Japan's farm minister has tried to calm concerns about possible shortfalls in the country's main source of flour for cake and other sweets after genetically modified wheat was discovered in the United States, saying the country has two months' inventory of the grade.

In the comments made on Tuesday, minister Yoshimawa Hayashi added that Japan could consider importing alternative types of wheat if U.S. investigations into the discovery of unapproved GM wheat growing wild in a field in Oregon dragged on.

Japan shunned U.S. shipments of the Western White grade of wheat at a tender last week and is not expected to restart imports until the conclusion of the U.S. investigation into the rogue strain of wheat, modified by Monsanto Co for herbicide tolerance but never put into commercial production.

"We're looking to the development of an investigation by U.S. authorities," Hayashi said. "But if the period of the halt is prolonged, we may have to consider the possibility of an earlier supply than usual of this year's locally grown wheat and the possibility of importing alternative types from abroad."

Millers have said, however, that it could be difficult to find an alternative foreign wheat to replace Western White as it is the sole low-protein type suitable for cake flour that the ministry currently buys. The world's sixth-biggest wheat buyer imports around 800,000 tonnes of the grade each year.

The U.S. Department of Agriculture announced the find last week after tests to identify the wheat strain and says there is no evidence that any GM crops have entered the supply chain.

South Korea said on Wednesday it has not detected any genetically modified wheat in tests so far on imports of the grain and flour from the state of Oregon, but that tests are ongoing.