Nano-Stimulated Immunity: Synthesis and Functionalization of CuS Induce Multilevel Defense Responses against Fusarium in Tomato ( Solanum lycopersicum )

This study investigated how doping-modified copper sulfide (CuS) micronanoparticles (MNPs) influence tomato resistance against fungal pathogens. Three cuboidal CuS MNPs─undoped (CuS), iron-doped (Fe-CuS), and cerium-doped (Ce-CuS)─were foliarly applied to Fusarium-infected plants in a greenhouse study. Fe-CuS led to the highest Cu accumulation in leaves─15.7 and 158.4% higher than undoped CuS and Ce-CuS, respectively, likely due to its positive charge facilitating stronger electrostatic interactions and more efficient NPs uptake. Compared to the untreated control, the Fe-CuS foliar application resulted in a 487.7% increase in shoot biomass and a 36.8% reduction in wilt damage through activation of jasmonic acid/ethylene signaling, indicating a dual role of CuS MNPs as both a micronutrient carrier and an immune stimulant. Importantly, copper amine oxidases (CuAOs) activation may link Cu homeostasis to stress-induced H2O2 production, indicating a novel mechanism for nanoparticle-enabled plant immunity. These findings underscore the significant potential for CuS MNPs as an alternative to conventional copper-based fungicides, though long-term environmental behavior and life cycle impacts warrant further evaluation.