Abstract: 【Objective】 The purpose of the study was to analyze the effects of exogenous spraying of jasmonic acid (JA) on the occurrence of sugarcane leaf scald,to reveal the role of JA in sugarcane resistance to leaf scald and its mechanism to enhance the resistance of sugarcane leaf scald, to provide important gene resources for molecular breeding of sugarcane resistance to leaf scald and to provide a reference for the prevention and control of sugarcane leaf scald.【Method】 Healthy sugarcane seedlings were inoculated with Xa-FJ1 bacterial solution(Xa solution). After spraying purified water (CK) or different concentrations of JA and jasmonic acid inhibitor(IBU) on sugarcane seedlings inoculated with Xa for 72 h,the incidence of sugarcane was observed and the disease index was counted,and the optimum concentrations of JA and IBU were selected. The sugarcane inoculated with Xa for 72 h was sprayed with the optimum concentrations of JA and IBU,respectively. The physiological indexes and related gene expression of defense in sugarcane were measured at different times after inoculation.【Result】 Spraying JA could slow down the occurrence of sugarcane leaf scald,and the inhibition effect on the incidence of leafscald was significant when the spraying concentration was 200 mmol/L(P<0.05, the same below). Spraying IBU promoted the occurrence of sugarcane leaf scald to a certain extent,and the resistance to leaf scald was the worst when the spraying concentration was 200 mmol/L. JA and IBU at 200 mmol/L were selected for subsequent experiments,respectively. At 72 h after inoculation with Xa,the JA content of sugarcane leaves treated with CK and JA was extremely significantly different(P<0.01,the same below). At 96 and 120 h after inoculation with Xa, the JA content of sugarcane leaves treated with CK and IBU was extremely significantly different. At 72,96 and 120 h after inoculation with Xa,the JA content of sugarcane leaves of JA and IBU treatment was extremely significantly different. At 72 h after inoculation with Xa,the MDA content of sugarcane leaves treated with JA and IBU increased obviously. The malonaldehyde(MDA) content of CK was extremely significantly different from that of JA and IBU treatments,and JA treatment was extremely significantly different from IBU treatment. At 24 h after inoculation with Xa,the activities of peroxidase(POD) and superoxide dismutase(SOD) in sugarcane leaves treated with CK,JA,and IBU reached the maximum,and then decreased. At 72 h after inoculation with Xa,the POD activity of CK and JA treatment was significantly different. Spraying JA and IBU at 72 h after inoculation with Xa,the relative expression levels of JA pathway genes in sugarcane leaves treated with CK and IBU generally showed a downward trend,while JA treatment showed an upward trend.【Conclusion】 After exogenous spraying of JA,the expression of JA pathway related genes in sugarcane plants increases,and the jasmonic acid content and the activity of related defense enzymes increase,and finally the resistance of sugarcane to Xa is enhanced.