Objective To discuss the field grading standard on sugarcane pokkah boeng disease severity, and study regional and varietal(clonal) differences in occurrence of pokkah boeng disease.

Method The occurrence of pokkah boeng disease on 11 new sugarcane varieties (lines) and the dominant cultivar ROC22 in Guangxi was investigated in six sites including Nanning, Liuzhou, Hechi, Baise, Beihai and Chongzuo cities. The grading standard on sugarcane pokkah boeng disease and the resistance evaluation system were established.

Result The incidence and disease severity index (DSI) of new-planting sugarcane were 0.16%-23.82% (average 3.51%) and 0.03-16.48 (average 3.45) respectively, and those of ratoon cane were 0-25.89% (average 4.27%) and 0-17.37 (average 4.61). According to the new standard, six resistance grades were established, including high resistance (HR), resistance (R), medium resistance (MR), medium susceptible (MS), susceptible (S) and high susceptible (HS). HR and HS sugarcane varieties (clones) were not found in the 12 tested materials. Among the 12 varieties, Guifu06-156, Guitang05-3846, GuixuanB9 and ROC22 belonged to R grade and demonstrated the highest resistance against pokkah boeng disease, and Guitang06-1023 and Guitang06-400 were S grade with the lowest resistance. The 12 tested sugarcane varieties(clones) were clustered according to the DSI, and the result agreed with that of resistance grading. The incidence of pokkah boeng disease showed regional difference in Guangxi. The sugarcane areas of Chongzuo, Liuzhou and Hechi were the most serious, followed by Beihai, and Baise and Nanning were the least serious.

Conclusion There were distinct differences among different sugarcane areas, among varieties(lines)and among planting seasons regarding the susceptibility and resistance against pokkah boeng disease.