Fungi associated with stem collar necroses of Fraxinus excelsior affected by ash dieback

Abstract

In recent decades the vitality and physical stability of European ash trees in Germany have been reduced by European ash dieback, especially when associated with stem collar necroses and rots. This study was carried out to investigate the composition of the fungal communities associated with stem collar necroses. Filamentous fungi were isolated from 58 ash trees out of nine forest stands in northern, eastern, and central Germany. Obtained isolates were identified to a genus or species level by means of morphological and molecular analyses. In total 162 morphotypes including endophytic, saprotrophic, and pathogenic fungi were isolated. For 33 species found no prior reports from Fraxinus excelsior were recognised, including Cryptostroma corticale and Diplodia sapinea. None of the identified species were found at all studied sites, though Diplodia fraxini was the most common fungus with regard to frequency within all isolates, occurring at seven sample sites. This species is followed by Hymenoscyphus fraxineus, Armillaria spp., Neonectria punicea, Diaporthe cf. eres, Fusarium cf. lateritium, and Paracucurbitaria sp. in order of frequency within all isolates. The aforementioned species are characterised and analysed in respect to their occurrence in stem collar necroses and at sample sites. The influence of site conditions on the fungal composition was described for five intensively sampled sites with a minimum of five studied trees (Schwansee, Rhüden, Berggießhübel, Satrup, and Schlangen). The sampling site of Schlangen was further subdivided into four subplots with different positions in the terrain. In the remaining four extensive sample sites, either one or two trees, respectively, were sampled and analysed (Oranienbaumer Heide, Woltershausen, Wolfenbüttel, and Neuhege). Over all sample sites, fungal communities of symptomatic stem tissue are similar concerning the most frequent fungi, but vary greatly according to singularly isolated fungi.

Comparative studies on the identification and assessment of basal stem necrosis in ash trees (Fraxinus excelsior) against the backdrop of the European ash dieback

“…This is mainly due to the fact that this damage to the roots and inside the lower trunk area is often not noticeable. However, the internal decomposition of the wood and the resulting instability of the tree pose a high risk of accidents (Peters et al 2023).…”

Botryosphaeriaceae Species Associated with Stem Canker, Shoot Blight and Dieback of Fraxinus ornus in Italy

“…Studies dealing with Fraxinus dieback in Europe, including the Mediterranean areas, have mainly focused on assessing the pathogenic role of the ascomycete fungus H. fraxineus [4][5][6][7]. Only recently, this and a few other investigations have started taking into consideration the possible role of fungi other than H. fraxineus, among which the Botryosphaeriaceae, in the onset of ash decline/dieback [10,31,32]. Here, we provide evidence that six important fungi of the Botryosphaeriaceae family attack trees or parts of trees that are injured or in a weak or stressed condition.…”

“…D. fraxini has already been reported in studies on the etiology of diseases affecting Fraxinus [32]. Data on the current distribution of this fungus are still lacking also due to the recent taxonomic re-classification that has reassigned the name D. fraxini to this fungus, previously included in the D. mutila complex [10,59]. The adaptability of this fungus has been demonstrated by its reports from sites with different climatic conditions (average annual temperature from 6.1 to 15.1 • C and average annual precipitation ranging from 650 to 2050 mm), a fact that confirms the plasticity of this fungus against environmental changes [31].…”

“…A diverse and more complex disease framework has been observed in recent years in Fraxinus forests, mostly concentrated in Mediterranean-climate areas characterized by lack of rainfall and prolonged drought. The varying set of symptoms observed on F. ornus collectively generates an undescribed syndrome, which is quite dissimilar from the welldefined symptomology caused by H. fraxineus [8][9][10]. Indeed, this new syndrome includes sunken cankers on the stem and branches, sometimes appearing numerous along the stem of young plants; a characteristic wedge-shaped necrotic sector in the cross section of declining branches and stems; leaf and shoot blight; and progressive dieback of the canopy [11,12].…”

Priming of ash saplings with a low virulent Hymenoscyphus fraxineus strain as a possible disease control approach for reducing symptoms of ash dieback

“…Isolates of H. fraxineus were obtained from a mature common ash stand (F. excelsior) near Rhüden (Lower Saxony, Germany;N 51° 57' 32.2092 E 10° 9' 46.89), which was sampled as part of the FraxForFuture project (Langer et al 2022;Peters et al 2023). These isolates where obtained from branch samples with visible signs of a necrosis, typically associated with H.…”