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Molecular Genetic Analysis of Cucumber mosaic virus Populations Infecting Pepper Suggests Unique Patterns of Evolution in Korea

First, second, third, and seventh authors: Crop Protection Division, National Academy of Agricultural Science, Rural Development Administration, Suwon 441-707, Korea; first and sixth authors: Department of Plant Medicine, Chungbuk National University, Cheongju 361-763, Korea; fourth author: Department of Plant Medicine, Andong National University, Andong 760-749, Korea; and fifth author: Department of Agricultural Biotechnology and Plant Genomics and Breeding Institute, Seoul National University, Seoul 151-921, Korea.

Studying genetic structure and diversity of viruses is important to understand the evolutionary mechanisms that generate and maintain variations in viral populations. Cucumber mosaic virus (CMV) is endemic in most pepper fields in Korea. Currently, no effective methods for control of CMV are available due to many environmental and biological factors such as the extensive evolutionary capacity of CMV. Thus, analyzing the genetic structure of CMV populations may facilitate the development of strategies for the control of CMV. In this study, 252 pepper (Capsicum annuum) samples showing virus symptoms were collected by field surveys performed throughout Korea in 2007. Reverse-transcription polymerase chain reaction analyses revealed that, in total, 165 collected samples were infected with CMV. Forty-five CMV isolates were randomly selected within each regional subpopulation and analyzed by full-genome sequencing. Analyses of genetic diversity showed that the 2b gene of CMV is under weaker purifying selection than the other genes. Based on the phylogenetic analysis of RNA1, the CMV isolates from pepper were divided into three clusters in subgroup I. Our full-genome sequence-based molecular analyses of the CMV Korean population suggest that the subpopulations of CMV have been geographically localized in pepper fields in Korea.