Evaluation of Mature Apple Fruit from Washington State for the Presence of Erwinia amylovora. R. G. Roberts, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Tree Fruit Research Laboratory, Wenatchee, WA 98801. S. T. Reymond, and R. J. McLaughlin. Biological Laboratory Technician, U.S. Department of Agriculture, Agricultural Research Service, Tree Fruit Research Laboratory, Wenatchee, WA 98801; and Postdoctoral Associate, U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Philadelphia, PA 19118. Plant Dis. 73:917-921. Accepted for publication 25 April 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/PD-73-0917.

Erwinia amylovora was not detected in core tissues or aqueous sonicates from 1,555 mature, symptomless fruit harvested from blighted trees of seven apple cultivars grown at five locations in Washington State. Strains typical of Enterobacteriaceae on selective media (Miller-Schroth medium alone or replica-plated onto the crystal violet medium of Ishimaru and Klos) were characterized by phenotypic and pathogenicity tests as belonging in the E. herbicola, Enterobacter agglomerans, Escherichia adecarboxylata complex. E. amylovora was not detected in either year. Detection sensitivities were about 20 and 30 bacterial cells per fruit for external and internal assays, respectively. None of the strains from either year were pathogenic on apple seedlings. Thus, healthy, symptomless apples produced in Washington State are unlikely to harbor detectable populations of E. amylovora.

Keyword(s): plant quarantine, postharvest.