Genetic and Phenotypic Characterization of Cryphonectria hypovirus 1 from Eurasian Georgia

Abstract

Cryphonectria hypovirus 1 (CHV-1) infects the chestnut blight fungus Cryphonectria parasitica and acts as a biological control agent against this harmful tree disease. In this study, we screened the recently characterized C. parasitica population in Eurasian Georgia for the presence of CHV-1. We found 62 CHV-1 infected C. parasitica isolates (9.3%) among a total of 664 isolates sampled in 14 locations across Georgia. The prevalence of CHV-1 at the different locations ranged from 0% in the eastern part of the country to 29% in the western part. Sequencing of two specific regions of the viral genome one each in ORFA and ORFB revealed a unique CHV-1 subtype in Georgia. This subtype has a recombinant pattern combining the ORFA region from the subtype F2 and the ORFB region from subtype D. All 62 viral strains belonged to this Georgian CHV-1 subtype (subtype G). The CHV-1 subtype G strongly reduced the parasitic growth of C. parasitica isolates from Georgia, with a more severe effect on the European genepool compared to the Georgian genepool. The CHV-1 subtype detected in Georgia provides a valuable candidate for biological control applications in the Caucasus region.

Hypovirulent effect of theCryphonectria hypovirus 1in British isolates ofCryphonectria parasitica

“…Six genetically distinct CHV‐1 subtypes have been identified in Europe (I, D, E, F1, F2 and G) . Subtype I (also known as Italian subtype) is the most widespread, probably because it is commonly associated with mild hypovirulence.…”

“…The CHV‐1 virus does not occur naturally in USA but is present in a few locations such as in Virginia where it has been released for the biological control of American chestnut blight, Wisconsin or Maryland . In Europe, several genetic recombinations have contributed to the evolution of the CHV‐1 …”

“…Six genetically distinct CHV-1 subtypes have been identified in Europe (I, D, E, F1, F2 and G). 24,40 Subtype I (also known as Italian subtype) is the most widespread, probably because it is commonly associated with mild hypovirulence. It is dominant in Italy, Switzerland, south-eastern France, Greece, 41 Bosnia, 42 Croatia, 43 Slovenia, 44 Macedonia 45 and Turkey.…”

“…15 In Europe, several genetic recombinations have contributed to the evolution of the CHV-1. 35,40 Following findings of chestnut blight in the wider environment in Britain from late 2016 onwards, 6 CHV-1 was first detected in C. parasitica populations at the end of 2017 but does not appear to be widespread based on the very low frequency of findings and the low concentration of detectable virus in affected isolates. 6 The E-5 haplotype was present in the two UK isolates used in this study (L-6 and Db-1), but its European distribution has not been well studied.…”

Determining the Suitability of MinION’s Direct RNA and DNA Amplicon Sequencing for Viral Subtype Identification

“…CHV-1 subtype I is the most widespread and is found along the Eastern Mediterranean [18]. The remaining subtypes are present in more localized populations: subtype F1 and F2 are found in France, E within Spain, D in Germany, and G within Georgia [18][19][20]. While the six subtypes have varying impacts on their fungal hosts and differing biocontrol potential, e.g., [21], all subtypes mitigate infection severity and reduce host tree mortality [13].…”