Overcoming obstacles to interspecies hybridization of ashThis article is part of a larger document. View the larger document here.
Tree species that share a long co-evolutionary history with insects and pathogens are likely to have developed mechanisms of resistance that allow them to coexist. When insects and pathogens are introduced to different parts of the world, high levels of susceptibility can be observed, presumably in part due to the lack of co-evolutionary history between the insect (or pathogen) and host. In such cases, use of non-native tree species as a source of resistance for introgression into native susceptible tree species can be quite helpful.