Premium
Hymenoscyphus pusillus , a new species on leaves of Fraxinus pennsylvanica in Poland
Author(s) -
Kowalski Tadeusz,
Bilański Piotr
Publication year - 2019
Publication title -
forest pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.535
H-Index - 49
eISSN - 1439-0329
pISSN - 1437-4781
DOI - 10.1111/efp.12481
Subject(s) - biology , botany , ascocarp , fraxinus , taxonomy (biology)
American green ash ( Fraxinus pennsylvanica ) is among the most widely distributed ash species in North America. In the 18th century, it was introduced to Europe where it is used for ornamental purposes or for timber production. None of the currently known Hymenoscyphus species has been found on F. pennsylvanica in North America. Hymenoscyphus fraxineus , the cause of ongoing ash dieback epidemics, occurs on F. pennsylvanica in Europe but this species seems to show some degree of tolerance to the pathogen. A new species, Hymenoscyphus pusillus , detected in F. pennsylvanica leaf litter in Poland is presented. The description is based on morphological and molecular studies. Hymenoscyphus pusillus produces, in summer, whitish apothecia developing on black pseudosclerotia formed in petioles, rachises and leaf veins, in the litter of the previous year's leaf fall. The new species differs from H. fraxineus in its smaller apothecia (up to 2.3 mm in diam.), absence of croziers at the ascus base, formation of superficial pseudosclerotia in the form of strips or isolated insular black areas on the thicker regions of rachises and petioles and rapidity of pseudosclerotia formation (6–8 weeks after leaf fall). The sizes of asci and ascospores of H. pusillus are similar to those of Hymenoscyphus linearis and smaller than those of other species in the H. fraxineus group. Optimal temperature for growth of H. pusillus in vitro is 20°C. The fungus does not produce an anamorph, distinguishing it from H. fraxineus , H. linearis and Hymenoscyphus occultus , which frequently form Chalara ‐like anamorphs. Analyses of sequence data for ITS rDNA and protein‐coding genes (partial actin, CAL and TEF1‐α) showed that H. pusillus forms a well‐supported clade in the phylogenetic trees. Hymenoscyphus pusillus is closely related to H. occultus , detected on F. chinensis subs. rhynchophylla in Korea. After inclusion of the new species, the H. fraxineus group now consists of seven species. Some ecological and trophic aspects concerning the occurrence of the new species are discussed. The possibility of competition between H. pusillus and H. fraxineus is discussed.