Physiological specialization of Puccinia triticina, the causal agent of wheat leaf rust, in Canada in 2012

Two hundred and thirty-three single pustule isolates of Puccinia triticina were recovered from leaf rust infected wheat leaves from across Canada in 2012. These were tested for virulence on 16 standard differential lines and two additional lines containing Lr21 and LrCen, respectively. There were 49 different virulence phenotypes found, the most common of which were TBBG (18.9%), TNBG (15.0%), TDBJ (7.7%) and MBDS (6.4%). From Manitoba and Saskatchewan, 28 virulence phenotypes were found among 177 isolates, with the most common being TBBG (22.0%), TNBG (18.6%), TDBJ (10.2%) and MBDS (7.3%). There were 13 virulence phenotypes among 22 isolates from Ontario–MBTN (34.8%), MCGJ and TDPN (9.1% each) were the most common. Thirteen virulence phenotypes were found from 20 isolates in Quebec, with TBBG (25%), TNBG, MBDS, MBTN (each at 10.0%) being the most frequent. Two virulence phenotypes were found from among 14 isolates from Prince Edward Island, 12 isolates were TBRK, and two were TBRJ. There were some changes in virulence frequencies in 2012 compared with 2011, including increases for Lr2a, Lr2c, Lr9, Lr18 and Lr21, while there were decreases to Lr24, Lr26, Lr3ka, Lr17, LrB and Lr14a. Virulence to Lr21 was first found at 5.2% in Canada in 2011, and this increased to 7.7% in 2012. Since many Canadian wheat cultivars have Lr21, this could lead to greater susceptibility to leaf rust. However, all the Lr21 virulent isolates were found only in western Canada and in just four virulence phenotypes.