Citrus aurantium Peel Extract Mediated Green Synthesis of Copper Oxide and Zinc Oxide Nanoparticles: Characterization and Antifungal Efficacy Against Post-Harvest Spoilage of Tomato Fruits by Locally Isolated Alternaria alternata

This study investigates the control of Alternaria alternata, a fungal pathogen accountable for the post-harvest deterioration of tomato fruits, using green-synthesized copper oxide nanoparticles (CuO-NPs) and zinc oxide nanoparticles (ZnO-NPs). The pathogenic fungi (5 isolates) were isolated from symptomatic tomato fruits collected in Riyadh, Saudi Arabia. All isolates were identified through morphological and molecular techniques, including ITS region sequencing and phylogenetic analysis. The green synthesis of CuO-NPs and ZnO-NPs was achieved using orange peel extract (OPE), and the nanoparticles were characterized using SEM, EDX, FT-IR, XRD, and TEM. The results confirmed the formation of spherical NPs with particle sizes of 23.80 and 28.80 nm for ZnO-NPs and CuO-NPs, respectively. Using the agar dilution method, the two NPs exhibited significant dose-dependent antifungal activity toward A. alternata. At a concentration of 2 mg/mL, the CuO-NPs and ZnO-NPs induced a fungal growth inhibition of about 1.35 ± 0.45 mm and 1.85 ± 0.36 mm, compared to the untreated control (5.2 ± 0.23 mm). Interestingly, the combined application of CuO-NPs and ZnO-NPs resulted in significantly reduced antifungal efficacy (3.11 ± 0.45 mm). This study highlights the potential of green-synthesized NPs as eco-friendly antifungal agents for controlling post-harvest Alternaria alternata infection. It also emphasizes the need for further research to optimize their synergistic applications.