Effect of silicon salts on physiological changes in broad bean infected by Phytophtora pistaciae

Background and Objectives
Silicon is the most common element in soil that has beneficial effects in enhancing tolerance to biotic and abiotic stresses in plants. The addition of silicon to plant nutrient solution causes decreasing sodium concentration, increasing plant growth, having positive effects on plant reproduction and increasing mechanical resistance. Silicon also affects absorption and translocation of several macro- as well as micronutrient elements and imposes the formation of precipitates under the cuticle, reduces plant transpiration and causes resistance to stresses such as side effects of excessive phosphorus and heavy metals (high concentration of manganese and aluminium) or salinity. Silicon salts such as sodium and potassium silicate causes significant reduction in growth, asexual organ reproduction and dry weight of hyphae, and also prevent the germination of cysts in some plant pathogens such as Phytophthora species. 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 mortality of the broad bean. In this study the in vivo activities of sodium and potassium silicate in controlling P. pistaciae and Rhizoctonia solani as a control were evaluated.
Material and Methods
To study the effect of sodium silicate (0.25, 0.5 and 0.7 mM) and potassium silicate (1, 2 and 4 mM) to increase the resistance of broad bean as a test plant against P. pistaciae and R. solani a factorial experiment in a completely randomized design with salt treatments before and after inoculation was conducted. In the case of R. solani as a control only 5.0 mM of sodium silicate and 2 mM of potassium silicate were applied. 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.
Results
The results showed that silicon salts may enhance broad bean resistance to P. pistaciae and 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 carbohydrate content of the plants and pH and the electrical conductivity of soil.
Discussion
According 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.