Venturia inaequalis is an ascomycete responsible for the scab disease on apples (Malus spp.) (Fig. 4), and appears to be a good model for sympatric speciation in fungal pathogens. Genes conferring resistance to the pathogen have been identified in apple trees and used in orchard production. Most of the resistance genes are however no longer efficient as novel virulences having evolved in the fungal populations. One interesting exception is the Vf resistance gene. This resistance gene has long been considered as a unique example of durable plant resistance, conferring complete field immunity to V. inaequalis during more than 40