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Host Range of Rhizomonas suberifaciens, the Causal Agent of Corky Root of Lettuce. Ariena H. C. Van Bruggen, Assistant Professor, Department of Plant Pathology, University of California, Davis 95616. Philip R. Brown, and Kenneth N. Jochimsen. Post Graduate Research Assistants, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 74:581-584. Accepted for publication 26 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0581.

Greenhouse experiments were conducted to investigate if Rhizomonas suberifaciens, the causal agent of corky root (CR) of lettuce, was pathogenic on various winter cover crops, vegetable crops, and weed species in eight plant families. R. suberifaciens induced CR symptoms on endive, common sowthistle, and prickly lettuce of the Compositae but not on safflower and sunflower. The pathogen was reisolated from each of the susceptible hosts, and the reisolated strains were similar to the original strain in affinity to polyclonal antibodies and pathogenicity on lettuce. Inoculation of species of the Chenopodiaceae, Cruciferae, Cucurbitaceae, Gramineae, Leguminosae, Solanaceae, and Umbelliferae with R. suberifaciens did not result in visible symptoms, except for a hybrid carrot cultivar that reacted with root proliferation and orange-brown discoloration of feeder roots. However, the pathogen was not reisolated from these plants. An open-pollinated carrot cultivar did not develop symptoms. R. suberifaciens was isolated from the root surface of inoculated broad bean, safflower, and soybean plants without CR symptoms. Strains of R. suberifaciens were also isolated from field-grown tomato, melon, sowthistle, and prickly sowthistle with CR symptoms. These strains were pathogenic on lettuce and sowthistle but not on tomato and melon. So far, only members of the Compositae closely related to lettuce have shown susceptibility to R. suberifaciens.