Several closteroviruses are associated with little cherry disease
Little cherry disease was first reported in the 1930s, in the Kootenay valley in British Colombia, Canada (see also EPPO RS 99/066). In recent years, a serious outbreak of the disease was observed near Hamburg in Germany. In Canada, a known vector of the disease is the apple mealybug (Phenacoccus aceris), whereas in Germany the mode of dissemination of the disease remains unknown as this insect is uncommon. Initial studies showed that long flexuous virus particles characteristic of closteroviruses were present in phloem cells of infected trees. In 1996, a closterovirus associated with the disease in Germany was identified, its complete genomic sequence was determined, and it was called Little cherry closterovirus. PCR primers were then designed to detect this virus specifically. However, a number of isolates consistently gave a negative result. Initial characterization of a Canadian isolate showed that it was distinct from Little cherry closterovirus. This observation was confirmed by recent studies of Eastwell ; Bernady (2001) who showed that the characteristics of the mealybug-transmitted virus in North America were very different from those of the Little cherry closterovirus associated with the disease in Europe. Studies done by Root ; Jelkmann (2001) led to the partial characterization of a second closterovirus associated with little cherry disease which was called Little cherry virus-2 (LChV-2). For consistency, the previously characterized virus was renamed Little cherry virus-1 (LChV-1). Based on a limited sequence comparison, it was found that LchV-2 is the same virus as the one previously described in association with the disease in Canada. The conclusion was that little cherry disease is caused by at least 2 distinct closteroviruses. However, of the 28 isolates tested, one still tested negative to both LChV-1 and LChV-2, suggesting the possible existence of a third virus. Interestingly, LChV-1 and LChV-2 are only distantly related, suggesting that the two viruses probably arose independently on cherry. More recently, further studies done by Theilmann et al. (2002) confirmed the existence of a third closterovirus which was partially described and named LChV-3. LChV-3 was isolated also from British Colombia, Canada. Sequence comparison between LChV-3 and LChV-1 showed that these viruses are only remotely related. More studies are needed to better understand the distribution and the epidemiology of LChV-1, LChV-2 and LChV-3.
Eastwell, K.C.; Bernady, M.G. (2001) Partial characterization of a closterovirus associated with apply mealybug-transmitted little cherry disease in North America. Phytopathology, 91(3), 261-267.
Rott, M.E.; Jelkmann, W. (2001) Detection and partial characterization of a second closterovirus associated with little cherry disease, Little cherry virus-2. Phytopathology, 91(3), 261-267.
Theilmann, J.; Mozafari, J.; Reade, R.; Wu, Z.; Xie, W.; Jesperson, G.; Bernardy, M.; Eastwell, K.C.; Rochon, D. (2002) Partial nucleotide and genome organization of a Canadian isolate of Little cherry virus and development of an Enzyme-Linked Immunosorbent Assay-based diagnostic test. Phytopathology, 92(1), 87-98.