Physiological specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2011

Abstract

Leaf rust collections were made across Canada in 2011 and 287 single-pustule isolates were tested for virulence on 16 standard differential lines and two additional lines containing Lr21 and LrCen, respectively. Of the 70 different virulence phenotypes found in Canada during 2011, the most common were TDBJ (12.5%), TDBG (10.5%) and MLDS (7.7%), which is similar to the findings from 2010. Three isolates from Alberta each had a unique virulence phenotype. From Manitoba and Saskatchewan, 33 virulence phenotypes were found among 216 isolates, with the most common being TDBJ (16.7%), TDBG (13.9%), MLDS and TBBG (both at 9.3%). There were 29 virulence phenotypes among 47 isolates from Ontario, with MBTN (25.5%), MCTN (8.5%) predominating. Ten virulence phenotypes were found from 11 isolates in Quebec, and six virulence phenotypes among 10 isolates from Prince Edward Island. Compared with 2010, there were increases in the frequencies of virulent isolates in Canada to Lr2a, Lr2c, Lr16, Lr26, Lr3ka, Lr11 and Lr30 while there were declines in the frequencies of virulent isolates to Lr9, Lr24, Lr10 and Lr14a. When a group of 161 representative isolates were tested on five adult plant differentials, all isolates were avirulent to Lr22a, most were virulent to Lr12, Lr13 and Lr37, while only 16 were virulent to Lr35. When this same group of isolates was tested on 12 additional lines at the seedling stage, all isolates were avirulent to Lr19, Lr32, Lr29 and Lr52 and virulent to Lr15, while they differed in their reactions to Lr2b, Lr3bg, Lr14b, Lr20, Lr23, Lr25 and Lr28. Virulence for Lr21 was detected for the first time in Canada from five different virulence phenotypes, though at a low frequency (3.8%). This finding has implications for wheat breeding in Canada, since Lr21 had been completely effective since its release in the cultivar ‘AC Cora’ in 1994.