The Diplodia Tip Blight Pathogen Sphaeropsis sapinea Is the Most Common Fungus in Scots Pines’ Mycobiome, Irrespective of Health Status—A Case Study from Germany

Abstract

The opportunistic pathogen Sphaeropsis sapinea (≡ Diplodia sapinea) is one of the most severe pathogens in Scots pine, causing the disease Diplodia tip blight on coniferous tree species. Disease symptoms become visible when trees are weakened by stress. Sphaeropsis sapinea has an endophytic mode in its lifecycle, making it difficult to detect before disease outbreaks. This study aims to record how S. sapinea accumulates in trees of different health status and, simultaneously, monitor seasonal and age-related fluctuations in the mycobiome. We compared the mycobiome of healthy and diseased Scots pines. Twigs were sampled in June and September 2018, and filamentous fungi were isolated. The mycobiome was analyzed by high-throughput sequencing (HTS) of the ITS2 region. 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. Sphaeropsis sapinea was the most common endophyte isolated and the second most common in the HTS data. The fungus was highly abundant in symptomless (healthy) trees, presenting in its endophytic mode. Our results highlight the ability of S. sapinea to accumulate unnoticed as an endophyte in healthy trees before the disease breaks out, representing a sudden threat to Scots pines in the future, especially with increasing drought conditions experienced by pines.

Sphaeropsis sapinea (Fr.) Dyko & B. Sutton in Pinus sylvestris L. stands affected by long-term drought

“…3). Blumenstein et al (2021b) recorded a significantly higher abundance of S. sapinea on P. sylvestris branches in Germany in June compared to September. Contrary, pycnidial colonization of S. sapinea on cones showed seasonal dynamics in our study, probably due to negative effect of low humidity, respectively low precipitations, and high summer temperatures.…”

“…In our study, colonization (presence) of S. sapinea without its relation to damage was evaluated. S. sapinea can be present on tree mass like a saprophyte, without harming the host (Bußkamp et al 2020;Blumenstein et al 2021b). So, relationship between colonization and infection of S. sapinea may not be always positively correlated.…”

“…So, relationship between colonization and infection of S. sapinea may not be always positively correlated. How-ever, S. sapinea has ability to accumulate unnoticed as an endophyte in healthy trees before the disease breaks out, representing a sudden threat to P. sylvestris in the future, especially with increasing drought conditions experienced by pines (Blumenstein et al 2021b).…”

“…Relationship between colonization and infection of S. sapinea may not be positively correlated. However, due to ability of S. sapinea to accumulate as an endophyte in healthy trees before the disease breaks out (Blumenstein et al 2021b), pycnidial colonisation and spore presence of the fungus can be useful indicators of possible threat of pine stands decline and dying in the coming years. Climate change, manifested by rising temperatures and more frequent extremes that include longer and stronger droughts (Lindner et al 2008), currently leads to the increased infections of S. sapinea.…”

“…S. sapinea also attacks trees from the seedling stage in nurseries to mature trees in ornamental planting, forest plantations and natural stands (Georgieva & Hlebarska 2016). S. sapinea has an endophytic life stage when it does not harm the host (Smith et al 1996;Flowers et al 2001;Terhonen et al 2020;Blumenstein et al 2021b). However, the fungus can accumulate unnoticed in healthy trees before the disease breaks out, representing a sudden threat to hosts (Stanosz et al 2001;Blumenstein et al 2021a).…”