VIEW ARTICLE

Ecology and Epidemiology

Irrigation Water as a Source of Inoculum of Soft Rot Erwinias for Aerial Stem Rot of Potatoes. M. R. Cappaert, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; M. L. Powelson(2), G. D. Franc(3), and M. D. Harrison(4). (2)Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902; (3)San Luis Valley Research Center, Colorado State University, Center 81125; (4)Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Phytopathology 78:1668-1672. Accepted for publication 6 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1668.

Seed pieces from a single seed lot of potato cultivar Russet Burbank were planted at two production areas in Oregon and Colorado in 1985 and 1986. Plots were established in fields irrigated from either surface- or well-water sources. Seed tubers, field soil, irrigation water, symptomless leaflets, and stems with aerial stem rot symptoms were assayed for the presence of soft rot erwinias. More than 95 and 90% of all strains recovered from Oregon and Colorado sources, respectively, were Erwinia carotovora subsp. carotovora. A total of 3,556 strains of E. carotovora were tested serologically against 21 different antisera by Ouchterlony agar double diffusion. In Oregon, seven different serogroups were detected in irrigation water first during the season, then on leaflets, and later in diseased stems. In Colorado, five different serogroups were detected in irrigation water before or at the same time they were detected on potato leaflets. However, only one plant developed aerial stem rot symptoms. In Oregon, 39% of the serogroups identified were common to irrigation water, leaflets, and diseased stems, whereas in Colorado 50% of the serogroups identified were common to irrigation water and leaflets. Contaminated water sources are a potential source of inoculum for aerial stem rot in Oregon.