Identification of physiological races of powdery mildew on melon in Gansu province.

Ten pathogen collections of powdery mildew,came from different melon(Cucumis melo L.)grown areas of Gansu province,were detected by standard system for identification of powdery mildew.According to the internationally recognized melon differential standards for identifying races of powdery mildew,we preliminarily confirmed that there were race 1 and race 2France of Podosphaera xanthii,and additional physiological race 7 of powdery mildew in Gansu province.Race 1 of Podosphaera xanthii occurred more frequently,which was the prevailing race.