Zinc-chitosan nanocomposites as guardians against the dreaded phytopathogenic fungus Macrophomina phaseolina in Vigna radiata L.

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Macrophomina phaseolina, a phytopathogenic fungus responsible for root rot in mung beans (Vigna radiata L.), produces resilient sclerotia that are not effectively managed by chemical fungicides. In this study, as an alternative management approach, zinc-chitosan nanoparticles (Zn-ChNPs) were prepared using the ionic gelation method and evaluated for their antifungal activity against M. phaseolina. The synthesis of Zn-ChNPs was confirmed by UV–visible spectroscopy with absorption peaks at 215 nm and 265 nm. XRD indicated hexagonal crystalline planes, verifying nanoparticle crystallinity, while FTIR showed strong ZnO-chitosan interactions with peaks at 3495 cm⁻¹ and 678 cm⁻¹. The particles averaged 80–100 nm in size. Antifungal bioassays demonstrated significant inhibition of fungal growth, achieving 50–100 % reduction at concentrations of 0.11 % and above, and an EC50 (effective concentration) value of 0.08 %. Microscopic analysis revealed sclerotia distortion at 0.15 % Zn-ChNPs, while enzymatic assays showed a 20–60 % increase in catalase, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase activities at concentrations of 0.03–0.11 %, followed by a sharp decrease beyond 0.11 %. In planta bioassays indicated that 0.4–0.6 % Zn-ChNPs reduced disease by 97 % and improved growth up to 100 %, surpassing the performance of chemical fungicides (Carbendazim). Multivariate analysis further underscored the superior efficacy of Zn-ChNPs in enhancing plant defense mechanisms and managing root rot disease. These findings highlighted the potential of Zn-ChNPs as a sustainable and effective alternative to chemical fungicides, offering dual benefits of disease control and growth enhancement in mung bean plants.