The powdery mildew is rarely reported on Rheum rhabarbarum (Polygonaceae).In 2003,Erysiphe polygoni was the first mentioned on R.rhabarbarum in China without morphological and molecular data.In August 2015,Powdery mildew on R.rhabarbarum in the medicinal garden was found at Jilin Agricultural University in Changchun(43.61°N,125.41°E),China.The isolate from the sample was identified as E.polygoni based on its morphological characters and internal transcribed spacer (ITS) sequence,which is firstly characterized by both biological and molecular features.Meanwhile,E.polygoni as a new pathogen on R.rhabarbarum is firstly reported in Jilin province.