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Physiologic Specialization and Pathogen Aggressiveness in Stripe Rust. R. B. Volin, Graduate Research Assistant, Department of Botany and Microbiology, Montana State University, Bozeman, Montana 59715, Present address of senior author: University of Florida, IFAS, Agricultural Research and Education Center, Homestead 33030; E. L. Sharp, Professor of Plant Pathology, Department of Botany and Microbiology, Montana State University, Bozeman, Montana 59715. Phytopathology 63:699-703. Accepted for publication 18 December 1972. DOI: 10.1094/Phyto-63-699.

Urediospores of stripe rust, Puccinia striiformis were collected from graminaceous hosts throughout the northwestern region of the USA. These were used to inoculate wheat and barley cultivars selected for their potential ability to differentiate genes for virulence among rust isolates. Many cultivars were unable to discriminate among any of the isolates under a controlled environment. By using wheat cultivars ‘Chinese 166’, ‘Druchamp’, ‘Leeds’, ‘Moro’, ‘Medeah’, ‘President Riverain’, ‘Marfed’, and ‘Red River 68’, 11 P. striiformis races were distinguished. The aggressiveness of 13 stripe rust isolates was measured by the ability of urediospores to germinate at 5, 10, 15 and 20 C. Two isolates, both virulent on Chinese 166, germinated at all temperatures.