Coevolution of a plant host-pathogen gene-for-gene system in a metapopulation model without cost of resistance or cost of virulence

A metapopulation model of a one-locus gene-for-gene system in a plant host and a biotrophic pathogen is described. The model allows subpopulations to go extinct, and, due to characteristic differences in life-history strategies, the plant host is assumed to be recolonized from a seed bank, whereas the pathogen is recolonized by migration. It is shown that variation in the gene-for-gene system can be maintained at a noticeable level without assuming cost of resistance or cost of virulence, if the probability of extinction depends on the host mean fitness in the subpopulation. The level of variation in the pathogen population increases with increasing extinction rate, genetic drift and fitness of the infected host, but decreases with increasing migration rate. Generally, these effects are magnified for life cycles in which selection occur before genetic drift and after migration. The metapopulation model generates positive associations between the virulence allele and the resistance allele without assuming cost of resistance or cost of virulence. Copyright 1999 Academic Press.