Occurrence and identity of Puccinia graminis on wheat, barley, andgrasses in Australia during summer - autumn 1992-93

Abstract

Levels of stem rust (Puccinia graminis) in Australian wheat and barley crops were generally low from 1980 to 1992. Exceptionally wet conditions in South Australia (SA) during early summer 1992-93 resulted in the establishment of vast areas of self-sown cereals, in which stem rust increased rapidly. The disease was also more common in Western Australia during the summer months of 1992-93. Collections from rusted wheat, barley, and selected grass species were analysed in greenhouse tests using an array of differential cereal genotypes. Five pathotypes of P. graminis f. sp. tritici were recovered from SA, 3 of which had not been isolated over the previous 10 years in Australia and for up to 20 years in SA. The recurrence of these pathotypes highlights the need for caution in redeploying resistance genes for which virulence has not been detected for several years. The majority (79%) of isolates taken from stem-rusted barley in SA were either P. graminis f. sp. secalis or `scabrum" rust, both of which do not infect wheat. In total, 6 of 7 isolates of pathotype 21-2,7 recovered from SA came from stem-rusted barley, and as most wheats in this region are resistant to this pathotype, it appears that hosts other than wheat must be important in perpetuating such avirulent pathotypes.