Size-engineered magnetite nanoparticles protect rice from Fusarium graminearum via direct antifungal activity and immune activation

Fusarium diseases threaten global food security through crop losses and toxin contamination, exacerbated by fungicide resistance and climate change. Here we demonstrate that magnetite (iron oxide) nanoparticles provide size-dependent protection against Fusarium graminearum in rice through dual antifungal and immunity mechanisms. Using antifungal assays, root iron layer analysis, and pathogen challenges under controlled and soil-based conditions, we evaluated 5 and 10 nanometer magnetite nanoparticles. Results reveal pronounced size-dependent activity, with 5 nanometer particles achieving 67.4% fungal inhibition in vitro versus 44.6% for 10 nanometer particles. In agricultural trials, 5 nanometer nanoparticles at 1.0 milligrams per liter reduced disease area by 82.7%, outperforming 10 nanometer particles (67.5%) and ionic iron (43.8%). The nanoparticles enhanced protective iron layers on roots and activated plant defense, increasing defense hormones 2.8–3.5-fold. Gene expression analysis revealed upregulation of plant immunity and antimicrobial compound pathways. Size-engineered magnetite nanoparticles offer promising sustainable alternatives to conventional fungicides. Custom-designed magnetite nanoparticles effectively reduce fungal growth and stimulate plant defense strategy against Fusarium graminearum in rice through dual antifungal and immunity mechanisms.