Synergistic effects of citrus waste-mediated silver and copper nanoparticles on the antioxidant defense system of kinnow in the management of citrus canker

This study investigated the synthesis and characterization of silver and copper nanoparticles derived from citrus peel extract and evaluated their synergistic effects on the antioxidant defense system of Kinnow for the management of citrus canker. UV-Vis spectroscopy confirmed nanoparticle formation with surface plasmon resonance peaks at 420 nm for AgNPs and 460 nm for CuNPs. Particle sizes ranged from 65-75 nm for AgNPs and 70-80 nm for CuNPs, with zeta potentials of -30 mV and -25 mV, respectively, indicating stable colloidal dispersions. X-ray diffraction analysis confirmed crystalline face-centered cubic structures, while FTIR analysis revealed that bioactive functional groups from citrus peel extract, including phenolics, flavonoids, and proteins, were involved in the reduction, capping, and stabilization of the nanoparticles. Scanning electron microscopy showed predominantly spherical morphologies with average sizes of 55 nm (AgNPs) and 65 nm (CuNPs). In vitro assays demonstrated that Ag-Cu hybrid nanoparticles exhibited the highest antibacterial activity against the citrus canker pathogen, producing an inhibition zone of 16.92 mm at 30 µg ml⁻¹, compared with AgNPs (14.48 mm) and CuNPs (11.52 mm). Greenhouse experiments showed that Ag-CuNPs significantly reduced disease incidence (16.23%), followed by AgNPs (18.91%) and CuNPs (27.97%). Field trials confirmed similar trends, with Ag-CuNPs recording the lowest disease incidence (19.33%). Antioxidant enzyme analyses indicated effective stress mitigation, as Ag-CuNP-treated plants exhibited reduced activities of SOD, POD, and CAT compared with other treatments. These findings highlight the potential of citrus waste-mediated nanoparticles as eco-friendly and sustainable tools for citrus canker management.