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.

Fusarium head blight (FHB), caused by Fusarium graminearum, is a predominant disease of wheat. Due to the lack of disease-resistant germplasm, chemical control is an important means to control wheat scab. Volatile substances produced in near-isogenic wheat lines were detected after inoculation with F. graminearum, and 4-propylphenol, which appears in FHB-resistant lines, was identified. In vitro and in vivo antifungal activity tests demonstrate that 4-propylphenol effectively inhibits the mycelial growth of F. graminearum. Metabolomics analysis showed changes in glutathione metabolism, indicating that 4-propylphenol triggered reactive oxygen species (ROS) stress. This was consistent with the increasing ROS levels in Fusarium cells treated with 4-propylphenol. Further results demonstrated that excessive accumulation of ROS induced DNA and cell membrane damage in the mycelium. Moreover, 4-propylphenol showed different degrees of inhibition against other soil-borne pathogens (fungi and oomycetes). These findings illustrated that 4-propylphenol has broad spectrum and high antifungal activity and should be considered for use as an ecological fungicide.