Insights into the genetic diversity and evolution of Little cherry virus 1

Little cherry virus 1 (LChV-1), a member of the recently proposed genus Velarivirus, is a sweet cherry pathogen that has been recently reported to infect other Prunus species and is associated with various plant disorders. In this work the incidence of the virus on its putative hosts and possible mechanisms driving its evolution were investigated. Due to problems encountered with LChV-1 detection, a new nested RT-PCR assay was developed and applied. The virus was found to be prevalent in cherry plantations in Greece and only occasionally detected in other Prunus species. Sequences corresponding to the partial RNA-dependent RNA polymerase (RdRp), heat-shock protein homologue (HSP70h) and coat protein (CP) genes were determined from Greek LChV-1 isolates originating from different hosts; these were analysed, along with published homologous genomic regions from other isolates. Phylogenetic analysis of the three genes revealed the segregation of four evolutionary distinct groups showing no host or geography-based clustering. Mean genetic distances among the four groups were high with the CP region showing the highest divergence, although intragroup variability levels were low. Nevertheless, estimations of the mean ratio of nonsynonymous substitutions per synonymous site to synonymous substitutions per synonymous site (dN/dS) for the partial RdRp, HSP70h and CP indicated that these genomic regions are under negative selection pressure. Interestingly, a recombination event was identified at the 3 end of RdRp on a Greek virus isolate, thus highlighting the role of this mechanism in the evolutionary history of LChV-1.