Other methods of inactivating vertical resistance

Robinson (1987) listed other methods of either inactivating or eliminating vertical resistance. In general, these alternative methods are not recommended, and anyone wishing to use them should consult the original descriptions for full details.

A genetic elimination of vertical resistance is sometimes possible, and parents without vertical genes can be identified either by using the universal avirulent (i.e., the vertical pathotype with no vertical genes) or by the 'Slopek technique'. The latter requires two simple pathotypes that do not have any vertical genes in common (e.g., vertical pathotypes 1 and 2). Potential parents are tested with one of these pathotypes, and all the susceptible lines are then tested with the other pathotype. Any that are susceptible to both vertical pathotypes obviously possess no vertical genes at all.

An epidemiological elimination of vertical resistance is occasionally possible by the 'saturation technique' in which the screening population is bombarded with a very wide range of vertical pathotypes. This is feasible, for example, when testing potatoes for horizontal resistance to blight (Phytophthora infestans) in the Toluca Valley in Mexico, which is the centre of origin of the blight fungus. Vertical resistances are matched very rapidly in this area. However, in general, this technique is not reliable.

The 'mechanism technique' relies on the identification of unmatched vertical resistances by the presence of hypersensitive flecks. Such material must be discarded. However, this approach may waste too much breeding material to be practical.

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