Genomic basis for resistance to acute oak decline and mildew infection in English oak

English oak (Q. robur) in Britain is at risk from a young age due to powdery mildew and at maturity due to acute oak decline (AOD). The contribution of oak genetic diversity to these conditions is a critical question that until recently would have required extensive clonal or family trials of juvenile and mature oak trees. Here we overcome this practical burden with genomic approaches inspired by medicine. We sequence 1868 oak trees from 78 sites and identify 1491 trees exclusively of the species Q. robur, which we analyse. Using single nucleotide polymorphism (SNP) based estimates of heritability ([Formula]), we estimate 20.9% of variation in AOD presence is genetically determined. For mildew symptoms, [Formula] is 27.8%. Using genome-wide association studies, no SNP markers show a significant association with AOD, but 183 are significantly associated with mildew. Genomic prediction models for AOD and its symptoms, using thousands of loci, give low to moderate accuracies, ranging from 0.187 to 0.617. These results suggest a highly polygenic heritable component of susceptibility to AOD, which perhaps reflects the number of biotic and abiotic factors known to contribute to it. In contrast, powdery mildew, caused by a single fungus, has an oligogenic heritable component controlled by fewer loci of large effect. These results could be used to inform breeding programs to develop trees more resistant to AOD and mildew.