An extremely narrow bottleneck limits cucumber mosaic virus RNA2 during phloem unloading within inoculated leaves

Abstract Previous studies have suggested that plant viruses experience genetic bottlenecks in phloem-mediated long-distance movement; however, the detailed mechanisms of these genetic bottlenecks have not been analyzed, and their size has not been estimated for segmented viruses. In this study, we used a tripartite RNA virus, cucumber mosaic virus, and showed that strong bottleneck events occurred at the phloem unloading step of RNA2 in Nicotiana benthamiana . Half-leaf inoculation method allowed us to estimate the genetic bottleneck size as 0.042 ± 0.021 (mean ± standard error), indicating that a strong genetic bottleneck occurs specifically at the phloem unloading step within inoculated leaves.