īelow the bark cankers infected trees usually produce epicormic shoots (fig. Wilted leaves during the growing season or brown hanging leaves in winter are a typical sign of chestnut blight that is visible from a long way off. As soon as a bark canker has girdled the entire branch or stem, the plant part above the point of infection dies.
In response, the tree attempts to cover the destroyed tissue and so-called bark cankers develop. 3), sinks inwards and later on cracks (fig. At the point of infection, the bark turns red (fig. Virulence = the extend to which a pathogen can cause a disease in a susceptible hostįind out more about hypovirulence in the extensive WSL information sheet (PDF, in German)Ĭryphonectria parasitica infects the bark of stem and branches of its host trees. However, in the meantime targeted treatment of the disease over many years has also established hypovirulence in many chestnut stands north of the Alps. parasitica populations north of the Alps. In contrast to there, no hypovirulent strains of the fungus appeared spontaneously in C. Genetic analyses have shown that in most cases the pathogen was introduced from south of the Alps. Since the 1980s, chestnut blight has also been found in chestnut stands north of the Alps in Switzerland. Thanks to natural hypovirulence, the survival of the chestnut in southern Switzerland is not under threat anymore.
These hypovirulent fungal strains spontaneously spread south of the Alps along the northern Mediterranean, thus preventing the destruction of local chestnut forests. On the one hand, the European chestnut ( Castanea sativa) is slightly less susceptible to the pathogen than the American chestnut on the other hand, strains of the fungus showing a reduced virulence appeared in Europe. Unlike in the USA, the impact of the disease in Europe has been less dramatic.
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