Submitted to: Acta Horticulture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/16/2005
Publication Date: 10/31/2006
Citation: Hammond, J., Reinsel, M.D., Maroon-Lango, C.J. 2006. Identification of potexvirus isolates from creeping phlox and trailing portulaca as strains of Alternanthera mosaic virus, and comparison of the 3'-terminal portion of the viral genomes. Acta Horticulture. 722:71-78. Interpretive Summary: Many different viruses infect plants grown commercially as ornamentals, and cause reductions in productivity and quality. Many ornamental plants are propagated by cuttings, and almost all plants produced from an infected mother plant will also be infected. Some infected plants may remain almost symptomless, but serve as a source of infection for other species that show severe symptoms. The ability to detect and identify the viruses present in infected material is critical to the ability of growers to select healthy plants from which to propagate. Visibly infected creeping phlox, and symptomless trailing portulaca plants from commercial nurseries were found to be infected with a potexvirus, which was easily transmitted to several standard virus assay host plants. The virus isolates from phlox and portulaca were detected with an antiserum against Papaya mosaic virus (PapMV), but molecular cloning and sequencing of a portion of the viral genome identified the isolates as strains of Alternanthera mosaic virus (AltMV), a potexvirus previously reported only from a weed host in Australia. The experimental host range of the AltMV isolates from phlox and portulaca was found to include several other species grown commercially as ornamentals. These findings suggest that AltMV may be quite widespread, and may be mis-diagnosed as PapMV. This knowledge will also allow growers to select plants free of this virus, to improve crop productivity.
Technical Abstract: Potexvirus isolates from creeping phlox (Phlox stolonifera) and trailing portulaca (Portulaca grandiflora) obtained from commercial nurseries were found to react strongly with polyclonal antiserum against Papaya mosaic virus (PapMV). Cloning and sequencing of a phlox isolate from Pennsylvania revealed that the coat protein (CP) gene was c.97% identical at the amino acid level to the CP gene sequence of Alternanthera mosaic virus (Geering and Thomas, 1999), and only c.75% to the CP of PapMV. The full genomic sequence of the phlox isolate was then determined. The regions to the 5' of the CP gene were found to be more closely related to (but distinct from) PapMV than to any other characterized potexvirus. This phlox potexvirus isolate was therefore named AltMV-PA. The host range of AltMV-PA was found to be similar to that of the Australian isolate, AltMV-Au. The 3'-terminal portion of the genome of the portulaca potexvirus isolate, and of additional potexvirus isolates from two phlox cultivars from commercial nurseries in Maryland, were also cloned and sequenced. The sequences of these isolates were similar to those of AltMV-Au and AltMV-PA, and the isolates were designated AltMV-Po (Portulaca), AltMV-SP (creeping phlox 'Sherwood Purple'), and AltMV-BR (creeping phlox 'Blue Ridge'). Each of the phlox and portulaca isolates reacted strongly with antiserum to AltMV-Au, and also with anti-PapMV antiserum. The host range of AltMV includes several ornamentals; these findings suggest that AltMV may be quite widespread, and may be mis-diagnosed as PapMV.