Image caption Varying stem rust epidemics on wheat stems

Scientists have engineered wheat that is resistant to stem rust, a fungal disease that has ruined crops in Africa, Yemen and Iran.

The genetic advance raises the possibility of breeding wheat that is resistant to the fungus, researchers report in the journal Science.

Stem rust is regarded as a major threat to wheat, one of the world's most important cereal crops.

It is a fungal disease that appears as reddish blisters on wheat.

The blisters contain millions of spores, which infect the plant tissues, and disrupt the crop's ability to produce grain.

Ug99, which was discovered in Uganda in 1999, is a form of black stem rust that can wipe out whole harvests.

The identification of these two genes from the wild relatives of wheat offers new possibilities to slow the spread of the Ug99 fungus and to deploy more sustainable resistance in farmers' fields Dr Cristobal Uauy, John Innes Centre

About 90% of wheat grown around the world is susceptible to Ug99 and similar strains of the pest.

Experts predict it could spread rapidly through Africa and the Middle East, and possibly further afield, potentially causing an agricultural disaster that would affect global food security.​

In the latest research, two international groups of scientists, led by Dr Cyrille Saintenac of Kansas State University, US, and Dr Sambasivam Periyannan of CSIRO Plant Industry, Canberra, Australia, investigated two previously identified genes associated with stem rust resistance.

They cloned parts of the gene of an ancient wheat crop (Sr33) that was common until the Bronze Age but is now rarely cultivated, and inserted it into modern wheat varieties.

They found wheat with this gene did not show susceptibility to stem rust.

A similar study on a second gene (Sr35), found in a wild plant related to wheat, showed that this gene also conferred limited resistance to the fungal disease, as well as related pests.

The scientists, from research teams in the US, China and Australia, say using biotechnology to develop wheat with both genes could slow the progression of Ug99 and avoid global wheat shortages.

Commenting on the study, Dr Cristobal Uauy of the department of crop genetics, John Innes Centre, Norwich, said the identification of the two genes provided a clear path to deploy resistance to the Ug99 fungus in the field, either through conventional means or biotechnological applications.

"The identification of these two genes from the wild relatives of wheat offers new possibilities to slow the spread of the Ug99 fungus and to deploy more sustainable resistance in farmers' fields," he said.

"This will lead to a deeper understanding of how plants fight back against the pathogen and allow scientist and breeders to establish new and more sustainable ways to defeat one of wheat's worst enemies."

Dr Brande Wulff of The Sainsbury Laboratory in Norwich added: "Resistance genes are typically overcome by the pathogen when deployed one at a time. However, the cloning of stem rust resistance genes allows the scientist to easily combine them.

"A stack of resistance genes with multiple resistance specificities should provide a more durable resistance to this devastating disease."