Fungal leaf endophytes can modify plant disease severity, either via direct interaction with pathogens (e.g., mycoparisitism, facilitation) or by altering the plant defense response. Species of Cladosporium, a ubiquitous, wind-dispersed endophyte associated with the leaves of the model tree, Populus trichocarpa (black cottonwood), have been shown to have variable effects on Melampsora leaf rust disease severity. Some Cladosporium species reduce rust disease severity while others appear to be commensal symbionts. Currently, we lack the ability to predict which Cladosporium endophytes will modify rust disease severity.
We investigated whether fungal traits can be used to predict endophyte function. In particular, we tested whether the ability to mycoparisitize rust spores, and endophyte relatedness within Cladosporium, predict disease modification phenotypes. We used multilocus sequence typing (5 genes: ITS and partial actin, β-tubulin, ef1α, rpb2) to characterize the phylogenetic relationship among 96 isolates collected from eight sites spanning the core of the tree’s geographic range in the Pacific Northwest of North America. Next, we conducted a double-inoculation leaf-disc assay (endophyte inoculated first, then pathogen), to characterize both mycoparasitic ability and disease modification for the 96 isolates.
Results/Conclusions
We found evidence that more closely related species within Cladosporium have more similar mycoparasitic abilities, and that species demonstrating greater mycoparisitism were associated with the greatest reductions in rust disease severity. Our results indicate that fungal traits can be used to predict endophyte function. We have sequenced genomes for nine species of Cladosporium from our study, and our ongoing analyses further seek to identify genomic traits that correlate with endophyte function.