Silicon-enhanced resistance to rice blast is attributed to silicon-mediated defence resistance and its role as physical barrier

A series of experiments were performed to study the effects of silicon (Si) on rice blast development, H2O2 accumulation and lipid peroxidation in a controlled rice-Magnaporthe grisea pathosystem. Rice plants supplied with Si as a single dose immediately after pathogen inoculation (-/+Si) exhibited the same high protection against disease as plants treated continuously with Si for the whole growth period (+/+Si), with disease severity indices of 20.8% and 19.6%, respectively, which were significantly lower than that for the control treatment with no Si supplied (63.7%). A single application of Si to rice plants before inoculation (+/-Si) conferred partial protection (disease severity index of 33.3%) compared with the control treatment. Silicon induced a rapid but transient burst of H2O2 at 24 h after inoculation. The addition of Si to rice plants significantly altered the activities of catalase and lipoxygenase and the concentration of malodialdehyde (indicative of lipid peroxidation) in rice plants. We propose that rice plants may respond to Si by increased H2O2 accumulation and lipid peroxidation. In turn, these responses are linked to host defence mechanisms such as lignin production, oxidative cross-linking in the cell wall, phytoalexin production, and the hypersensitive reaction. Thus, the mechanisms of Si-stimulated plant disease protection may extend beyond its established role in physically strengthening cell walls.