The invasive pathogen, ash dieback fungus Hymenoscyphus fraxineus, is spreading rapidly
across Europe. It shows high levels of outcrossing and limited population structure, even at
the epidemic front. The anamorphic (asexual) form produces prolific conidia, thought to
function solely as spermatia (male gametes), facilitating gene flow between sympatric
strains. Here, we show that conidia are capable of germination on ash leaves and in vitro,
and can infect seedlings via leaves or soil. In leaves, germlings form structures resembling …