Silicon Dioxide (SiO2) Nanoparticles as a Alternaria alternata Fungi Mitigator on Biomass, Photosynthetic Machinery, Nutriome and Antioxidant Capacity of Barley (Hordeum vulgare L.)

Nowadays Alternaria is considered one of the main fungi causing damage in cereal crop such barley. This work was designed to assess the potential role of silicon dioxide nanoparticles (SiO₂ NPs) in enhancing barley's tolerance against A. alternata attack. For this purpose, twenty day-olds, seedlings were irrigated either with tap water or with SiO₂ NPs solutions at 20 and 200 ppm for one week. After that, different group of seedlings were exposed to fungus inoculation and the others serve as control. The results showed that the fungi attack reduced seedlings biomass, hydration status, transpiration, stomatal conductance, total antioxidant activity, and DPPH levels compared to non-inoculated seedlings. Meanwhile, there was an increase in total phenolic compounds and flavonoid contents. The application of SiO₂ NPs in absence of inoculation, resulted in an increase in seedling shoot length, shoot and root biomass, and water content at any NPs concentrations. Furthermore, when applied prior to inoculation at both concentrations (20 and 200 ppm), SiO₂ NPs mitigated the effects of pathogen attack by enhancing net CO₂ assimilation rate, internal CO₂ concentration, transpiration, and stomatal conductance and increasing total antioxidant activity and DPPH antioxidant profiles compared to inoculated plants. The shoot exhibited a significant increase in zinc, iron, manganese, and potassium with SiO₂ NPs at 200 ppm, regardless of the presence of fungi. The substrate's pH and conductivity remained unchanged compared to the control. However, there was a notable increase in nitrogen, manganese, potassium, and iron contents. On the other hand, levels of zinc and copper slightly decreased. This exploratory work highlights the protective role of SiO₂ NPs in barley seedlings under pathogen attack conditions possibly due to the Si-mediated protection against oxidative stress and photosynthesis modulation. Using SiO₂ NPs as a supplement offers a cost-effective and an eco-friendly and avenue for sustainable agriculture. They aid in nutrient delivery, help plants combat biotic stress, and enhance plant tolerance.