The Opportunistic Pathogen Sphaeropsis Sapinea is Found to be one of the Most Abundant Fungi in Symptomless and Diseased Scots Pine in Central-Europe

Abstract

Background: The opportunistic and latent pathogen Sphaeropsis sapinea is one of the most important forest pathogens on pine. The fungus may cause Diplodia tip blight on several coniferous trees and disease symptoms come visible when trees are weakened by stress, usually related to injuries and drought. This project compares the mycobiome of healthy and diseased Scots pines. Twigs were sampled in June and September 2018 in a German forest stand with varying health status of the sampled Scots pines. Growth of 2017 and 2018 were sampled and cultivable, filamentous fungi isolated and the mycobiome was analysed by high-throughput sequencing (HTS) of the internal transcribed spacer 2 (ITS2) region. Results: A PERMANOVA analysis confirmed that the mycobiome community composition significantly differed between growth years (p < 0.001) and sampling time (p < 0.001) but not between healthy and diseased trees. Higher amount of S. sapinea was observed in June and the growth year 2017. Besides yeasts which were neglected, 23 ascomyceteous fungal endophytes were isolated. S. sapinea was the most common endophyte isolated and the second common in HTS data. It was highly abundant in symptomless (healthy) trees. Conclusion: Results highlights the ability of S. sapinea to accumulate unnoticed before disease outbreaks, implementing the sudden threat for Scots pines in the future.

Sphaeropsis sapinea and Associated Endophytes in Scots Pine: Interactions and Effect on the Host Under Variable Water Content

“…No S. sapinea could be detected from the tested seedlings prior to the experiments, whereas the other fungal strains used for the greenhouseinfections were found to be present. We concluded that these species belong to the naturally observed Scots pine endophyte community (Blumenstein et al, 2020;Bußkamp et al, 2020).…”

“…The fungal strains chosen are regularly isolated from Scots pine tips in German forests according to Bußkamp et al (2020). Origin and locations of the strains are described in Blumenstein et al (2020). One strain (Didymellaceae sp., NW-FVA ID 5756) originated from a sample of the nursery pine plants (see section "Pre-experiment Detection of Endophytes Including Sphaeropsis sapinea in Plant Material") that were used in this study for the antagonism assay.…”

“…In order to identify endophytic fungal isolates that may have the ability to antagonize the pathogen S. sapinea inside the pine trees' tissue (in planta), the interactions of 27 isolated pine endophytes (Blumenstein et al, 2020) against two different S. sapinea strains were investigated by means of a pairedgrowth assay (antagonism assay in vitro) as described in Rigerte et al (2019). The ability of an endophyte to antagonize the pathogen was determined based on the inhibition level (defined as pathogen growth with and without the endophyte) over a given period of time.…”

“…Recently, the disease Diplodia tip blight has been increasing in Germany, especially after the hot and dry years of 2018 and 2019 (Blumenstein et al, 2020). Sphaeropsis sapinea has a latent endophytic stage (Burgess et al, 2004;Flowers et al, 2006;CABI, 2019;Bußkamp et al, 2020;Terhonen et al, 2021) and disease symptoms become visible when trees have been weakened by stress, usually related to temperature and drought, allowing S. sapinea to switch its lifestyle from endophytic to pathogenic (Blodgett et al, 1997a;Stanosz et al, 2001;Blumenstein et al, 2020). The production of reactive oxygen species (e.g., hydrogen peroxide, H 2 O 2 ) and the accumulation of free amino acids are common plant responses to drought (Sherwood et al, 2015).…”

“…S. sapinea can be considered a very good model to test the direct effects of environmental changes on a fungal pathogen (lifestyleswitch), as well as indirect effects on the host susceptibility (stress). The high levels of Diplodia tip blight symptoms in forest stands are not due to a high abundance but rather depend on environmental conditions (Feci et al, 2002;Bußkamp, 2018;Blumenstein et al, 2020). The impact of climate change could shift the endophyte communities and will probably also affect the nature of fungal pathogens.…”