Susceptibility of autochthonous German Fraxinus excelsior clones to Hymenoscyphus pseudoalbidus is genetically determined.

Context: It might be possible to establish a new generation of Fraxinus excelsior which is insusceptible towards ash dieback (agent: Hymenoscyphus pseudoalbidus) by efficient breeding. However, a considerable number of highly tolerant individuals which have the ability to pass on this trait to their progeny are needed. Aims: The aim of this study was to identify the potential of provenances from southwestern Germany as a source of future selection for resistance or resistance breeding. Methods: In July 2012 and 2013, ash dieback severity was scored by assessing the crown defoliation and the portion of epicormic shoots in the crowns in clonal seed orchards with a total of 1,726 ash trees in southwestern Germany. Results: Ash dieback severity differed strongly between the orchards and the clones. Broad-sense heritability ranged from 0.18 to 0.55 for crown defoliation and from 0.48 to 0.58 for the portion of epicormic shoots between the orchards. Clones from nearby populations did not show differences in general levels of susceptibility. Conclusion: The study highlights that there is high genetic variation in susceptibility and considerable genetic potential for resistance breeding in provenances from southwestern Germany. [ABSTRACT FROM AUTHOR]