Barley. A crop that is as old as wheat, dating from about nine thousand years ago. It is salt-tolerant, and it often substituted for wheat, in ancient times, in soils that had become salty from inappropriate irrigation. However, it is little used in human nutrition today. The main use is for animal feed, and for malting to make beer. There is plenty of scope for developing horizontal resistance, and the crop is probably amenable to the use of male gametocides. Horizontal
In a plant epidemiological context, this term is entirely abstract, and it means that a gene-for-gene relationship is absent. Horizontal resistance and horizontal parasitic ability are both defined by the absence of a gene-for-gene relationship. A horizontal subsystem of a pathosystem is also defined by the absence of a gene-for-gene relationship.
See also: Horizontal parasitic ability, horizontal resistance, Horizontal pathotype, and Horizontal pathodeme. Horizontal parasitic ability
Parasitic ability that does not result from a gene-for-gene relationship. Horizontal parasitic ability is the parasitic ability of the Biometricians, and its inheritance is usually controlled by many polygenes. Although it has been very little studied, it seems always to vary quantitatively. It is the parasitic ability that enables a parasite to obtain nutrients from its host after the vertical resistance has been matched, and in spite of the horizontal resistance. (See also: vertical parasitic ability). Horizontal pathodeme
A population of a host in which all individuals have the same horizontal resistance. Many different cultivar with the same horizontal resistance, but with differing agronomic characteristics, all belong to the same horizontal pathodeme.
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