7/29/2021 By Karl Plume FARGO, North Dakota, July 29 (Reuters) - The average spring wheat yield in North Dakota, the top-producing state, was estimated at 29.1 bushels per acre on Thursday by the annual Wheat Quality Council tour, the lowest on record going back to 1993 due to a severe drought in the northern Plains. The figure was well below the crop tour average from 2015-2019 of 43.6 bpa and the U.S. Agriculture Department's 2021 latest spring wheat yield estimate for the state of 28.0 bpa. The Wheat Quality Council did not hold a tour in 2020 due to the coronavirus pandemic. A severe drought slashed harvest potential for spring wheat, used in pizza crusts and bagels and to increase protein content of lower-quality wheat, sending prices to their highest in nearly nine years as millers, bakers, and global buyers assessed tightening supplies.