Abstract
The virulence of 19 strains of E. amylovora was compared by inoculating several apple [Malus pumila, M. domestica] cultivars in orchard tests conducted during 2 growing seasons. The virulence of 6 strains was compared on 5 cultivars during both growing seasons. Virulence was measured by determing the percent of current season''s shoot length that developed fire blight symptoms. There was a significant cultivar .times. strain interaction. E. amylovora strain 266 was differently virulent to plants of ''Quinte'' apple in both seasons of orchard tests. Greenhouse tests confirmed the differential virulence of this strain for ''Quinte''.