Disease Note

Fire Blight of Raspberry Caused by Erwinia amylovora in Wisconsin. M. F. Heimann, Department of Plant Pathology, University of Wisconsin-Extension, Madison 53706. G. L. Worf, Department of Plant Pathology, University of Wisconsin-Extension, Madison 53706. Plant Dis. 69:360. Accepted for publication 4 January 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-360c.

A raspberry specimen with symptoms similar to those of fire blight on apple shoots was submitted to the University of Wisconsin Plant Disease Clinic in late August 1983. The specimen had the typical 'shepherd’s crook' symptom on the terminal portion of the stem, and stem tissue of the blighted areas was dark blue-black. A bacterium isolated from the affected tissue formed smooth red-orange colonies typical for Erwinia amylovora (Barr.) Winslow et al on Miller-Schroth medium. A typical culture was sensitive to phage specific for E. amylovora. Raspberry plants in the greenhouse were inoculated with a pure culture of this strain. Soft green stem tissue of five plants each of cvs. Latham and June were inoculated by a needle-puncture method. Host response included formation of shepherd’s crooks and discoloration of the stem. Cross-inoculations of the raspberry strain to apple and of apple strains to raspberry were negative. Isolations from specimens submitted in 1984 resulted in cultures similar to those obtained previously. To our knowledge, this is the first report of fire blight on raspberry in Wisconsin.