Other examples of unconscious selection

In the United States, the curly top virus of sugar beet has undergone a decline similar to that of flax wilt due to a gradual increase in the level of horizontal resistance during both breeding and cultivation. Similarly, tobacco varieties showed a gradually increasing horizontal resistance to bacterial wilt (Pseudomonas solanacearum). The same is probably true of wheat cultivars and resistance to Take-All disease caused by Gaumannomyces graminis. No doubt, other examples can be found, particularly against parasites which lack a gene-for-gene relationship, and for which no formal breeding was undertaken during the twentieth century.

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