DuPont Pioneer, one of the world's largest seed companies, is refusing to give up on efforts to cultivate genetically modified crops in Chinese fields in the face of regulatory hurdles, even as rivals pull back.

The Iowa-based agricultural seed and chemical unit of DuPont this autumn harvested its first test crops of GMO corn in China in six years after lengthy efforts to win government approval for the new field trials.

The company is pressing ahead while Monsanto Co is retreating from efforts to grow GMO crops in China amid mounting frustrations within the U.S. seed industry about Beijing's slow regulatory processes.

Industry leaders say they are focusing on winning Chinese clearance for imports of new genetically engineered crops rather than for cultivation approval.

China is already a large producer of genetically engineered cotton, but has not approved commercial cultivation for any type of biotech corn. Approval to sell GMO corn seed to Chinese farmers would mark a big victory for a U.S. seed maker because China is the world's fastest-growing corn market.

But Chinese consumers have become increasingly concerned over GMOs in the past two years, and Beijing has all but stopped issuing approvals for imports of new GMO crops. Another hurdle is China's desire to promote its own domestic biotech innovations, industry members said.

Pioneer is in the first steps of the application process for commercial cultivation of GMO corn, which could take at least six years, Firoz Amijee, who leads the company's efforts to win regulatory approval for new biotech crop products, told Reuters.

Researchers this year have worked with Chinese government scientists to plant, harvest and analyze Pioneer corn genetically altered to control insects and tolerate herbicides.

"We're not sure what we'll get to do next year or the year after," said William Niebur, general manager of Pioneer's China operations.

Pioneer, which has established three joint ventures in China since 2002, was last allowed to conduct similar field trials on GMO corn there in 2008.

Matthew O'Mara, director of international affairs for the Biotechnology Industry Organization, whose members include major seed companies, said cultivation approval for GMO corn was unlikely anytime soon.

China's "intention is to have their biotech innovation be home grown and specifically not from multinationals," he said.

Monsanto, which also has a joint venture in China, has backed away from pursuing cultivation approval there after conducting small field trials from 2009 to 2012.

The company's "focus right now is on supporting farmers in the country through our conventional seed businesses, not on biotech cultivation efforts," said Juan Ferreira, vice president of international business.

Monsanto's biotech traits could benefit Chinese farmers "when the opportunity is available in the future," he added.

Seed makers have seen the risks of doing business in China.

Syngenta AG is facing lawsuits from grain handlers after China rejected imports of U.S. crops containing a GMO Syngenta corn trait approved in the United States but not by China.