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First Report of Nerine yellow stripe virus in Amaryllis in the United States

Ornamental flower bulbs (including true bulbs, bulbils, corms, tubers, and rhizomes) are increasingly important floriculture crops. Amaryllis is a small genus of flowering bulbs, with two species. The South African native, Amaryllis belladonna, also known as belladonna lily, Jersey lily, naked lady, Amarillo, or March lily, is one of numerous ornamental species with the common name “lily” due to their flower shape and growth habit. Amaryllis are popular for their 6- to 10-inch trumpet shaped colorful flowers that are borne on 1- to 2-foot stalks. In January, 2011, a home gardener in California observed mosaic symptoms on the leaves of A. belladonna growing in her garden. Leaf samples were sent to Agdia Inc. for testing. Samples tested positive for the presence of Potyvirus in a reverse transcription (RT)-PCR screen using universal potyvirus primers (2) yielding the expected ∼1,600-bp product corresponding to the partial nuclear inclusion body (NIb) gene, full-length coat protein (CP) gene, and 3′ end untranslated region (UTR). Electron microscopy of symptomatic leaves confirmed the presence of filamentous potyvirus-like particles. The RT-PCR amplicon was cloned and sequenced (2); the 1,616-bp consensus sequence was deposited in GenBank (Accession No. JX865782). NCBI BLAST analysis of the consensus sequence revealed highest identities with isolates of Nerine yellow stripe virus (NeYSV; family Potyviridae, genus Potyvirus). Pair-wise analyses of the 261 amino acid sequence of the predicted CP had 88% sequence identity with a Stenomesson isolate reported from the Netherlands (EU042758); 87% identity with Hymenocallis and Nerine isolates, both also from the Netherlands (EF362622 and EF362621, respectively); and, 86% with two New Zealand isolates infecting Amaryllis or Vallota (FJ618537 and DQ407932, respectively). The five Netherlands and New Zealand isolates are more closely related to each other than to the U.S. isolate as they share 93 to 98% CP identity. When using viral genome sequence relatedness as a criterion for defining potyvirus species, isolates with CP amino acid identity greater than 80% are considered the same species (1). The predicted coat protein gene of the California isolate was sub-cloned into the bacterial expression vector pET44 EK/LIC. Serological analysis of coat protein expressing clones in ELISA and Western Blot analysis using a potyvirus broad-spectrum reacting monoclonal antibody PTY-2 (3) and a NeYSV-specific rabbit antiserum (Applied Plant Research, Lisse, The Netherlands) resulted in positive reactions. NeYSV has previously been reported in the United Kingdom, the Netherlands, Australia, and New Zealand. Based on the results of electron microscopy, RT-PCR, nucleotide and amino acid identity, and serological reactivity, we identify this virus as a U.S. isolate of NeYSV, NeYSV-US. To our knowledge, this is the first report of Nerine yellow stripe virus in the United States. Development of antisera specific to this U.S. isolate is in progress.

References: (1) A. Gibbs and K. Ohshima. Ann. Rev. Phytopathol. 48:205, 2010. (2) R. L. Jordan et al. Acta Hortic. 901:159, 2011. (3) R. L. Jordan and J. Hammond. J. Gen. Virol. 72:1531, 1991.