# Hymenopleella and Diaporthe dominate the fungal community of dieback affected sea Buckthorn from Northern Germany

## TL;DR

Fungal communities in diseased sea buckthorn plants in Germany are dominated by Hymenopleella and Diaporthe, suggesting a link to dieback symptoms.

## Contribution

Combined culture-dependent and culture-independent methods reveal fungal dysbiosis in dieback-affected sea buckthorn.

## Key findings

- Hymenopleella and Diaporthe were most frequently isolated from symptomatic sea buckthorn plants.
- Fungal community composition differed significantly between symptomatic and asymptomatic plants.
- Capnocheirides abundance was a strong predictor for absence of dieback symptoms.

## Abstract

Since recent years, German sea buckthorn (SBT) cultivation is increasingly affected by dieback. Wildly growing plants from dunes and cultivated plants from plantations show symptoms of wilt, lesions and discolorations in shoot cross sections. The cause of final plant death is not yet resolved and asymptomatic plants are rare to find. Our aim was to investigate the associated fungal communities of visibly dieback affected plants. A culture-dependent isolation approach in parallel with a culture-independent sequencing approach by metabarcoding of ITS1 was used to investigate SBT shoot fungal communities. Evaluation of the sequencing data was supported with random forest modelling.

Results of both approaches complement each other and are consistent. Members of the ascomycete genera Hymenopleella and Diaporthe were most frequently isolated from symptomatic samples. Alternaria, Aureobasidium, Cladosporium, Epicoccum and Penicillium could be identified in both sample types, i.e. symptomatic and asymptomatic plants, with high frequencies. Sequencing of shoot samples revealed that the fungal community composition differs significantly between symptomatic and asymptomatic plants. Pielou’s evenness was significantly reduced for symptomatic plants indicating a dominance of few fungal taxa in symptomatic samples pointing to a dysbiosis in fungal communities. In a random forest modelling approach, abundance of Capnocheirides amplicon sequence variants had the highest relative importance for the model and high relative abundance is considered as predictor for absence of SBT symptoms. In symptomatic plants, Hymenopleella and Diaporthe had high relative abundances and were suggested as predictors.

Overall, our combined approach has revealed an increased abundance of Hymenopleella and Diaporthe in symptomatic sea buckthorn in Germany along with changes in the total fungal community. The relative abundances derived from amplicon sequencing were reflected by the isolation frequencies of the respective taxa.

The online version contains supplementary material available at 10.1186/s40793-025-00804-4.