Physiologic specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2008

Abstract

Commercial fields and research plots of wheat across Canada were surveyed for leaf rust during 2008. Leaf samples infected with the causal fungus, Puccinia triticina, were used to generate 407 single pustule isolates, 13 from Alberta, 302 from Manitoba and Saskatchewan, 71 from Ontario, 10 from Quebec and 11 from Prince Edward Island. Single pustule isolates were tested for virulence to 16 lines of ‘Thatcher’ wheat with single leaf rust resistance genes. Forty-six virulence phenotypes were identified; the most common were TDBJ (23.6%), TDBG (23.1%) and MLDS (18.9%). The frequency of virulence to both Lr9 and Lr17 increased compared with 2007, whereas it decreased for Lr24 and Lr2a. The populations from eastern Canada were more diverse than those from western Canada and contained many unique virulence phenotypes, and virulence to gene Lr18, which was not found in western Canada. Fifty-five isolates, representing each of the virulence phenotypes, were tested on six and 12 additional differential wheat lines at the adult and seedling stages, respectively. On the adult plant differentials, no isolates were virulent to Lr22a or Lr34, whereas all isolates except two were virulent to Lr13, and virulence varied for Lr12, Lr35 and Lr37. On the additional seedling differentials, all isolates were avirulent to Lr19, Lr21, Lr29 and Lr32, and only one isolate was virulent to Lr25. All isolates had similar infection types to Lr2b and Lr2a, varied in virulence to Lr3bg, Lr14b, Lr20, Lr23 and Lr28, and except for two were virulent to Lr15.