Effects of Powdery Mildew on Yield and Quality of Isogenic Lines of ‘Chancellor’ Wheat1

The effect of powdery mildew (Erysiphe graminis DC. f. sp. tritici E. Marchal) infection on yield, and milling and baking quality was determined under natural field conditions. Near‐isogenic lines of ‘Chancellor’ wheat (Triticum aestivum L.), involving at least seven independent genes for resistance to powdery mildew, were grown at College Park and Queenstown, Md. in 1974 and 1975. A regression equation was determined to predict the effects of disease severity on yield. The severity of powdery mildew infection varied among years and locations. Chancellor yielded 34% less than the average yield of the resistant lines. Yield was negatively correlated with percent powdery mildew on the whole plant and on the flag leaf (r = ‐0.78** and −0.80**, respecively). The regression equation of yield in q/ha (Ŷ) on percent powdery mildew on the flag leaf was Y = 33.4 − 0.18 X, r2 = 0.65**. The gene in ‘Michigan Amber’ and the three Pm 3 genes were highly effective in reducing infection. The isolines differed significantly for percent flour protein, cookie diameter, and adjusted cookie diameter when grown under severe powdery mildew infection. The lines with the highest disease rating also had the lowest flour protein content. Percent flour protein was negatively correlated with percent powdery mildew on the whole leaf and the flag leaf (r = −0.77** and −0.80**, respectively). However, severe powdery mildew infection did not adversely affect the over‐all baking quality. Milling quality (flour yield and flour ash percent) was not affected by the severity of powdery mildew infection.