In November 2003, two Phalaenopsis orchids from two different nurseries with symptoms of chlorotic rings on leaves were observed in Changhua County of central Taiwan. Symptomatic plants were collected and examined for the presence of viruses. Electron microscopic examination of ultrathin sections of leaf tissues from the symptomatic orchids found isometric virions of 32 nm in diameter. Subsequently, an isolate (herein designated as ‘92-orchid-1’) with particles of similar size were isolated from one symptomatic orchid and established in Chenopodium quinoa (3). After indirect ELISA tests using antisera against Carnation mottle virus (CarMV), Cucumber mosaic virus, Cymbidium ringspot virus, Tomato bushy stunt virus, Capsicum chlorosis virus, Impatiens necrotic spot virus, Tomato spotted wilt virus, Tomato ringspot virus, and Lisianthus necrosis virus, this isolate reacted positively with the antiserum produced against CarMV (1). CarMV-TW-infected and healthy C. quinoa were used as positive and negative controls, respectively. To further characterize this virus, the conserved region of the polymerase gene (ORF1RT) of Carmoviruses was amplified with degenerate primer pairs, FJJ2003-17 (5′-TATATCTCGAGCAA(A/C)TAGGGG(G/T)GCCT) and FJJ2003-18 (5′-TATAGGATCCCC(C/T)A(A/T)(A/G)GC(A/T)GTGTTCA), by reverse transcription (RT)-PCR using the total RNA isolated from the leaves of 92-orchid-1-, CarMV-TW-infected, and healthy C. quinoa (3). The 894-nt ORF1RT conserved region of isolate 92-orchid-1 (GenBank Accession No. HQ117873) shared 97.1, 65.6, 61.7, and 63.5% nucleotide identities and 98.3, 70.2, 66.1, and 64.7% amino acid identities with those of CarMV (X02986), Pelargonium flower break virus (NC_005286), Saguaro cactus virus (NC_001780), and Angelonia flower break virus (NC_007733), respectively. The sequence comparison of the ORF1RT conserved region indicated that 92-orchid-1 was a carmovirus related to CarMV. Sequence analyses of the coat protein (CP) gene (GenBank Accession No. HQ117872) amplified with the specific CP primer pairs of CarMV (FJJ2004-53: 5′-ACTGCGCTCGAGCTACTCTGTTGACAGTTCTA, and 2004-54: 5′-ATATATGGATCCCGTCCCGCCGTGTGTGTCTA) showed the isolate shared 95.8 to 98.8% nucleotide identities and 96.8 to 98.9% amino acid identities with those of 40 CarMV isolates. Furthermore, the CP gene shared 96.9, 97.0, and 98.8% nucleotide identities and 98.0, 95.7, and 98.3% amino acid identities with isolates from carnation (GenBank Accession No. AY383566) (1), calla lily (GenBank Accession No. HQ117870) (2), and lisianthus (GenBank Accession No. FJ843021), respectively, in Taiwan. These results suggested that this isolate was CarMV but distinct from the above-mentioned three isolates and designated CarMV-Ph. From 2004 to 2007, a further survey of 280 symptomatic Phalaenopsis plants by ELISA using CarMV polyclonal antibodies (1) found that approximately 4% of those tested were infected. To our knowledge, this is the first report of CarMV in Phalaenopsis orchids and the occurrence has substantial implications for the important nursery and floral industry in Taiwan.
References: (1) C. C. Chen et al. Plant Pathol. Bull. 12:199, 2003. (2) C. C. Chen et al. Plant Dis. 87:1539, 2003. (3) Y. X. Zheng et al. Eur. J. Plant Pathol. 121:87, 2008.
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