Cultivar and Climatic Effects on the Protein Content of Soft White Winter Wheat

High-protein wheats (Triticum aestivum L.) are not preferred for Oriental diets. Because the protein content of soft white winter wheat grown extensively in the U.S. Pacific Northwest is often higher than the optimum (100 g kg⁻¹) for export, there has been a decline of wheat exports to Japan and other Pacific Rim countries. The present study was undertaken to examine the trends in protein levels during 1979 to 1988 and to evaluate the influence of wheat cultivars and climatic parameters on protein content of SWW wheat in the Pacific Northwest. The maximum and minimum temperatures, precipitation, and evaporation during each of 9 wk prior to crop harvest were tested for their effect on protein content. Data on protein content used in the analysis were obtained from the annual reports of USDA Western Wheat Quality Laboratory for wheat grown at 10 different locations in Washington, Idaho, and Oregon. Five-year moving averages indicated a rising trend in the protein content at Lind, WA, and Moro, OR, the two driest locations. Commercially grown cultivars had no significant influence on protein content in the presence of climatic parameters. Climatic parameters were found to have a significant influence on wheat protein content with coefficients of multiple determination ranging from 0.36 to 0.82 for the 10 locations. Maximum temperature during the grain-filling stage influenced the protein content at 9 out of 10 locations, and, generally, a rise in temperature resulted in higher protein contents. With climatic factors significantly influencing protein levels in SWW wheat, suitable agronomic and fertility management practices are needed to ameliorate the climatic effects. Contribution of the USDA-ARS and the Dep. of Crop and Soil Sciences, Dep. of Pure and Applied Mathematics, and Program in Statistics, Washington State Univ., Pullman.