Confirmation of the colonization path of Hymenoscyphus fraxineus from leaves to shoots in Fraxinus excelsior

Abstract : Ash dieback, caused by Hymenoscyphus fraxineus, is a disease that has emerged during the past 25 years. It was first observed in Poland and has now expanded over most of the distribution area of its host, the European ash (Fraxinus excelsior). It is appraised that H. fraxineus may infect and kill 95% of all European ash trees. Ash dieback is associated with numerous symptoms on all plant parts. Necrosis in shoots is assumed to develop after infection through leaf petioles. The main objective of this work was to provide new insights on the life cycle of H. fraxineus and, more particularly, on its presumed colonization path from the leaves to the shoots of F. excelsior. Here, we used 18 microsatellites markers to analyze 84 isolates obtained from symptomatic petioles and shoots of 42 F. excelsior seedlings. The goals of this work were to identify differentially encoded alleles, establish genetic profiles to characterize fungal individuals and confirm the progression of H. fraxineus from a petiole into a shoot. We determined that 17 markers were polymorphic and 14 were bi-allelic. Likewise, we distinguished 63 different multilocus haplotypes. Furthermore, the infection route of H. fraxineus from a single leaf petiole to a shoot was confirmed in 50% of cases, but the true proportion may be substantially higher. In conclusion, we confirmed here that the majority of ash shoot infections are caused by H. fraxineus individuals originating from leaves, entering woody parts through the petiole-shoot junction.
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Master Thesis
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Astrid Koehl. Confirmation of the colonization path of Hymenoscyphus fraxineus from leaves to shoots in Fraxinus excelsior. Life Sciences [q-bio]. 2018. ⟨dumas-01962507⟩

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