Pest survey card on Davidsoniella virescens

This pest survey card was prepared in the context of the EFSA mandate on plant pest surveillance (M-2020-0114), at the request of the European Commission. Its purpose is to guide the Member States in preparing data and information for surveys for Davidsoniella virescens, the causal agent of sapstreak of maple (Acer saccharum). The pathogen is a well-defined and distinguishable fungal species of the family Ceratocystidaceae, native to the eastern areas of North America. Davidsoniella virescens is a Union quarantine pest not known to occur in the EU. It is a vascular pathogen that infects the host plant mainly through wounds on the roots and the lower part of the stem, but its life cycle is not fully understood. The main host of the pathogen is A. saccharum, but Liriodendron tulipifera, A. saccharinum and A. rubra can also become infected. It has been suggested that the fungus behaves as a saprotroph on the freshly cut logs of a number of other hardwood species. However, uncertainty remains as to whether the saprophyte species is synonymous with the D. virescens that causes sapstreak of sugar maple. Detection surveys of D. virescens in the EU should focus mainly on A. saccharum. For delimiting surveys, the other confirmed and potential EU hosts should be included. Host availability and climatic conditions are not a limiting factor for the establishment of D. virescens. The natural spread of the pathogen is not fully understood; however, infections occur mainly by the entry of spores via wounds near the ground, but, uncommonly, also through root grafts or insects. The spread of the pathogen can be facilitated by human activity of importing infected wood, plants for planting and cut branches. Sapstreak disease can be detected in the field by the observation of external and internal symptoms on the host plants (a distinctive transparency of the crown, unusually small leaves, characteristic stains on the diseased wood of roots and lower stems) and consequent sampling. The fungus can be isolated from chips of xylem tissue from stained areas and stained wood samples. Morphological identification is possible for D. virescens but identification is based on sequences of the internal transcribed spacer (ITS) region. A rapid, specific and sensitive molecular detection tool for D. virescens is still lacking.