Long-Term Effects of Disease Epidemics

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Abstract
(1) Four lines of seed were developed on the basis of high or low seed weight and whether the seed came from wheat (Triticum aestivum) that was healthy or infected by mildew (Erysiphe graminis f. sp. tritici). Plants from these four seed lines were grown alone or in the presence of other individuals in a disease-free environment for two post-epidemic generations. (2) In the competition treatments of the first generation, plants from disease-derived seed lines produced, or tended to produce, fewer ears than the healthy lines. The reduction in ear number in the diseased lines resulted in a commensurate reduction in total seed number. In the absence of competition, plants from the diseased lines responded in a similar manner producing fewer ears than those from the healthy lines, regardless of seed weight. This again resulted in a reduction in the total number of seeds reduced. In neither case were there any differences in the average weight of the seed produced. (3) In the second post-epidemic generation, no differences were detected among the four seed lines. (4) The effects of disease infection were carried over for two 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 reduced nitrogen 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.

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