Physiologic specialization of wheat leaf rust (Puccinia triticina) in Canada in 2002

Abstract

Forty virulence phenotypes of Puccinia triticina were identified from 295 isolates collected across Canada in 2002 on 16 Triticum aestivum ‘Thatcher’ near-isogenic lines. The most frequent virulence phenotypes across Canada were MBDS (30.2%), TGBJ (22.0%), TBBJ (9.5%), and TBDS (7.8%). There were 10 virulence phenotypes identified among 24 isolates from Quebec; MBRK (29.2%), TBRJ (16.7%), MBRJ (12.5%), and TLGJ (12.5%) were the most frequent. Ten virulence phenotypes were identified among 22 isolates from Ontario, with PCLR and PCMR (both 22.7%) being the most frequent. There were 25 virulence phenotypes identified from 234 isolates collected in Manitoba and southeastern Saskatchewan; MBDS (32.9%), TGBJ (27.4%), and TBBJ (11.5%) were the most frequent. The frequency of virulence to Lr16 declined in Manitoba and Saskatchewan from 74.1% in 2001 to 33.3% in 2002 while the frequency of virulence to Lr17 increased from 23.8% in 2001 to 53.4% in 2002. Five virulence phenotypes were identified from 15 isolates collected in Alberta. These were MBDS (11 isolates), TBBJ, TBDS, TCRK, and TGBJ (all one isolate each). A subsample representative of the field isolates collected in 2002 was tested for virulence on adult plants. All 71 isolates tested were avirulent to adult-plant resistance genes Lr22a, Lr34, and Lr3, and to seedling genes Lr21 and Lr32 which are best expressed in adult plants. The isolates varied for virulence to adult-plant resistance genes Lr12 and Lr37, and only one isolate was avirulent to Lr13.