Evaluation of the potential of commercial post-harvest application of essential oils to control citrus decay

The potential of using essential oils instead of synthetic fungicides to control Penicillium digitatum and P. italicum on citrus fruits was evaluated. The objectives of this study were to determine the antifungal activity of 20 essential oils on colony growth of P. digitatum and P. italicum in vitro and to evaluate their efficacy in vivo by simulating fungicide application in the packing-line or incorporating them into packaging of oranges. In vitro antifungal activity against mycelial growth of P. digitatum and P. italicum was evaluated both by direct contact, and in the vapour phase. Thyme oregano, clove and cinnamon essential oils completely inhibited P. digitatum and P. italicum growth either when added into the medium at 1000 mul l(-1) or by their volatiles with 10 mul per 5 cm diameter Petri dish. In in vivo experiments, none of the oils tested effectively reduced the incidence of P. digitatum and P. italicum on oranges after being applied directly over the inoculated wound at 10, 100 or 1000 mul l(-1). Thyme and cinnamon essential oils applied at 50 ml l(-1) significantly (P < 0.05) reduced the incidence of P. digitatum and P. italicum after 7 d at 20 degreesC. The use of essential oils in combination with citrus wax, or incorporated into packaging by soaking pads, failed to reduce the incidence of P. digitatum. Instead, these treatments caused severe rind damage, which makes implementation unrealistic and impractical. Further studies should focus on the volatility of essential oils in order to further evaluate their use.