Enhanced control of Sclerotinia sclerotiorum using pH-responsive chitosan nanoparticles loaded with a synergistic ternary fungicide.

Abstract

Sclerotinia sclerotiorum causes stem rot on many crops. Current management faces fungicide resistance and low pesticide efficiency. A ternary mixture of fludioxonil, fluindapyr, and difenoconazole (FFD) at a 3 : 6 : 1 mass ratio showed strong synergy (SR = 2.58). This mixture was loaded into pH-responsive chitosan nanoparticles (FFD-CS NPs). The nanoparticles were spherical, with a mean size of 176.1 nm and a zeta potential of 46.4 mV. pH-dependent assays showed higher antifungal activity at pH 3.0 (EC50 = 0.0022 vs. 0.0038 µg/mL for FFD-CS NPs vs. FFD) than at pH 7.0 (0.0121 vs. 0.0238 µg/mL), exceeding non-encapsulated FFD. On detached oilseed rape leaves, FFD provided 100% protective efficacy at 5 µg/mL. On potted plants, FFD-CS NPs achieved 97.6% curative efficacy on oilseed rape at 5 µg/mL and 83.1% protective efficacy on cucumber at 1 µg/mL, significantly higher than those of both FFD and single fungicides. The pH-responsive FFD-CS NPs enable on-demand fungicide release, enhancing efficacy and offering a sustainable strategy for the management of Sclerotinia stem rot.

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