In 1991, leaf rust of wheat (Triticum aestivum) caused by Puccinia recondita f. sp. tritici was first observed on June 11 in spring wheat fields in southeastern Manitoba. Leaf rust severities were very high in susceptible winter wheats and in moderately resistant spring wheat cultivars by the end of July throughout Manitoba following the early arrival of urediniospores. Abundant rainfall in June and July provided excellent conditions for the rust to increase and spread in Manitoba and eastern Saskatchewan. Leaf rust caused significant yield losses, averaging 10% in the moderately resistant spring wheat cultivars. Yield losses in the highly resistant spring wheats were minimal, although higher levels of leaf rust infection were also noted on these cultivars as a result of the high inoculum pressure. A total of 20 virulence phenotypes of the fungus in Canada were detected using 15 isogenic Thatcher differential lines. Isolates with virulence to resistance gene Lr11 continued to increase in prevalence in the prairie region, while isolates with virulence to Lr24 and Lr26 declined slightly in this region from 1990. The prevalent virulence phenotypes in Ontario and British Columbia remained relatively unchanged from previous years.
