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Physiologic Specialization of Puccinia triticina in Canada in 1997

In 1997, leaf rust of wheat (Triticum aestivum), caused by Puccinia triticina, was widespread throughout the prairies of western Canada. Warm summer temperatures with frequent dew periods favored spread of the disease in wheat fields in Manitoba, Saskatchewan, and Alberta. The leaf rust epidemic of 1997 was the most widespread and severe in western Canada since 1991. The Canada Prairie Spring wheat cultivars (AC Vista, AC Foremost, AC Crystal) were susceptible to leaf rust, while the bread wheats (AC Domain, AC Barrie, AC Cora, AC Majestic) were more resistant. Forty-seven virulence phenotypes of leaf rust were described in 1997 using 16 near-isogenic differential lines of Thatcher wheat. Phenotypes with virulence to Lr16 comprised 16% of the isolates in Manitoba and Saskatchewan in 1997. Many recently released Canadian spring wheats have Lr16 in addition to adult plant resistance genes. Thirty-three isolates also were tested for virulence to plants with adult plant resistance genes Lr12, Lr13, Lr34, and Lr13,34. Most isolates were virulent to genes Lr12 and Lr13. All isolates had lower infection types on lines with Lr34 compared with the susceptible line Thatcher.