First report of Davidsoniella virescens in Poland
In southern Poland, during research studies conducted in two distant forest sites (Ojców National Park in 2018 and in the village Rozpucie (Brzozów Forest District) in 2021), mycelium and spore-forming structures resembling those of a Davidsoniella species were found on cross sections of logs and branches of Fagus sylvatica. Based on morphological and phylogenetic analysis, the fungus isolated from diseased wood was identified as Davidsoniella virescens (EU A1 quarantine pest). Inoculation tests were conducted on seedlings of F. sylvatica and Acer saccharum. They confirmed the pathogenicity of D. virescens to F. sylvatica with 5 of 36 inoculated seedlings showing wilting symptoms and showed that all six Polish isolates tested caused wood discoloration within the stems, occasionally in the roots, and bark necrotic lesions. None of the 36 inoculated A. saccharum seedlings showed symptoms of early leaf discoloration or wilting, nor of bark necrosis but they showed internal wood discoloration.
Previously, D. virescens had only been recorded in Eastern Canada and the USA where it causes ‘sapstreak disease’ of Acer saccharum. It has also been found as a saprophyte on logs of a number of other woody species. Sapstreak disease is characterized by a distinctive stain of internal wood in the roots and at the base of the stem. Stained wood is greenish yellow with reddish streaks and appears water soaked. In cross-sections of the wood, stain streaks have a radial arrangement and are surrounded by a dark-green zone. This disease significantly lowers the commercial value of wood, and affected trees have smaller leaves, as well as gradual branch dieback, eventually followed by tree death. D. virescens is also able to survive and sporulate on air-dried boards for several months, indicating that wood products could potentially transport the pathogen to new areas.
After the article by Kowalski & Bilański (2024) was published, the NPPO of Poland undertook actions to confirm the identification of the pathogen. The isolates provided by the authors of the article were analysed using morphological and molecular tests by the EU Reference Laboratory (EURL for Plant Pathogenic Fungi and Oomycetes). At the end of July 2025, the EURL confirmed the identity of the pathogen. As this is the first record on F. sylvatica, the question arises whether there are host-specific lineages or two forms of the pathogen (pathogenic and saprophytic). However, the EURL considers that the limited amount of data on the diversity of D. virescens does not allow a reliable conclusion to be drawn on either possibility. The pathogenicity of the fungus across the known host range, its diversity and several aspects of its biology still need to be elucidated. Limited data exist in the literature on D. virescens. The phylogenetic analyses performed by the EURL showed that the two strains of D. virescens isolated from A. saccharum in the USA diverge from strains isolated from F. sylvatica in Poland, as well as from Quercus sp. and F. grandiflora in the USA.
The NPPO of Poland underlined that the circumstances of detection (an old tree with broken branches or cut logs in protected areas) suggest that the fungus, in its saprophytic form, may have been present in Europe for a long time but has not been detected until now. As a consequence, no eradication measures will be implemented for the time being, but research will be conducted to assess the pathogenicity of the detected forms, and forest stands will be monitored in the areas where the fungus was isolated.
No official pest status for Davidsoniella virescens has been declared yet in Poland.
Sources
Kowalski T, Bilański P (2024) Recognition of Davidsoniella virescens on Fagus sylvatica wood in Poland and assessment of its pathogenicity. Journal of Fungi 10(7), 465. https://doi.org/10.3390/jof10070465
NPPO of Poland (2025-09).
EFSA Panel on Plant Health (2017) Pest categorisation of Davidsoniella virescens. EFSA Journal 15(12), e05104, https://doi.org/10.2903/j.efsa.2017.5104
EFSA (2023) Pest survey card for Davidsoniella virescens. EFSA supporting publication 2023:EN-8186, doi:10.2903/sp.efsa.2023.EN-8186