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Confronting a New Threat to Wheat Production

Posted by | May 6, 2009

WSU Scientist Tackles Ug99, a New Threat to Global Wheat Production

Tim Murray, a WSU plant pathologist, is collaborating with scientists around the world to address Ug99, a fungus that threatens wheat production worldwide.

Ug99 is a virulent new race of stem rust first found in research plots in Uganda in 1999. The new race, and variants discovered since, has been able to overcome resistance genes bred into wheat varieties commonly planted around the world. Some estimates say that 80 percent of all wheat varieties planted in Asia and Africa are susceptible.

“It’s a concern in the United States because a large percentage of our varieties are susceptible,” Murray said. “The last major epidemic of stem rust in the United States was 1954.”

Ug99 is of concern especially in the Midwest where the climate favors the disease. Climatic conditions are less favorable in Washington because it requires summer rainfall, warm days, and warm nights to thrive.

Murray is chairing a committee of land-grant university and government scientists tasked with preparing a recovery plan should Ug99 be introduced to the United States. His committee is preparing a non-technical briefing paper on Ug99 for policymakers and is making plans to conduct surveillance for the disease. Surveillance will include planting and monitoring trap plots of vulnerable varieties around the United States.

“The real challenge will be to know when it arrives,” Murray said. “You can’t tell Ug99 apart from any other stem rust by looking at it. They all look alike.”

In March, Murray and Xianming Chen, a USDA Agricultural Research Service cereal rust expert stationed at WSU, traveled to Mexico to attend an international conference sponsored by the Borlaug Global Rust Initiative. The Initiative is a continuation of an interdisciplinary research and development consortium begun in Africa in 2005 to develop new wheat varieties with stable resistance to the new stem rust.

Researchers have identified sources of genetic resistance to Ug99 and breeding lines with resistance are in the pipeline, but it will take several years of breeding to put seed with multi-gene resistance into the hands of farmers.

In a 2005 report assessing global vulnerability to Ug99, Norman Borlaug, Nobel laureate and father of the Green Revolution, compared the dynamics of a rust epidemic to a forest fire. “Once started, both are difficult to stop,” he said in the forward of the report. “The prospect of a stem rust epidemic in wheat in Africa, Asia, and the Americas is real and must be stopped before it causes untold damage and human suffering.”

No one knows when the disease will reach the United States, but if it follows the path that Asian soybean rust took a few years ago, the spores will cross the Atlantic from the west coast of Africa and move north through South America.

Based on its current location, according to Murray, it should take about 10 years for the disease to reach the United States following natural pathways. Accidental or even intentional introductions could shorten the time frame.

“Asian soybean rust and barley stripe rust were in South America long before they got here,” Murray said. “Both of those diseases were introduced here in years in which we had significant hurricanes. The equatorial coriolus winds are a real barrier to movement north and south across the equator for airborne pathogens, but once a hurricane comes through, it disrupts that.”

Tim Murray

WSU plant pathologist Tim Murray is a member of an international team confronting Ug99, a new fungal threat to wheat production.