Fungi toxicity of essential oils in controlling Sclerotium rolfsii

The fungus Sclerotium rolfsii has a wide occurrence in Brazil and stands out as one of the pathogens that cause severe damage to agriculture and to affect a wide range of hosts. Its control has been difficult due to its ability to form structures of resistance, the sclerotia. The present study aimed to evaluate the in vitro toxicity of essential oils of Lippia sidoides and Lippia gracilis on S. rolfsii. The essential oils were added to the medium Potato Dextrose Agar (PDA) at concentrations of 0.3, 0.6, 0.9, 1.2 and 1.5 mu L mL(-1), where a disc was added of the mycelium of the pathogen. The evaluations were performed daily by measuring the diameter of the colonies. Qualitative and quantitative analyses of the essential oils of the species were performed using gas chromatography-mass spectrometry (GC-MS) and flame ionization (GC-FID), respectively. The identification of the oil constituents was performed by comparing their mass spectra with spectra from the literature and databases and comparison of their retention indexes. All concentrations effectively controlled the pathogen in vitro. Through the identification of chemical constituents present in essential oils it could be concluded that there are two major chemical components in the genus Lippia, thymol and carvacrol. The L. sidoides oil contained 42.33 and 4.56% of thymol and carvacrol while the essential oil of L. gracilis contained 18% of thymol and 27.59% carvacrol. The results suggest that these components can be investigated as potential fungicides for controlling S. rolfsii.