Pathogen-microenvironment-responsive and antioxidant-buffered propiconazole nanofungicide for safe and effective fungal disease control

Although fungicide application via unmanned aerial vehicle (UAV) is increasingly used and has proven effective, concentrated deposition of fungicides can lead to phytotoxicity. Here, we developed Pro@CS/PQ, a nanofungicide comprising a chitosan (CS) core loaded with propiconazole (Pro) and a pectin–quercetin conjugate (PQ) shell. This dual-functional platform combines on-demand release with antioxidant buffering. Pro@CS/PQ released propiconazole more rapidly under acidic or pectinase-rich conditions, reaching 87.4% cumulative release within 72 h. Quercetin simultaneously protects plant tissues from oxidative stress and maintains redox homeostasis under excessive fungicide exposure. Compared with propiconazole emulsifiable concentrate (Pro EC), Pro@CS/PQ showed enhanced antifungal activity against Rhizoctonia solani, Fusarium fujikuroi, Botrytis cinerea, and Magnaporthe oryzae. In detached rice leaves infected with R. solani, Pro@CS/PQ at 50 mg·L⁻¹ achieved protective and curative efficacies of 85.8% and 70.8%, which were significantly higher than those of Pro EC. Pro@CS/PQ also exhibited improved foliar adhesion, maintaining over 60% leaf retention after water washing, approximately twice the retention of Pro EC. At concentrations up to four times the recommended rate, Pro@CS/PQ caused no visible phytotoxicity, whereas Pro EC induced severe leaf damage at half that concentration. Metabolomic analysis confirmed that Pro@CS/PQ mitigated propiconazole-induced metabolic perturbations and preserved homeostasis of key metabolic pathways involving amino acids, carbohydrates, and pyrimidines. This work offers a promising solution for safe and effective application of triazole fungicides.