Preparation to be tested as Ug99 edges closer

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The stem rust strain causing global concern, Ug99, has spread along Africa’s east coast and reached South Africa. That movement increases the chances of Ug99 reaching Australia, but experts still rate the likelihood of an incursion as extremely low.

Professor Robert Park, the GRDC Chair of Cereal Rust Research who heads Ug99 global monitoring efforts, says rust spores can be carried on high-altitude winds from Africa to Australia. Two stem rust pathotypes that first appeared in 1969 are believed to have been transported to Australia from central Africa in this way.

However, years of preparation – including at the international level through the Durable Rust Resistance in Wheat initiative – have left Australian farmers in a strong position should Ug99 cross the Indian Ocean.

“Currently, I would say Australia is fairly well placed,” Professor Park says. “We have resistant wheat varieties and we continue to develop DNA markers for resistance genes that are broadly effective against Ug99.

“But rust can possess other features we don’t fully understand that can make a pathotype more dangerous than we realise. So there are some gaps in our understanding of what is likely to happen.”

This seems to be the case in South Africa, where Professor Park says stem rust generally has become a bigger problem since the arrival of Ug99. It was certainly the case with the Western Australian stripe rust incursion in 2002.

“Based on its virulence, we did not expect stripe rust to be as serious as it was in WA,” he says. “That pathotype turned out to be aggressive and adapted to higher temperatures and as a result was a bigger problem than expected.”

That interplay of factors and pathogens means researchers are more likely these days to view Ug99 as just one part of a greater challenge posed by crop diseases. That means diseases other than Ug99 are the focus of concern, with Professor Park ranking it alongside exotic threats such as stripe rust of barley, Karnal bunt, Russian wheat aphid and leaf rust of durum wheat.

Nationally, there are concerns with stem rust generally, with Professor Park noting Yitpi’s vulnerability and the build up of stem rust inoculum over the past 12 months in the wetter weather. The season has also already recorded its first incidence of stripe rust. “

Conditions currently are ripe for problems, especially in south-eastern Australia,” Professor Park says. “If wet conditions continue, we are quite concerned. It highlights that Ug99 is not happening in isolation and needs to be viewed along with other threats.”

That was the view taken at the Borlaug Global Rust Initiative workshop recently convened at the University of Minnesota by Cornell University and the US Department of Agriculture. Researchers working within the Durable Rust Resistance in Wheat initiative met to discuss progress on various rust-control fronts.

Highlights included work by CSIRO’s Dr Peter Dodds to identify the mechanisms that allow rust to infect wheat (so-called effector proteins), an update from the stem rust genome-sequencing project, and the announcement from Professor Jorge Dubcovsky, of the University of California Davis, that they are close to isolating the stem rust resistance genes Sr13 and Sr35.

“The progress that has been made is quite amazing and that is a function of the resources that have been put into this area, especially by the Bill and Melinda Gates Foundation,” Professor Park says.

“From the rust resistance gene discovery point of view, there has been a tremendous increase in the number of genes identified, characterised and mapped in the past three years that are effective against stem rust.”

– Gio Braidotti

More information: Professor Robert Park, 02 9351 8806,;

GRDC Project Code CSP00099

Region National, Overseas