• aggressiveness;
  • Bayesian theory;
  • host heterogeneity;
  • natural selection;
  • trade-off

Field-based experimental evolution is a research approach in which study species are allowed to evolve across several generations under well-defined field conditions. Field-based experiments in pathogen evolution became feasible with advances in molecular markers and computing technologies. Critical to success of these experiments is the choice of parental genotypes, molecular markers, experimental sites and field plot design. The current study used field-based experimental evolution based on a mark–release–recapture strategy to analyse the dynamics of interstrain competition and host specialization in the cereal pathogens Zymoseptoria tritici, Phaeosphaeria nodorum and Rhynchosporium commune. In all three pathogen–plant interactions, compelling evidence was found indicating that increasing host heterogeneity by growing cultivar mixtures slowed down the evolution of the corresponding pathogen populations. Evidence for differential selection between parasitic and saprophytic phases of the life cycle in P. nodorum and R. commune was also found. The effect of partial resistance on the evolution of the experimental pathogen populations was mixed. A decreased rate of evolution was found in the pathogen populations sampled from partially resistant hosts in Z. tritici and P. nodorum but not R. commune. The findings indicate that field-based experimental evolution offers a powerful approach to test hypotheses associated with the evolution of plant pathogens.