Effect of CuO Nanoparticle Size on Inhibition of <i>Fusarium graminearum</i>

The application of nanoparticles (NPs) in agriculture has increased remarkably in recent years as a promising strategy for sustainable crop protection. Strategies involving the foliar use of NPs can significantly improve plant resistance to soilborne fungal diseases. NPs have been shown to be transported from leaves to roots, with potential release to the rhizosphere, although the precise mechanisms for reduced infection and damage from soilborne pathogens are complex, likely varying with disease system, nanoparticle type, and growth conditions. In this study, we investigated 100 ppm of CuO NPs of different sizes [sCuO NPs, 20–50 nm and lCuO NPs, 100 nm], along with 200 ppm of CuSO4, for potential ability to inhibit Fusarium graminearum PH-1 in an in vitro leaf bioassay, as well as an in vivo assay on wheat leaves. Three days after treatment, the Cu salt and NPs (20–50 nm) both restricted fungal growth on wheat leaves in vitro. Laser scanning confocal microscopic observations revealed that the CuO NPs (20–50 nm) inhibited F. graminearum growth by direct effects on the hyphae, spores, and conidial spore germination. Reactive oxygen species (ROS) were significantly (p ≤ 0.05) increased by 214.84 and 191.55 J/cm2 in the hyphae and conidia when treated with CuO NPs (20–50 nm), respectively; intracellular ROS content also increased with the treatment of the CuO NPs (100 nm), although inhibition on the conidial spore germination was limited. CuO NPs also compressed the membrane, which was different than the CuO ions-induced ROS caused cell membrane damage and apoptosis. We observed the smaller NP size (20–50 nm) had greater toxicity than the larger size (100 nm). The study demonstrates that size-dependent CuO NPs offer a promising approach for sustainable crop protection, with multiple mechanisms of pathogen control that may provide greater versatility than conventional CuO products. These findings have important implications for developing more effective and environmentally sustainable strategies to combat fungal diseases in agricultural systems, particularly for managing Fusarium head blight in wheat production.