Synergistic antifungal action of chitosan‑zinc oxide nanocomposite against sclerotial-forming phytopathogenic fungus Sclerotium rolfsii.

The soil-borne pathogen Sclerotium rolfsii presents a significant challenge to global agricultural productivity due to its persistent sclerotia and resistance to conventional fungicidal treatments. In this study, chitosan‑zinc oxide nanocomposites (CS-ZnO NCs) were synthesized and comprehensively characterized using UV-Vis spectroscopy, FTIR, XRD, DLS, zeta potential analysis, SEM, and EDX. The results confirmed the successful incorporation of ZnO nanoparticles into a chitosan matrix, forming a stable nanocomposite with a positive zeta potential of +41 mV and an average particle size of 204 nm. Structural imaging revealed a compact network with well-distributed ZnO particles. In vitro antifungal assays demonstrated that CS-ZnO NCs significantly inhibited the radial growth of S. rolfsii (87% inhibition) compared to the commercial fungicide Iprodione (Rovral) (70%), and completely suppressed sclerotia formation and reduced mycelial biomass by 98%. Biochemical analysis further revealed marked reductions in fungal total phenolics (77%) and key defense-related enzymes, including peroxidase, phenylalanine ammonia lyase, and polyphenol oxidase (up to 76%). FTIR spectral analysis revealed substantial alterations in fungal protein and membrane structures, indicating that the enhanced antifungal activity results from the synergistic action of chitosan-induced membrane disruption and ZnO-mediated oxidative stress. These findings highlight CS-ZnO NCs as a highly effective and environmentally sustainable alternative to chemical fungicides for the management of S. rolfsii.