By MATTHEW D. ERNST

Missouri Correspondent

MINNEAPOLIS, Minn. — University of Minnesota and USDA scientists collaborated with colleagues in Australia and Europe to discover the wheat stem rust pathogen gene that wheat plants first detect when “switching on” genetic resistance to wheat stem rust.

A potent strain of wheat stem rust, which infected resistant wheat varieties, emerged in Africa in 1998, infecting rust-resistant genes first bred into wheat varieties by Norman Borlaug and other plant breeders during the Green Revolution.

“It is important to look at this gene in worldwide rust strains, to gain a picture of where virulence is most likely to evolve,” said Melania Figueroa, UM assistant professor of plant pathology.

The new gene discovery enables a quick DNA test to determine whether a wheat stem rust outbreak could overcome the rust-resistant gene and decimate wheat yield. This allows producers in susceptible regions, such as Africa and the Middle East, to make informed decisions about whether signs of wheat stem rust in a field would require treatment with fungicides.

The discovery, published in December 2017 in the journal Science, could also have implications for the U.S. soybean industry. Researchers say understanding how wheat plants interact with rust fungi at the molecular level aids understanding of how rust develops in other crops – namely soybeans and coffee.

“Close examination of the sequence of this gene in strains from diverse origin can provide important clues to understand the evolution of this pathogen and how virulence emerges,” said Figueroa.

An important contribution to the research came from Yue Jin, a USDA Agricultural Research Service plant pathologist at the Cereal Grain Research Center in St. Paul, Minn. Jin collected a strain of wheat stem rust from barberry, an alternate host of fungi that cause stem rust.

That strain contained a genetic variation of the fungus causing wheat stem rust that is not recognized by Sr50, the rust-resistant wheat gene.

Wheat stem rust was last a major disease of wheat in the United States during the 1950s, and the last epidemic in Australia was in 1973. But stem rust is making a comeback, overcoming formerly resistant wheat varieties in Africa, the Middle East and Europe, where stem rust was detected in Sweden in 2017.

“The highly virulent Ug99 race of the stem rust fungus – which emerged in 1998 in Uganda – has become even more potent as it has spread through Africa and the Middle East, with winds threatening to carry it into Asia,” said Kostya Kanyuka, a scientist at Rothamsted Research in the United Kingdom.

The discovery included contributions from scientists at Rothamsted, UM, USDA and researchers from the University of Sydney and the Commonwealth Scientific Industrial Research Organization (CSIRO) in Australia.

The gene discovery is important for maintaining the world’s wheat supply, according to Peter Dodds from CSIRO. He said demand for wheat in the developing world was expected to jump 60 percent by 2050.

“Now that we’ve identified how stem rust strains are able to overcome Sr50 resistance – by mutation of a gene we’ve identified called AvrSr50 – this information can be used to help prioritize resistance genes for deployment,” said Dodds, who also has an adjunct appointment in the UM Department of Plant Pathology.