Effect of postharvest application of chitosan combined with clove oil against citrus green mold

• Chitosan combined with clove oil showed in vitro synergistic antifungal activity against P. digitatum.
• The combined treatment caused alterations in P. digitatum hyphal morphology and disruption of cell membranes.
• The combined coating did show synergistic effects with artificial green mold on mandarins.
• A combined coating improved the activities of PAL and chitinase at the later stage of incubation.

The antifungal activity of chitosan combined with clove oil against Penicillium digitatum, the causal agent of citrus green mold, was tested in vitro and in vivo. Chitosan combined with clove oil inhibited mycelial growth more than individual treatments, which was related to the greater release of cellular material and the largest alterations in hyphal morphology of P. digitatum. However, compared to chitosan alone, 1% chitosan coatings combined with various amounts of clove oil (0.5, 1 or 2 mL/L) showed no greater ability in controlling decay development on artificially inoculated citrus fruit. 1% chitosan combined with 0.5 mL/L clove oil appeared to slightly reduce lesion diameter and enhanced the activities of defense enzymes, including chitinase and phenylalanine ammonia-lyase at the later stages of incubation. This study indicated that the synergistic antifungal activity of chitosan-clove oil observed in in vitro studies was not found in in vivo tests. Therefore, the data suggest that a coating of 1% chitosan alone, not combined with clove oil, can effectively contribute to the control of green mold on citrus fruit.