Effect of silicon salts on physiological changes in broad bean infected by Rhizoctonia solani

Silicon is the most common soil element which has beneficial effects to enhance the tolerance to biotic and abiotic stresses in plants. The addition of silicon to plant nutrient solution decreases sodium concentration, increases plant growth, has positive effects on plant reproduction, and increases mechanical resistance.  Also, silicon affects absorption and translocation of several macro- as well as micronutrient elements and imposes the formation of precipitates under cuticle reduces plant transpiration, and causes resistance to stresses such as side effects of excessive phosphorus and heavy metals (high concentration of manganese and aluminum) or salinity. Furthermore, silicon salts can significantly reduce the diseases in broad bean by reducing the percentage of root colonization and plant death, as well as decreasing root rot compared to controls. Silicon salts such as sodium and potassium silicate cause significant reduction in growth, asexual organ reproduction, and dry weight of hyphae, and prevent cysts' germination in some plant pathogens such as Phytophthora species. The application of silicon salts before and after inoculation of sterilized soil with Phytophthora pistaciae significantly reduces the disease by reducing the percentage of colonized roots and the broad bean's mortality. In this study, in vivo activities of sodium and potassium silicate in controlling Rhizoctonia solani were evaluated.

Studying the effect of sodium silicate (0.5 mM) and potassium silicate (2 mM) to increase the resistance of broad bean against R. solani a factorial experiment in a completely randomized design with salt treatments before and after inoculation was conducted. The level of catalase, peroxidase, polyphenol oxidase, proline, total protein, and carbohydrates in plants, as well as pH and the electrical conductivity of soil were examined.

The results showed that silicon salts might enhance broad bean resistance to R. solani by increasing the level of catalase, peroxidase, polyphenol oxidase, and total protein and decreasing proline. None of the salts had any effects on the level of the plants' carbohydrate content and pH, and the electrical conductivity of soil. As a result, controlling the pathogen is not directly affected by soil pH.

Due to the results, it can be concluded that the role of silicon salts in promoting broad been tolerance could be due to increasing the activities of the antioxidant enzymes which in turn reduced the oxidative damages of reactive oxygen species produced under disease stress.