Biochemical Characterization and Disease Control Efficacy of Pleurotus eryngii-Derived Chitosan—An In Vivo Study against Monilinia laxa, the Causal Agent of Plum Brown Rot

Chitin (Ct) is a crucial biopolymer present in fungi, algae, arthropods, and is usually obtained from crustacean shells. Chitosan (Cs) is a derivative from Ct deacetylation, and possesses numerous uses in various agro-industrial fields. Research on fungal-derived Ct and Cs is mostly focused on pharmaceutical uses, however their uses for plant disease control remain less explored. The main objective of the current study is to evaluate the possibility of using chitosan obtained from mushroom <i>Pleurotus eryngii</i> (Cs-Pe) for controlling some phytopathogens compared to commercial chitosan (C.Cs). This study is focused on the following key areas: (i) extracting Ct from <i>P. eryngii</i> mycelium and converting it to Cs through deacetylation, using both bleaching and non-bleaching methods; (ii) conducting a physico-chemical characterization and in vitro evaluation of the antimicrobial activity of the obtained Cs; (iii) performing an in vivo assessment of the phytotoxic and cytotoxic effects of Cs; and (iv) investigating in vivo the impact of the studied chitosan on fruit quality and its biocontrol efficacy against <i>Monilinia laxa</i> infections in plum fruits. Results showed that Cs-Pe, especially the unbleached one, displayed promising in vitro antimicrobial activity against the majority of tested pathogens. Regarding the cytotoxicity, the highest significant increase in cell abnormality percentage was observed in the case of C.Cs compared to Cs-Pe. In the in vivo study, Cs-Pe acted as a protective barrier, lowering and/or preventing moisture loss and firmness of treated plums. The studied Cs-Pe demonstrated notable efficacy against <i>M. laxa</i> which decreased the fruits' percentage decline. These results strongly suggest that Cs derived from <i>P. eryngii</i> is a potential candidate for increasing plums' shelf-life. This research shed light on the promising applications of <i>P. eryngii</i>-derived Cs in the agri-food field.