Background: This study was conducted to examine the potential antifungal activity and protective effect of some nanoparticles in controlling root rot disease of sugar beet. Magnesium oxide, titanium dioxide and zinc oxide nanoparticles (MgO, TiO 2 and ZnO NPs) were investigated against three pathogenic fungi isolated from sugar beet roots, Fusarium oxysporum f. sp., betae , Sclerotium rolfsii and Rhizoctonia solani in vitro and under greenhouse conditions. Materials and Methods: Solutions of particles of MgO, TiO 2 and ZnO nanoparticles (NPs) were used in different concentrations in vitro to study the inhibition of fungal radial growth and by spraying fungal culture of the tested fungi to test the effect of nanoparticles on hyphal and spore formation and Scanning Electron Microscopy (SEM) was used to visualize the effect of this application. Greenhouse experiment was conducted and sugar beet seeds (cv., Kawamera) were treated with the nanoparticles concentrations as seed dressing then seeds were planted in infested soil with the tested fungi. Disease assessment was evaluated, also the effect of nanoparticles on the vegetative and the chemical characteristics of sugar beet were examined. Results: Obtained results showed that the three NPs tested with concentrations investigated (25, 50 and 100 ppm) increased the in vitro fungal growth inhibition by reducing the radial fungal growth with the best effect was recorded with the highest concentration. Meanwhile, TiO 2 NP (100 ppm) showed the highest effect in decreasing mean radial growth by 77.25. Also, TiO 2 showed 100 inhibition on sclerotia formation of Sclerotium rolfsii , while MgO was most effective and decreased sporulation (number of conidia) of Fusariun oxysporum f. sp., betae by 69.23. The greenhouse experiment showed that the tested all tested NPs significantly decreased the developed root rot severity and TiO 2 was most effective and decreased it to 1.39 compared to 28.2 for the untreated. On the other hand, treatments with the tested NPs significantly increased root fresh weight (biomass) of the plants and also the dry weight compared to the untreated infested control. This was accompanied with an increase in sucrose and Total Soluble Solids (TSS) and also the total phenol content and activity of the defense related enzyme, polyphenol oxidase. Conclusion: Based on the obtained results the use of magnesium oxide, titanium dioxide and zinc oxide nanoparticles could be a good and environmentally safe alternative of fungicides in controlling damping-off and root rot disease of sugar beet.
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