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Disease Note

Puccinia jaceae var. diffusa and P. acroptili on Knapweeds in Washington. F. M. Dugan, Department of Plant Pathology, Washington State University, Pullman 99164-6430. L. M. Carris, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Plant Dis. 76:972. Accepted for publication 11 March 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0972E.

Diffuse knapweed (Centaurea diffusa Lam.) and Russian knapweed (C. repens L.) were found infected with rusts in Wenatchee, Washington, in mid-September 1991. The rust on diffuse knapweed had chestnut brown teliospores 28-38.5 × 24-28 µm, scarcely constricted at the septum, with walls 1.7-2.8 µm thick. Urediniospores were 24-32 × 22-28 µm, with two slightly supraequatorial germ pores and echinulations diminished or absent below the pores. These and other characters correspond with those of Puccinia jaceae Otth var. diffusa Savile reported in British Columbia (2). The rust on Russian knapweed had chestnut brown teliospores 32-46 × 21.5-25 µm, slightly constricted at the septum, with walls 2-5 µm thick. Urediniospores were 21-25.5 (27.5)× 20-23 µm, with three equatorial germ pores. These and other characters conform to those of P. acroptili P. Syd. & Syd. (I). This is the first report of P. j. diffusa from the United States and the first formal report of P. acroptili from Washington.

References: (1) G. B. Cummins. Mycotaxon 10:1, 1979. (2) K. Mortensen et al. Can. J. Plant Pathol. 11:322, 1989.