Development of Organic-Inorganic Hybrid Coatings with Silica Nanoparticles, Biopolymer, and Clay for Onion Seeds: 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 efficiency of conventional fungicide treatments. Silicon has been reported to contribute to plant defense and disease suppression and when incorporated into membranes, may contribute to the formation of a mechanical barrier against external agents, making its action interesting in conjunction with low concentrations of fungicidal active ingredients, used commercially. Hybrid membranes containing fungicidal active ingredients and SiO₂ nanoparticles were developed and evaluated for their effects on onion seed germination and mycelial growth inhibition of S. cepivora. The membranes containing silicon nanoparticles and fungicidal active ingredients (CS5-TR and CS5-TE) showed 100% mycelial growth inhibition under in vitro contact conditions. The Raman and FTIR-ATR spectroscopy techniques were associated with the presence of the CMC polymer and the Laponite^® RD clay, showing a reduction in the intensity of the bands of the fungicidal actives triadimenol and tebuconazole, which is related to the low concentrations of incorporation of the actives in the membranes. The XRD technique combined with SEM images confirmed the presence of SiO₂ in the hybrid membranes, amorphizing the (001) peak, characteristic of the presence of Laponite^® RD, confirming the interaction of silicon in the interlayer space of the clay, promoting disorganization of the structure and reduction in the thickness of the membranes. The thermal analysis TG-DSC showed a significant decomposition in the region of 300 ºC, indicating a process of membrane dehydration. Energy dispersive X-ray spectroscopy (EDS) confirmed the presence of the elements O, Na, Si, Mg, and F in the membranes, suggesting the formation of SiO₂ NP clusters on the surface during the drying process. The use of SiO₂ NPs and fungicidal actives incorporated into the synthesis of organic-inorganic hybrid materials demonstrated enhanced antifungal performance, highlighting the potential of hybrid membranes as a multifunctional strategy for the control of white rot.