Race differentiation in Pyrenophora tritici-repentis and survey of physiologic variation in western Canada

Four hundred and seventy isolates of the wheat leaf spot pathogen, Pyrenoph ora tritici-repentis, were collected from the Canadian Prairies during rout ine annual surveys of leaf spot diseases from 1990 to1994. A differential s et of spring wheat lines was inoculated with a conidial suspension of each isolate to determine virulence patterns and race frequency. Races 1 and 2 w ere predominant in all years and, together, represented more than 90% of th e population. Isolates of race 4 were found at low levels from 1990 to 1992 . In 1994 only, three isolates of race 3 were detected. Isolates of race 3 were all from the Swift Current (Saskatchewan) region and were obtained fro m durum wheat. The wheat differential set and the virulence patterns of the known races of P. triticirepentis are described.