Ash dieback, an emerging fungal disease incited by Hymenoscyphus pseudoalbidus (anamorphChalara fraxinea), causes immense damage to Fraxinus excelsior in many parts of Europe. There is hope that some individuals of this tree species display high levels of resistance to the disease. In 2009 and 2010, the intensity of ash dieback was investigated in an ash seed plantation in Upper Austria, consisting of 51 clones of local provenance. A specific rating system for visual inspections was developed to assess shoot, twig and branch dieback as well as leaf shedding. Considering all 187 evaluated trees, mean ash dieback intensity was 18.1% in July 2009 and 17.6% in July 2010. Disease intensity varied greatly between clones, ranging in both years from almost no dieback to more than 80% dieback in the most severely affected clone. Likewise, levels of leaf shedding in July and September differed considerably between clones. However, no clear relationship between leaf shedding and dieback intensity was observed. The results indicate that F. excelsior clones in the seed plantation may indeed differ substantially in their resistance to H. pseudoalbidus.
Key words: Chalara fraxinea, common ash, disease assessments, emerging fungal disease, resistance.
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