Resources for the development of ash trees resistant to ash dieback

The fungal pathogen Hymenoscyphus fraxineus, which is the cause of Ash dieback (ADB), has severely affected ash tree (Fraxinus excelsior) populations in Europe. At the same time, the insect herbivore emerald ash borer (EAB) has wreaked havoc in North America and is beginning to spread in Europe from the east. Ash species native to Asia seem to show signs of tolerance and/or resistance to both of these threats. This thesis aims to develop genetic resources and knowledge for addressing these threats and tools to aid researchers and breeders. Ash species can be hard to identify morphologically, so this thesis describes the development of three DNA barcoding regions for accurate identification of 26 Fraxinus species native to Europe, Asia and North America. These barcodes are used to confirm the parentage of Fraxinus hybrids generated at Teagasc (Ireland) via crosses between Asiatic and European ashes. To investigate the biochemical basis of resistance to ADB and EAB, this thesis predicts the protein structure of 73 coding sequence loci identified by association studies as candidate genes. These predicted structures allow identification of particular amino acid substitutions that could be altering the activity of these enzymes. To test the newly available 4TREE array for genotyping 13407 loci in ash, including some previously identified candidate genes, two-half sibling families of F. excelsior generated in Belgium and a strategic collection of F. excelsior held at Teagasc, Ireland, are genotyped. These data are used to assess the potential of these tree collections for the basis for future breeding programmes. To lay the groundwork for understanding genome evolution in the wild, we phenotyped ~800 trees in an ancient ash woodland in England, representing a broad range of ages and levels of ash dieback damage