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Disease Note.

The Occurrence of Uromyces punctatus on Astragalus mulfordae, a Rare Vascular Plant from Western Idaho and Eastern Oregon. W. R. Owen, Boise National Forest, 1750 Front Street, Boise, ID 83702. J. T. Hoffman, Forest Pest Management, Boise Field Office, 1750 Front Street, Boise, ID 83702, J. F. Hennen, Arthur Herbarium, Purdue University, IN 47907, and L. C. Smithman, Smithman Consulting Service, 819 N. 18th Street, Boise, ID 83702. Plant Dis. 78:1217. Accepted for publication 19 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1217E.

In June 1993 a collection of Astragalus mulfordae M. E. Jones, a federal candidate 1 species under the Endangered Species Act of 1973 (as amended), which is endemic to coarse sandy soils in western Idaho and adjacent Oregon, was collected with lesions on its flowering stems. These lesions were determined to be the uredinial sori of Uromyces punctatus J. Schrot., a rust that commonly infects species of Astragalus and Oxytropis. Because the host species is rare, there is a concern that the pathogen may negatively affect the viability of host plant populations (per the Endangered Species Act Section 4a 1C). Two herbaria known to have extensive collections of A. mulfordae from throughout its known range were searched (Harold M. Tucker Herbarium of Albertson's College of Idaho and the Snake River Plains Herbarium of Boise State University). All collections of A. mulfordae in both herbaria were inspected for evidence of infection. The collections represented specimens from throughout the host species' range and from 1954 to 1993. Every specimen observed that had been collected in June (the time when the host plant is fruiting) or later displayed fungal infections. Specimens collected earlier in the year were generally asymptomatic. The rust was noted on A. mulfordae collections from each of the host's major population centers: Boise, Idaho; Weiser, Idaho; and Malheur County, Oregon. The aecial hosts for U. punctatus are expected to be species of Euphorbia, however euphorbs are not known to occur in A. mulfordae habitats. Collections of U. punctatus on A. mulfordae are deposited in the Arthur Herbarium at Purdue University.

Reference: (1) J. C. Arthur. Manual of the Rusts in the United Stales and Canada. Hafner Publ., New York, 1962.