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Assessment of Vegetative Compatibility and Virulence of Verticillium dahliae Isolates from Idaho Potatoes and Tester Strains. C. A. Strausbaugh, Department of Plant, Soil, and Entomological Sciences, Division of Plant Pathology, University of Idaho, Research and Extension Center, 3793 North 3600 East, Kimberly 83341; Phytopathology 83:1253-1258. Accepted for publication 20 August 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1253.

Thirty-three wild-type strains of Verticillium dahliae were isolated from potato stems from 25 fields in southern Idaho. These strains were all assigned to vegetative compatibility group (VCG) 4 based on pairings of nitrate-nonutilizing mutants induced on medium containing chlorate. The Idaho strains and VCG 4 testers were divided into nine subgroups. These subgroups relate to previously designated VCG 4 subgroups as follows: 4A = 4A1, 4A2, 4A3, 4A4, 4A5, and 4A6; 4A/B = 4A/B1; and 4B = 4B1 and 4B2. Subgroup 4A contained 29 of the 33 Idaho strains. All subgroup 4A strains and most of the strains from subgroups 4A/B and 4B were pathogenic in greenhouse studies. When placed into three subgroups for analysis, the strains from subgroup 4A were significantly more virulent than those from subgroups 4A/B and 4B. However, not all individual subgroup 4A strains were significantly more virulent than strains in subgroups 4A/B and 4B. This continuum of virulence and genetic diversity among V. dahliae strains was evenly distributed throughout potato-growing areas in southern Idaho.

Additional keywords: pathotype.