WHEAT-STEM RUST IN AUSTRALIA - 1969-1985

Pathogenic changes in Puccinia graminis f. sp. tritici (P. g. tritici) in Australia during the period 1969-1985 are reviewed. As found in a previous study covering the period 1954-1968, the frequencies of individual pathotypes were influenced by the combinations of resistance genes present in the most common wheat cultivars. From 1969 to 1978, pathotype composition and diversity varied between the four regions comprising the Australian wheat-growing area. However, from 1978 to 1985, pathotype 343-1,2,3,5,6 predominated in all regions. It is suggested that this pathotype was repeatedly derived from pathotype 326-1,2,3,5,6 at widely separated locations, and that these events facilitated its widespread increase. Another significant event was the specialization of P. g. tritici on triticale. Survey data suggest that pathotype 34-2,12, which rendered cultivar Coorong susceptible, developed from pathotype 34-2, possibly during 1979. A second pathotype which attacked cultivar Satu (designated 34-2,12,13) was detected in 1984. The deployment of different resistant genes in triticale and wheat has resulted in distinct populations within P. g. tritici adapted to each crop. Future cultivar development for triticale should be aimed at maintaining this divergence.