Hypovirulence in chestnut blight fungus,Cryphonectria parasitica, in Slovakia

The recovery of the European chestnut from chestnut blight in Europe is attributed to hypovirulence, a viral disease that reduces the virulence of its host – Cryphonectria parasitica. Hypovirulence has been used in biocontrol programmes throughout Europe with the aim of not only treating individual chestnut blight cankers but causing the natural spread and establishment of viruses in C. parasitica populations. Almost 40 years after the first appearance of chestnut blight and more than 20 years after the first biocontrol treatment implementation in Slovakia the establishment and natural spread of hypovirulence were studied. The morphological characteristics of 179 chestnut blight cankers and 161 C. parasitica strains were evaluated for the presence of hypovirus from three chestnut cultivation sites in Slovakia. Nineteen cankers and isolates were considered hypovirulent based on visual assessment of their morphological characteristics. The hypovirus presence by RNA extraction was confirmed in 6 cankers/strains.