Dutch elm Disease fungi world wide whole genome sequencing

The Dutch Elm Disease (DED) pandemics led to the death of millions of elm trees in the past 200 years. Three lineages have been recognized within the DED species complex: Ophiostoma ulmi, Ophiostoma novo-ulmi novo-ulmi and Ophiostoma novo-ulmi americana. These lineages are not completely reproductively isolated and thus have permeable species barriers. However, their population structure, the extent to which they hybridize and the consequences of hybridization remain to be fully examined. Using whole genome sequences of worldwide samples and phenotyping experiments, we show that these species largely lack geographical structure and that hybridization has been a major driver of genomic diversity within species. Hybridization led to the introgression of many genomic regions from O. ulmi to the O. novo ulmi lineages, enhancing genetic diversity in regions that are enriched for cazymes and vegetative incompatibility genes. Fast evolving genes in these populations are enriched for membrane transport and quinone binding, which is consistent with selection pressure from the host trees. Altogether our results offer unprecedented insight into DED fungal lineages and the role of hybridization in the evolution and adaptation of fungal pathogens.