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The Relative Survival Ability of Pathogenic Types of Puccinia striiformis in Mixtures. J. F. Brown, Postdoctoral Research Associate, Department of Botany and Microbiology, Montana State University, Bozeman 59715; E. L. Sharp, Professor, Department of Botany and Microbiology, Montana State University, Bozeman 59715. Phytopathology 60:529-533. Accepted for publication 22 October 1969. DOI: 10.1094/Phyto-60-529.

The relationship between the relative survival ability and the number of genes for virulence in two pathogenic types of Puccinia striiformis was studied on susceptible wheat varieties, using an albino mutant as a marker. The relative survival ability and the host range of the albino culture was identical with that of the wild type from which it was derived. When urediospore mixtures of a rust isolate from Bonnerís Ferry, Idaho, and an albino isolate derived from a collection made at Bozeman, Montana, were used to inoculate the susceptible varieties Lemhi and Itana for successive uredial generations, the pathogenic type with the widest host range (Bonnerís Ferry) predominated at 2 C/18 C (night/day) and 15 C/24 C (night/day) temperature regimes, regardless of the original proportions of urediospores of each pathogenic type in the mixtures. However, despite the competitive advantage shown by the Bonnerís Ferry culture, the albino culture persisted in low frequencies (about 1%) after seven successive uredial generations. When the wheat variety President Riverain was inoculated with a mixture of the two pathogenic types, a marked increase in susceptibility to the albino isolate was observed. This increase in susceptibility was apparently not related to exchange of nuclei between the two pathogenic types.