Mountain ash (Sorbus aucuparia L.) is a tree that is native to northern Europe. It was recently found to be infected with European mountain ash ringspot-associated virus (EMARaV) in Germany and Finland (2,3). EMARaV is not transmitted mechanically and no vector is known, but it is related to negative-sense RNA viruses transmitted by eriophyid mites (3) and represents a new viral species of the genus Emaravirus, which is not assigned to any family. In Finland, EMARaV is common, widely distributed, and detected in all tested ringspot disease-affected and symptomless mountain ash trees (2). Ringspot symptoms occur in mountain ash also in Sweden (west from Finland). In this study, ringspot-affected mountain ash trees were found in Ustreka, which marks the eastern edge of the geologically defined Baltic Shield and the eastern geobotanical borderline of Fennoscandia in eastern Karelia, Russia (1). This border zone can be recognized by changes in vegetation, including occurrence of Siberian larch (Larix sibirica Ledeb.), which does not belong to Fennoscandian flora. Three young mountain ash trees (4 to 5 years old and 2 to 3 m tall) displayed symptoms characteristic of EMARaV at Lake Tsumba (61°50′58″N, 37°45′34″E) in August 2009. EMARaV was detected in collected leaves by reverse transcription-PCR using virus-specific primers as described (2). The nucleocapsid protein genes (944 nucleotides) of the three isolates (Rus1, Rus2, and Rus3) were 97 to 99% identical (GenBank Accession Nos. GU563317, GU563318, and GU563319). On the basis of phylogenetic analysis, the Russian isolates, and three previously characterized isolates from Finland (Ris60, Ris61, and Kuo 12) formed a distinct cluster separate from the remaining 14 previously characterized isolates from Finland and one isolate from Germany. Division of EMARaV to two genetically distinguishable groups was realized for the first time. EMARaV-infected mountain ash trees suffer from chlorosis and growth reduction of varying severity, which impairs their value as an ornamental and for carpentry. To our knowledge, this is the first report in Russia on definite identification of a virus and virus disease in an economically important native plant of northern Europe in the natural habitat as far east as the geobotanical border zone of Fennoscandia.
References: (1) T. Ahti and M. Boychek. The Botanical Journeys of A. K. Cajander and J. I. Lindroth to Karelia and Onega River in 1898 and 1899. Finnish Museum of Natural History, Helsinki, Finland, 2006. (2) A. K. Kallinen et al. Phytopathology 99:344, 2009. (3) N. Mielke and H. P. Muehlbach. J. Gen. Virol. 88:1337, 2007.
