Falling prices have lured a big buyer to U.S.-grown, low-protein wheat, raising the prospect for farmers of more exports and the hope that the market for low-protein wheat may have reached its nadir. U.S. wheat prices have tumbled 60 percent since reaching a four-year high in 2012 as large harvests around the world have reduced export demand. Global wheat inventories are at record-high levels, due in part to heavy production from Russia.