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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. |