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First Report of Alfalfa mosaic virus Occurrence in Tecoma capensis in the USA
Benham E. Lockhart and Dimitre Mollov, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108
Corresponding author: Ben Lockhart. email@example.com
Lockhart, B., and Mollov, D. 2012. First report of Alfalfa mosaic virus occurrence in Tecoma capensis in the USA. Online. Plant Health Progress doi:10.1094/PHP-2012-0824-02-BR.
Tecoma capensis [Tecomaria capensis (syn.)] or cape honeysuckle is an evergreen vine-line shrub that is widely used as a landscape plant in many areas of the southern and western USA (USDA hardiness zones 9-11). Plants of T. capensis at a commercial nursery in southern California displayed virus-like symptoms consisting of bright yellow foliar mosaic, and reduced leaf size and plant vigor (Fig. 1), that affected marketability. Partially-purified extracts (1) of symptomatic leaf tissue were negatively stained with either aqueous uranyl acetate (UA) or 2% sodium phosphotungstate, pH 7.0 (PTA), following fixation in 5% (v/v) glutaraldehyde in 100 mM phosphate buffer, pH 7.0, and examined by transmission electron microscopy (TEM). The only virus-like particles observed in these preparations were bacilliform and quasi-spherical particles resembling those of Alfalfa mosaic virus (AMV) (2). The identity of the virus was first confirmed by immunosorbent electron microscopy (ISEM) (Fig. 2) using antibodies to a clover isolate of AMV (American Type Culture Collection PVAS 92). Additional information on the identity of the Tecoma virus was obtained by reverse-transcription PCR (RT-PCR) using total RNA extracted from symptomatic leaf tissue with a Qiagen RNeasy kit and a pair of oligonucleotide primers designated AMV1F (5’-ATCCACCGATGCCAGCCTTA) and AMV1R (5’-TTCCGCCTCACTGCTGTCTG) designed to amplify a 1047-bp fragment of AMV RNA-1 (Genbank Accession No. NC_001495). An amplicon of the expected size, as determined by agarose gel electrophoresis, was obtained, cloned using a TOPO TA cloning kit (Invitrogen), and three selected clones sequenced. These had 98% nuclueotide sequence identity to the Spanish Tecoma AMV isolate (4) (Genbank Accession No. FR715040.1). A disease similar to that occurring in T. capensis in California was first identified in Israel in 1972 (3), and was demonstrated to be caused by AMV infection (3). The first report of AMV infection in T. capensis in Europe, also associated with similar calico-like foliar symptoms, was reported from Spain in 2011 (4). Foliar symptoms observed in T. capensis were similar in both cases, but slight differences in indicator plant reaction (3,4) may suggest that different isolates of AMV were involved in these two cases. This is the first report of AMV infection associated with a disease of T. capensis outside of Israel and Spain. In addition to the effect on marketability, AMV infection in cape honeysuckle may be a source of infection of other susceptible crop species since AMV is readily transmitted in a nonpersistent manner by at least 13 species of aphid (2).
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2. Bos, L., and Jaspars, E. M. J. 1971. Alfalfa mosaic virus. Descriptions of Plant Viruses No. 47. Commonw. Mycol. Institute/Association of Applied Biologists, Kew, Surrey, England.
3.Marco, S., and Car-Joseph, M. 1972. A mosaic disease of Tecomaria capensis caused by Alfalfa mosaic virus. Plant Dis. Reptr. 56:1035-1037.
4.Parrella, G., Acanfora, N., Orilio, A. F., and Navas-Castillo, J. 2011. Complete nucleotide sequence of a Spanish isolate of alfalfa mosaic virus: Evidence for additional genetic variability. Arch. Virol. 156:1049-1052.