Evolutionary Function of the Genefor Gene Relationship

It appears that the sole evolutionary function of the gene-forgene relationship is to confer stability on the pathosystem. It does this by reducing the massive population explosion of an asexually reproducing r-strategist parasite (see 4.21). This stabilisation is particularly important during an abnormal season, which greatly favours that parasite. If it were uncontrolled, such an epidemic could devastate the host population, and this would threaten the survival of both host and parasite.

Most often, this stability is conferred by the prevention of infection. That is, the proportion of allo-infections that are matching infections is greatly reduced. In some instances, however, the vertical resistance is quantitative (see 10.18), and the effect of the resistance is then to allow infection but to prevent, or greatly reduce, parasite reproduction.

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