Inhibitory activity of essential oils components against the fungal plant pathogen Botrytis cinerea

Botrytis cinerea is the fungus responsible of the grey mould disease of grape and other fruits. Chemical control is necessary when environmental conditions are favorable to the disease. In order to protect plants from disease the European Union by directive 2009/128/EC gives priority to non-chemical methods and encourages the use of natural non-toxic substances. Natural compounds are used as an alternative to chemical fungicides mostly to control post-harvest diseases. The major aim of this work is to compare the fungicidal activity against B. cinerea of 11 natural compounds that are produced in plants through the shikimate/phenylalanine pathway. In a spore germination assay six compounds (eugenol, thymol, carvacrol, isoeugnol, cinnamaldehyde and vanillin) completely inhibited the germination of conidia. These natural products also reduced the viability of the spores and inhibited the growth of B. cinerea mycelium (strain PM10) even if with different efficiency. These compounds are the major constituents of essential oils of many aromatic species. Some chemical characteristics, like the high lipophilic and the low value of polar surface area, are common among these compounds indicating an high affinity for phospholipids compartment and their difficult to overcome the external layer of the cell.