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Etiology

Pathogenicity and Host Specificity of Rhizoctonia solani Isolated from Carrots. M. P. Grisham, Former graduate research assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108, Present address of senior author: Department of Plant Sciences, Texas A&M University, College Station 77843; N. A. Anderson, professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Phytopathology 73:1564-1569. Accepted for publication 14 June 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1564.

Twenty-eight isolates of Rhizoctonia solani representing anastomosis groups (AG) 1, 2, 4, and 5 were obtained from cankered carrots and hymenia formed on carrot petioles in Minnesota. Isolates differed in the type and amount of disease they caused and in host specificity on carrots, radishes, and potatoes. One AG1 isolate and six AG4 isolates caused damping-off of carrot seedlings, slight damage to mature carrot roots, and lesions on radish roots. The AG2 isolates were divided into two groups based on anastomosis tests and pathogenicity on carrot and radish. Fourteen AG2 type 2 isolates caused damping-off of carrot seedlings and cankers on mature carrot roots, and two representatives of this group caused lesions on radish roots. A second group of three AG2 type 1 isolates, obtained from hymenia on petioles of carrots, was nonpathogenic on seedling or mature carrots, but caused lesions on radish roots. The AG5 isolates were nonpathogenic on carrot seedlings or roots, or radish roots.