Horizontal Resistance to Disease

Abstract

Horizontal resistance has been plagued by being given meaningful names that turn out in the end to have the wrong meaning. Plant pathologists have been slow to realize the value of nondescript appelations. Name your child Jack or Jane rather than Hercules or Rose because you never know how it will grow up. Every preconception embodied in synonyms for horizontal resistance has been found to be false. General resistance is a favorite, but, as we shall show, one of the features of horizontal resistance is great specificity. Polygenic resistance is commonly used, but it has yet to be shown that there is a single instance of resistance that is polygenic according to the accepted usage of the word, or that major variation in horizontal resistance involves more genes than in vertical resistance. Partial resistance has its advocates, but vertical resistance is also partial, and, as we shall discuss in the next chapter, some forms of horizontal resistance seem to be total and complete. Mature plant resistance or adult plant resistance, as a name used out of direct context with plant age is plainly silly, when seedlings also have horizontal resistance, and many examples are known of vertical resistance manifested only in the adult plant.