Pathogenic specialization and pathotype distribution of Puccinia hordei in Australia, 1992 to 2001

Annual surveys of pathogenic variability in the leaf rust pathogen of barley, Puccinia hordei, from 1992 to 2001 revealed a significant shift in the composition of populations across Australia. Virulence for the resistance gene Rph12, first detected in a single pathotype, 4610P+, in Tasmania in 1991, was subsequently detected in 1993 in South Australia, Victoria, and southern New South Wales. By the end of 2001, eight pathotypes with virulence for Rph12 had been isolated, and virulence for this gene was present in all Australian barley growing regions. Virulence was not detected for the resistance genes Rph3, Rph7, Rph11, or Rph14. The distribution and spread of the pathotypes detected, their possible origins, pathogenicity on several uncharacterized seedling resistance sources, and implications for resistance breeding are discussed.