Virulence of Puccinia coronata var avenae f. sp. avenae (oat crown rust) in Canada during 2010 to 2015

Abstract

Crown rust, caused by Puccinia coronata var. avenae f. sp. avenae (Urban & Marková) (Pca), is an economically significant problem in oat in Canada. The growing of crown rust resistant oat cultivars has been an important management practice. The development of oat cultivars with effective resistance requires knowledge of the virulence genes present in the pathogen population. This study’s objective was to determine the presence and frequency of virulence to 24 oat lines with single Pc genes in isolates of Pca collected in Canada during 2010 to 2015. A total of 692 distinct races were identified, of which 603 were from the eastern Prairie region (EPR) and 89 from eastern Canada. None of the 24 Pc resistance genes studied was effective against all of the Pca isolates from the EPR. The frequency of virulence increased on 15 of the Pc differential lines in the EPR between 2010 and 2015, with the most dramatic increase from 0% to 67% being to Pc91. The most effective resistance genes were Pc94, Pc50, Pc96, Pc97, Pc98 and Pc101. Virulence to Pc58, Pc94, Pc98 and Pc101 was not observed in Pca isolates from eastern Canada. The race structure of the Pca population in Canada was highly variable, with more than 80% of the races identified each year represented by one Pca isolate. The race structure of the Pca populations in eastern Canada and the EPR were distinct, as 80% of the races identified from Pca isolates collected in eastern Canada were not detected in the EPR. The results of this study indicate that the Pca populations in the EPR and eastern Canada continue to evolve in their virulence dynamics, creating a challenge to breed oat lines with effective and stable resistance.