Cereal rust corner with Professor Robert F. Park and Dr Colin R. Wellings University of Sydney Plant Breeding Institute Cobbitty. (Dr Wellings is on secondment from NSW Agriculture.): Rust diseases of barley

Rust Diseases of barley in Australia:- Left: Leaf rust is present in all barley-growing regions of Australia and has been a problem in recent years in southern regions of WA. Right: Stem rust of barley can be largely prevented by controlling stem rush in wheat or rye, and by avoiding spring sowings of barley. Bottom: The stripe rust that infects barley grass is either the wheat-attacking form or a second form that is specialised to barley grass. The barley grass stripe rust pathogen can infect some barley cultivars. However, the level of infection is low and no yield losses have been recorded to date.

AUSTRALIAN BARLEY crops can be affected by leaf rust, stem rust and a form of stripe rust that, although specialised to barley grass, does have some ability to infect some barley cultivars.

Leaf rust. This disease is found in all barley-growing regions of Australia. It has reached epidemic levels at times, including recent outbreaks in southern parts of the WA cereal belt. Some 12 years ago, the pathogen acquired the ability to overcome a resistance gene that is present in the cultivars GairdnerPBR logo, FitzgeraldPBR logo, BaudinPBR logo, Tallon and LindwallPBR logo, and since. then, this ability (virulence) of the pathogen has either spread to or reappeared in all barley-growing regions.

An additional challenge in controlling this disease is that it can reproduce sexually. This occurs on the bulbous weed 'Star of Bethlehem' (Ornithogalum umbeliatum), which occurs at the southern end of the Yorke Peninsula in SA. The barley leaf rust pathogen infects this weed during autumn, undergoes sexual reproduction, and then re-infects barley the following spring.

The result is a genetically variable pathogen population with an increased chance of pathogen variants developing which have the ability to attack resistant cultivars .

The 'Star of Bethlehem' thus poses a threat to leaf rust-resistance breeding efforts. It is only partially controlled by herbicides.

Barley should not be sown in paddocks infected with this weed.

Efforts are underway to incorporate new sources of resistance to leaf rust in future Australian barley cultivars.

Stripe rust of barley. A common feature of each of the pathogens that cause cereal rust diseases is the existence of forms that are specialised to a particular cereal crop species. Stripe rust, for example, has one form that is specific for wheat and another that is specific for barley. The barley form has not been recorded in this country.

Recent Mexican studies have shown that Australian barley cultivars are generally susceptible to the barley form of stripe rust, and so it represents a significant exotic disease threat to the Australian barley industry.

Barley grass stripe rust. A different form of stripe rust, found in Australia in 1998, appears to be specialised to barley grass - believed to have been introduced into Australia around 1998. While this pathogen can infect some Australian barley cultivars (notably Skiff and its relatives, including Tantangara) , the level of infection is generally low and there is no evidence of yield losses. Breeders do nonetheless screen their germ plasm routinely to avoid any potential vulnerability to the disease.

Stem rust. Barley crops can be affected by either the wheat stem rust pathogen, the rye stem rust pathogen, or a third stem rust pathogen that is a hybrid between the wheat and rye stem rust forms. Where stem rust is found on barley, it is important to determine which one of these three pathogens is responsible in order to assess any potential threat to nearby wheat crops (wheat is not affected by the rye stem rust pathogen or the hybrid form).

Stem rust in barley can be largely prevented if stem rust is controlled in wheat and rye crops, and by avoiding spring sowings of barley.