Eco-Friendly ZnO Nanoparticles Derived from Nigella sativa Seeds with Potential to Control Soil-Borne Fungal Pathogens

The present study reports a sustainable, phytochemical-mediated synthesis of zinc oxide nanoparticles (ZnONPs) using Nigella sativa (black cumin) seed extract as a reducing and stabilizing agent. The synthesized ZnONPs were characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and dynamic light scattering (DLS) to evaluate their optical, structural, morphological, elemental, and colloidal properties. The ZnONPs exhibited characteristic features of crystalline ZnO with good colloidal stability and nanoscale dimensions. Their antifungal activity was evaluated against the soil-borne fungal pathogens Rhizoctonia solani and Pythium myriotylum. The ZnONPs exhibited strong and concentration-dependent antifungal activity against both pathogens. The minimum inhibitory concentration (MIC) was 50 ± 2 μg/mL for R. solani and 75 ± 3 μg/mL for P. myriotylum, while the corresponding minimum fungicidal concentrations (MFCs) were 100 ± 3 μg/mL and 150 ± 4 μg/mL, respectively. Mechanistic investigations revealed that ZnONPs inhibited ergosterol biosynthesis and induced membrane disruption, as evidenced by increased extracellular nucleic acid and protein leakage. The antifungal activity was primarily associated with nanoparticle-membrane interactions, oxidative stress generation, and disruption of key metabolic pathways. Phytocompatibility assessment using Vigna radiata demonstrated concentration-dependent effects, with lower ZnONP concentrations (25-50 mg/L) promoting seed germination and vigor, whereas higher concentrations (≥100 mg/L) caused moderate phytotoxicity. Overall, the green-synthesized N. sativa-derived ZnONPs demonstrated potent antifungal activity together with acceptable phytocompatibility, highlighting their potential as an eco-friendly nanobiotechnological approach for the management of soil-borne fungal pathogens.