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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 fungi living in elm tree shoots to understand how different elm species, tree health, and location affect fungal communities. Researchers found that diseased elms had more diverse fungi than healthy ones, and that a fungus called Sphaeropsis ulmicola may be as damaging as the classic Dutch elm disease pathogen. Urban elm trees hosted more different types of fungi than rural ones, suggesting that city conditions influence which fungi can grow on elms.

Background

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

Objective

To investigate the diversity and composition of fungal endophyte communities in twig-associated fungi across symptomatic and asymptomatic individuals of three elm taxa (highly susceptible U. glabra, less susceptible U. laevis, and hybrid elms) growing in Estonia and Russia. The study aimed to determine how host identity, health status, environment, and pathogen presence shape fungal communities.

Results

Tree species exhibited distinct fungal community profiles with U. glabra showing highest richness (159 taxa) and hybrids lowest (112 taxa). Ophiostoma novo-ulmi was detected exclusively in symptomatic trees and dominant in U. glabra but absent in hybrids. Sphaeropsis ulmicola was dominant in symptomatic U. laevis and associated with higher fungal diversity. Urban environments showed greater fungal species richness than rural areas.

Conclusion

Fungal community dynamics in elm shoots are shaped by complex interactions between environmental conditions, pathogen presence, and host genetics, with urban versus rural settings and pathogen presence emerging as stronger drivers than host species identity or visual health status. Sphaeropsis ulmicola appears to be an emerging pathogen in northern elm populations, potentially acting as a DED alternative in resistant hosts.
  • Published in:Microbial Ecology,
  • Study Type:Observational Study,
  • Source: PMID: 40707845, DOI: 10.1007/s00248-025-02585-2
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