Studies on winter survival strategies of Erysiphe pisi in Manitoba

Erysiphe pisi, the causal agent of powdery mildew, is an important disease of field pea in western Canada, but very little information is available on whether or how it survives the winter in the prairie provinces. Therefore, studies were conducted of the role of cleistothecia on pea stubble, the possibility of seed transmission, and survival on other plant species. In 1996 and 1997 cleistothecia were abundantly formed on heavily infected plants in late August to September under field conditions. Microscopic observation during the winter indicated that by May more than 95% of the cleistothecia had degenerated under field conditions, whereas in samples stored at room temperature, 50% of the cleistothecia contained intact ascospores. When seeds from plants heavily infected with powdery mildew were grown in a greenhouse, none of the 4200 plants examined developed powdery mildew symptoms, suggesting that the possibility of transmission of E. pisi through infected seed is remote. When isolates of powdery milde...