Fungal endophytes are ubiquitous in plant leaves. While some endophytes are commensal symbionts, others can modify plant disease severity either by interacting directly with pathogens (e.g., mycoparisitism, antibiosis) or by altering the plant defense response. It is often assumed that species within common fungal endophyte genera, e.g. Cladosporium, Alternaria, Epicoccum, exhibit cosmopolitan distributions. However, few studies have investigated the phylogeographic structure of common endophytes, or tested for variation in ecological function within clades.
We examined Cladosporium, a ubiquitous, wind-dispersed endophyte associated with the leaves of the model tree, Populus trichocarpa (black cottonwood). Cladosporium populations were sampled by amplicon metabarcoding leaf samples (ITS1) and multilocus sequence typing (5 genes: ITS and partial actin, β-tubulin, ef1α, rpb2) of 96 Cladosporium cultures collected from eight sites spanning the core of the tree’s geographic range and a strong climatic gradient from west (wet) to east (dry) of the Cascade Range in the Pacific Northwest of North America. Our ongoing experiments test the degree of rust pathogen antagonism (via mycoparisitism) across the 96 strains using both in agaro and in planta assays.
Results/Conclusions
Our multigene phylogeny supports ~15 previously described species within Cladosporium, and as many as five undescribed species. While the majority of these species are thought to have near global distributions, ITS1 metabarcodes and multigene data both indicate strong phylogeographic structure across the study area with particular species largely restricted to either west or east of the Cascade Range. We are working to link the phylogenetic structure of Cladosporium endophytes to variation in mycoparisitism.