Number of Colonies Produced by 22 Isolates of Powdery Mildew on Primary Leaves of 10 Barley Cultivars

Primary leaves of 10 barley cultivars were uniformly inoculated with 22 virulent powdery mildew isolates using a jet spore trap. The number of colonies per unit area leaf was counted. Significant differences in number of colonies among cultivars were found, indicating different degrees of susceptibility among cultivars. While cultivars were rather consistent in their rankings for number of colonies produced by most isolates, interactions between some cultivars and isolates were found. In spite of great differences in geographical origin of cultivars and isolates, the interactions were not associated with origin.