Dahlia Virome Analysis Reveals Multiple Novel Viruses in Mixed Infections

Dahlia is an economically important ornamental crop in the United States and worldwide. Dahlia is primarily propagated vegetatively through bulbs, which can result in vertical transmission of and constant accumulation of viruses. In this study, mosaic and yellowing symptoms were observed in Dahlia plants in a residential garden in California. Dahlia samples were collected and sequenced using high-throughput sequencing (HTS). HTS analysis was used to explore the Dahlia virome in the symptomatic plants, which revealed the presence of several contigs with homology to known Dahlia-infecting viruses, such as Dahlia common mosaic virus (DCMV) and tobacco streak virus (TSV), and Dahlia latent viroid. However, two contigs showed that they belong to the genera Potyvirus and Miraophiovirus with low to medium homology to previously known Potyvirus and Miraophiovirus species. Sequence identity showed that these two contigs represent two novel viruses tentatively named Dahlia potyvirus 1 (DaPoV1) and Dahlia miraophiovirus 1 (DaMV1). In addition, two other contigs showed low homology to a partitivirus and yue-like virus, indicating novelty. Mechanical inoculation of infected Dahlia tissue did not result in successful transmission onto indicator hosts. Electron microscopy of symptomatic plants showed typical potyviral-like flexuous virions. Phylogenetic analysis confirmed the placement of DaPoV1 and DaMV1 in their respective genera. This study represents a significant expansion of the known Dahlia virome and uncovers the complexity of viral infections where DCMV and TSV have been historically the primary focus in Dahlia. Widespread surveys should reveal the distribution of these viruses at commercial production sites.