Silicon Dioxide Reduces the Lesion Length on Soybean Stems and In Vitro Production of Sclerotia of Sclerotinia sclerotiorum

Silicon (Si) is an element that has been associated with plant defence against pathogens and pests. Silicon dioxide (SiO₂) is one of the available forms of Si, but it is still underexplored in agriculture. Among the diseases that can affect soybean, white mould (caused by Sclerotinia sclerotiorum) stands out because of its destructive potential and worldwide occurrence. The objective of this study was to evaluate the in vitro action of SiO₂ on S. sclerotiorum and whether its foliar application can reduce the lesion length on soybean stems. There was no effect of increasing the concentration of SiO₂ (0; 0.1; 1; 10 and 100 mg L⁻¹) on mycelial growth in vitro; however, at the highest concentration (100 mg L⁻¹), there was a reduction of 91.0% and 35.1% in the number and mass of sclerotia, respectively. A controlled-environment study was carried out with four treatments (0; 1; 2.5% and 5% of SiO₂) that were applied five times as foliar spray to soybean plants prior to their inoculation with S. sclerotiorum. The lesion length on the soybean stem linearly decreased with increasing SiO₂ concentration. There was a 46.3% reduction in the lesion length at 5% of SiO₂ (to 43.6 mm) compared to the control (81.2 mm) at 6 days after inoculation. Thus, on the basis of the observed in vitro and in vivo effects, it can be concluded that SiO₂ application may offer a promising complementary strategy for white mould management.