Cereal Rusts - Surveys highlight important issues for growers

By Professor Robert F Park and Dr Colin R Wellings, University of Sydney Plant Breeding Institute Cobbitty. (Dr Wellings is on secondment from NSW Agriculture.)

Every year, the Australian Cereal Rust Control Program (ACRCP) at the University of Sydney conducts Australia-wide surveys of cereal rust pathogen populations, and isolates are assessed in greenhouse tests to see if they can overcome the resistance of current cereal cultivars.

Over 1000 samples of rusted cereals were received by the ACRCP for pathotype analysis in 2003. The table shows some important issues and findings which emerged.

The 2003 winter cropping season witnessed the most widespread stripe rust epidemic in 20 years.

The dominating factors leading to this epidemic were:

Foliar sprays were used to contain the disease and minimise crop losses. These chemical applications were generally effective, although timing was critical.

Limited data indicated yield increases of up to 20 percent where sprays were applied to MS-S varieties.

The new pathotype that appeared in eastern Australia in 2003 was first detected in WA during 2002, and current thinking is that it was introduced to WA from North America.

The VPM resistance is a triple rust resistance that has been used in the development of several Australian wheat cultivars (Bowie, CammVariety protected under the Plant Breeders Rights Act 1994, Rudd, Sunbri, Sunlin, SunstateVariety protected under the Plant Breeders Rights Act 1994 and Trident).

Unfortunately, the stripe rust component of the VPM resistance (known as Yr17) is now ineffective in eastern Australia (it remains effective in WA), and during 2003, a leaf-rust pathotype virulent for the leaf-rust component (Lr37) and a stem-rust pathotype virulent for the stemrust component (Sr38) were detected in SA.

Both of these pathotypes were first detected in WA and, like the new stripe rust pathotype, presumably spread to the east on prevailing winds.

Rust nurseries at the Plant Breeding Institute Cobbitty this year will use the VPM virulent pathotypes of stripe rust, leaf rust and stem rust to assess the vulnerabilities of cultivars carrying this resistance.

Stem rust was uncommon in the east in 2003 but was present on volunteer cereals in WA in autumn, where it became more widespread as the season progressed.

The cultivar WyalkatchemVariety protected under the Plant Breeders Rights Act 1994 carries two genes for resistance to stem rust (Sr8a and Sr15) and was resistant to all pathotypes of this pathogen.

However, a new pathotype was detected from WA during 2003 that can overcome the resistance of this cultivar.

Crops of WyalkatchemVariety protected under the Plant Breeders Rights Act 1994 in WA should therefore be monitored carefully for stem rust in 2004.

An important practice in the management of cereal rusts is destruction of the green bridge. Recent inspections have confirmed the presence of wheat stem rust on selfsown barley in southern parts of the WA wheat belt, all well as three wheat rusts at Narracorte in SA and Horsham in Victoria.

Greenhouse tests have identified the stripe rust at Narracorte and Horsham as the "WA" pathotype and the stem rust at Horsham as the VPM-attacking pathotype.

Given the extensive cereal rust problems over the past two years, and the evidence of over-summer survival in early 2004, there is considerable potential for these pathogens to threaten crop yield in the current season.

Although seasonal conditions will influence rust development during 2004, growers are advised to give careful thought to pre-plant decisions (variety choice, fungicide applications on seed or in furrow) and to monitor crop health carefully during the season.

Variety protected under the Plant Breeders Rights Act 1994 Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.