Coated Cu-doped ZnO and Cu nanoparticles as control agents against plant pathogenic fungi and nematodes

In the current study, coated copper nanoparticles with polyethylene glycol 8000 (Cu@PEG NPs) and copper-doped zinc oxide nanoparticles with diethylene glycol (Cu-doped ZnO@DEG NPs) have been synthesized via solvothermal and microwave-assisted process, physicochemical characterized, and studied as nano-fungicides and nano-nematicides. Spheroidal Cu-doped ZnO@DEG NPs and urchin-like Cu@PEG NPs have been isolated with average crystallite sizes of 12 and 21 nm, respectively. The Cu doping (11.3 wt%) in ZnO lattice (88.7 wt%) was investigated by Rietveld refinement analysis and confirmed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The Cu-doped ZnO@DEG and Cu@PEG NPs revealed a growth inhibition of fungi Botrytis cinerea (B. cinerea) and Sclerotinia sclerotiorum (S. sclerotiorum) and nematode paralysis of Meloidogyne javanica in a dose-dependent manner. Cu-doped ZnO@DEG NPs were more effective against M. javanica (EC₅₀ = 2.60 μg/mL) than the Cu@PEG NPs (EC₅₀ = 25 μg/mL). In contrast, the antifungal activity was approximately similar for both NPs, with EC₅₀ values at 310 and 327 μg/mL against B. cinerea, respectively, and 260 and 278 μg/mL against S. sclerotiorum, respectively. Lettuce (Lactuca sativa) plants were inoculated with S. sclerotiorum or M. javanica and sprayed with either Cu-doped ZnO@DEG NPs or Cu@PEG NPs. The antifungal effect was evaluated based on a disease index (DI), and nematicidal activity was assessed based on the total number of galls and nematode females per root gram. NPs successfully inhibited the growth of both pathogens without causing phytotoxicity on lettuce. The DI were significantly decreased as compared to the positive control (DI = 5.2), estimated equal to 1.7, 2.9 and 2.5 for Cu@PEG NPs, Cu-doped ZnO@DEG NPs and the chemical control (KOCIDE 2000), respectively. The reduction in galling and population of M. javanica ranged from 39.32% to 32.29%, statistically like chemical control. The treatment of lettuce plants with Cu-doped ZnO@DEG NPs increased the leaf net photosynthetic value at 4.60 and 6.66 μmol CO₂^-2 s^-1 in plants inoculated with S. sclerotiorum and M. javanica, respectively, as compared to the control (3.00 μmol CO₂^-2 s^-1). The antioxidant capacity of NPs treated lettuce plants was evaluated as 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity in leaf extracts. Plants inoculated with S. sclerotiorum and sprayed with Cu-doped ZnO@DEG and Cu@PEG NPs, exhibited a 34.22% and 32.70% increase in antioxidant capacity, respectively, higher than the control. Similarly, an increase in antioxidant capacity was measured (39.49 and 37.36%) in lettuce inoculated with M. javanica and treated with Cu-doped ZnO@DEG and Cu@PEG NPs, respectively. Moreover, an increase of phenolic compounds in lettuce leaf tissue treated with NPs was measured as compared to the control. Overall, foliar applied Cu and Cu-doped ZnO NPs could be a promising tool to control phytopathogenic fungi and nematodes contributing to sustainability of agri-food sector.