News in Science

Wild genes block growing rust threat

Rust resistance Researchers have identified two genes in ancient varieties of wheat that could combat a disease threatening one of the world's major food crops.

Since 1999, a fungal rust known as Ug99 has decimated wheat crops throughout Africa, Yemen and Iran. The rust targets the plant's stem and leaves, robbing it of nutrients and reducing crop yield by up to 80 per cent.

The last major epidemic of fungal rust disease broke out in 1950s, but was quelled with the introduction of a resistant strain of plants in the 1970s.

In a study published online today in the journal Science Express, researchers have shown that a gene known as Sr33 provides resistance against Ug99.

Team research leader, Dr Evans Lagudah of CSIRO Plant Industry, says the research is part of a global effort to reduce the spread and impact of the disease.

"The biggest concern is that it's got a foothold in Iran, which is near Pakistan and India -- both big 'bread baskets'," says Lagudah.

"The fear is that once it gets into those countries the impact in terms of global food security would be enormous."

He says while Ug99 can easily be transported on clothing, it is also possible for the pathogen to float along air currents over large distances.

"Not only has it migrated northwards into Yemen and into Iran, but has also moved southwards in South Africa. Historically the wind currents that move from Southern Africa move into western parts of Australia and eventually eastern Australia."

Tracking the immunity gene

Lagudah says the Sr33 gene, which is found in an ancient wheat relative known as goat grass (Aegilops taushii), provides resistance against a range of fungal rust types.

"It tends to show a broad spectrum resistance, but it's not what you could call a strong immune response," he says. "It allows some of the rust to grow, but it doesn't allow the rust to grow fully."

To test the effectiveness of the Sr33 gene, researchers transplanted DNA from the wild goat grass into a commercial wheat variety, using a technique known as transgenics. This allowed the researchers to create new seedlings at a much faster rate than through traditional cross-breeding techniques.

They then used DNA fingerprinting to identify the location of the Sr33 genes.

"[We] compare the plants that have the resistance with those that do not have the resistance and look for specific differences," says Lagudah. "We were able to show that all these differences were 100 per cent associated with the presence or absence of this resistance against Ug99."

In a second study, also appearing in Science Express, a US-led team of researchers investigated another rust resistance gene Sr35. This gene was previously identified in an ancient wheat variety known as Titicum monococcum, which is closely related to bread and pasta wheat.

They found that Sr35 provides a stronger level of rust resistance against Ug99 than Sr33. But, unlike Sr33, it does not provide resistance against other rust strains.

Lagudah says short-term the outcomes of this research could be the development of wheat strains that contain both the Sr33 and Sr35 genes.

"[Ideally] we'd like to stick the genes together so that they go to one chromosome and make breeding much simpler … because two heads are better than one."