Quercetin‑loaded chitosan nanoparticles for enhanced control of Zanthoxylum armatum rust: Antifungal action and induced resistance

Zanthoxylum armatum DC. is an economically important industrial crop, while Z. armatum rust caused by Coleosporium zanthoxyli severely restricts its productivity. Current reliance on chemical fungicides poses risks of resistance and environmental contamination. Here, we developed an eco-friendly nanopesticide by loading quercetin—a key antifungal metabolite screened from the biocontrol fungus Ramularia collo-cygni via UPLC-MS/MS metabolomics—into chitosan (CS) nanoparticles (QUE-NPs) using ionic gelation. The preparation was optimized via single-factor experiments and artificial neural network modeling, achieving 84.85% encapsulation efficiency and spherical morphology (207.4 nm). Quercetin loading occurred through hydrogen bonding and electrostatic interactions, with optimal stability at pH 4–6 and storage life of 13 d at 4 °C. In vitro , 0.8 g/L QUE-NPs inhibited 88.81% of urediniospore germination. In pot and field trials, preventive foliar application of 0.6–0.8 g/L QUE-NPs significantly reduced disease incidence and index, outperforming curative treatments. The formulation persistently elevated activities of defense enzymes (SOD, POD, PAL, CAT), confirming induced resistance as a key mode of action. With straightforward preparation, high biocompatibility, and dual antifungal and immune-priming effects, QUE-NPs offer a sustainable and effective strategy for managing Z. armatum rust, aligning with the goals of green agriculture and industrial crop protection. • Quercetin from biocontrol fungus HJ01 loaded into chitosan nanoparticles. • ANN model optimized QUE-NPs for high encapsulation efficiency (84.85%). • QUE-NPs at 0.8 g/L inhibited 88.81% of pathogen spore germination. • QUE-NPs directly inhibit fungi and induce plant defense enzymes (SOD, POD, PAL, CAT). • Preventive spraying of 0.6–0.8 g/L QUE-NPs significantly controls rust in field trials.