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Differential Host Pathogen Interactions Among Cultivars of Apple and Strains of Erwinia amylovora. J. L. Norelli, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; H. S. Aldwinckle(2), and S. V. Beer(3). (2)Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456; (3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 74:136-139. Accepted for publication 30 July 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-136.

The virulence of 19 strains of Erwinia amylovora was compared by inoculating several apple cultivars in orchard tests conducted during two growing seasons. The virulence of six strains was compared on five cultivars during both growing seasons. Virulence was measured by determining the percent of current season' s shoot length that developed fire blight symptoms. There was a significant cultivar strain interaction. E. amylovora strain 266 was differently virulent to plants of apple cultivar Quinte in both seasons of orchard tests. Greenhouse tests confirmed the differential virulence of this strain for Quinte.

Additional keywords: apple breeding, disease resistance, Malus pumila, Malus domestica, phytopathogenic bacteria.