Chitosan inhibits the growth of Penicillium digitatum and Penicillium italicum and protects oranges from green and blue mold during postharvest

Postharvest losses in oranges caused by Penicillium spp. infections are a major concern for the citrus industry worldwide. In this study, we examined the antimicrobial properties of chitosan against various Penicillium strains, including some resistant to fungicides. We also assessed the effectiveness of chitosan as a protective coating for navel oranges to prevent infections. Chitosan at 0.5 % concentration in media inhibited Penicillium digitatum growth, while Penicillium italicum required 1 % chitosan for complete inhibition. We then coated oranges by dipping them with chitosan, either alone or combined with commercial wax, to compare their effectiveness in controlling Penicillium infections against a conventional treatment with fungicide and wax. Additional controls included oranges treated with wax only or left untreated. Oranges were later contact-inoculated with P. digitatum and P. italicum strains under favorable conditions for disease development. Oranges coated with chitosan 1 %, 2 %, and 1 % + wax had a significantly lower cumulative incidence of infections than those treated with wax only or left untreated. Chitosan-based edible coatings also outperformed fungicide and wax treatments. Chitosan 2 % reduced the incidence of decay caused by fungicide-resistant P. digitatum and P. italicum strains by 68 % and 76 %, compared to conventionally treated oranges. Additionally, combining chitosan with wax extended the shelf life and enhanced the marketability of the oranges compared to all other treatments. These findings suggest chitosan as a viable complement or alternative to synthetic fungicides for managing green and blue mold on navel oranges in the postharvest supply chain.