Syngenta AG said that grain prices have played a role in China's rejection of U.S. corn shipments containing an unauthorized, genetically modified trait developed by the company.
China, the world's third-biggest corn buyer, has turned away since November more than 900,000 tonnes of U.S. corn containing Syngenta's Agrisure Viptera trait.
"There's unquestionably a global trade issue at play here relating to contracts and prices," said David Morgan, Syngenta's regional director of North America.
Syngenta, the world's largest crop chemicals company, has been waiting for China to approve Viptera, known as MIR 162, for import for more than four years.
Beijing started cracking down on shipments containing the trait late last year, even though Viptera corn had been mixed in with other varieties since China increased imports of U.S. corn in 2011.
The rejections have fueled speculation among grain traders that China was strictly enforcing its ban as a way to exit contracts for pricey corn and to prevent imports into a well-supplied market. U.S. corn futures soared to $8 a bushel last summer and dropped almost 50 percent by November.
Pressure from Chinese who believe the country should be more self sufficient in food production is another explanation for the government's rejections of U.S. corn containing Viptera, Morgan said. There is no one reason behind the rejections, he added.
China's Biosafety Committee is due to meet this week or next to decide whether to approve Viptera, engineered to offer protection against crop-damaging insects.
After years of waiting for approval, Morgan said he had become "sober" in his expectations of what would come out of China.
"I'm hopeful that they will proceed in the next discussion but until we hear from them, I'm not going to count any chickens, as they say," he said in a telephone interview.
Niu Dun, China's vice agriculture minister, said in December that Viptera corn could not be accepted because it had not been approved by the ministry for import.
China has found its debate over imports of GMO farm products "to be a convenient tool to use to try and protect the Chinese market," Fred Gale, the U.S. Department of Agriculture's China chair, said at a conference this month.
China holds more than 90 million tonnes of corn in state stockpiles. Traders are expecting the government to sell some grain as early as May.