CuO-ZnO nanocomposites mitigate root-knot nematode stress in Vigna radiata by enhancing physiological and antioxidant defense responses

Abstract

Meloidogyne incognita is a major root-knot nematode causing severe crop damage globally. Chemical nematicides are widely used for its control, despite environmental and health concerns. In this study, the nano-pesticidal efficacy of CuO-ZnO nanocomposites synthesized from Catharanthus roseus (L.) leaf extract was evaluated against M. incognita infested greengram. The X-ray diffraction (XRD) analysis of the nanocomposite revealed that the CuO and ZnO nanoparticles in CuO-ZnO nanocomposites exhibited crystallite sizes of approximately 23 and 25 nm, respectively. FTIR spectroscopy identified various aromatic and aliphatic chemicals, proteins, and metal-oxygen bonds. Scanning electron microscopy images showed spherical ZnO nanoparticles dispersed over polygonal CuO surfaces. In vitro, results demonstrated that CuO-ZnO nanocomposites at 50 ppm and 100 ppm caused 68 % and 85 % juvenile mortality and inhibited egg hatching by 71.5 % and 87.1 %, respectively. Pot experiments indicated that 100 ppm of CuO-ZnO nanocomposites significantly enhanced root length (192 %), biomass (226 %), chlorophyll (87.3 %), carotenoids (103 %), leaf nitrogen (82 %), protein (81 %), and pod yield (56.6 %) compared to nematode-infected controls. Additionally, nanocomposites improved gas exchange traits such as stomatal index, frequency, and aperture in treated plants. Antioxidant enzyme activities, including peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), were considerably increases in treated plants when compared with nematode inoculated controls. Nematode parameters, including gall and egg mass numbers and root-knot index (RKI), were significantly reduced. In conclusion, CuO-ZnO nanocomposites effectively manage root-knot nematodes and improve plant health, offering a promising eco-friendly alternative to conventional nematicides.