In a head-to-head contest in a small corner of agricultural futures markets, a legacy spring wheat contract that has traded for more than 140 years is fending off a challenge from a competing contract launched this spring by CME Group, the world’s largest futures exchange. Spring wheat, grown in the northern Plains of the U.S. and Canada, is favored for bagels and frozen dough. The contract was introduced in 1883 on the Minneapolis Grain Exchange and has long set the price for premium-quality wheat used by North American millers and exported around the world. Get a daily digest of breaking business news straight to your inbox with the Reuters Business newsletter. Sign up here. Compared to other commodities, trade in spring wheat contracts is relatively modest. But it is among the only major agricultural commodity derivatives not dominated by CME Group, which in recent decades has expanded from its 19th-century origins as the Chicago Mercantile Exchange into a $99 billion behemoth ...