Effect And Physiological Basis Of Exogenous Silicon On Smut Resistance Of Sugarcane

Smut caused by Sporisorium scitamineum is the most serious fungal disease in sugarcane production,which seriously affects the production of sugarcane in China.The most effective means to prevent and treat this disease is to breed disease-resistant varieties,however the process is complex and long,and due to the rapid differentiation of pathogenic physiological races,disease-resistant varieties can easily become susceptible varieties.Therefore,it is necessary to explore new ways to prevent and control sugarcane smut.Studies have shown that silicon enhances the disease resistance of crops,but the mechanism of disease resistance is still unclear totally.A series of pot experiment were performed in this study by using two susceptible varieties?ROC22 and Badila?to investigate the silicon-enhanced sugarcane growth,smut resistance and silicon absorption.The effect of exogenous silicon on pathogenesis-related proteins,secondary metabolites and antioxidant defense enzymes in leaves in sugarcane and S.scitamineum interaction were also examined.The preliminary study on the mechanism of silicon-enhanced resistance to sugarcane smut from agronomic traits and physiological and biochemical changes.The main results were as follows:?1?Exogenous silicon addition significantly increased silicon content in leaf,stem and root tissues of both two sugarcane lines regardless of the pathogen inoculation,and has a significant positive correlation with the amount of silicon application?except for the stem silicon content of Si treatment of ROC22?.The appropriate silicon addition?the silicon application respectively is 5 g,10 g,15 g/pot?can not only promote the growth of root tissues,but also enhance the photosynthetic and transpiration of sugarcane,so it can effectively increase the plant height,stem diameter,dry weight of shoot and root.?2?Exogenous silicon addition significantly enhanced sugarcane resistance to S.scitamineum,and comparing with no silicon application,the sugarcane smut incidence of two lines decreased significantly,and the declines were respectively reduced to 11.57-22.58%and 27.75-46.67%,while the incidence index was significantly negatively correlated with the silicon content in leaf,stem and root tissues of both two sugarcane lines?except for the leave silicon content of Sis treatment of ROC22?.In addition,silicon content increased significantly in examined tissues of both two lines after the pathogen inoculation comparing with the without inoculation.?3?Under smut stress,as compared to no silicon treatment the activities of chitinase and?-1,3-glucanase in leaves were significantly increased after adding exogenous silicon,which effectively increased resistance to smut.These show that silicon could participate in disease resistance process by regulating the physiological and biochemical metabolism of sugarcane.?4?Under smut stress,as compared to no silicon treatment the activities of PPO and PAL in leaves were increased obviously after adding exogenous silicon,which was consistent with the decrease of the smut incidence.The content of total soluble phenol and lignin increased significantly,which was consistent with the increase of PPO and PAL activity.These demonstrate that silicon participates in the secondary metabolism of sugarcane and plays a positive role.?5?Under smut stress,as compared to no silicon the contents of MDA and H₂O₂ in leaves increased significantly after applicating exogenous siliconat the seedling and tillering stage,and the activities of LOX and SOD increased significantly,but the activities of POD,CAT and APX decreased,which was beneficial to the accumulation of active oxygen to initiate the defense response.At the jointing stage,the content of MDA and H₂O₂ was significantly decreased,while LOX,SOD,CAT,POD,and APX were both significantly increased,which favored the removal of excess reactive oxygen species.These show that silicon participates in the active oxygen metabolism and plays an active rolein sugarcane and S.scitamineum interaction.In addition,the trend of changes in CAT,POD,and APX was different in various silicon applications,and the activities of CAT,POD,and APX with high silicon application levels were lower than those of appropriate silicon treatments.The result shows that high exogenous silicon addition is beneficial to resist smut,but excessive Si concentration will cause new stress to sugarcane,which is not conducive to sugarcane growth.In conclusion,proper exogenous silicon not only facilitates the growth of sugarcane,but also significantly increases the resistance of sugarcane to smut caused by S.scitamineum.The mechanism of disease resistance may be that sugarcane can increase the absorption of silicon under the smut stress to construct a physical barrier against the pathogen infection,and silicon can regulate physiological and biochemical metabolism to resist disease in sugarcane and S.scitamineum interaction.