Some thoughts on Ceratocystis virescens
In North America, Ceratocystis virescens (EU Annex II/A1) causes sapstreak disease of sugar maple (Acer saccharum). This fungus has been considered by many authors as a synonym of Ceratocystis coerulescens which is widespread in Europe on conifers, as the teleomorphs cannot be morphologically differentiated. In addition to taxonomic problems, its pathogenicity, particularly to European maple, still needs to be clarified. From a quarantine point of view, these difficulties have led to different attitudes. EPPO has not considered that C. virescens was a quarantine pest, essentially on the grounds that it presented a negligible risk as a pathogen of Acer saccharum. The European Union has considered that it was synonymous with C. coerulescens, but that it could present a danger for European maples. But seen from the outside, it appears that quarantine measures are required against a ubiquitous and more or less harmless fungus, which is not satisfactory.
The authors also made the following points. More recent studies on isozyme variation and on morphological differences between the anamorphs tend to suggest that C. coerulescens and C. virescens could be two different species. Concerning host range, C. virescens occurs essentially on A. saccharum, although a few cases of infestation have been reported on Liriodendron tulipifera. C. coerulescens occurs on conifers. Recently, however a Ceratocystis species belonging to the C. virescens/C. coerulescens complex has been found in Europe on a broad-leaf tree species (Quercus robur). Experiments have shown that C. virescens could survive in the wood, and could still be isolated from air-dried boards 5 months after being cut. Its introduction on wood or wood products is therefore possible. They felt that quarantine measures are then justified. The problem of pathogenicity of C. virescens to European maple cannot be appraised with the current state of knowledge.
The authors concluded that there is an urgent need to clarify taxonomy, pathogenicity and host spectrum, for a better evaluation of the phytosanitary risk presented by C. virescens.
Zajonc, J.; Wulf, A. (1997) [European maple species endangered by sapstreak (Ceratocystis virescens)?]
Nachrichtenblatt des Deutschen Pflanzenschutzdienstes, 49(12), 297-300.