Virulence dynamics in Puccinia graminis f.sp. avenae in Canada

Abstract

Virulence in Puccinia graminis f.sp. avenue has been studied in Canada since 1921. Changes in host resistance, the succession of avirulence–virulence combinations, and changes in the composition of the pathogen population during the ensuing 57 years are presented graphically and indicate that the organism is highly dynamic even when the host population is relatively static. The early years are characterized by the presence of races virulent only on the universally susceptible host or cultivars with a single resistance gene followed by a gradual increase in virulence beginning in 1943 and a differentiation of eastern and western pathogen populations. By 1950 the zero- and one-gene virulence races were being displaced by Pg-1, -2 and Pg-1, -2, -3 virulence combinations in eastern Canada, an event that did not occur in the west until 1961. The latter period was characterized by the combining of virulence on all resistance genes except Pg-8 and Pg-13 in the east and Pg-9 and Pg-13 in the west. Virulence on resistance conferred by gene Pg-13 is still rare.