Physiologic specialization of wheat leaf rust [Puccinia triticina] in Canada in 2000

Abstract

Virulence in the wheat leaf rust [Puccinia triticina] population was surveyed throughout Canada in 2000, as part of an ongoing effort to monitor changes that could affect Canadian wheat. Twenty-three virulence phenotypes, differentiated on 16 wheat lines with single resistance genes, were detected from 122 infected-leaf collections. Virulence phenotypes MBDS (54.1%), TGBJ (21.6%), and THBJ (5.7%) were most frequently identified. The overall distribution of virulence phenotypes in Canada in 2000 was similar to that in 1999, although seven virulence phenotypes (MBPS, PBDG, PBDQ, SBDG, SGBJ, TBPS, and TGMJ) found in 2000 were not present in either 1998 or 1999. There were four virulence phenotypes (MBDS, 50.0%; TKBJ, 25.0%; THBJ, 12.5%; and THMJ, 12.5%) detected among eight isolates from Ontario. Virulence phenotypes TKBJ and THMJ were relatively rare in other regions. Of 21 virulence phenotypes detected among 339 isolates from Manitoba and Saskatchewan, the most common were MBDS (56.0%), TGBJ (22.4%), and THBJ (5.6%). From Alberta, there were six virulence phenotypes among 19 isolates and the most common were PBDG (42.1%), MBDS (21.1%), and TGBJ (15.8%). While each region had unique virulence phenotypes, the virulence phenotypes MBDS and THBJ were common to all regions. The percentage of virulence to resistance gene Lr16 was 35.5%, which is similar to that in 1999 (35.3%). Twenty-three of the 27 isolates virulent to Lr16 that were tested on adult plants were also virulent to Lr13 and would be virulent to the predominant wheat cultivar in western Canada, 'AC Barrie', which contains these resistance genes. Less than 1% of the isolates in Canada were virulent to wheat lines containing either Lr9, Lr11, or Lr18 while more than 95% were virulent to wheat lines containing either Lr1, Lr3, Lr10, or Lr14a. Frequency of virulence was intermediate for resistance genes Lr2a, Lr2c, Lr16, Lr24, Lr26, Lr3ka, Lr17, Lr30, and LrB. From a subset of 49 isolates, representing 21 of the 23 virulence phenotypes identified in 2000, 40 were virulent to both the adult-plant genes Lr12 and Lr13. Of the 49 isolates, none were virulent to the seedling resistance genes Lr19, Lr21, Lr29, and Lr32, all were virulent to Lr20 and Lr15, while some were virulent to Lr2b, Lr3bg, Lr14b, Lr23, Lr25, and Lr28.