Third consequence horizontal resistance ignored

The third consequence is that the very existence of horizontal resistance, to say nothing of its evolutionary significance, and its agricultural importance, have been generally over-looked, and even denied outright. At the systems level of the pathosystem, it is clear that the two kinds of resistance complement each other, and that horizontal resistance is essential. It is the resistance that invariably remains after vertical resistance has been matched. And most vertical resistances inevitably are matched, because their function is merely to reduce the frequency of matching, rather than to eliminate the matching entirely. But, so long as research was confined to single-gene qualitative resistances, the much less obvious, quantitative effects of horizontal resistance remained unobserved and unused. This bias was greatly strengthened by several sources of serious error (see 7.16).

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