Physiological Mechanisms Of Silicon Compounds On Resisting Against Fungal Diseases Of Melon

The techniques of pathology, physiology, biochemistry and botany were used to study resistance mechanisms and effects of resistance-pathogen on seedlings and fruit of 'Yujingxiang' melon which treaed by different silicon compounds. Morphology, localisation and quantity of silicon compounds in the melon tissue were detected by microscopy, electronic microscopy and X-ray microscope analysis. The results were as follows.1. The three silicon compounds did not affect spore germination. All the silicon compounds inhibited disease caused by Erysiphe ciicurbitacearum. Of the three silicon compounds, sodium silicate was the most effective, followed by silicon acid, with nanosize silicon the least effective.The silicon compounds caused some injury to the leaves of 'Yujingxiang' melon. Phytotoxic concentrations of nanosize silicon oxide, sodium silicate and silicon acid were >25mmol/L, 25mmol/L and 25mmol/L for mature leaves, respectively; and 25mmol/L, 15mmol/L and 15mmol/L for juvenile leaves, respectively. Sodium silicate caused the most severe injury to the leaves of' Yujinxiang' melon, silicon acid caused less severe damage, and nanosize silicon caused the least injury.2. The peroxidase (POD) activity of the secondary leaves of 'Yujingxiang' melon was induced by sodium silicon treatment without a challenging inoculation. This induced effect lasted for 240h. Nanosize silicon did not induce POD activity without a challenging inoculation. The POD activity of the melon leaves was induced by all treatments after a challenging inoculation. Sodium silicate was more effective than the other treatments, with an induced effect that lasted 240h. The POD activity of the melon leaves had increased significantly 24h after sodium silicon treatment, and 24h and 120h after a challenging inoculation.The p-1, 3-glucosidase (GLU) activity of the secondary leaves of 'Yujingxiang' melon increased 24h after sodium silicate treatment. The induced effect lasted for 240h, and was enhanced by inoculation with a pathogen. The GLU activity after sodium siliate treatment continued to mcrease 240h after treatment. GLU activity of control fruit did not change without pathogen inoculation, but increased after a pathogen inoculation. The increase in GLU activity following sodium silicate treatment was significantly higher than the increase in the control sample following pathogen inoculation.3. The calcium levels of both sides of the melon leaves were higher than the silicon levels. The calcium level peaked at the site of villus. The silicon and calcium levels had similar levels of variation, although the silicon levels were much lower than the calcium levels. The upper sides of the leaves had less villus than the lower sides.Line scanning by X-SEM showed that calcium and silicon levels of upper and lower sides of treated and untreated secondary leaves were similar. Dot scanning af the base of villus indicated greater deposits of calcium and silicon at the base of villus. The silicon to calcium ratio of nanosize silicon oxide treatment at the base of villus was 2.04 times greater than the control sample. The silicon to calcium ratio of sodium silicate treatment was 3.95 and 1.79 times greater than the control and nanosize silicon oxide samples, respectively. Area scanning of stomatashowed that silicon was readily deposited at stomata. The silicon to calcium ratio of nanosize silicon oxide treatment at the site of stomata was 6.51 times greater than the control sample. The silicon to calcium ratio of sodium silicate treatment was 36.82 and 5.65 times greater than the control and nanosize silicon oxide samples, respectively. Cross-section scanning indicated a peak in silicon content occurred at the surface, which suggests that the movement of silicon was limited.4. The respiration of 'Yujingxiang' melon was significantly decreased by sodium silicate treatment (p<0.05) , but not by nanosize silicon oxide treatment at 5癈. The respiration of 'Yujingxiang' melon was significantly decreased by both sodium silicate treatment and nanosize silicon oxide trea...