Cellulase- and pH-Stimulating Selenium Nanopesticide Enhances Antifungal Efficacy to Anthracnose: Action Mechanism and Environmental Safety

Nanopesticides (NPs) provide a sustainable approach to reducing the use of chemical pesticides and mitigating their environmental risks in agriculture. In the present study, a pH and cellulase dual-stimulating system with the loaded pesticide penthiopyrad (PEN) was developed by incorporating hydroxypropyl cellulose (HPC) on the surfaces of mesoporous nanoselenium (MSe). In the measurement of antifungal efficacy of PEN against Colletorichum orbiculare Arx, compared to the neutral environment, i.e., pH = 7 without cellulase, the cumulative release of PEN from HPC@PEN@MSe NPs increased 5.7 and 4.8 times of the amount released at pH 3 and 5, respectively; at pH 7, the presence of cellulase solution substantially enhanced PEN release by 6.1 times more than that without cellulase. The HPC@PEN@MSe NPs demonstrated 3.2-fold of antifungal efficacy greater than the commercial 20% PEN suspension concentrate (20% PEN SC). This dual-stimulating NPs can induce oxidative stress responses and cell structural damage in pathogens, demonstrating a broad spectrum of antifungal activity. Mechanistic investigations illustrated that HPC@PEN@MSe NPs specifically promote the accumulation of reactive oxygen species, including hydroxyl radicals (•OH), superoxide radicals (•O2–), and singlet oxygen (1O2) in pathogenic cells by regulating gene expressions relevant to oxidative phosphorylation and lipid metabolism pathways, ultimately leading to eradication of pathogens. In vivo, HPC@PEN@MSe NPs sprayed could be transported in plants and specifically activated at the infected leafy, stem, and root tissues of cucumber plants, with the maximum PEN concentration at 0.93 mg/kg detected in the infected leaves at 12 h. The PEN residual concentration still had 0.09 mg/kg after 14 days, which suggests long-lasting activity. Moreover, the results of detached cucumber leaves and pot experiments indicated that HPC@PEN@MSe NPs significantly increased antioxidant enzyme levels, enhanced resistance to anthracnose, and manifested no apparent effects on plant growth. This eco-friendly plant protection strategy developed in this study exhibits apparent potential in practical applications while maintaining ecological sustainability and providing a potential path to address plant health management in modern agriculture.