Abstract
Hymenoscyphus fraxineus is an invasive fungal species causing the most serious disease of ashes (Fraxinus spp.) in Europe—ash dieback. The biology of this fungus is not totally elucidated, neither its relation to the saprophytic species Hymenoscyphus albidus, native in Europe. Our study is focused on the description of seasonal spore dispersal of both fungi and its relation to meteorological conditions, which is needed for more precise and effective control of the disease. For this experiment one long time infected mixed forest in the SE Czech Republic was chosen. A seven-day automatic volumetric spore trap and a weather station were installed to continuously sample the aerospora from April to October 2014. In seven periods a rotating arm spore trap was also used to obtain 48-h air samples to compare the efficiency of these two types of air samplers. Air samples were evaluated solely by qPCR with a very low detection limit. Results show co-occurrence of inoculum of both fungi throughout the entire sampling period with peak levels in August. The origin of the inoculum sampled in the periods without apothecia is discussed. Air-inoculum occurrence of both fungi is significantly correlated with each other, suggesting their coexistence in this forest.
Highlights
H. albidus is a widespread indigenous ascomycetous fungus in Europe, which behaves as a saprotroph, decomposing fallen petioles of common ash (Fraxinus excelsior L.)
Our results demonstrate that H. fraxineus and H. albidus are present in the air of the infected forest Hackerova školka since the beginning of April until the end of October (Figure 3), what means some time before and after the ascospores are known to be released and wind-dispersed in nature [7,12,13,14]
Based on the hypothetical life cycle of H. fraxineus depicted by Gross et al [7], we consider that, despite not observing fresh fruiting bodies on ash rachises, the air-inoculum detected in October may correspond to late produced ascospores that remain in the air
Summary
H. fraxineus is a lethal invasive pathogen from East Asia [3] and the main causal agent of ash dieback (ADB) in Europe [4,5]. It attacks living shoots [6], leaves [7] and, later, stems, collars, and roots [8] of all ages of F. excelsior, F. angustifolia Vahl, and F. ornus L. Airborne ascospores seem to be the only infectious propagules and outset of new infections on green leaves [2,12] They are released by apothecia on decomposing, pseudosclerotial leaf petioles and rachises found in the leaf litter mainly in summer [1]
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