A new variant of Puccinia striiformis causing stripe rust on barley and wild Hordeum species in Australia

Stripe rust of wheat (caused by Puccinia striiformis Westend f.sp. tritici, Pst) was first detected in Australia in 1979 and progressively evolved from a single progenitor pathotype through single step mutational events for pathogenicity (Wellings & McIntosh, 1990). Annual surveys of the pathogen population have monitored these events to provide advice to growers and wheat breeders concerned with the selection, release and management of stripe rust resistant wheat cultivars. During the survey in 1998, stripe rust samples were collected from wheat and grasses (principally barley grass Hordeum spp.) and occasionally barley. These collections were expected to yield various pathotypes of Pst. However, the samples were unusual in two respects. First, approximately half were collected from barley grass, whereas samples from previous surveys were predominately from wheat. Secondly, approximately 30% of samples from barley grass were highly avirulent on seedlings of most wheat differentials, partially virulent on the wheat differential Chinese 166, and pathogenic on certain barleys, notably cv. Skiff. One sample collected from Skiff in a field trial had the same features.