WASHINGTON — U.S. trading partners that purchase western white wheat considered their next moves in the wake of the announcement May 29 by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service that it detected the presence of an unapproved bioengineered trait in wheat plant samples from an Oregon farm. At the same time, Monsanto, the company that field tested wheat with its glyphosate-tolerance (Roundup Ready) gene several years ago vowed to cooperate with the U.S.D.A. to confirm its test results and considers appropriate next steps.

Japan passed on offers of U.S. western white wheat in its weekly tender, and its ministry of agriculture indicated it would import no more western white wheat until the situation becomes clearer.

Indications were South Korean flour mill groups cancelled plans to tender for U.S. soft white wheat and awaited results of the U.S.D.A. investigation. Taiwan flour millers said they’d put U.S. wheat imports under review and will require their suppliers to offer guarantees that only non-bioengineered wheat was in shipments.

The European Commission was said to have contacted Monsanto seeking a method to detect the company’s bioengineered wheat and advised member countries to test imports of soft white wheat.

Monsanto said its field testing of its Roundup Ready wheat variety ended nine years ago.

“Accordingly, while the U.S.D.A.’s results are unexpected, there is considerable reason to believe that the presence of the Roundup trait in wheat, if determined to be valid, is very limited,” Monsanto said. “We will work with U.S.D.A. to confirm their test results and as they consider appropriate next steps. We will also conduct a rigorous investigation to validate the scope of and to address any presence of a Monsanto Roundup Ready event in commercial wheat seed.”