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Pectolytic Erwinia spp. in the Root Zone of Potato Plants in Relation to Infestation of Daughter Tubers. S. H. De Boer, Former Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin–Madison, Madison, WI 53706, Current address: Agriculture Canada, Research Station, 6660 N.W. Marine Drive, Vancouver, B.C., Canada V 6T 1X2 ; D. A. Cuppels(2), and A. Kelman(3). (2)(3)Former Graduate Research Assistant and Professor, respectively, Department of Plant Pathology, University of Wisconsin–Madison, Madison, WI 53706; (2)Current address: Department of Plant Pathology, University of Nebraska, Lincoln, NE 63503. Phytopathology 68:1784-1790. Accepted for publication 16 June 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1784.

Populations of pectolytic Erwinia spp. in the root zones of potato plants (cultivar Sebago) grown from Erwinia-infested seed pieces were assayed at periodic intervals during two growing seasons. Populations of E. carotovora usually were not detected until seed pieces decayed, at which time high populations were observed; thereafter, populations were variable until tubers were harvested. The maximum number of cells of E. carotovora per gram dry wt of roots plus soil detected in root zone samples was 3 × 108. Cells of E. carotovora also were detected in soil sampled between plants, but in smaller numbers than in the root zone. Although few plants showed symptoms of blackleg during the growing season, almost all tubers were infested with E. carotovora at harvest. Both E. carotovora var. carotovora and E. carotovora var. atroseptica were isolated consistently from the root zones of growing plants and from tubers before harvest and in storage. During a 9-mo storage period at 5 C the percentage of tubers from which E. carotovora could be isolated decreased from about 90% to 33%. Certain daughter tubers produced on Erwinia-free Russet Burbank and Sebago stem cuttings planted in field plots became infested with E. carotovora (5-80%) by the time of harvest. With one exception, the strains obtained in isolations from the tubers on a crystal violet pectate medium were characterized as E. carotovora var. carotovora. However, when a specific fluorescent antibody stain procedure was used, cells of E. carotovora var. atroseptica were detected in 9/40 of these tubers.

Additional keywords: bacterial soft rot.