North Carolina researchers battle wheat disease

Two researchers in North Carolina State University’s College of Agriculture and Life Sciences are members of a team racing against the clock to find solutions to a fungus that is destroying wheat crops on the other side of the globe.

David Marshall and Gina Brown-Guedira with the U.S. Department of Agriculture’s Agriculture Research Service (ARS) and North Carolina State’s Crop Science and Plant Pathology departments, are examining wheat grown each year in Kenya in hopes of developing varieties with resistance to a virulent form of wheat stem rust.

Wheat stem rust is not a new disease. Up until the 1950s, it was a constant threat to U.S. wheat growers. But the development of new varieties with genetic resistance to stem rust made the problem far less common, though still dangerous when it strikes.

As a researcher at Texas A&M University, Marshall saw stem rust wreak havoc on a Texas wheat field. “We had an outbreak of stem rust on the Gulf Coast in 1986. And that field went from green to dead in two weeks. So it can spread very rapidly.

“Wheat stem rust is not a new disease in the United States. This stem rust is a new virulence, a new race that we’ve found in Africa that can overcome resistance genes. Most of the wheat varieties in the world are based on two to three genes for resistance (to wheat stem rust). This new race can take out all those genes,” he said.

The new virulent stem rust was first detected in Uganda in 1998 and reported the following year, 1999. Known as Ug99, this stem rust has now spread north and east across Africa in areas where little wheat is grown. Since 2000, the fungus has been found in Kenya, Ethiopia, Egypt and Yemen and has been reported in the Sinai Peninsula. Researchers fear the disease will soon reach China and India, where the population relies on a large wheat crop as a food staple.

“The international centers CIMMYT (International Maize and Wheat Improvement Center) and ICARDA (International Center for Agricultural Research in the Dry Areas), as well as in-country wheat programs in India and China, have been working feverishly to develop and increase new varieties that have resistance. I know they’ve identified them, and the question is how quickly can they increase these lines and get them out to folks. So we know that the resistance is there,” Marshall said.

With the world’s grain supplies already low, another blow to the world’s food production system could be devastating. So Marshall and his ARS colleagues, along with other agricultural researchers, are in a race to find or develop wheat varieties that can withstand the effects of this fungus.

ARS is partnering with researchers with the Kenya Agricultural Research Institute to identify resistant wheat varieties. In March, KARI researchers planted both winter wheat and spring wheat varieties in trial plots. Because Kenya is close to the equator, researchers must refrigerate the winter wheat seed for eight weeks in order to force it to flower.

Marshall is responsible for assessing the winter wheat crop in September, while another ARS colleague assesses the spring crop. He is looking for varieties that have some resistance to the stem rust.

A quarter of the wheat grown in the United States is spring wheat. It is grown in the most northern states, while winter wheat — 75 percent of the U.S. crop — is grown in states primarily south of South Dakota.

Germplasm samples are brought to the U.S. to be analyzed by ARS researcher Yue Jin at the agency’s Cereal Disease Laboratory in St. Paul, Minn. The work can only be done during the frozen months of January through March under authorized and contained conditions to avoid any risk to the U.S. wheat crop.

Though fungicides can work against wheat stem rust, they are not economical, particularly in developing countries. In Kenya, Marshall said, even four sprays of fungicide were not enough to prevent the stem rust from destroying wheat fields.

Researchers around the world have joined the search for resistance to this new wheat stem rust, Marshall said. The virulent race of stem rust has not appeared in the U.S., although researchers are not taking any chances.

“We believe we have a few years before things pop here,” Marshall said. “We are getting a head-start on protecting U.S. wheat before the new rust gets here.”

e-mail: [email protected]

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