Green Synthesized Copper-Oxide Nanoparticles Exhibit Antifungal Activity Against Botrytis cinerea, the Causal Agent of the Gray Mold Disease

<b>Background/Objectives:</b><i>Botrytis cinerea</i> is a necrotrophic fungal plant pathogen responsible for the gray mold disease, affecting several crops of economic importance worldwide. The primary line of control for the disease in the field and post-harvest fruits includes the application of fungicides. However, the emergence of fungal populations resistant to one or more fungicides has increased their application and diminished their effectiveness. Looking at new control strategies, metallic nanoparticles have appeared as a promising alternative for disease treatment. Green-synthesized copper oxide nanoparticles (CuONPs) are considered a feasible alternative, aiming to reduce the generation of environmentally toxic waste through chemical methods. <b>Methods:</b> In this work, CuONPs biosynthesized using the supernatant of <i>Trichoderma asperellum</i> and <i>Trichoderma ghanense</i> were evaluated to determine their antifungal activity against <i>B. cinerea</i>. <b>Results:</b> Four different formulations of CuONPs were obtained: Ta1, Ta2, Tg1, and Tg2. All formulations displayed antifungal properties, with Tg2 being the most effective and having a high potential in controlling the phytopathogen. CuONPs in the Tg2 formulation were quasi-spherical, ranging in size from 1 to 2.7 nm. <b>Conclusions:</b> Furthermore, Tg2 demonstrated greater efficacy than the copper-based commercial fungicide NORDOX^® 75W, which showed no inhibitory effect on <i>B. cinerea</i> mycelial growth. In summary, the CuONPs reported in this work offer a sustainable and effective alternative for managing the gray mold disease.