A team of researchers from the University of California, Davis, and Kansas State University has identified a gene that enables resistance to a new race, or strain, of stem rust, a disease that is producing large wheat yield losses throughout Africa and Asia and threatening global food security.

By transferring this gene to commercial wheat varieties, wheat breeders will have a distinct advantage in controlling the epidemic, the researchers say.

Findings from the study will appear in the June 27 edition of Science Express, the online publication of the journal Science.

“A new race of a wheat disease, called stem rust Ug99, has been spreading over large distances since 1999, threatening important wheat production areas of the world,” said co-author Jorge Dubcovsky, a wheat geneticist at UC Davis and a Howard Hughes Medical Institute investigator. “This study identifies a gene called Sr35 that confers near-immunity to this new race,” he said.

Ug99, named for the country of Uganda and the year the new race was discovered, appears on wheat as small red growths, dotted across the stems and leaves. About 90 percent of the wheat varieties grown worldwide are susceptible to Ug99.

Previous resistance genes that had proven effective for fighting the disease for 50 years are ineffective against this new race. Scientists are now looking for new sources of resistance to protect the global wheat crop, which millions of people depend on for food. 

The study is part of the Borlaug Global Rust Initiative, a five-year effort funded by the Bill and Melinda Gates Foundation to coordinate international efforts in fighting Ug99. It is supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

The researchers selected the resistance gene Sr35 for its immunity to Ug99 and related races. Sr35 was known to be present in the wheat species Triticum monococcum, a close relative of pasta and bread wheat.

The team sequenced a region of 300,000 base pairs — the building blocks of DNA — in T. monococcum and identified four candidate genes. Using natural populations, mutants and transgenic plants, they identified the gene responsible for the resistance. They then inserted the gene into a wheat variety that is susceptible to the diseases, engineering a resistance to Ug99.

“This discovery opens the door for biotechnological approaches to fight this devastating disease,” said Eduard Akhunov, an associate professor at Kansas State University and co-director of the project.

The challenge now is to identify which combination of resistance genes can deliver a more durable resistance against the disease.

The study also included: Wenjun Zhang of the UC Davis Department of Plant Sciences; Matthew Rouse of the USDA-ARS Cereal Disease Laboratory; and Cyrille Saintenac, Andres Salcedo and Harold N. Trick, all of Kansas State University.