Morphological and molecular characterization of Geosmithia species on European elms

Species of the genus Geosmithia (Ascomycota: Hypocreales) are regularly associated with many insect species, in particular bark beetles (Coleoptera: Curculionidae, Scolytinae). On Ulmus spp., the same bark beetles also serve as vectors of Ophiostoma ulmi s.l., the agent of Dutch elm disease (DED), a widely known disease affecting elms worldwide. The aim of this paper is to characterise Geosmithia species associated with elms and/or elm beetles in the Czech Republic and Italy. Seventy-two strains representative of all morphological taxonomic units obtained from elm branches were selected among 200 wild isolates. A phylogenetic tree based on ITS, β-tubulin and elongation factor 1-α gene regions was built and combined with morphological and physiological characters. On the basis of both molecular and morphophysiological traits, seven taxonomic entities were identified in the populations of Geosmithia associated with elms. In addition to the species previously known on elms, such as Geosmithia langdonii and Geosmithia flava, our phylogenetic analysis assigned strains previously identified as Geosmithia pallida to two separate taxa provisionally named Geosmithia sp. 2 and Geosmithia sp. 5. Two new species, Geosmithia omnicola and Geosmithia ulmacea, are described in this paper. Geosmithia omnicola is very common on many different plant species, while G. ulmacea is restricted to elms. Finally, two strains were assigned to the partially described species Geosmithia sp. 20. Geosmithia species living on Ulmus do not discriminate between elm species, it rather seems that different Geosmithia species are favoured under markedly different environmental conditions. The association between Ulmus and Geosmithia is common, stable, and seems to be related to the presence of a specific population of vectors. The relationship between Ge osmithia species on elm and DED pathogens would deserve further investigation, as these fungi share the same vectors and habitat for a significant part of their life cycles.