One of the most prevalent diseases affecting sugar beet crops globally is damping-off disease, which is caused by fungi or soil-borne bacteria. The objective of the current study was to assess the antimicrobial activity of various concentrations of CuO-NPs against Fusarium oxysporum, Macrophomina phaseolina, and Pectobacterium carotovorum in a lab setting and how they influenced vegetative growth, physiological traits, antioxidant enzymes, disease incidence percentage, and mineral nutrients of sugar beet plants in a greenhouse experiment. Sugar beet (Beta vulgaris cv. Oscar poly) seeds were soaked in different concentrations (50, 100, and 150 µg L−1) of the tested NPs for two hours pre-sowing. According to in vitro studies, as compared to aqueous copper sulphate and control, CuO-NPs at 25, 35, and 100 µg mL−1 had the greatest inhibitory effect (100%) on the mycelial growth of M. phaseolina, F. oxysporum, and P. carotovorum, respectively. Results from the greenhouse experiment showed that the 150 µg mL−1 concentration produced the greatest reduction in disease incidence %, with efficacy values of 24.53, 13.25, and 23.59% for F. oxysporum, M. phaseolina, and P. carotovorum, respectively. In addition, as compared to untreated control plants, the same concentration of CuO-NPs significantly (p ≤ 0.05) increased the vegetative development, physiological characteristics, antioxidant enzymes, and mineral nutrients of sugar beet plants. Therefore, the antimicrobial activity demonstrated by the biosynthesized CuO NPs indicates that they can resist plant pathogenic microorganisms of sugar beet plants.
