Chitosan-Coated Mesoporous Silica Nanoparticle Treatment of Citrullus lanatus (Watermelon): Enhanced Fungal Disease Suppression and Modulated Expression of Stress-Related Genes

This work assesses the potential of mesoporous silica nanoparticles with or without a chitosan coating to suppress Fusarium wilt (Fusarium oxysporum f. sp. niveum) in watermelon (Citrullus lanatus) by virtue of dissolution to release silicic acid. Plant health was assessed by monitoring the total biomass and fruit production in both healthy and pathogen-infected plants up to 100 days after a single nanoparticle application (500 mg/L) was applied at the seedling stage. Both types of mesoporous silica nanoparticles enhanced the innate defense mechanisms of watermelon, with mesoporous silica nanoparticles (MSNs) and chitosan-coated mesoporous silica nanoparticles (CTS-MSNs) reducing disease severity by ∼40% and ∼27%, respectively, as measured by the area-under-the-disease-progress curve. Changes in gene expression measured several weeks after nanoparticle application demonstrated reduced expression of several stress-related genes after CTS-MSN and MSN treatments, indicating a reduced disease burden on the plant. Although treatment did not impact fruit production from diseased plants, a single application of chitosan-coated mesoporous silica nanoparticles at the seedling stage led to a 70% increase in the fruit yield of uninfected watermelon. Monitoring plant biomass revealed that MSNs and CTS-MSNs had no significant impact on the biomass reductions in diseased plants, likely because seedlings were treated and biomass was measured weeks later in the fully grown plants. These findings demonstrate the utility of a single application of mesoporous silica nanoparticles with or without a chitosan coating as a nanoenabled agricultural amendment, and current work is focused on optimizing the material synthesis and treatment regimens for maximum benefit.