Silicon application unveiled: A review of insights into plant defense mechanisms under biotic challenges

Silicon (Si) is the second most abundant element after oxygen in soil. Nevertheless, it was not considered essential for plant growth and development. In the last decades, many researchers have reported that silicon can mitigate to some extent the adverse effects of variable biotic and abiotic stresses caused by salinity, chilling, heating, nutritional imbalance, heavy metals, diseases, herbivores, and many others. There are different hypotheses regarding the mechanisms of the silicon mode of action. Some of them propose that the silicon treatment is probably related to the structural modification of the plant cells and tissues. Others speculate that silicon could be involved in plant metabolism. The interaction between the two mechanisms is also a very reliable hypothesis. Most of the studies focused on the influence of silicon on alleviating the negative effects of abiotic stress factors. The reports about the effect of silicon under biotic stress are not so abundant. Today, there is no doubt about the positive effect of silicon application in alleviating stress and reducing the pest and disease incidence and severity. However, the mechanisms of the silicon-induced plant responses are not yet completely clear. This motivated the current study to analyze the data presented about the silicon-induced alleviation of biotic stress. Keywords: silicon, stress, disease, pest, physical barrier, plant metabolism