The Effect of Sodium Silicate in Inducing Systemic Resistance in Cucumber Fusarium Stem and Root Rot

 One of the most important diseases of cucumber is cucumber stem and root rot by agent Fusarium oxysporum f.sp. radicis-cucumerinum. The use of resistance inducers, which on the one hand activate the plant's defense mechanisms before confronting the pathogen and on the other hand do not pose environmental risks, has been considered by researchers in recent years. Recently, the use of sodium silicate as a potential activator of acquired resistance is being developed. Sodium silicate plays an important role not only in systemic acquired resistance but also in the expression of genetic resistance and stimulates the production of pathogen-related proteins (markers of systemic acquired resistance). The use of sodium silicate increases the tolerance of plants to environmental stresses and increases the quality and quantity of agricultural products. Hence it modulates the time and amount of plant defense responses and acts as a secondary messenger in induced systemic resistance.The effect of sodium silicate was investigated in order to induce defense reactions in cucumber cultivars and control the disease.

First, different concentrations of sodium silicate were applied on the growth of the pathogen in the laboratory. The effect of different concentrations of sodium silicate on pathogen growth was tested by mixing with culture medium. Different concentrations of sodium silicate (1, 2, 4 mM) are each combined in 100 ml of PDA culture medium and poured into 9 cm culture dishes. The percentage of sodium silicate inhibition on fungi is calculated according to the following formula: N = A-B / A. The effects of different concentrations of sodium silicate were applied in the soil on cucumber in the greenhouse. At time intervals of 0, 48, 72 and 96 hours after inoculation with pathogen, sampling of treated seedlings was performed to measure secondary metabolites and enzymatic activity. Disease severity, growth factors, production of secondary metabolites and activity of defense enzymes in cucumber plant and thus disease control were evaluated. Disease severity and growth factors were studied in a completely randomized design and Biochemical factors in a completely randomized design with factorial arrangement in which the main factors are the applied treatments and the sub-factors are the sampling times with three replications.

Sodium silicate showed a direct antifungal effect on fungal growth after 5 days and by increasing its concentration up to 4 mM caused a significant increase in antifungal effects. A significant decrease in colony diameter compared to the control was observed only at concentrations of 2 and 4 mM . This effect was observed as termination the growth of fungi at 72 hours after cultivation of fungi in culture medium containing sodium silicate. This effect remained stable with increasing incubation time. Fusarium fungi are root pathogens and reduce the absorption of water and minerals and clog the vessels, thus directly affecting the growth parameters in the roots and green parts of the plant. Infected control compared to healthy control showed a significant decrease in all growth parameters measured. Disease severity and growth factors were significantly affected by the effects of sodium silicate at a probability level of 1%. Application of sodium silicate in all concentrations had favorable results in significantly reducing the symptoms of the disease. Application of sodium silicate in diseased plants improved growth parameters. The mean value of growth parameters in different treatments and their treatment grouping based on LSD test is done at 5% probability level. Based on the results of this study, a decrease in chlorophyll and carotenoids and an increase in phenolic compounds and antioxidant enzymes and proline were observed in infected control plants compared to healthy controls. In this study, in the presence of sodium silicate in diseased plants, the amounts of pigments, phenol, flavonoids, anthocyanins, proline, protein and the activity of oxidative enzymes were significantly increased compared to the infected control.

According to the results, sodium silicate had direct antifungal effects in culture medium. In addition, a reduction in disease severity was observed in plants treated with sodium silicate in the greenhouse. Sodium silicate can be used as a chemical stimulant of plant defense and plant growth enhancer, for effective protection of cucumber plant against disease. Therefore, induction of resistance has found its place as a new technology for controlling plant diseases and its effect has been proven in laboratories and some farms.