Perspectives Online

Racing the Clock - CALS researchers battle wheat 
disease in Kenya. By Natalie Hampton

In Kenya, Dr. David Marshall (above) examines wheat for signs of the stem rust fungus.
Photo Courtesy David Marshall

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

Dr. David Marshall and Dr. Gina Brown-Guedira with the U.S. Department of Agriculture’s Agriculture Research Service (ARS) and N.C. 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.

These photos show the effects of the fungus on wheat crops in Kenya. Marshall and his fellow scientists seek to find or develop wheat varieties that will be resistant to the new virulent form of the disease that has been spreading in Africa since 1998.
Photos by David Marshall
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,” he said.

“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 of those genes.”

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.

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 that 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 that 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.

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 to force it to flower.)

Marshall was responsible for assessing the winter wheat crop in September, while another ARS colleague will assess the spring crop. He looks 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 United States to be analyzed by ARS researcher Dr. Yue Jin at the agency’s Cereal Disease Laboratory in St. Paul, Minn. The work can be done only 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 United States, although researchers are not taking any chances.

“We believe that 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.”