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Susceptibility of Musk Thistle and Related Composites to Puccinia carduorum. D. J. Politis, Research associate, Department of Plant Pathology, Pennsylvania State University, University Park 16802; A. K. Watson(2), and W. L. Bruckart(3). (2)Associate professor, Macdonald College, McGill University, Ste-Anne-de-Bellevue, Quebec H9X 1C0 Canada; (3)Research plant pathologist, USDA, ARS, Plant Disease Research Laboratory, Frederick, MD 21701. Phytopathology 74:687-691. Accepted for publication 11 February 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-687.

Evaluation of the rust fungus Puccinia carduorum for biological control of musk thistle (Carduus nutans) was initiated with a host range study, the first phase in determining the potential and safety of an exotic plant pathogen for use in biological weed control. Representatives of the 13 tribes in the Asteraceae (26 genera and 63 species) were tested for susceptibility to P. carduorum. Only members of the subtribe Carduineae in the tribe Cynareae were susceptible under greenhouse conditions. Most collections of musk thistle from the United States, Canada, and France were highly susceptible. Carduus thoermeri and Cynara scolymus (globe artichoke) also were susceptible to infection. Pustules occurred on six additional species of Carduus, eight Cirsium spp. and Cynara cardunculus. Seedlings of globe artichoke were much more susceptible to infection than older plants grown from seed or crowns. Further work, now in progress, will determine the impact of P. carduorum on globe artichoke, the only species of economic importance found susceptible to the fungus under greenhouse conditions.