WASHINGTON—Scientists from the U.S. Department of Agriculture (USDA) have discovered a gene that could make wheat more resistant to Ug99, a deadly stem rust posing a potential threat to 90% of the world's wheat. The discovery could strengthen wheat crops as the world's growing population requires an increase in wheat products.
The Wheat Initiative coordinated research in 2013 to help increase production, improve quality and implement sustainable practices for growing wheat, estimating that by 2050, the population will require an increase of approximately 60% in wheat production. Agricultural Research Service (ARS) scientists Matt Rouse and Yue Jin, along with the agency's Cereal Disease Research Laboratory, were searching for genes that could make wheat more resistant to Ug99 (Puccinia graminis), which is constantly evolving. The scientists pinpointed the gene while studying the DNA of ancient grasses.
Ug99 has not yet been found in the United States, but it is continually spreading overseas. Genes in wheat that seem to offer immunity during one growing season become susceptible to newly developed "races" during the next season. Ug99 was first reported by scientists in Uganda in 1999, and controlling it has since become an international priority.
Scientists often study a crop's wild relatives for genes that will confer resistance to pests and pathogens. Rouse and Jin studied a wide variety of grasses, including einkorn wheat, emmer wheat and goatgrass. In one study, Rouse and his colleagues at Kansas State University and the University of California at Davis focused on locating a gene in einkorn wheat that confers near immunity to Ug99. They focused on locating a gene, known as Sr35, which was previously discovered in einkorn. However, the exact location of this gene in the plant's vast genome remained a mystery. The wheat genome is huge, containing nearly two times more genetic information than the human genome.
To find Sr35's position, the researchers sequenced areas of the plant's genome where they suspected it was located. In one set of mutant plants, they knocked out the cloned sequences and found it made those plants susceptible to Ug99. In another set, they inserted the same sequences into previously susceptible plants and found it made them resistant.
The results marked the first time that scientists managed to isolate and clone a Ug99 resistance gene. This achievement should make it easier to insert useful genes into wheat varieties.