Long-term effects of disease epidemics.
Plants from 4 seed lines, developed on the basis of high or low seed wt and whether the seed came from wheat that was healthy or infected by mildew (Erysiphe graminis f.sp. tritici), were grown alone or in the presence of other individuals in a disease-free environment for 2 post-epidemic generations. In the competition treatments of the first generation, plants from disease-derived seed lines produced, or tended to produce, fewer ears than healthy lines. This reduction in ear number resulted in a commensurate reduction in total seed number. In the absence of competition, plants from the diseased lines responded similarly, producing fewer ears than those from the healthy lines regardless of seed wt. This again resulted in a reduction in the total number of seeds produced. In neither case was there any difference in av. wt of the seed. In the second post-epidemic generation, no differences were detected among the 4 seed lines. The effects of infection were carried over for 2 post-epidemic generations. In the first generation, both the number and competitive ability of individual plants were reduced, since infected plants produced fewer seeds which weighed less and had a lower N content. In the second generation, only numbers were reduced, since the diseased lines produced fewer seeds at the end of the first post-epidemic generation.