Physiological specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2011
McCallum, B.D., Seto-Goh, P., Xue, A. (2017). Physiological specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2011, 39(4), 454-463. http://dx.doi.org/10.1080/07060661.2017.1386715
Plain language summary
The fungus that causes wheat leaf rust, Puccinia triticina, was sampled from across Canada in 2011 and tested for virulence to many of the common and important leaf rust resistance genes. There were 287 isolates tested, three from Alberta, 216 from Manitoba and Saskatchewan, 47 from Ontario, 11 from Quebec and ten from Prince Edward Island. In total 70 different virulence phenotypes were found among these isolates, the most common were TDBJ (12.5%), TDBG (10.5%) and MLDS (7.7%). The frequency of virulence within this population changed for many of the resistance genes compared to 2010. The most important change was the detection of virulence to Lr21 which has been used extensively in developing leaf rust resistant wheat cultivars in Canada and the USA. Though virulence was detected at a low frequency this is the first detection in Canada and has important implications on the effectiveness of resistance from Lr21, which is expected to decline if the frequency of Lr21 virulence continues to increase in future years. This virulence analysis represents part of a continuous record of annual monitoring of this important pathogen that started in the 1930s up to the present day.
© 2017 Her Majesty the Queen in Right of Canada, as represented by Agriculture and Agri-Food Canada (AAFC).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.