Development of organic–inorganic hybrid coatings with silica nanoparticles, biopolymers, and clay for onion seeds: a multifunctional strategy for controlling white rot

Abstract

White rot, caused by Stromatinia cepivora, remains one of the most challenging soil-borne diseases affecting onion crops due to the long-term persistence of sclerotia and the limited effectiveness of conventional fungicide treatments. Silicon has been reported to contribute to plant defense and disease suppression, and when incorporated into coatings, it can contribute to the formation of a mechanical barrier against external agents, making its action interesting in conjunction with low concentrations of commercially used fungicidal active ingredients. Hybrid coatings containing fungicidal active ingredients and SiO₂ nanoparticles were developed and evaluated for their effects on onion seed germination and inhibition of S. cepivora mycelial growth. The coating containing SiO₂ nanoparticles and fungicidal active ingredients (CS5-TR and CS5-TE) showed 100% inhibition of mycelial growth under in vitro contact conditions. Raman and FTIR-ATR spectroscopy techniques confirmed the presence of CMC and LAPONITE® RD precursors in the coatings, as well as slight shifts and a reduction in band intensity when combined with fungicidal actives and SiO₂ NPs. X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) confirmed the presence of SiO₂ NPs in the hybrid coatings, amorphizing the (001) peak, characteristic of the presence of LAPONITE® RD. This suggests structural reorganization of the polymer–clay–silica matrix after the addition of SiO₂ in the interlayer spaces of the clay, consistent with a reduction in stacking order and changes in the coating morphology. TG-DSC thermal analysis showed an event around 300 °C, mainly attributed to the degradation of the organic matrix and the loss of bound water. Energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of O, Na, Si, Mg, and F in the coatings, suggesting the formation of SiO₂ nanoparticle agglomerates on the surface during the drying process. The use of SiO₂ NPs and fungicidal active ingredients incorporated into the synthesis of organic–inorganic hybrid materials demonstrated enhanced antifungal performance, highlighting the potential of hybrid coatings as a multifunctional strategy for controlling white rot, although their release kinetics, permeability, fungal cell damage, and soil/greenhouse performance still need to be investigated.