Effect of structurally related essential oil components on growth of Botrytis cinerea.

Essential oils are used as an alternative to chemical fungicides mostly to control post-harvest diseases, included grape grey mould. Main components of some essential oils are structurally related but may differ in fungicide activity. The major aim of this work was to compare the fungicidal activity against Botrytis cinerea Pers. of some related components of essential oils. The compounds, compared by a plate growth assay, showed the following order of decreasing activity: eugenol, thymol, cinnamaldehyde, isoeugenol, carvacrol, vanillin and guaiacol. The EC50 for eugenol was about 100 µg/ml for the strain B05.10 but was even less against the PM10 strain. Treatment with eugenol affected also conidia germination, in particular a MIC of 500 µg/ml completely inhibited spore germination of the PM10 strain also at 60 hpi. The same eugenol concentration was used in a leaf assay and was effective in preventing the infection of both strains of B. cinerea for the entire duration of experiment (10 days). Treatment of grape berries was also performed and confirmed the effectiveness of eugenol in delaying B. cinerea infection. However, the effect was influenced by the grapevine cv; in fact, treated cv. Cabernet Sauvignon was more sensitive to B. cinerea infection than cv. Merlot, although both cvs were similarly infected in the untreated controls. Although eugenol is known to be an antioxidant compound and increases bacterial membrane permeabilization, and it is reported as a strong inhibitor of soybean lipoxygenase activity, the mechanism by which it affects B. cinerea spore germination and growth is not yet known. In order to better understand the targets of eugenol and the fungal response to this phenolic compound, transcriptomic analysis of B. cinerea mycelium grown for 72 h and then treated for 6 and 12 hours with eugenol by using EC50 and EC80 concentrations is currently under investigation.