Comparison of Puccinia graminis f.sp tritici from South America and Europe

Twenty isolates of Puccinia graminis f.sp. tritici from South America were compared with 19 from Europe using virulence, isozymes and random amplified polymorphic DNA (RAPD) markers. The isozyme and virulence patterns for the se isolates were also compared with those of 11 isolates representative of the common race clusters in North America. All three types of marker showed a level of similarity between the South American and European isolates com parable with that between isolates from the same continent. The average sim ilarity coefficients between the South American and European isolates were 0.65 for virulence, 0.67 for isozymes, and 0.70 for RAPD markers. Among Sou th American isolates the values were 0.63 for virulence, 0.64 for isozymes and 0.72 for RAPDs. For the South American and European isolates, correlati on between the similarity matrices based on RAPDs and on isozyme markers, r espectively (r = 0.52), was higher than that between the RAPD and virulence matrices (r = 0.32) or between isozyme and virulence matrices (r = 0.16). The North American isolates had a comparable level of similarity for virule nce and isozymes to both the South American and European populations. There was no clear distinction between the South American, North American and Eu ropean isolates, which is consistent with the hypothesis that these populat ions may have had a common origin.