Biosynthesis, Physicochemical Characterization, and Functional Evaluation of Chitosan from Ganoderma lucidum for the Inhibition of Apple Brown Rot Caused by Monilinia fructicola

Chitosan, a chitin-derived biopolymer, is widely used in agriculture and food preservation. Fungal-derived chitosan offers a sustainable alternative to crustacean sources, and Ganoderma lucidum represents a promising source of this functional material. This study characterized fungal chitosan (F.Cs) extracted from G. lucidum cell-wall chitin by FT-IR, molecular weight, viscosity, and degree of deacetylation. Its antimicrobial activity was evaluated in vitro, and its preservative and disease control efficacy against Monilinia fructicola on postharvest apples was compared to commercial chitosan (C.Cs). DNA/protein leakage of the studied FGs and C.Cs were investigated to reveal the antimicrobial mechanisms. In particular, F.Cs exhibited promising in vitro antimicrobial activity, with MIC/MFC values of 0.75/0.75 mg/mL against M. fructicola and 0.75/1.5 mg/mL against Botrytis cinerea, compared to C.Cs. In addition, F.Cs induced greater membrane damage in M. fructicola than C.Cs, as evidenced by higher DNA leakage (24% vs. 13%) and more pronounced protein leakage (102% vs. 98%). In vivo assay demonstrated that F.Cs formed an effective protective coating layer, reducing fruit moisture loss, preserving firmness s, and significantly limiting M. fructicola-induced decay compared to C.Cs. Particularly, F.Cs (1.5%) were most effective, reducing disease incidence to 12.5% (preventive) and 20.8% (curative), with decay rates of 18 and 31%, respectively. C.Cs (1.5%) provided moderate protection, with disease incidences of 37.5 and 43.7% in preventive and curative treatments, respectively. These results demonstrate the superior efficacy of F.Cs over C.Cs in preserving apple quality and enhancing resistance to M. fructicola, highlighting the potential of G. lucidum-derived chitosan as a sustainable, multifunctional biopolymer for postharvest disease control and fruit quality preservation.