Chemical composition and antifungal activity of five essential oils and their major components against Fusarium oxysporum f. sp. albedinis of Moroccan palm tree

Abstract

The effects of essential oils (EOs) and their eight major components extracted from five aromatic and medicinal plant (AMP) species on the development of Fusarium oxysporum f. sp. albedinis, the phytopathogenic fungus responsible for fusarium wilt (referred to as Bayoud in Morocco) on date palm in Moroccan oases (Errachidia region), were studied. The EOs were extracted from the plants by hydrodistillation and chemically analyzed by gas chromatography–mass spectrometry. The major chemical components extracted from the EOs of each AMP were: Origanum compactum (carvacrol 29.26%, thymol 18.52%, O-cymene 11.89%, γ-terpinene 10.77%); Thymus satureioides (borneol 22.73%, carvacrol 16.96%, α-terpineol: 12.20%); Rosmarinus officinalis (eucalyptol 26.45%, camphor 15.51%, α- and β-pinene 21.31%); Lavandula dentata (linalool 30.22%, linalyl anthranilate 23.47%, eucalyptol 9.17%); Myrtus communis (myrtenyl acetate 50.28%, eucalyptol 15.01%). The antifungal activity of the isolated EOs and their major components in comparison to that of two synthetic fungicides was evaluated by calculating the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of each antifungal product. The results of this analysis showed that the EOs of O. compactum and T. satureioides were able to inhibit the growth of F. oxysporum at very low concentrations (MFC 5 and 13 μl ml−1, respectively); these values were relatively better than those of the mancozeb synthetic fungicide (MFC 6 μl ml−1) and very much better than the EOs of R. officinalis, L. dentata and M. communis (MFC 40 μl ml−1). Thymol and carvacrol were effective fungicides at a very low concentration (MFC 0.94 and 2.08 μl ml−1, respectively), followed in increasing concentration by α-terpineol (MFC 10 μl ml−1), linalool (MFC 13.00 μl ml−1) and borneol (MFC 26.67 μl ml−1). α-Pinene, eucalyptol and myrtenyl acetate were shown to have comparable fungicide properties, but at high concentrations ranging from 20 to 80 μl ml−1. The effectiveness of the EO of Origanum and Thymus species would therefore appear to be linked to the abundant presence of carvracrol and thymol compounds. Given the damage caused by F. oxysporum on date palm trees and other plants in Morocco, as well as the environmental and health impacts of fungicides, the use of O. compactum and T. satureioides EOs or their major components (thymol and carvacrol) against this pathogen could be an alternative to commercially available synthetic fungicides.