Cereal Rust Corner with Professor Robert F. Park and Dr Colin R. Wellings, University of Sydney Plant Breeding Institute Cobbitty (Dr Wellings is secondedfrom NSW Agriculture): Review of cereal rusts in 2002
THE 2002 season in eastern Australia was characterised by dry conditions, with little rust reported in commercial crops, apart from stripe rust in crops of H45 in NSW. The two most significant rust events of 2002 were the detection of virulence for Lr37 in WA in early 2002 and later in SA, and of wheat stripe rust in WA. Fortunately, through collaborative efforts with WA colleagues, information has been gathered on the responses of current cultivars and advanced breeding lines to this new disease (see Ground Cover 43 for more detail).
Leaf rust of wheat. The leaf rust pathotype that can infect cultivars which have resistance gene Lr24 is now well established in all eastern states. Cultivars grown in the east that are most affected by this pathotype are Krichauff and Worrakatta, while the cultivars Anlace, Babbler, Cunningham, Janz, Lang, Mira, Mitre, Mulgara, Perouse, Tasman and Sunpict are moderately susceptible and may develop some leaf rust.
A new pathotype of leaf rust with virulence for the resistance gene Lr37 was isolated in early 2002 from self-sown Camm wheat on the south-west fringe of the wheatbelt north of Albany, WA. This pathotype was subsequently detected in many other samples forwarded from that state throughout 2002 and it appears to be well established. It was also isolated from the south-eastern corner of SA in samples collected from Bool Lagoon and Mt Benson in December 2002, indicating that it has managed to spread from the west to the east.
Efforts are underway to obtain accurate information on the response of other cultivars with resistance gene Lr37 to this new pathotype.
Stem rust of wheat. Stem rust of wheat was again rare in eastern Australia, and was found only in experimental plots. Samples forwarded from WA included a pathotype detected for the first time in 2001 , which is able to overcome the stem rust resistance of Camm (Sr38). This resistance is also present in several other cultivars, and tests have indicated that some of these have additional resistance that will provide some protection from the new pathotype (Trident, Bowie, Sunlin, Sunbri, Sunstate.
Stripe rust of wheat. The first detection of wheat stripe rust in WA in late August 2002 is probably the most significant rust event to happen in Australia since this disease was first detected in eastern Australia in 1979. It is now clear that a single pathotype of the stripe rust pathogen is present in WA, and that it is of foreign origin. The epidemic in WA was extensive, although dry conditions in the north restricted pathogen establishment.
Crop losses in the Great Southern region were estimated to range from 30 to 50 per cent, with some losses up to 65 per cent.
Recent experiments using the WA pathotype suggest that certain triticales are more vulnerable to the WA pathotype than to pathotypes present in eastern Australia. Further work is underway to evaluate commercial wheats and triticales in order to determine the nature and extent of the threat posed to eastern cereal-growing areas from a potential incursion of the WA pathotype.
Despite the drought in eastern Australia, some crops of cultivar H45 grown under irrigation or in favoured dryland situations in the eastern highlands were generally affected by stripe rust. Fungicide sprays were employed although response data are not available. The problems with H45 arise from the increase in a pathotype that can overcome the seedling resistance of this cultivar.
Cultivars to replace H45 in mid-season to late sowing windows are recommended, especially in Silo Group North (NSW) where H45 has gained popularity despite not being recommended.
Rust in barley. Barley crops in eastern Australia not experience any significant levels of rust infection in 2002. Epidemics of leaf rust developed in southern parts of the WA cereal belt, mainly affecting the cultivars Gairdner and Fitzgerald. There are now three different pathotypes of barley leaf rust in WA, all of which can infect these two cultivars.
Only Galaxy has effective seedling resistance to leaf rust in Australia. However, not all cultivars will become severely infected and cultivars like Gilbert are known to have good levels of resistance at later growth stages.
Rust in oats. There were no reports of significant levels of rust in oat crops during 2002. Achieving stable resistance to rust in oats continues to be a problem, with very few current cultivars possessing resistance to leaf or stem rust.
While pathotypes with virulence for Bettong, Barcoo, Nugene, Taipan and Gwydir have been detected in recent years, surveys continue to indicate that these pathotypes are rare and crops of these cultivars may remain rust-free until the respective pathotypes have had a chance to build up. These cultivars will therefore require careful monitoring.
National perspective. The spread of the Lr37- attacking leaf rust pathotype from WA to SA in 2002 confirms previous observations of the Australia-wide movement of rusts. This stresses the point that rust diseases are a national problem, and that a nationally coordinated resistance-breeding approach is essential if stable economic crop protection is to be achieved. We now have several rust threats that remain localised to either eastern Australia (Lr24 virulence, eastern Australian isolates of stripe rust) or WA (the new WA stripe rust, Sr38 virulence), and the potential for rust exchange between the two regions must be recognised.
All people involved in the grains industry who visit cropping areas in other states in the coming season are strongly advised to exercise care, and, once home, to change and launder clothing before venturing out into crops.