Australian wheat production is on course to miss official forecasts by more than 20 percent as dry weather crimps yields in the world’s fourth-largest exporter, exacerbating fears of tightening global supplies. The expectation of Australia’s shortfall follows news that one of the worst heat waves in decades is devastating wheat crops in southern Europe. Output in the United States is also tumbling due to hot, dry weather. Growing concerns about dwindling global supplies have already pushed benchmark global prices to a two-year high.