Cryphonectria parasitica hypoviruses (antagonist)
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Cryphonectria parasitica hypoviruses (antagonist) (CHVs)
Several mycoviruses have been described as infecting the chestnut blight fungus Cryphonectria parasitica. This page deals with those belonging to the family Hypoviridae. For other mycoviruses see the page "other Cryphonectria mycoviruses".
The hypoviruses are important antagonists, suppressing the chestnut blight disease. A number of species are known to contribute to this suppression in the field. Mainly Cryphonectria hypovirus 1 (CHV1), a double stranded RNA virus, is involved. This virus has spread naturally to Europe (first isolated in Italy in 1964), resulting in the spontaneous recovery of many chestnut stands. The virus is also present in Asia and probably native there. It has further been intentionally introduced into some areas of North America.
Infected fungi are characterized by a loss of pigmentation, low reproductive activity and reduced virulence. This enables the defence system of the host tree to overcome the infection. The hypoviruses spread via spores, insects or mites. When infected and uninfected hyphae of the host fungus come in contact the virus can be transmitted when hyphae fuse by anastomosis, provided both hyphae are vegetative compatible.
The natural transmission rate can be accelerated by transferring the virus manually to fungus-infected chestnut trees. For example by drilling holes into the cankers and pouring into it an inoculum of a fungus strain infected with the hypovirus. The best combination of fungal strains and virus isolated can be selected in the laboratory.
CHV1 is a positive stranded RNA virus with 12,712 nucleotides. It is the type species of the genus Hypovirus and of the family Hypoviridae.