To beat stem rust, wheat crops get new gene

UC DAVIS (US) — Scientists have found a gene in wild wheat that could make commercial wheat varieties resistant to a new strain of stem rust.

The stem rust disease 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. Their findings are available in Science Express.

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“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,” says co-author Jorge Dubcovsky, a wheat geneticist at University of California, Davis, and a Howard Hughes Medical Institute investigator. “This study identifies a gene called Sr35 that confers near-immunity to this new race,” he says.

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 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,” says 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 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 US Department of Agriculture’s National Institute of Food and Agriculture.

Additional researchers from UC Davis Department of Plant Sciences, the USDA-ARS Cereal Disease Laboratory, and Kansas State University also contributed to the study.

Source: UC Davis