Stem rust is the most destructive of the three rust diseases of wheat. It decimated wheat production in Australia in the early years, with losses including £3 million in 1889, £400,000 in 1903, £2 million in 1916, £7 million in 1947 and $200 to $300 million in 1973.
The losses from the epidemic in 1973, which was worst in south-eastern Australia, are considered to be the most severe in the history of the Australian wheat industry. It was in response to this epidemic that the National Rust Control Program (currently the Australian Cereal Rust Control Program – ACRCP) was established.
Concerted efforts to develop and release only wheat cultivars with genetic resistance to Stem rust have paid big dividends to the Australian grains industry. The disease was estimated in 2009 to have the potential to cause $478 million worth of damage in an epidemic year, but it has been hard to even find in commercial wheat crops for the past 30 years. Much of this control has stemmed from the use of genetic resistance, which was estimated to save $438 million per year on average, with cultural practices and chemical control accounting for about $32 million.
The very low incidence of Stem rust in Australian wheat crops has in turn extended the life of the resistance genes used by breeders. Only one important Stem rust resistance gene in wheat, Sr38, has been overtaken by the development of a new Stem rust pathotype in the past 35 years.
Two very important Stem rust resistance genes that remain effective throughout all of Australia are Sr24 and Sr26. The gene Sr24 was bred into wheat from the grass species Thinopyrum ponticum by researchers in the US , and was first deployed in Australia in the cultivar Torres (released in 1983). Since then it has been deployed in many wheat cultivars and protects 16 current wheat cultivars from Stem rust – Bremer, Chief CL Plus, Cutlass, Elmore CL Plus, Espada, Impress CL Plus, LRPB Gazelle, LRPB Lancer, LRPB Oryx, LRPB Parakeet, Magenta, Naparoo, Shield, Sunchaser, Sunguard and Supreme.
The gene Sr26, also derived from Thinopyrum ponticum, was bred into wheat by Canadian researchers and first deployed in Australia in the cultivar Eagle (released in 1971). Current wheat cultivars that likely carry Sr26 include DS Faraday, Hydra, LRPB Dart, LRPB Gauntlet, LRPB Hellfire, LRPB Spitfire, Merlin, LRPB Phantom, SEA Condamine, Sunchaser and Sunlamb.
Stem rust continues to affect wheat production in some parts of the world; its re-emergence in the Horn of Africa in the late 1990s was of great concern due to the ability of the pathotypes found (the ‘Ug99’ pathotypes) to overcome many resistance genes, including Sr24. Through its work at the University of Adelaide, Commonwealth Scientific and Industrial Research Organisation (CSIRO), the University of Sydney and at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, the ACRCP continues its efforts to find new sources of resistance to Stem rust that are effective against local and important exotic pathotypes, and to provide support to wheat breeders to benefit Australian wheat growers.
More information: Robert Park, 02 9351 8806, robert.park@sydney.edu.au