Virulence in populations of Puccinia graminis f.sp. tritici in Canada from 1952 to 1998: a non-parametric analysis

Abstract

Six hundred and twenty six isolates of Puccinia graminis f.sp. tritici that were collected and stored between 1952 and 1998 were identified using 32 single-gene differential wheat lines. These pathotypes represented isolates from field surveys, nursery collections, and from greenhouse experiments. Infection type data was converted to a binary data matrix with a 0 (resistant) or 1 (susceptible) numeral assigned to each isolate for each differential line. The Gower coefficient of similarity was determined for every pair of isolates, then they were clustered using the non-parametric cluster analysis MODECLUS. Eight significantly different clusters were obtained from an overall heterogeneous database of 405 unique pathotypes representing all regions of Canada. For further analysis, isolates obtained only from field survey collections were selected and divided by region of collection into Pacific (45 pathotypes), prairie (191 pathotypes), and eastern Canadian (83 pathotypes) populations. The Pacific population, which was both sexually and asexually reproducing, consisted of two clusters. The prairie population, strictly asexually reproducing, consisted of nine clusters, and the eastern population, which may be partially sexually reproducing, had three clusters. The Pacific population was shown to be significantly different from the prairie and eastern populations, while the prairie and eastern populations were less distinct. The pathotype composition of the regional clusters, reliability of cluster segregation using non-parametric analysis, and usefulness of the data to contribute to a revised nomenclature of P. graminis f.sp. tritici, are evaluated.Key words: stem rust, black rust, wheat, specific virulence.