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Isozyme and Virulence Variation in Asexually Reproducing Populations of Puccinia graminis and P. recondita on Wheat. J. J. Burdon, Senior research scientist, Division of Plant Industry, CSIRO, P.O. Box 1600, Canberra City, A.C.T. 2601 Australia; A. P. Roelfs, research plant pathologist, Cereal Rust Laboratory, Agricultural Research, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108. Phytopathology 75:907-913. Accepted for publication 1 February 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/Phyto-75-907.

Simultaneous isozyme and virulence surveys of North American asexual populations of Puccinia graminis and P. recondita on wheat detected marked differences between the pathogens in absolute levels of isozymic diversity and in the relative levels of isozyme and virulence diversity. In both pathogens, many virulence phenotypes were detected. In P. recondita, however, this diversity of virulence contrasted sharply with the very low level of isozymic diversity found (two phenotypes; one variable locus), while in P. graminis rust nine different isozyme phenotypes were detected. It is suggested that the two isozyme phenotypes of P. recondita present in the existing population represent past introductions, while most, if not all, of the nine isozyme phenotypes occurring in the population of P. graminis probably have their origin in the sexual population extant in the Great Plains in the 1920s.