Virulence of Puccinia coronata f. sp. avenae in the Eastern Prairie Region of Canada during 2007–2009

Abstract

Unfavourable environmental conditions for crown rust [Puccinia coronata f. sp. avenae] during 2007–2009 resulted in light incidence of crown rust on oat (Avena sativa) in Manitoba and eastern Saskatchewan. The first appearance of crown rust on 11 August in 2008 and on 15 August in 2009 was the latest ever seen in this region over the past three decades. Using 19 oat crown rust differentials, a large number of races were identified from isolates from wild oat each year, and a large proportion of the races were represented by a single isolate. There were significant differences between isolates from wild oat and cultivated oat in frequency of virulence to several genes in some years. Virulence frequency to Pc48, a gene in ‘Triple Crown’, was between 8.2–14.1% in isolates from wild oat and between 11.5–18.2% in isolates from cultivated oat during 2007–2009. Frequency of virulence to Pc68 was between 42.3–45.9% and 70.8–81.8% in isolates from wild oat and cultivated oat, respectively. As cultivars with the Pc38, 39, 68-gene combination were still commonly grown during these years, races with virulence to this gene combination were abundant. These cultivars were gradually replaced by new cultivars with different resistance genes. By 2009, ‘Leggett’ (Pc68, 94) accounted for 17.9% of the total oat hectarage, and ‘HiFi’ (Pc91) accounted for 3.0%. During 2007–2009, virulence to Pc94 was low (≤ 1.8%) or not detected, virulence to Pc91 was found in a single isolate, and virulence to gene temp_pc97 or temp_Pc98 was either low or not detected. The huge increase in frequency of virulence to Pc45 in 2008 and 2009 was most likely a result of isolates with this virulence migrating into the prairie region from the USA.