Unapproved genetically modified wheat found growing in the United States is threatening the outlook for U.S. exports of the world's biggest traded food commodity, with importers keenly aware of consumer sensitivity to gene-altered food. Major importer Japan has canceled a tender offer to buy U.S. western white wheat, while other top Asian wheat importers South Korea, China and the Philippines said they were closely monitoring the situation. The European Union is preparing to test incoming shipments, and will block any containing GM wheat. GM wheat was discovered this spring on a farm [in] Oregon, in a field that grew winter wheat in 2012. Scientists found the wheat was a strain field-tested from 1998 to 2005 and deemed safe before St. Louis-based biotech giant Monsanto withdrew it from the regulatory approval process on worldwide opposition to genetically engineered wheat. No GM wheat varieties are approved for general planting in the U.S. or elsewhere, the USDA said. The EU has asked Monsanto for a detection method to allow its controls to be carried out. With high consumer wariness to genetically-modified food, few countries allow imports of such cereals for direct human consumption. However, the bulk of U.S. corn and soybean crops are genetically modified.