Hymenoscyphus fraxineus and two new Hymenoscyphus species identified in Korea

Abstract

Hymenoscyphus fraxineus is an invasive fungal pathogen that causes ash dieback in Europe. Recent investigations have identified H. fraxineus on herbarium specimens in Korea. In this paper, these specimens, plus five additional collections, were studied by internal transcribed spacer (ITS) screening and subsequent phylogenetic analysis using three additional sequence markers (actin, calmodulin, EF1-α). Using the concept of genealogical concordance phylogenetic species recognition (GCPSR), H. fraxineus was confirmed in five of the collections on petioles of Fraxinus mandshurica and F. chinensis subsp. rhynchophylla. The remaining collections revealed two novel species, both occurring on petioles of F. chinensis subsp. rhynchophylla. They are described as Hymenoscyphus occultus sp. nov. and Hymenoscyphus koreanus sp. nov., based on morphological and molecular data. Both develop a Chalara-like anamorph similar to that of H. fraxineus. Together with the newly described H. albidoides from China and H. linearis from Japan, the clade containing H. fraxineus now consists of six species. Within this clade, H. koreanus forms a sister species to H. albidus and both share highly similar morphological and molecular features. Hymenoscyphus occultus is more distantly related to H. fraxineus and shows proximity to H. linearis. Ascocarp production on ash leaf malt-extract agar could be shown for the two new species, and for H. linearis and H. albidus. The experiment demonstrated these species’ ability to self-fertilize. Our findings suggest the diversity of Hymenoscyphus species on Fraxinus sp. might be higher than currently known, calling for further investigations on petioles of other Fraxinus species.