Isozyme and Virulence Variation in Asexually Reproducing Populations ofPuccinia graminisandP. reconditaon Wheat

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Abstract
Simultaneous isozyme and virulence surveys of North American asexual populations of P. 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 (2 phenotypes: one variable locus), while in P. graminis rust 9 different isozyme phenotypes were detected. It is suggested that the 2 isozyme phenotypes of P. recondita present in the existing population represent past introductions, while most, if not all, of the 9 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.