Physiologic specialization of Puccinia recondita f. sp. tritici in Canada in 1996

In 1996 leaf rust of wheat (Triticum aestivum) caused by Puccinia recondita f. sp, tritici was first observed on June 26 in winter wheat fields in southern Manitoba. Cooler than normal spring temperatures delayed wheat planting and also the onset and subsequent spread of leaf rust infections in Manitoba in 1996. Only trace levels of leaf rust infection were-found in farm. fields in southern Manitoba and Saskatchewan due to the combination of weather conditions and the increased planting of highly resistant cultivars such as AC Domain and AC Cora, Susceptible cultivars grown in rust nurseries in Manitoba had high levels of leaf rust infections. Fifty virulence phenotypes of P. recondita f. sp. tritici were identified in 1996 in Canada using 16 near-isogenic Thatcher differential wheat lines. The most important change in virulence in 1996 was the rapid increase in phenotypes with virulence to Lr17 and LrB in Manitoba and Saskatchewan. Phenotypes with virulence to Lr16 did not increase from the 1995 level. Twenty-five isolates were also tested for virulence to adult plants of Thatcher lines with genes Lr22b, Lr12, Lr13, Lr34, and Lr13,34. Two of the isolates had low infection type to Thatcher, which has Lr22b. The remaining isolates were polymorphic for virulence to Lr12 and Lr13 and had lower infection types on Thatcher lines with Lr34 and Lr13,34 compared to the recurrent parent Thatcher.