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Chestnut blight - Cryphonectria parasitica | deutsch

Symptoms    Wilt, crown dieback; dead leaves remaining attached to the twigs during winter, dropping in the following year; on the surface of smooth-barked trees and on twigs red to orange discolored necroses; in these areas yellow-orange pustules (fruiting bodies of the asexual stage), later the dark red sexual stage; necroses usually swollen by callus production, deep cracks develop; at the border of the necroses the tree often produces epicormic shoots. If the surface of the cankers is not reddish, but grey, it is a necrosis of the same fungus with reduced aggressiveness.
Impact    Most dangerous disease of edible chestnut; the disease origins from Asia, where it occurs on other chestnut species doing not much harm to them. In the beginning of the 20th century it was introduced to North America, where it caused (and still causes) disastrous damage on Castanea crenata. Afterwards the disease appeared in Europe as a deadly disease of European edible chestnut. Trees of all ages, single trees and trees in stands as well as orchards are attacked to the same extent. Climatic parameters do not play any role, only the presence of fungal spores is essential. The disease also affects oaks to a certain extent (Hungary, Czech Republic).
Control    About half a century ago abnormal bark necroses were observed in Italy, which showed a grey surface colour and didn't cause the death of the trees. Intense research resulted in the detection of strains of the same fungus containing a virus, which reduces the pathogenicity. This feature, defined as hypovirulence can be transmitted by mycelial contacts to aggressive strains turning them into strains with reduced virulence. Therefore in forests as well as in orchards, the aggressive form can be replaced during time and the stands survive. For a number of years, the non aggressive strains have been propagated artificially in labs and released in diseased forests to accelerate the process of healing (artificial introduction of hypovirulence). A chemical treatment is not effective. The same refers to hygienic measures alone (pruning, removal of infective material from the stand).
Hosts   Edible chestnut; Oak;
Affected plant parts    Shoot/Twig/Branch; Stem;


Cryphonectria parasitica: virulent strain: orange surface of the necrosis
Cryphonectria parasitica: hypovirulent strain: grey surface of the necrosis
Cryphonectria parasitica: dead tree
Cryphonectria parasitica: late stage of a necrosis. Cracks, stem swollen, coppices, sporocarps>/em>
Cryphonectria parasitica: sporocarps>/em>
Cryphonectria parasitica: fruiting bodies (sexual stage)

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