Resistance to certain strains of the pathogen is observed, while other strains are not affected. This phenomenon is usually associated with oligogenic resistance cases where there is a gene-for-gene correlation between the host and the pathogen. The term “horizontal resistance” is more appropriate than the interchangeable term “vertical resistance” because it precisely defines the state it represents. It should not be considered a synonym for oligogenic resistance since the latter is not necessarily limited to specific pathogen races; the two terms relate to different characteristics of resistance.