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Fungal Assemblages in Northern Elms—Impacts of Host Identity and Health, Growth Environment, and Presence of Dutch Elm Disease

Summary

This study examined the different fungi living in elm tree shoots to understand why some elm species are more resistant to Dutch elm disease than others. Researchers found that healthy elms host fewer fungal species compared to diseased trees, and that fungal communities differ significantly between elm species and urban versus rural locations. Importantly, a fungus called Sphaeropsis ulmicola appears to be a significant emerging threat to elms in northern Europe, separate from the classic Dutch elm disease pathogen.

Background

Dutch elm disease (DED), caused by Ophiostoma novo-ulmi, has devastated elm populations across Europe and North America. Elm species vary in their susceptibility to this vascular disease, which may reflect differences in their associated fungal communities. Understanding fungal endophyte diversity in relation to host genotype and health status is crucial for disease management and conservation.

Objective

To investigate the diversity and composition of fungal endophyte communities in elm twigs in relation to host species identity, health status, growth environment (urban vs. rural), and presence of DED pathogens. The study examined three elm taxa: highly susceptible U. glabra, less susceptible U. laevis, and hybrid elms.

Results

Three elm taxa exhibited distinct fungal community profiles with 305 OTUs identified. O. novo-ulmi was detected only in symptomatic trees and was dominant in U. glabra but absent in hybrid elms. S. ulmicola was frequently found in symptomatic trees and associated with higher fungal diversity. Urban environments had higher fungal species richness than rural areas.

Conclusion

Fungal community dynamics in elm shoots are shaped by complex interplay of environmental conditions, pathogen presence, host genetics, and tree health. While species-specific effects exist, environmental stressors and pathogen presence emerged as stronger drivers than host identity alone. S. ulmicola appears to be an emerging pathogen in northern elm populations.
  • Published in:Microbial Ecology,
  • Study Type:Observational Study,
  • Source: PMC12289760, PMID: 40707845, DOI: 10.1007/s00248-025-02585-2
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