Chestnut Crab
| Chestnut Crab | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Cryphonectria parasitica | ||||||||||||
| ( Murr. ) Barr |
The chestnut crustacean ( Cryphonectria parasitica , syn .: Endothia parasitica ) is a representative of the real hose fungus that parasitizes on chestnuts . In America it caused the complete collapse of the American chestnut ( Castanea dentata ) stocks, in Europe the sweet chestnut ( Castanea sativa ) stocks were severely affected.
Biology and symptoms
The spores get into the trees through small wounds, such as cracks in the bark, broken branches or areas of refinement. The fungus forms a yellowish mycelium in the bark and cambium of the tree. In doing so, it destroys the growth and transport tissue of the tree. The first signs of disease are sinking or swelling of the affected tissue and cracks in the bark. Symptoms that occur later are withering of the parts of the plant above the infected area and the formation of water veins below the infected area. Wilted leaves or leaves on the tree that are dry in winter are a symptom of an infestation that is visible from afar.
The fungus reproduces both sexually and asexually. The small, yellow-orange to red fruit bodies are formed on the surface of the bark. The asexual pycnidia release a yellow-orange, tendril-like mass that contains the pycnospores in damp weather. These are spread by rain, wind, insects and birds. The sexual, two-celled ascospores are formed in the perithecia . They are thrown out in dry weather and spread over great distances by the wind.
Host organisms
The chestnut crayfish attacks species of the genus chestnut ( Castanea ). It also attacks oak trees ( Quercus ), but hardly causes any symptoms in them.
Hypovirulence
Some strains of chestnut crayfish cause only superficial cancer symptoms instead of severe symptoms, which in the sweet chestnut ( Castanea sativa ) heal again. This phenomenon of decreased virulence was called hypovirulence by its discoverer MJ Grente. In culture these strains form little or no pycnidia and these appear white in contrast to the normal orange forms.
The cause of hypovirulence is a virus with double-stranded RNA as hereditary material (dsRNA). This virus, the Chestnut Hypovirus 1 or CHV1, is exchanged between fungal strains that come from the same vegetative compatibility group (vc group). The transmission occurs through anastomoses between the fungal hyphae , whereby the hypovirulence is transmitted to the normally virulent strain.
The dsRNA is contained in 20 to 90% of the ascospores.
The number of vc groups varies greatly per location. In Europe there are a total of around 64 vc groups, of which over 40 are known in France, 20 to 30 in Italy, Bosnia and Switzerland, 15 in Austria, and in Greece, where all chestnut stocks are infested, but only 4. The number of vc groups is much higher in the US.
history
The chestnut crayfish is native to East Asia and causes only minor damage to the chestnuts native there. It was first discovered in North America in 1904. By 1950 he destroyed the vast stocks of American chestnuts ( Castanea dentata ) practically completely. The species was once a dominant tree species in the East American deciduous forests and is now almost entirely shrubby in the undergrowth.
In Europe, the chestnut crab was first discovered in 1938 in the hinterland of Genoa. It spread rapidly throughout the Mediterranean, in the 1940s in Spain and Switzerland, in the 1950s in France, Croatia, Slovenia, in the 1960s in Albania, Bosnia-Herzegovina, Greece, Hungary, Austria and Turkey, in the 1970s in Macedonia and Slovakia, then also in Romania (1984), Portugal (1989) and Germany (1992). In 2001, only northern France and Great Britain were free from chestnut crayfish. The disease is, however, less dramatic than in the USA. The sweet chestnut is more resistant, and the hypovirulent strains are an effective treatment method.
activities
The chestnut crab is a quarantine pathogen . In order to prevent its spread, the export of chestnut and oak wood is regulated worldwide, and plant protection certificates are required.
Infested parts of plants or trees are quickly removed and burned in newly infested areas. When processing, disinfected tools and good covering of the wounds are important to avoid infestation.
The biological control with hypovirulent strains is successful in Europe with the sweet chestnut. Infested trees are vaccinated with hypovirulent trunks of the corresponding vc group. This is mainly practiced in France, Hungary, Greece, Slovakia and Switzerland.
supporting documents
- Rigling, D .; Schütz-Bryner, S .; Heiniger, U .; Prospero, S .: The chestnut crab. Damage symptoms, biology and countermeasures . Leaflet for practice 54, Federal Research Institute for Forests, Snow and Landscape, 2014.
Individual evidence
- ↑ a b c d e f C. Robin, U. Heininger: Chestnut blight in Europe: Diversity of Chryphonectria parasitica, hypvirulence and biocontrol . Forest, Snow and Landscape Research, Volume 76, 2001, pp. 361-367.
Web links
- The chestnut crab. Symptoms of damage, biology and countermeasures - WSL information sheet for practice - PDF (4 MB)
