Professors Eduard Akhunov of Kansas State University and Jorge Dubcovsky from the University of California-Davis, led a research project that identified a gene that gives wheat plants resistance to one of the most deadly races of the wheat stem rust pathogen, Ug99.

Ug99 was first discovered in Uganda in 1999, since then the disease has spread across Africa, Asia and the Middle East, becoming more virulent as it does so.

The two scientists said their discovery may help in the race to develop new wheat varieties and strategies that protect the world's food crops against the spreading pathogen. They published their findings in the journal Science.

The pair identified a stem rust resistance gene named Sr35; an Australian team, working concurrently with the US researchers, have identified another effective resistance gene called Sr33.

Commenting on his team's discovery, Professor Akhunov said, "This gene, Sr35, functions as a key component of plants' immune system. It recognizes the invading pathogen and triggers a response in the plant to fight the disease."

Ug99 overwhelmed known rust-resistance genes

Wheat stem rust is caused by a fungal pathogen. Although wheat breeders have been able to develop varieties that are largely resistant to this pathogen since the 1950s, the emergence of the new strain in Uganda 14 years ago has proven problematic.

"Until that point, wheat breeders had two or three genes that were so efficient against stem rust for decades that this disease wasn't the biggest concern," Akhunov elaborated. "However, the discovery of the Ug99 race of pathogen showed that changes in the virulence of existing pathogen races can become a huge problem."

As a first line of defence, wheat breeders and researchers began looking for resistance genes among those that had already been discovered in the existing germplasm repositories, he said. "The Sr35 gene was one of those genes that was discovered in einkorn wheat grown in Turkey," Akhunov said. "Until now, however, we did not know what kind of gene confers resistance to Ug99 in this wheat accession."

To identify the resistance gene Sr35, the team turned to einkorn wheat that is known to be resistant to the Ug99 fungal strain. Einkorn wheat has limited economic value and is cultivated in small areas of the Mediterranean region. It has been largely replaced by higher yielding pasta and bread wheat; the discovery appears to validate calls by the UN Food and Agriculture Organisation to preserve agricultural biodiversity for use in adapting to climatic changes or combating new diseases.

Researchers spent nearly four years trying to identify the location of the Sr35 gene in the wheat genome, which contains nearly two times more genetic information than the human genome. Eventually, by using two complementary means of identifying their target, they isolated the gene they were looking for and demonstrated its resistance to Ug99.

"It was a matter of knocking out each candidate gene until we found the one that made a plant susceptible," Akhunov said. "It was a tedious process and took a lot of time, but it was worth the effort."

The team are now trying to learn more about the Sr35 gene, as well as improving understanding of how Ug99 infects plants, in a bid to boost control efforts.

Although the two discoveries of resistant genes represent a major step in efforts to tackle Ug99, as wheat is grown across a broad range of environments, breeding programs will have to introduce resistance into regionally adapted germplasms, which may take time even when more is understood about the resistant genes.