill.), laurel (Laurus nobilis L.) and myrtle (Myrtus communis L.) against root and stem rot of cucumber, caused by Fusarium oxysporum f. sp. radicis-cucumerinum (Forc) in vitro and in vivo. Inhibitory effects of contact and volatile phases of essential oils on mycelial growth and conidial germination were determined at various concentrations. Results clearly revealed that those essential oils had a strong detrimental effect on mycelial growth and spore germination in a concentration-dependent manner. Essential oil of O. onites was strongly inhibitory to Forc as compare with essential oils of F. vulgare, L. stoechas, L. nobilis and M. communis. Volatile phases of essential oils were consistently found to be more effective on inhibition of mycelial growth and spore germination at lower concentrations in comparison to contact effect of the oils tested. Light and scanning electron microscopic (SEM) observations on inhibited fungal hyphae revealed considerable morphological degenerations on the fungal hyphae. Essential oil of O. onites, being the most efficient essential oil in vitro, was further evaluated under greenhouse conditions. The essential oil of O. onites displayed potent in vivo biofungicidal activity against the Forc on greenhouse-grown cucumber plants. Results of in vitro and in vivo studies demonstrated that the O. onites essential oils could be used as natural biofungicide to control root rot disease caused by Forc on cucumber.