The phytopathogenic basidiomycetous fungus, Rhizoctonia solani, has a wide range of host plants including members of the family Poaceae, causing damping-off and root rot diseases. In this study, we biosynthesized spherical-shaped silicon dioxide nanoparticles (SiO2 NPs; sized between 9.92 and 19.8 nm) using saffron extract and introduced them as a potential alternative therapeutic solution to protect wheat seedlings against R. solani. SiO2 NPs showed strong dose-dependent fungistatic activity on R. solani, and significantly reduced mycelial radial growth (up to 100% growth reduction), mycelium fresh and dry weight, and pre-, post-emergence damping-off, and root rot severities. Moreover, the impact of SiO2 NPs on the growth of wheat seedlings and their potential mechanism (s) for disease suppression was deciphered. SiO2 NPs application also improved the germination, vegetative growth, and vigor indexes of infected wheat seedlings which indicates no phytotoxicity on treated wheat seedlings. Moreover, SiO2 NPs enhanced the content of the photosynthetic pigments (chlorophylls and carotenoids), induced the accumulation of defense-related compounds (particularly salicylic acid), and alleviated the oxidative stress via stimulation of both enzymatic (POD, SOD, APX, CAT, and PPO) and non-enzymatic (phenolics and flavonoids) antioxidant defense machinery. Collectively, our findings demonstrated the potential therapeutic role of SiO2 NPs against R. solani infection via the simultaneous activation of a multilayered defense system to suppress the pathogen, neutralize the destructive effect of ROS, lipid peroxidation, and methylglyoxal, and maintain their homeostasis within R. solani-infected plants.

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Silver nanoparticles (AgNs) are known as a promising alternative tool to control fungal diseases. AgNs were biologically synthesized using Trichoderma harzianum filtrate as an ecofriendly approach. The presence of AgNs was confirmed by changing the color to brown, followed by UV-Vis spectroscopy, transmission electron microscopy (TEM), and Energy-dispersive spectra (EDS). TEM studies showed that the size of AgNs average was 31.13 nm and the shape was spherical. In vitro assays of AgNs showed a significant inhibitory effect on the growth of Sclerotinia sclerotiorum (S. sclerotiorum) and Sclerotium rolfsii (S. rolfsii). The percentage inhibition on mycelial linear growth, dry weight, and sclerotia formation of S. sclerotiorum and S. rolfsii at 100 μgm−l were 87.8, 82.7, 96.4, 52.8, 55.1, and 85.4%, respectively. The obtained results suggested that the biosynthesized AgNs have antifungal activity against S. sclerotiorum and S. rolfsii. Foliar spray of bean and sunflower plants with AgNs caused a decrease in disease severity, which promoted the plant protection against S. sclerotiorum and S. rolfsii, respectively. Substantially, this study will extend our understanding of the AgNs antifungal action for suppressing fungal diseases.

Attempts are being made to minimize the use of synthetic chemicals such as fungicides. There is an interest toward the use of environmentally-friendly products to minimize impact of toxic residuals on human, animals, and environment. Two-season field experiments were conducted in 2018 and 2019to investigate the effectiveness of foliar sprayings of three products [potassium silicate (PS), perbicarbonate (PB), and peroxyacetic acid (PAA)] as singular or sequential treatments (totaling 10 treatment combinations) on growth (plant height, number of leaves, number of branches, leaf area), yield, yield attributes (number of pods plant-1 , pod length, pod weight), chlorophyll a, b, and carotene contents, and resistance of okra plants (cv. Baladi) to powdery mildew disease. All treatments were significantly reduced powdery mildew infection with highest resistance observed with PAA+PS or PAA+PB, or PB+PAA treatments. Growth characteristics were enhanced by most treatments with the highest increases detected with singular PS or PAA treatments and with sequential PB+PS treatment. PS was superior in increasing the number of leaves, branching number, and leaf areas. The only treatments that significantly increased total yield were PAA+PB, PAA, PS, PS+PAA, and PAA+PS with the former two treatments giving the highest total yield. In conclusion, foliar spraying of okra with singular or sequential treatments with PS, PAA, and PB significantly improved plant resistance to powdery mildew infection. Nevertheless, singular PS or PAA treatments as well as sequential PB+PS, PAA+PS, PS+PAA, and PAA+PB treatments were the most effective in improving growth and yield while controlling powdery mildew disease.