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First Report of Freesia sneak virus in Freesia sp. in Virginia

In the spring of 2008, freesia, cvs. Honeymoon and Santana, with striking virus-like symptoms similar to freesia leaf necrosis disease were received by the Virginia Tech Plant Disease Clinic from a cut-flower nursery in Gloucester, VA and forwarded for analysis to the USDA-ARS Floral and Nursery Plants Research Unit in Beltsville, MD. Approximately 25% of the plants had coalescing, interveinal, chlorotic, whitish, necrotic or dark brown-to-purple necrotic spots on leaves. Symptomatic plants were scattered within the planting. Fifteen symptomatic plants were collected between March and May of 2008, and nucleic acid extracts were analyzed for ophiovirus infection by reverse transcription (RT)-PCR with ophiovirus-specific degenerate primers (2). The diagnostic 136-bp ophiovirus product from the RdRp gene was amplified from 14 of 15 freesia plants tested. A partially purified virus preparation was analyzed by transmission electron microscopy and potyvirus- and ophiovirus-like particles were detected. The potyviruses, Freesia mosaic virus (FreMV) and Bean yellow mosaic virus (BYMV), each cause mosaic symptoms (3), although BYMV may induce necrosis late in the season. RT-PCR performed on the same nucleic acid samples using potyvirus coat protein (CP)-specific degenerate primers D335 and U335 (1) amplified the diagnostic 335-bp fragment from 2 of 15 plants. Cloned sequence from these plants was identified as FreMV. The ophiovirus CP gene was amplified by RT-PCR and cloned from two symptomatic freesia plants using primers FreSVf-CP-XhoI 5′-GACTCGAGAAATGTCTGGAAAATACTCTGTTC-3′ and FreSVf-CP-BamHI 5′-CCAGGATCCTTAGATAGTGAATCCATAAGCTG-3′, based on the sequence of Freesia sneak virus (FreSV) isolates from freesia (GenBank No. DQ885455) and lachenalia (4). The approximate 1.3-kb amplicon was cloned and sequences of two cDNA clones were identical (GenBank No. FJ807730). The deduced amino acid sequence showed 99% identity with the Italian FreSV CP sequence (GenBank No. DQ885455), confirming FreSV in the symptomatic freesia plants. To our knowledge, this is the first report of FreSV in Virginia and the United States. Soilborne freesia leaf necrosis disease has been reported in Europe since the 1970s (3); several viral causal agents have been hypothesized but recent findings correlate best with the ophiovirus. In Virginia, the presence of FreSV, but not FreMV, was strongly correlated with the leaf necrosis syndrome. FreSV, likely soilborne through Olpidium brassicae, may pose a new soilborne threat for bulbous ornamentals, since it has been recently detected also in Lachenalia spp. (Hyacinthaceae) from South Africa (4). Although specific testing of O. brassicae was not performed, the disease may potentially persist in the soil for years in O. brassicae resting spores and development of symptoms may be affected by environmental conditions (3).

References: (1) S. A. Langeveld et al. J. Gen. Virol. 72:1531, 1991. (2) A. M. Vaira et al. Arch.Virol. 148:1037, 2003. (3) A. M. Vaira et al. Acta Hortic. 722:191, 2006. (4) A. M. Vaira et al. Plant Dis. 91:770, 2007.