Evaluation of Nanomaterials (Copper, Silver, and Chitosan) in management of Downy Mildew Disease on Basil (Ocimum basilicum)

Abstract

Basil downy mildew (BDM), caused by the oomycete Peronospora belbahrii, is a devastating foliar disease that causes severe yield losses in basil production. This study evaluated the antifungal potential of biosynthesized copper (Cu), chitosan (Cs), and silver (Ag) nanoparticles as eco-friendly alternatives to synthetic fungicides. The efficacy of these nanomaterials (50–400 mg L⁻¹) was evaluated against potassium silicate and the fungicide Redomil Gold in laboratory and greenhouse trials. In vitro assays showed CuNPs (400 mg L⁻¹) had the highest inhibition of conidial germination (96.7%), performing slightly better than Redomil Gold (96.4%) and CNPs (96.0%). In preventive greenhouse trials, CNPs (400 mg L⁻¹) provided protection statistically comparable to Redomil Gold. The most significant
finding was in the curative trial, where CuNPs (400 mg L⁻¹) demonstrated significantly superior efficacy to the fungicide, reducing final disease severity to 16.0% (compared to 27.6% for Redomil Gold). Furthermore, CuNPs and CNPs acted as biostimulants, significantly improving plant anatomical structure, growth parameters, and the induction of defense-related enzymes (e.g., PO, PPO, CAT) and
phenols. These results demonstrate that biosynthesized nanoparticles, particularly CuNPs, offer a highly effective, dual-action approach for controlling BDM, acting as both a direct antifungal and a plant defense elicitor.