The race against rust in wheat

 In recognition of outstanding research in the fight against wheat rust diseases, researchers of the Australian Cereal Rust Control Team were recently awarded the Borlaug Global Rust Initiative’s Gene Stewardship prize in New Delhi, India. A couple of CSIRO’s top young researchers are part of the team of scientists involved in the race against rust.

Healthy wheat is vital to global food security

Australian research into wheat rust disease is shedding light on ways to combat this devastating disease of an all-important food crop. Rust fungi can infect the wheat’s stems, leaves and grains and cause up to 80% loss in crop yield.

By far the best way to prevent rust disease and crop losses is to grow rust-resistant varieties of wheat. But the fungus is ever evolving, and new types that can overcome resistant wheat inevitably spring up. One particular wheat rust, known as Ug99, has done just that.

The Ug99 rust is a major concern because it’s capable of causing disease on many of the world’s current commercial wheats. It has decimated wheat crops throughout Africa, Yemen and Iran since 1999.The impact on global food security would be enormous if this fungus affected the big ‘bread baskets’ of Pakistan and India.

So the race is on for genes that can confer resistance to Ug99 and other rusts in wheat. ACIAR-funded research with Indian and Australian partners (from the Australian Cereal Rust Control Program) is well and truly in this race. The research is part of a wider international collaboration and aims to identify new potential genes and markers for resistance to wheat stem rust (particularly Ug99).

Dr Sam Periyannan and Dr John Moore, CSIRO (Photo: CSIRO)

Dr Sam Periyannan and Dr John Moore are two CSIRO postdoctoral scientists studying stem rust resistance. Their research started in 2007 while Sam was doing his PhD research at CSIRO with financial support from ACIAR (project CIM/2007/084).

Sam and John recently isolated and characterised a resistance gene, Sr33, from an ancient relative of wheat (Aegilops taushii, or ‘goatgrass’). This gene was introduced into bread wheats through repeated backcrossing, and plants containing Sr33 showed rust resistance, not only to Ug99 but also to a range of other rust fungi. From this work a new Australian wheat called ‘Sunguard’ was recently released for commercial cultivation.

Sam says 'While the resistance to rust is not absolute, the results are very promising especially when the Sr33 gene is combined with similar effective genes. Using gene combinations like this will also help slow down the rate of mutation in rust, which is a strategy often used by pathogens to overcome useful resistance genes.'

Wheat stem rust can be devastating to the crop
(Photo: E. Lagudah & Z.Pretorius)

John explains 'The isolation of Sr33 provides an exciting opportunity to examine the mechanisms of rust resistant at the molecular level. Along with Sr35—another resistance gene effective against Ug99 stem rust—isolated by a team of US scientists at Kansas State University and University of California, we are now at the point where we can begin to dissect how rust resistance actually works in wheat.'

This knowledge is crucial for researchers to be able to design and breed new wheats (like Sunguard), and to keep ahead in the race against rust.

By Dr Wendy Henderson, ACIAR's Science Communicator

More information:
ACIAR project CIM/2007/084  Linking India and Australia to a global strategy for the Ug99 stem rust pathotype
ACIAR’s policy statement on biotechnology

ABC article Wild genes block growing rust threat
Borlaug Global Rust Initiative blog: Aussie team recognized for responsible gene stewardship

Science articles:
Periyannan et al (2013). The gene Sr33, an ortholog of barley Mla genes, encodes resistance to wheat stem rust race Ug99. Science 341:786-788
Saintenac et al (2013). Identification of wheat gene Sr35 that confers resistance to Ug99 stem rust race group. Science 341: 783-786