CLASSICAL PLANT BREEDING FOR DURABLE RESISTANCE TO DISEASES
Classical plant breeding has produced many improvements to crop cultivars, including disease resistance. It is a dynamic process in which the objective is usually the improvement of many characters simultaneously, including disease resistance. Some introduced resistances failed rather soon after its introduction, because of evolution to virulence in the pathogens; others did not fail in this way and remained effective despite widespread and prolonged use, thus being identifiable as providing durable disease resistance. Examples of durable resistance achieved by classical breeding are given, and show that there is no single genetic model for durable resistance and also, no typical phenotype by which to identify it. It is the durability that initially allows the identification of it. Disease resulting from introduction of genetic male sterility in maize is described and used to illustrate risk in the use of widespread genetically uniform material. Such risk will be associated with disease resistance introduced by biotechnology just as much as it has been by classical plant breeding. Resistance introduced by biotechnology will only be shown to be durable after widespread and prolonged testing.