First Report of Potato Virus Y in Ornamental Calibrachoa in Argentina

Abstract

Calibrachoa is a genus of the Solanaceae family endemic to South America that is used as an ornamental plant. Calibrachoa grows vigorously and has flowers of different colors such as pink, violet, red, yellow, and salmon (Milicia et al. 2016). Even though Calibrachoa hybrida in Argentina is mainly sold in the local markets and in a small percentage, the importance of this genus lies in being the main source of germplasm for ornamental varieties of great international impact. Viral diseases represent a serious problem for calibrachoa production because they decrease its commercial value and productivity. To date, only calibrachoa mottle virus (genus Carmovirus) and tobacco mild green mosaic virus (genus Tobamovirus) have been described to infect calibrachoa plants (Liu et al. 2003). The genus Potyvirus is one of the largest and most widespread important genera of plant viruses. Potato virus Y (PVY), the type species of the genus, is a major pathogen of solanaceous crops (potato, tobacco, pepper, and tomato), ornamentals (dahlia and petunia), and weeds (Karasev and Gray 2013; Quenouille et al. 2013). In 2017, C. hybrida cultivars ?Pampa Salmón INTA? and ?Overá Fucsia INTA? in a production greenhouse at Buenos Aires, Argentina, displayed virus-like symptoms, including leaf mosaic and growth retardation. Samples from symptomatic leaf tissue were collected from 20 plants of C. hybrida cultivar Overá Fucsia INTA and tested by indirect ELISA using polyclonal antibodies against potyviruses (BIOREBA Poty group test). The results of that study revealed that all samples were positive for a potyvirus. Reverse transcription polymerase chain reaction (PCR) with degenerate primers was performed to identify this potyvirus. Total RNA was extracted from symptomatic leaves of one ELISA-positive sample using TRIzol reagent, and cDNA was synthesized following the manufacturer?s instructions, using SuperScript III reverse transcription and primer AP from a 3′ rapid amplification of cDNA end kit (Thermo Fisher Scientific). The universal Potyviridae S-primer (Chen et al. 2001) and the abridged universal amplification primer (Thermo Fisher Scientific) were used to amplify a ∼1.7-kb PCR product spanning the nuclear NIb and the coat protein cistrons and the 3′ untranslated region with platinum Pfx DNA polymerase (Thermo Fisher Scientific). This ∼1.7-kb PCR product was cloned into pGEM-T Easy vector (Promega) and sequenced on an ABI 3500 XL automated sequencer. The 1,772-nt nucleotide sequence was deposited in GenBank database under the accession number MH880833. A BLASTn analysis of the 1,772-nt region of the virus isolate with the nucleotide sequences available in the GenBank database showed 82 to 88% nucleotide identity with different PVY isolates. The highest nucleotide identities were 88% with PVY (KC823271) isolated from Nicotiana tabacum in Brazil and 83% with PVY (KC296439) isolated from tobacco in China. At the amino acid level, the 480 amino acid partial polyprotein sequence showed 93% identity with the same Brazilian isolate (AGX27991) and 88% with the Chinese isolate (AGH27746). PVY complex includes five nonrecombinant strains and 36 recombinant patterns, presenting a challenge for strain typing (Green et al. 2018). The identification of the calibrachoa-infecting PVY strain is vital for resistant-cultivar selection, and therefore it should be addressed in future studies. To our knowledge, this is the first report of PVY as a pathogen of Calibrachoa in Argentina.