First consequence vertical resistance is ephemeral

The first effect of this suboptimisation is that a single-gene resistance is ephemeral, when it is extracted from a gene-for-gene relationship, and is then employed on a basis of host population uniformity. To produce a new cultivar on this basis is the equivalent of giving every door in the town the same lock. As soon as the parasite produces a matching strain, the resistance stops functioning, and the system of locking has been wrecked by uniformity. The entire cultivar is then ruined.

When matching occurs, the cultivar is abandoned, and it must be replaced with a new one that has a different resistance gene (or genes). This procedure has produced a long repetition of expensive failures of resistance that has been called the "boom and bust" cycle in plant breeding. There are some exceptions to this rule that vertical resistance is ephemeral resistance (see 5.7), but too few to invalidate its general applicability.

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