Is yield a measure for breeding improvement in wheat?

Between 1845 and 2005 yields of German wheat production increased more than 6-times to 75,2 dt/ha. Reasons are not only improved agricultural technology, but also particularly plant breeding. In combination with increasing yields, quality improved too. The negative correlation between yield and crude protein still exists. Breeding of new varieties, which takes current diseases into account, leads to a steady or even rising resistance level. High standards of yield, quality, resistance and other traits lead to an increasing breed diversity, which meets farmers demand.