Nov 19 (Reuters) - Archer Daniels Midland Co sued seed company Syngenta AG on Wednesday over sales of a genetically modified corn variety not approved for import by China, joining more than 100 farmers and exporters in pursuing damages from the Swiss-based company. The lawsuit alleges that Syngenta commercialized the MIR162 corn variety, also known as Agrisure Viptera, without creating an effective stewardship program to ensure the grain would not be shipped to markets that have not approved it. China has over the past year rejected shipments of more than 1 million tonnes of U.S. corn and corn products because they contained MIR162 grain. The variety, planted on about 3 percent of U.S. corn acres during the past two years, can be found throughout the American supply chain because it has not been segregated from other varieties since its launch in 2011.