MINNEAPOLIS (AP) — The first of tens of thousands of U.S. lawsuits is about to go to trial against Swiss agribusiness giant Syngenta over its decision to introduce a genetically engineered corn seed variety to the U.S. market before China had approved it for imports.

The lawsuits allege that Syngenta's move wrecked an increasingly important export market for U.S. corn, and that the resulting price drops hurt all producers. Court filings show that Syngenta aggressively marketed the seeds even when it knew that Chinese approval was going to be a problem.

Plaintiffs' experts estimate the economic...