The crop-biotechnology wars are heating up again, with Monsanto Co. filing a patent-infringement lawsuit against archrival DuPont Co., which responded by calling Monsanto a monopolist. The lawsuit, filed Monday in federal district court in Monsanto's hometown of St. Louis, is aimed at forcing DuPont's Pioneer Hi-Bred seed business to dismantle a herbicide-resistant soybean plant that DuPont hopes to begin selling to farmers in 20U. The new seed contains two genes that have been modified to make the plant tolerate herbicides. One is a DuPont gene that allows the soybean plant to tolerate exposure to glyphosate-based weed killer as well as to another herbicide called acetolate synthase. The seed project has long been touted by DuPont, of Wilmington, Del., as part of its strategy to offer farmers an alternative to herbicide-tolerant soybeans using Monsanto biotechnology. Such crops are popular with farmers because they make weed control much easier. The suit was prompted by the other gene, developed by Monsanto. Monsanto argues in its lawsuit