The battle against stripe rust is far from lost. The Cereal Rust Laboratory, at the University of Sydney"s Plant Breeding Institute in NSW, hosts the Australian Cereal Rust Control Program, where resistance genes recently identified in Australian germplasm, together with CIMMYT and European germplasm, are believed to hold the promise of durable resistance.
Senior research scientist Dr Harbans Bariana says the key lies in using genetically diverse sources of resistance in Australian breeding populations to produce varieties with combinations of resistance genes.
When it comes to stripe rust, he says, researchers are better off concentrating on adult plant resistance (APR). This is achieved by "minor" resistance genes, and the secret to durable resistance is a combination of three or more of these genes. This means the pathogen has to acquire virulence for more than one resistance gene and the probability of that is low.
The wheat varieties Sunco and Tasman have been shown to have previously unidentified resistance genes. The offspring of the cross between Tasman and Sunco show better levels of resistance than either of the parents. Sunco and Tasman carry three APR genes each, with stripe rust Yr18 and leaf rust Lr34 resistance genes in common.
Dr Bariana says these minor genes, when in combination, can provide near-immunity to stripe rust.
Some of them control leaf rust resistance as well, and researchers are in the process of identifying closely linked molecular markers for them.
They are also developing lines carrying genes from the variety Kukri , with material derived from Sunco/Tasman and Sunco/Kukri resistant to all three rust diseases.
Describing the combination of pathology, genetic and plant breeding services provided by the Australian Cereal Rust Control Program as "unique", Dr Bariana says the program gives breeders the opportunity to screen their breeding populations under artificially-created epidemic situations at any stage of development.
In 2004, about 90,000 breeding lines were subjected to preliminary testing and breeders were provided with a detailed assessment of the performance of their advanced lines.
Dr Bariana believes that if breeders use seedling resistances as a protection against stripe rust, they should be making the effort to introduce two stripe rust seedling resistance genes to maintain resistance throughout the variety"s commercial life.
He stresses the need to maintain stem rust resistance while improving stripe and leaf rust resistance.
He says a commitment to breeding for rust resistance is needed, and that the prospect of higher yields should not be used as an excuse to promote susceptible varieties.
The value of rust-resistant varieties is not only in better management of rust epidemics during the life of the crop, but also in reducing the number of susceptible plants that can form a "green bridge" to carry disease from one season to the next.
GRDC Research Code US00030
For more information: Dr Harbans Bariana, 02 9351 8809
Can we manage cereal rust blow-ins? page 27
Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.