Prochloraz-Based Hydrogen-Bonded Formulations with Salicylic Acid, Ascorbic Acid, or Sorbic Acid for Postharvest Control of Penicillium expansum in Korla Fragrant Pears

Postharvest diseases caused by fungal pathogens remain a major constraint on fruit storage and quality. Prochloraz (PRO) is widely used for disease control, but its practical application is limited by poor water solubility, relatively high toxicity, and the absence of antioxidant activity. In this study, three PRO-based hydrogen-bonded formulations were prepared using salicylic acid (SA), ascorbic acid (AA), or sorbic acid (SOR) as co-formers at a 1:1 molar ratio. The formulations were characterized by 1H NMR, and their physicochemical properties, antifungal activity, disease control efficacy, and acute toxicity to zebrafish larvae were evaluated. All three formulations formed through hydrogen bonding and showed improved water solubility compared with pure PRO. PRO-SA exhibited the strongest antifungal activity against Penicillium expansum (60.57% reduction in EC50) and the best disease control on Korla fragrant pears at 400 mg/L. PRO-AA showed the greatest reduction in acute toxicity to zebrafish larvae (8.04-fold) and a 54-fold increase in water solubility. PRO-SOR provided a balanced improvement in antifungal activity (41.33% reduction in EC50) and moderate toxicity reduction (1.48-fold). These results indicate that the choice of co-former determines the functional profile of PRO-based formulations, allowing tailored optimization for antifungal efficacy, reduced acute toxicity, or a balanced combination. This work offers a practical strategy for improving the performance of existing fungicides.