Resistance controlled by one or a few major genes, in which varieties with this type of resistance are usually highly resistant to one or several pathogen races or several disease races or insect biotypes of a given species but are susceptible to others. A type of resistance which is expressed against only some biotypes of a pest species and is governed by one or more genes in the host plant, each of which corresponds to a matching gene for parasitic ability in the pest species, sometimes called gene-for-gene resistance (See also Horizontal resistance).