The population structure of Rose rosette virus in the USA.

Rose rosette virus (RRV) (genus Emaravirus) is the causal agent of the homonymous disease, the most destructive malady of roses in the USA. Although the importance of the disease is recognized, little sequence information and no full genomes are available for RRV, a multi-segmented RNA virus. To better understand the population structure of the virus we implemented a Hi-Plex PCR amplicon high-throughput sequencing approach to sequence all 7 segments and to quantify polymorphisms in 91 RRV isolates collected from 16 states in the USA. Analysis revealed insertion/deletion (indel) polymorphisms primarily in the 5' and 3' non-coding, but also within coding regions, including some resulting in changes of protein length. Phylogenetic analysis showed little geographical structuring, suggesting that topography does not have a strong influence on virus evolution. Overall, the virus populations were homogeneous, possibly because of regular movement of plants, the recent emergence of RRV and/or because the virus is under strong purification selection to preserve its integrity and biological functions.