Pathotypes and Pathodemes

Robinson (1969) proposed a system of naming the strains of both hosts and parasites that are defined by criteria of parasitism. This system was intended to replace the antiquated plant pathological terminology which used the terms 'physiologic race' and 'pathologic race' to describe pathologically defined strains of pathogens. There was no corresponding terminology for the host. Entomologists spoke of 'biotypes' when describing insect strains defined by resistance in the host. They too had no corresponding terminology for the host.

Robinson proposed that, in a pathosystem context only, the suffix '-type' should be reserved for strains of the parasite, and the suffix '-deme' should be reserved for strains of the host. The prefix 'patho-' indicates that these strains are defined by criteria of parasitism. This prefix is used in its wide biological sense of pathos (Gk = suffering) rather than its narrow agronomic sense of plant disease. It accordingly applies equally to the various animal and Angiosperm parasites of plants, as well as to the various categories of plant pathogens. A pathotype is a strain of a parasite, in which all individuals have a stated character in common, defined by criteria of parasitism. Similarly, a pathodeme is a strain of a host, in which all individuals have a stated character in common, defined by criteria of parasitism.

The two kinds of host resistance in plants, known as vertical resistance and horizontal resistance, define the vertical pathotype and vertical pathodeme, as well as the horizontal pathotype and the horizontal pathodeme. In each of these terms, 'vertical' means that a gene-for-gene relationship is present, while 'horizontal' means that a gene-for-gene relationship is not present.

It should be made clear that a pathodeme can consist of many different cultivars. Thus, vertical pathodeme '1' includes all cultivars that possess only vertical resistance gene '1' to a particular parasite, even though these cultivars may differ widely in other respects. This comment applies equally to vertical pathotypes, and to horizontal pathodemes and horizontal pathotypes.

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