Molecular and biological characterization of Potato virus Y detected in zucchini in China

Potato virus Y (PVY) is an important viral pathogen of the plant family Solanaceae. However, it has not been reported that PVY infects zucchini (Cucurbita pepo L). Zucchini plants showing symptoms of leaf mosaic and fruit ringspot were collected from Inner Mongolia, China. Using RT-PCR, we amplified the PVY-specific bands in zucchini (PVY-Zu isolate). Further, we found that the viral pathogen could infect Nicotiana benthamiana via mechanical inoculation with the extract of the zucchini leaves. Filamentous virions were observed in infected N. benthamiana plants under a transmission electron microscope. Additionally, the complete genomic fragment of the PVY-Zu isolate was obtained via RT-PCR and RACE analysis, containing 9662 nucleotides (nt) excluding the 3′-terminal poly (A) tail. The 5′ and 3′ untranslated regions (UTRs) were 150 nt and 329 nt, respectively, while the putative polyprotein contained 3061 amino acids. Comparison of the PVY-Zu isolate with 19 other PVY isolates revealed that they shared nucleotide sequence identities of ~ 83.1–99.8% at the complete genomic level. Based on the complete genome sequences, phylogenetic analysis showed that PVY-Zu clustered with PVY strain N605 (X97895-PVY), a Swiss necrotic isolate of PVY. Compared with the complete genome sequence of X97895-PVY, the PVY-Zu isolate had a deletion of a 39-nt fragment in its 5′ UTR and 22 mutated nucleotides without changes in the amino acids. Moreover, although the similarity in the identities of the PVY-Zu isolate and PVY N isolate N-Jg (AY166867) was about 96.2%, the former had a deletion of a 38-nt fragment in its 5′ UTR and 334 mutations among the viral genome, which resulted in 61 amino acid changes. However, we could not detect any recombination throughout the PVY-Zu genome. To our knowledge, this is the first study reporting that PVY could infect zucchini plants, thus broadening the host diversity of the viral pathogen.