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A Bacteriophage-Typing System for Surveying the Diversity and Distribution of Strains of Erwinia carotovora in Potato Fields. D. C. Gross, Department of Plant Pathology, Washington State University, Pullman 99164-6430; M. L. Powelson(2), K. M. Regner(3), and G. K. Radamaker(4). (2)Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; (3)(4)Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 81:220-226. Accepted for publication 19 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-220.

A bacteriophage-typing system was developed and used to survey the diversity and distribution among strains of Erwinia carotovora subsp. carotovora and E. c. subsp. atroseptica from the rhizospheres and stems of potatoes grown in the Columbia Basin of the Pacific Northwest. With a phage enrichment method and strains of E. carotovora from 25 serogroups as hosts, 13 phages displaying distinct host-range activities were isolated from potato and soil samples. In addition, a potato strain of E. chrysanthemi was used to isolate phage N (Ech-3), which did not infect strains of E. carotovora. All strains of E. c. atroseptica were sensitive to at least one of five phages, and strains in both subspecies of E. carotovora were sensitive to phage isolates C (304-32), E (101-1), and J (465-2-3-6). In three commercial fields in 1981, the phage groups occurring at mid-season were AEJ, E, and EJ for E. c. atroseptica and G, GI, EF, and F for E. c. carotovora; total rhizosphere and stem populations of E. carotovora from symptomless plants ranged from 2 103 to 3 106 cfu/g (fresh weight) at midseason. In 1982, numbers of E. carotovora recovered from stems and rhizospheres increased from low and sporadic levels in late May to over 105 cfu/g (fresh weight) by early July. Phage group EJ of E. c. atroseptica was predominant among the strains from Norgold Russet and Russet Burbank seed tubers, and it composed 3543% of the total strains of E. carotovora recovered from rhizosphere and stem samples later in the season. No specific phage group was clearly associated with cultivar, date of isolation, and either rhizosphere or stem samples. Of the 389 strains of E. carotovora collected over a 2-yr period, 44% and 48% were typed, respectively, to one of 14 phage groups and one of nine serogroups. All strains of E. c. atroseptica were members of sero-group I, whereas IV and XXXVII were the two most common serogroups of E. c. carotovora. A few phage groups and serogroups were composed of the same strains, including phage group CDGIM and serogroup XVIII, phage groups E and EF and serogroup XXIX, and phage groups D and DL and serogroup XXXVII.

Additional keywords: bacterial soft rot, black leg, Solanum tuberosum.