Antifungal activity of monoterpenoids against postharvest pathogens Botrytis cinerea and Monilinia fructicola

Twenty two naturally occurring monoterpenoid compounds were selected for antifungal evaluation against two of the most common postharvest pathogens on temperate fruits, Botrytis cinerea and Monilinia fructicola. Experiments were carried out in order to examine the separate effects of these compounds on spore germination and mycelial growth. The growth inhibition test was conducted by incorporating the compounds into the medium, or by exposing the fungi to the vapor of the monoterpenoids. The results showed that carvacrol and thymol, the only two phenolic monoterpenoids, were the most potent inhibitors to the two pathogens in the germination and growth inhibition tests. Both of the compounds completely prevented the spore germination and mycelial growth of B. cinerea and M. fructicola at 100 mu g/mL. Even at 10 mu g/mL medium (0.25 mg/petri dish) in the volatility test, carvacrol and thymol had 85% and 82% inhibition at 48 h against B, cinerea, and 38% and 57% against M. fructicola, respectively. Other monoterpenoids such as eugenol, citronellol, geraniol, citral, (-)-perillaldehyde, citronellal, (-)-perillyl alcohol and (-)-menthol were good growth inhibitors (by contact) although their activities toward the two pathogens were slightly different, with higher inhibition found against the M. fructicola.