Breeding crops for horizontal resistance is easy. This is one of the more important messages of this book. Without any scientific knowledge, ancient farmers were working with horizontal resistance since the dawn of agriculture. It is possible that they unwittingly employed vertical resistance also, as mixtures of resistances in their local landraces. However, the effects of these vertical resistances would have been relatively small. These farmers cultivated their crops with few parasite control measures. At best, they practised either shifting cultivation or mixed cropping, and they may have burned their crop residues.

The yields of these early farmers were not high by modern standards, mainly because they lacked fertilisers, other than manure consisting of animal and human excrement. They also lacked crop protection chemicals. The point here is that they could grow their crops without crop protection chemicals, because these crops had adequate horizontal resistance to provide an economically effective control all locally important parasites. Had this not been so, these crops could not have been cultivated.

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