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Dieback of Fraxinus excelsior

biology of ash dieback and genetic variation of the fungus Hymenoscyphus pseudoalbidus

Bengtsson, Stina (2013). Dieback of Fraxinus excelsior. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2013:18
ISBN 978-91-576-7775-4
[Doctoral thesis]

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Ash dieback caused by Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea) is a disease that has emerged during the past twenty years. It was first observed in Poland and has expanded over most of the distribution area of European ash (Fraxinus excelsior) in Europe.

This thesis comprises four scientific papers. The first reports the production of a phytotoxin, viridiol, by the fungus, and shows that it causes necrotic spots on ash cotyledons.

The second paper describes a working tool, a species-specific DNA primer situated in the internal transcribed spacer (ITS) region of the ribosomal DNA, which can be used to detect the fungus in diseased host material and confidently identify fungal cultures.

In the third paper, microsatellites and arbitrary primed PCR were used to investigate the genetic population structure of the fungus. The genetic variation was evenly distributed in the whole European population, implying a high level of gene flow. Double alleles in apothecia compared with single alleles in mycelia cultures strongly indicated sexual reproduction. H. pseudoalbidus was clearly distinct from the native closely related Hymenoscyphus albidus and it is unlikely that the disease is derived from a H. albidus ancestry. The low number of microsatellite alleles per locus indicated a recent founder effect in H. pseudoalbidus.

In the fourth paper disease development was surveyed in 261 naturally infected ash trees over a 32 month period. A clear seasonal pattern was demonstrated, with lesion activity and growth rate peaking during the summer. A substantial proportion of the lesions ceased to develop, often when the lesion reached a branch base; however the rate at which new lesions emerged was greater than the rate at which lesions entered a resting phase. During the course of the survey a third of the trees died and only a few seedlings remained healthy. In addition, the lower temperature limit for the fungus in culture was estimated to be 0.5°C.

Authors/Creators:Bengtsson, Stina
Title:Dieback of Fraxinus excelsior
Subtitle:biology of ash dieback and genetic variation of the fungus Hymenoscyphus pseudoalbidus
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :28 February 2013
Number of Pages:51
I.P. F. Andersson, S. B. K. Johansson¹, J. Stenlid and A. Broberg (2010). Isolation, identification and necrotic activity of viridiol from Chalara fraxinea, the fungus responsible for dieback of ash. Forest Pathology 40, 43–46.
II.S. B. K. Johansson¹, R. Vasaitis, K. Irhmark, P. Barklund and J. Stenlid (2010). Detection of Chalara fraxinea from tissue of Fraxinus excelsior using species-specific ITS primers. Forest Pathology 40, 111–115.
III.S. B. K. Bengtsson, R. Vasaitis, T. Kirisits, H. Solheim and J. Stenlid (2012). Population structure of Hymenoscyphus pseudoalbidus and its genetic relationship to Hymenoscyphus albidus. Fungal Ecology 5, 147– 153.
IV.S. B. K. Bengtsson, P. Barklund, C. von Brömssen and J. Stenlid. Seasonal pattern of lesion development in Fraxinus excelsior diseased by Hymenoscyphus pseudoalbidus (Manuscript).
Place of Publication:Uppsala
Publisher:Dept. of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-7775-4
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:H Protection of plants and stored products > H20 Plant diseases
K Forestry > K01 Forestry - General aspects
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Forest Science
Agrovoc terms:fraxinus excelsior, forest trees, dieback, fungal diseases, chalara, genetic variation, phytotoxins, lesions, dna, microsatellites
Keywords:Chalara fraxinea, phytotoxin, population, lesion, microsatellite
Permanent URL:
ID Code:9468
Department:(NL, NJ) > Dept. of Forest Mycology and Plant Pathology
(S) > Dept. of Forest Mycology and Plant Pathology
External funders:FORMAS
Deposited By: Stina Bengtsson
Deposited On:01 Mar 2013 07:25
Metadata Last Modified:02 Dec 2014 10:55
Project info:
Name:mekanismer hos askskottsjuka

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