Monsanto Co. and DuPont kicked off the latest round of their long fight over genetically modified seed technology in a St. Louis courtroom Tuesday.

The suit dates back to 2009, when Monsanto sued DuPont for allegedly infringing patents on its herbicide-tolerant Roundup Ready crops. The agriculture giant says DuPont added Monsanto’s patented seed technology to its own crops, violating a 2002 licensing agreement between the two companies.

Meanwhile, DuPont accuses Monsanto of obtaining the Roundup Ready soybean patent through fraudulent means. “We will … demonstrate that Monsanto sought to enforce the RE 39,247 patent against farmers and against DuPont even though Monsanto and its lawyers knew the patent was invalid,” DuPont attorney Thomas Sager told Reuters.

In 2010, the U.S. District Court in St. Louis ruled that the licensing agreements in question include an “implied” term preventing DuPont from combining Monsanto’s herbicide-tolerant genes with its own Optimum GAT soybean seeds. The court added, however, that DuPont’s antitrust and patent fraud claims against Monsanto could proceed.

This trial is slated to last for three weeks, but it appears the companies’ legal tussles will continue indefinitely. In a separate suit last month, Monsanto sued the chemical company for infringing patents on Monsanto’s “seed chipper” technology. And DuPont filed its own lawsuit in 2011, claiming that Monsanto had infringed its patents for “enhancing the vigor of maize seed.”

Read more coverage at Reuters.

For more InsideCounsel coverage of Monsanto, read:

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