Physiologic specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2006

Puccinia triticina, the causal agent of wheat leaf rust, was collected from across Canada in 2006 to determine the virulence spectrum of this pathogen. From 353 single-pustule isolates, 31 virulence phenotypes were identified. There were 20 virulence phenotypes among 315 isolates from Manitoba and Saskatchewan. The most common phenotypes were TDBG (56.2%), TDBJ (18.7%), and MFPS (5.4%). The frequency of virulence to Lr24 (86.3%) was very high, whereas it was very low for Lr16 (0.3%) when compared with years prior to 2005. From 19 isolates collected in Ontario, 14 isolates were MFDS; 2 were TBDS; and 1 isolate each were MBMR, MDNS, and TFPJ. MFDS was the only virulence phenotype identified from three isolates collected in Quebec. There was a similar rise in 2006 in the frequency of virulence to Lr24 in Ontario (84.2%) and Quebec (100%), although different virulence phenotypes were responsible for this increase in eastern Canada compared with western Canada. Nine virulence phenotypes were identified among 16 isolates from Prince Edward Island (PEI). The most common of these were MCPR (four isolates), MBPR (three isolates), and MBDS and MDDS (two isolates each). Five of these nine virulence phenotypes were not found in the rest of Canada in 2006 nor in the past 5 years. This is an indication that the PEI population is somewhat distinct from those in the other regions of Canada. When 50 isolates representing most of the virulence phenotypes and the different regions in Canada were inoculated onto adult plants, there were 47, 45, 1, and 30 isolates virulent to Li12, Lr13, Lr35, and Lr37, respectively. These 50 representative isolates were also inoculated on 12 additional 'Thatcher' near-isogenic lines at the seedling stage, and there were 25, 46, 48, 50, 43, 43, 2, and 25 isolates virulent to Lr2b, Lr3bg, Lr14b, Lr15, Lr20, Lr23, Lr25, and Lr28, respectively. All isolates tested were avirulent to Lr19, Lr21, Lr22a, Lr29, Lr32, and Lr34.