Fungi on stems and twigs in initial and advanced stages of dieback of European ash (Fraxinus excelsior) in Poland

Abstract

F. excelsior is affected by dieback in the major part of its natural geographical range in Europe, which results in economic and ecological losses. The disease is caused by the ascomycetous fungus Hymenoscyphus fraxineus, a pathogen introduced to Europe most probably from East Asia. This paper presents data on fungi identified on F. excelsior trees representing two different stages of ash dieback in Poland. Fungal communities were identified in initial necrotic lesions on living stems and twigs using the classical method of isolation on malt extract agar and morphological and molecular analyses. In dead apical parts of stems and twigs, fungi were identified by microscopic analyses of fruit bodies formed in situ. Seventy-one fungal taxa were found in 720 samples with symptoms of initial or advanced necrosis. The most common fungus detected in initial necrotic lesions in each forest site was Hymenoscyphus fraxineus (59.2 % of analysed samples). Other frequently isolated fungi included Alternaria alternata, Diaporthe eres, Diplodia mutila, Fusarium avenaceum, F. lateritium and Phomopsis spp. Fruit bodies on dead apical parts of stems and twigs were produced mostly by Diaporthe eres, Diplodia mutila, Lophiostoma corticola, Phomopsis spp., Sirodothis sp. and Valsa cypri. Fungal communities from different sites were similar, as shown by high Sørensen similarity index values. Greatest variation in fungal community structure at the initial necrotic stage was realized by D. mutila and F. avenaceum, and at the advanced necrotic stage by D. eres, D. mutila and Phomopsis spp. Data show a close affinity of certain fungi to site, suggesting geographical relatedness. The ecological effects of distribution of the invasive H. fraxineus and of other fungi sporulating on diseased ash trees in Europe are discussed.

Effect of fungal pathogens and climatic factors on production, biodiversity and health status of ash mountain forests

“…The amount of precipitation has positive effect on the latewood growth (Karpavičius & Vitas, 2006). On the other hand, the occurrence of fungi pathogens is not so frequent in high mountain areas, where annual temperatures are lowest (Kowalski et al, 2016). Global warming probably would increase their pathogenic role in European ash stands (Thompson et al, 2010;Kowalski et al, 2016).…”

“…Ash dieback depends on habitat site, stand conditions and climatic factors (precipitation, temperature) (Kowalski, 2006;Bakys et al, 2009;Dobrowolska et al, 2011;Kowalski, 2016). Infection by H. fraxineus is strongly influenced by air and soil humidity (Kirisits, 2012;Havrdová et al, 2014).…”

“…Infection by H. fraxineus is strongly influenced by air and soil humidity (Kirisits, 2012;Havrdová et al, 2014). Interactions between fungal pathogen and host tree are particularly important in relation to global climatic changes, with respect to reproduction, distribution and survival (Kowalski, 2016). Ash dieback is also closely connected with silvicultural practices, such as thinning of suppress trees susceptible to diseases and infected trees, suitable changes of tree species composition, selection of resistant genotypes and others (Dobrowolska et al, 2011;Skovsgaard, 2013;Havrdová et al, 2014Havrdová et al, , 2016.…”

Do increases in the availability of standing dead trees affect the abundance, nest-site use, and niche partitioning of great spotted and middle spotted woodpeckers in riverine forests?

“…In an area of the oldest stands (59 ha), the density of dead oaks with a diameter at breast height (Dbh) C14 cm increased by 38%, from 5.4 snags 1 ha -1 in 2006 to 7.5 snags 1 ha -1 in 2007, and remained stable in the years 2009. The causal agent of ash dieback is fungal disease caused by the ascomycete Hymenoscyphus fraxineus (Pautasso et al 2013;Kowalski et al 2016). Large-scale ash dieback, which first appeared in Poland in the 1990s (Przybył 2002), spread rapidly.…”

Identification and characterization of the fungus Dothiorella sarmentorum on necrotic shoots of declining ash in Slovakia

“…Although H. fraxineus is considered to be the main cause of ash trees dieback, this damage is associated with many other fungal genera colonizing ash shoots and branches (Kowalski and Czekaj, 2010;Kowalski et al, 2016). The fungi detected after isolation from the initial necrotic lesions on ash leaves and branches represent taxa with different heterotrophy: parasites prefering to colonize living plant tissues, saprophytes feeding on dead or decaying substrates and endophytes.…”