Infection genetics: gene-for-gene versus matching alleles models and all points in between

Here we address the controversy between plant pathologists and invertebrate zoologists as to the genetic basis of infection. We show that the alternative models proposed by these groups represent two ends of a continuum. Specifically, the gene-for-gene (GFG) model of plant pathologists represents one end of a continuum, where a very broad host range is expected to occur in one pathogen genotype. The matching alleles (MA) model, favoured by invertebrate zoologists, represents the opposite end of the same continuum, where an exact genetic match is required for infection. Since it is known that matching-alleles models give highly dynamical behaviour and selection for recombination if parasites exert strongly negative effects on host fitness, we were especially interested in determining the nature of any such behaviour in the interior regions of the MA–GFG continuum. We found that the highly dynamical aspects of matching-alleles models were observed across most of the continuum, and that recombination would increase geometric mean fitness over about half of the continuum