Races of Puccinia graminis on wheat, oat, and barley in Canada in 2009 and 2010

© 2015 Her Majesty the Queen in Right of Canada, as represented by Agriculture and Agri-Food Canada (AAFC).Stem rust, caused by Puccinia graminis, is an important disease on wheat, oat, and barley crops worldwide. Because the disease is primarily controlled in Canada using resistant cultivars, determining the virulence structure in pathogen populations is necessary for the early detection of novel virulent races. Surveys of wheat (Triticum aestivum), oat (Avena sativa), and barley (Hordeum vulgare) fields and trap nurseries were conducted in 2009 and 2010 across Canada to provide information on incidence and severity of stem rust infection, and to identify the virulence structure in the pathogen populations. Stem rust was not found on cultivated wheat, and was at trace levels in oat and barley fields in both years. Race QFCSC of P. graminis f. sp. tritici was dominant in 2009 (88.0% of all samples), and was the only race detected in Canada in 2010. Races MCCFC, RFCSC, and TPMKC were found at low levels (<5%) in 2009. Thirteen races of P. graminis f. sp. avenae were found in 2009, with TGD (30.4%), TJN (16.2%), TGN (14.9%), TJJ (11.2%), TJS (9.9%), and TGB (8.6%) the most frequent. Twelve races of P. graminis f. sp. avenae were found in 2010, and TGN (27.3%), TGB (19.8%), TGD and TJN (14.0% each), and TJS (9.9%) were the most frequent. Race TJJ, which is virulent on all Canadian oat cultivars and was first detected in 1998, fell to only 5.2% frequency (total samples) in 2010. One new race (TJL) was detected in three samples from Manitoba in 2009, but is avirulent to gene Pg13 and does not pose a threat to oat production in Canada.