Identification of physiological races of watermelon and melon powdery mildew in Shanghai.

The disease-producing germs and physiological races of six powdery mildew samples collected from the watermelon and melon cultivated by different methods in different sites of Shanghai were identified by using the current international differential hosts and standardized differential system. It was preliminarily ascertained that the melon powdery mildew was caused mainly by Podospha-era xanthii which was composed of two physiological races,or Race 1 and Race 2 France.The Race 1 was predominant,and the Race 2 France occurred only on the melon crops in Pudong New District.