Population Genetics of the Pathogen

Abstract

Plant breeders introduce resistance genes into crop plants. Whether the introduction will be successful or not depends on the pathogen. If it can match the resistance genes, i.e., if matching virulence alleles become prevalent in the population of the pathogen, the work of the plant breeder is largely undone. This is an old story in plant pathology. It is retold here simply to make the point that the decisive factor in breeding for resistance is the population genetics of the pathogen. The genetics of host resistance, which has received far more attention in the literature, is one step removed from the core of the problem. Resistance genes in the host influence the durability of resistance only indirectly, through their influence on the population genetics of the pathogen. In vertical resistance an influence is present. In horizontal resistance it is absent. That is what Chapter 1 was about.