Hybridization and the resulting introgression can drive the success of invasive species via the rapid acquisition of adaptive traits. The Dutch elm disease pandemics in the past 100 years were caused by three fungal lineages with permeable reproductive barriers: Ophiostoma ulmi, Ophiostoma novo-ulmi subspecies novo-ulmi and Ophiostoma novo-ulmi subspecies americana. Using whole-genome sequences and growth phenotyping of a worldwide collection of isolates, we show that introgression has been the main driver of genomic diversity and that it impacted fitness-related traits. Introgressions contain genes involved in host–pathogen interactions and reproduction. Introgressed isolates have enhanced growth rate at high temperature and produce different necrosis sizes on an in vivo model for pathogenicity. In addition, lineages diverge in many pathogenicity-associated genes and exhibit differential mycelial growth in the presence of a proxy of a host defence compound, implying an important role of host trees in the molecular and functional differentiation of these pathogens.
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All custom codes, as well as descriptions, versions and URLs of all open-source software used in this study are provided at https://github.com/Landrylab/Ophiostoma_Hybridization_2019.
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This work was funded by Genome Canada, Genome British Columbia and Génome Québec within the framework of project bioSAFE (Biosurveillance of Alien Forest Enemies; project number 10106). Additional funding was provided by the Canadian Food Inspection Agency, Natural Resources Canada and FPInnovations and by the NSERC Discovery Grant of C.R.L. We thank A. Dubé, A. Gagné, I. Giguère and A. Potvin for help with the experiments, W. Babik and the Landry laboratory for comments and discussions, the McGill University and the Centre d’Expertise et de Services Génome Québec and the Institut de Biologie Intégrative et des Systèmes bioinformatics platform for technical support.
The authors declare no competing interests.
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Hessenauer, P., Fijarczyk, A., Martin, H. et al. Hybridization and introgression drive genome evolution of Dutch elm disease pathogens. Nat Ecol Evol 4, 626–638 (2020). https://doi.org/10.1038/s41559-020-1133-6