Host-pathogen interactions in the novel ash dieback disease: Implications for management strategies
Common ash (Fraxinus excelsior) is currently threatened by an aggressive invasive fungus, Hymenoscyphus pseudoalbidus, which is causing severe tree mortality throughout Europe. The origin and infection biology of H. pseudoalbidus is not yet fully established but an intriguing aspect is its high resemblance to H. albidus, a native decomposer of ash litter believed to have a benign association to F. excelsior. Our previous works have revealed highly significant differences in susceptibility among ash clones to ash-dieback disease and that the performance is inherited from mother to offspring.
The present project will explore genetic and biological mechanisms behind the diverse performance of ash trees (Fraxinus excelsior and other Fraxinus species) to the disease. The objective is to secure the future use of Fraxinus and increase the general understanding of host-pathogen interactions in plants with long generation time. Based on a unique living collection of global Fraxinus species, and characterized genotypes of F. excelsior, the proposed project will characterise the genes involved in the resistance mechanism. The project compares gene expression profiles in susceptible and resistant individuals of F. excelsior and other Fraxinus species using next generation sequencing technologies. We test the hypothesis that the disease has been triggered by a host shift with a change from a neutral relationship between plant and fungus to a pathogenic relationship with the new host species. We estimate the level of susceptibility in other species of Fraxinus by controlled inoculations and hereby reveal the risk for future epidemics. The work will create fundamental knowledge for the future design of sustainable genetic management of F. excelsior and its close relatives. The disease causes alarming forest health problems throughout the continent in line with the Dutch elm disease of the late 1990’ties and we anticipate large interest by the public and the scientific community.