March 28 (Reuters) - A group of U.S. family farmers said on Wednesday it is appealing its lawsuit against Monsanto Co to challenge the company's patents on technologies for genetically modified seeds.

The group of organic farmers and seed dealers says its industry is at risk from Monsanto's growing market dominance.

"Farmers are under threat. Our right to farm the way we choose, and to grow pure organic seed and healthy food on our farms for our families and for our customers is under assault," said Maine organic seed farmer Jim Gerritsen, president of the Organic Seed Growers and Trade Association, lead plaintiff in the case.

The group sued Monsanto in March 2011. U.S. District Court Judge Naomi Buchwald, for the Southern District of New York, threw out the case last month, criticizing the groups for a "transparent effort to create a controversy where none exists".

The group of more than 50 organizations filed its notice of appeal o n Wednesday, seeking review by the U.S. Court of Appeals for the Federal Circuit.

The lawsuit challenges the company's patents on its genetically modified seeds and seeks to prohibit Monsanto from suing the farmers or dealers if their organic seed becomes contaminated with Monsanto's patented biotech seed germplasm.

Monsanto spokesman Thomas Helscher said the company was aware of the filing of an appeal.

"We remain confident about our legal and practical stance," he said.

Monsanto is the world's largest seed company and a leader in development and marketing of genetically altered soybeans, corn and other crops.

The company has developed a reputation for zealously defending patents on its genetically altered crops, which include patented "Roundup Ready" soybeans, corn and cotton. The crops are favorites of U.S. farmers because of their ability to withstand herbicide treatments.

Monsanto filed 144 patent-infringement lawsuits against farmers between 1997 and April 2010, and won judgments against farmers it said made use of its seed without paying required royalties.

Many U.S. farmers have said their fields were inadvertently contaminated with Monsanto's biotech seeds without their knowledge. The issue has been a topic of concern for not only farmers, but also companies that clean and handle seed.

The court ruling said there was no likelihood that Monsanto would pursue patent-infringement cases against the organic farmers, who have no interest in using the company's patented seed products. (Reporting by Carey Gillam)

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