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 MemberStates in preparing data and information for surveys for Davidsoniella virescens, the causal agentof sapstreak of maple (Acer saccharum). The pathogen is a well-defined and distinguishablefungal 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 vascularpathogen that infects the host plant mainly through wounds on the roots and the lower part ofthe 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 beensuggested that the fungus behaves as a saprotroph on the freshly cut logs of a number of otherhardwood species. However, uncertainty remains as to whether the saprophyte species issynonymous with the D. virescens that causes sapstreak of sugar maple. Detection surveys ofD. virescens in the EU should focus mainly on A. saccharum. For delimiting surveys, the otherconfirmed and potential EU hosts should be included. Host availability and climatic conditionsare not a limiting factor for the establishment of D. virescens. The natural spread of the pathogenis not fully understood; however, infections occur mainly by the entry of spores via wounds nearthe ground, but, uncommonly, also through root grafts or insects. The spread of the pathogencan be facilitated by human activity of importing infected wood, plants for planting and cutbranches. Sapstreak disease can be detected in the field by the observation of external andinternal symptoms on the host plants (a distinctive transparency of the crown, unusually smallleaves, characteristic stains on the diseased wood of roots and lower stems) and consequentsampling. The fungus can be isolated from chips of xylem tissue from stained areas and stainedwood samples. Morphological identification is possible for D. virescens but identification is basedon sequences of the internal transcribed spacer (ITS) region. A rapid, specific and sensitivemolecular detection tool for D. virescens is still lacking.