"Ash dieback damage was assessed and analysed on 16–22 year-old grafts in two ash seed orchards (Fraxinus excelsior L.). The grafts originated from 106 plus-tree clones selected from 27 stands in southern Sweden based on their phenotypes. The results obtained indicate that ash dieback disease is strongly genotypically controlled. There was considerable genotypic variation among individuals. None of the clones seemed to be totally resistant, but some exhibited reduced susceptibility and retained this resistance after 6 years under heavy infection pressure."