Fungi associated with woody tissues of Acer pseudoplatanus in forest stands with different health status concerning sooty bark disease (Cryptostroma corticale)

Abstract

From 2018 to 2020, Germany experienced periods of exceptional weather conditions. Extremely high summer temperatures and precipitation deficits induced stress and mortality in forest trees. Acer pseudoplatanus (sycamore) was one of the affected tree species. Symptoms of sooty bark disease (SBD) and severe damage of entire stands, both caused by the fungal species Cryptostroma corticale, were reported more frequently. To explore the non-symptomatic distribution of C. corticale, wood cores from visibly healthy sycamore stems were sampled and all outgrowing fungi were identified and recorded. In total, 50 trees, aged 30–65 years, were sampled at five different forest stands, from which 91 endophytic filamentous morphotypes could be isolated. The fungal endophytic community in the woody tissue of the sycamore trees varied greatly at the different sites and between the trees. The number of isolated morphotypes at the different sites ranged from 13 to 44 and no morphotype was found at all sites. At 1.20-m stem height, 3.3 fungi could be isolated from woody tissue per tree on average. The most abundant species isolated from visibly healthy sycamore in regard to both occurrence at the studied sites and continuity was C. corticale. It was recorded at four of the studied forest stands, from 26% of all studied sycamore trees, and had a frequency of 7.85% relative to the 293 isolated filamentous strains that were isolated. The second most abundant species was Xylaria longipes followed by Lopadostoma turgidum. In this study clear evidence for the endophytic lifestyle of C. corticale is presented which thus appears to be spread further than expected based on visible SBD symptoms.

Endophytic community in juvenile Acer pseudoplatanus and pathogenicity of Cryptostroma corticale and other associated fungi under controlled conditions

“…Since the first record of C. corticale in Germany in 1964 (Plate and Schneider 1965), the causal agent of sooty bark disease has spread throughout German forests (Schlößer et al 2023). It is now known that C. corticale can also be detected latently in woody tissues of adult healthy sycamore (Schlößer et al 2023). The question of whether this pathogen also occurs in juvenile sycamores was the aim of our investigations and can be answered in the negative, at least for the sycamore saplings examined.…”

“…Since the first record of C. corticale in Germany in 1964 (Plate and Schneider 1965), the causal agent of sooty bark disease has spread throughout German forests (Schlößer et al 2023). It is now known that C. corticale can also be detected latently in woody tissues of adult healthy sycamore (Schlößer et al 2023).…”

“…In particular, the invasive pathogen C. corticale (Ascomycota), inducing the bark-and vascular sooty bark disease (SBD), is widely distributed in Europe and has an increasing importance as a fatal maple pathogen. Sycamore maple was the most affected tree species in the disease outbreaks of SBD in Central Europe following the exceptional warm and dry year of 2018 (Bork 2018;Delb et al 2016;Rohde et al 2019;Schlößer et al 2023;Wenzel et al 2019).…”

“…Cryptostroma corticale has often been described as an example for latent pathogens (Enderle et al 2020;Kelnarová et al 2017), which can remain symptomless in the woody tissue over an extended period of time following infection (endophytic/latent phase; Verhoeff 1974;Schulz and Boyle 2005). However, clear evidence for endophytism of C. corticale in maple was not provided until recently when Schlößer et al (2023) isolated this fungus from symptomless woody tissue of A. pseudoplatanus in healthy forest stands with no signs of SBD in the vicinity. Previous reports of isolations from symptomless woody tissue originated from trees already showing symptoms of SBD, such as wood discoloration or defoliation (e.g.…”

“…Kowalski and Kehr 1992). The most extensive dataset about this particular community is provided by the study of Schlößer et al (2023), who report a total of 91 different fungal taxa from 30 to 65 year-old trees in Germany. Several other studies about endophytic fungal communities of A. pseudoplatanus focus on other tissue types, such as leaves (e.g.…”