Nanoselenium-driven reduction in chemical fungicide usage: Eco-safety enhancement in pepper Phytophthora capsici control

Abstract

Phytophthora blight, caused by Phytophthora capsici, poses a devastating threat to pepper production, driving heavy reliance on chemical pesticides like azoxystrobin. However, the rapid evolution of fungicide resistance in P. capsici and the environmental risks of conventional agrochemicals demand sustainable alternatives. While nano‑selenium (nano-Se) is known to enhance plant antioxidant capacity and modulate secondary metabolism, its role in regulating plant secondary metabolite-microbe interactions for oomycete resistance remains underexplored. Here, we engineered a nano-Se formulation as a green nanofungicide, demonstrating superior anti-oomycete efficacy (EC₅₀ = 8 mg/L) compared to azoxystrobin and berberine. Nano-Se directly triggered peroxidative damage in P. capsici hyphae, inducing intracellular leakage, respiratory suppression, and irreversible cell death. Bidirectional translocation of nano-Se within pepper plants enhanced systemic antioxidant defenses and growth, while reprogramming coumarin and phenylpropanoid biosynthesis pathways. This metabolic rewiring elevated antifungal coumarins (6-nitrocoumarin, 6-hydroxycoumarin), phytohormones (JA, SA), and phenolic acids (ferulic acid, sinapic acid), with 6-nitrocoumarin (10 mg/L) exhibiting potent P. capsici suppression via dual modulation of redox homeostasis and secondary metabolism. Critically, nano-Se remodeled the rhizosphere microbiome, enriching plant-beneficial taxa and fostering pathogen-suppressive microbial consortia. By synergizing coumarin-mediated antifungal activity with microbiome engineering, nano-Se reduced chemical dependency while enhancing pepper resistance to P. capsici. Our findings provide a mechanistic roadmap for deploying nano-Se as an eco-safe agrochemical, addressing fungicide resistance and environmental hazards in soilborne disease management.