Physiologic specialization ofPuccinia triticinain Canada in 20051

Abstract

Collections of Puccinia triticina, the causal agent of wheat (Triticum aestivum) leaf rust, were sampled across Canada in 2005 to determine the virulence spectrum of this pathogen and detect changes in virulence to important resistance genes. Forty virulence phenotypes were identified from 420 P. triticina isolates. Four virulence phenotypes, MBBJ, NBBR, TDBG, and TLGJ, were identified from five isolates collected in Quebec and six virulence phenotypes, MBJD, MCDS, MCPS, MFDS, MFPS, and TCTF, from six isolates from Ontario. Thirty-five virulence phenotypes were identified from the 396 isolates collected in the eastern prairie region (Manitoba and eastern Saskatchewan) of Canada, with TDBG (46.7%), TBBG (10.9%), and TDBJ (9.1%) being the most common phenotypes. Virulence phenotypes TDBG and TBBG and other similar phenotypes found in high frequency in 2005 had some unusual virulence characteristics, including avirulence to LrCen, Lr14a, and Lr20, which had previously been rare in Canada. Four virulence phenotypes, MBBJ, MBDS, MBGJ, and MBPS, were identified among 13 isolates from Alberta or British Columbia. Of 81 representative isolates, 74, 77, 4, and 67 isolates were virulent to wheat lines with the adult plant resistance genes Lr12, Lr13, Lr35, and Lr37, respectively. None of these were virulent to Lr22a. When tested on an extended set of wheat leaf rust differentials, 46, 43, 74, 60, 51, and 39 of the 81 isolates were virulent to the seedling resistance genes Lr3bg, Lr14b, Lr15, Lr20, Lr23, and Lr28, respectively, yet no virulence was detected to Lr19, Lr21, Lr25, Lr29, or Lr32