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Wheat spike infected by TCK: Link to photo information

Find out more in Agricultural Research magazine.

Fungal Risk Assessment Helps Clear Trade Hurdles

By Jan Suszkiw
December 26, 2000

WASHINGTON, Dec. 26—Dwarf bunt fungus concerns in milling wheat exports that threatened foreign trade have been addressed by a pest risk assessment (PRA) system developed by U.S. Department of Agriculture and industry researchers.

Such concerns surfaced in spring 1999, when U.S. trade officials presented a 57-page PRA report during negotiations with China to ease restrictions on U.S. wheat imports. The negotiations centered around China’s concern that accepting such grain could spread the fungus to their domestic wheat crops.

The fungus, Tilletia controversa Kuhn (TCK), sporadically infects winter wheat crops in the Pacific Northwest, but poses no human health risk. Under certain conditions, it damages the wheat kernel.

“With the pest risk assessments, our trade negotiators were able to present compelling scientific evidence showing TCK poses a negligible risk to China’s domestic wheat crop from U.S. grain imports,” Agricultural Research Service administrator Floyd Horn said today. “The PRAs have also proved invaluable in similar negotiations with India, Brazil and Mexico in 1998.”

As part of the agreement signed with the United States on April 10, 1999, China eased its zero-tolerance policy to a threshold level of 30,000 TCK spores per 50 grams of grain. According to USDA estimates, that opened the door to $150 million worth of possible U.S. wheat exports.

The PRAs draw on more than 10 years of laboratory and field research on TCK’s genetic variability, geographic distribution, spore growth, virulence and survival under various crop-production practices and grain handling regimens.

In 1997, this led to the creation of the TCK Task Force by Wilda H. Martinez, who assembled a network of collaborators at various USDA agencies, the U.S. wheat industry, Chinese scientific and regulatory entities, and international wheat pathogen experts. Martinez is ARS’ North Atlantic Area director.

A key element of the team’s PRA research involves using various computer models, including the “geophytopathological” model, or GPM for short. With it, researchers can identify climatic regions around the globe favorable to the fungus’s survival. When applied to China, for example, the GPM showed that regions conducive to the fungus were few as well as far from China’s import grain terminals and mills.

When applied to Brazil and Mexico, the model showed a lack of conditions necessary for the fungus to thrive--45 days of uninterrupted moisture, temperatures of -2 to 10 degrees Celsius, and mild winters under continuous snow cover.

Martinez said the priority now is “conducting research to develop a pest risk assessment on another wheat disease pathogen, Tilletia indica or Karnal bunt fungus.” Discovered in the southwestern United States in 1996, Karnal bunt fungus is currently on the quarantine lists of 72 countries.

An article about TCK research appears in the December issue of Agricultural Research magazine, and on the World Wide Web.

Contact: Wilda H. Martinez, Director, ARS North Atlantic Area, Wyndmoor, Pa., phone (215) 233-6593, fax (215) 233-6719,