Physiologic specialization of wheat leaf rust (Puccinia triticina) in Canada in 1999¹

Abstract

There were high levels of wheat leaf rust in the eastern prairies of Canada in 1999. Late-seeded crops were subjected to heavy inoculum pressure and favorable conditions for rust infection. A total of 38 virulence phenotypes were identified from 394 Puccinia triticina isolates collected from leaf rust infected wheat plants across Canada. The most common virulence phenotypes were MBDS (42.1%), TGBJ (16.0%), and THBJ (14.5%). Many current spring wheat cultivars contain the resistance gene Lr16, which was less effective in 1999 than in previous years. In Manitoba and Saskatchewan the proportion of virulence phenotypes virulent to Lr16, such as TGBJ and THBJ, increased from 24.3% in 1998 to 38.0% in 1999. This continues an annual trend of increasing Lr16 virulence that started in 1995. Most of the virulence phenotypes virulent to Lr16 were also virulent to the adult plant resistance gene Lr13, which is found in combination with Lr16 in some current spring wheat cultivars. The virulence phenotypes identified from Alberta, and their relative proportions, were similar to those from Manitoba and Saskatchewan. Although there were only 36 isolates from Ontario, nine of the 15 virulence phenotypes identified were unique to eastern Canada. Virulence to Lr18 was also detected in Ontario but not from western Canada. The data are consistent with the hypothesis that the eastern Canadian population is distinct from the western Canadian population.

Keywords:

• virulence
• brown rust