Temporal development of ash dieback symptoms and spatial distribution of collar rots in a provenance trial of Fraxinus e
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ORIGINAL PAPER
Temporal development of ash dieback symptoms and spatial distribution of collar rots in a provenance trial of Fraxinus excelsior Rasmus Enderle • Franziska Peters • Aikaterini Nakou • Berthold Metzler
Received: 19 March 2013 / Accepted: 26 July 2013 / Published online: 9 August 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract European ash (Fraxinus excelsior) is threatened by Hymenoscyphus pseudoalbidus, the agent of ash dieback disease. Beside ordinary ash dieback symptoms, collar rots have been reported on declining ashes as an additional problem of increasing severity. Since 2009, ash dieback has been surveyed annually in a provenance trial on four different sites in southwest Germany (Metzler et al. in Ger J For Res 183:168–180, 2012). The trial was established in 2005. Data of tree growth, ash dieback symptoms and collar rot prevalence were collected by surveying the trial in summer 2012 and compared with previously published data of the trial. Evaluations revealed a continuous and considerable increase in dieback severity since 2009. The results suggest that the infection process has not come to a standstill yet. Up to 2012, 6 % of the trees remained symptomless, whereas mortality added up to 9 %. There were significant differences in ash dieback severity between the investigated provenances. Collar rot prevalence ranged from 19 to 59 % between study sites. Moreover, high spatial dependency of collar rot prevalence could be detected within sites. Collar rots were more abundant on trees of severe ash dieback intensity, but could also be detected on 15 % of otherwise healthy trees. Mycelium from collar rots could be identified by means of RFLP analyses and sequencing of the ITS region as most likely belonging to Armillaria gallica. The possible roles of Armillaria spp. and H. pseudoalbidus in collar rot formation are discussed.
Communicated by C. Ammer. R. Enderle (&) F. Peters A. Nakou B. Metzler Department Forest Protection, Forest Research Institute BadenWuerttemberg, Wonnhaldestrasse 4, 79100 Freiburg, Germany e-mail: [email protected]
Keywords Ash dieback Hymenoscyphus pseudoalbidus Fraxinus excelsior Armillaria gallica Collar rot Provenance trial
Introduction Ash dieback is a novel and severe disease on Fraxinus excelsior L. in Europe. The causal agent, the fungus Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea) (Kowalski 2006; Queloz et al. 2011), is an invasive ascomycete in Europe and originates from Asia (Zhao et al. 2012). The disease results in dieback of twigs and branches, dwarf growth and, in severe cases, the death of the trees within a few years (Pautasso et al. 2013). Main symptoms are brown to orange bark necroses on twigs, cankers on branches and the wilting of leaves. Beside these frequent symptoms, the occurrence of butt or collar rot on declining ash trees has been reported (Lygis et al. 2005; Skovsgaard et al. 2010; Bakys et al. 2011; Orlikowski et al. 2011; Goudet and Piou 2012; Husson et al. 2012) and Armillaria spp. colonizing
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