Researchers from the Royal Botanic Gardens, Kew, Forest Research, and other partners have created the first-ever pangenome for the European ash tree (Fraxinus excelsior), publishing their findings in the journal Nature Communications. A pangenome is a comprehensive genetic map that includes the complete set of genes from multiple individuals, rather than just one. In this study, scientists used high-quality DNA from 50 ash trees of diverse origins to analyze a dataset from over 1,000 trees. This effort identified 211 genes possibly linked to resistance against ash dieback, a deadly disease caused by the fungus Hymenoscyphus fraxineus. Of these, 16 genes were found to be "dispensable," meaning they were present in only some of the trees. These dispensable genes, which make up 9% of the genome, may be responsible for differences in traits like disease resistance and drought tolerance. The pangenome includes over 3,400 dispensable genes and is 22% larger than the genome of a single ash tree when accounting for these variable genetic elements. This expanded genetic view allows scientists to study how different individuals respond to diseases more thoroughly than using a single genome. The research could help identify ash trees that are naturally resistant to ash dieback and support breeding programs to develop more resilient tree populations. The study involved ash trees collected from various locations, including Kew Gardens in London, a trial site near Norwich, private land, and Paradise Wood in Oxfordshire. Non-UK trees were grown at Paradise Wood as part of the Realizing Ash's Potential Trial, using seeds gathered from across Europe. The research is part of the Center for Forest Protection (CFP), a collaboration between Kew and Forest Research, supported by the UK government's Department for Environment, Food and Rural Affairs (Defra). Dr. Daniel Wood, a research fellow at Kew and lead author of the study, explained that the pangenome reveals genetic variation in wild ash populations, comparing it to different versions of a movie. Dr. Laura Kelly, a senior author and research leader at Kew, highlighted the importance of this work in combating ash dieback and another threat to ash trees, the emerald ash borer beetle. Jess Allan, coordinator of the CFP, called the research a vital step toward building a more resilient ash population. Ash dieback has had a devastating impact on UK forests since its discovery in 2012, with most ash trees dying from the disease. The fungus spreads through spores that invade the tree’s inner tissues, often leading to its death. However, researchers have observed signs of natural resistance in some young ash trees in East Surrey, showing that evolution is helping some populations survive. Earlier research by Kew scientists also found that different ash species have independently evolved similar genetic defenses against the emerald ash borer, a destructive insect. These findings offer hope for the future of ash trees in Europe.