Dahlia mosaic, caused by Dahlia mosaic virus (DMV), is one of the most important viral diseases of dahlia. Molecular characterization of DMV showed the association of two distinct caulimoviruses (DMV-D10, DMV-Portland) and a D10-like sequence variant (DMV-Holland) with the disease. Using primers specific to these two viruses and the sequence variant, a polymerase chain reaction–based assay was used to determine their relative incidence in several dahlia samples from the United States and the Netherlands. Testing was done on samples collected in 2005 and 2006 in the United States and in 2006 in the Netherlands. Results indicated the predominance of DMV-D10 over DMV-Portland and DMV-Holland in both the United States and the Netherlands. Using conserved regions of the viral genome, primers were designed and used to detect all three sequences. Results suggested that DMV-D10 is predominantly associated with dahlia mosaic, but diagnostics should also include testing for DMV-Portland and DMV-Holland.

Canna (Canna indica) is an important nursery/landscape plant in Washington State with several nurseries producing canna plants for wholesale and retail businesses. Canna plants showing symptoms such as mottling, general yellowing, and veinal chlorosis were found to be widespread (40% symptomatic plants in a nursery of more than 2,000 plants) in Grant County, WA in September 2007. Symptomatic leaves from five plants of each of the following cultivars were tested: Richard Wallace, Crimson Beauty, Wyoming, Petoria, Pink Beauty, Robert Kemp, and Black Knight. Electron microscopic examination of leaf-dip preparations from symptomatic leaves showed badnavirus-like particles of approximately 120 × 30 nm. A badnavirus, Canna yellow mottle virus (CaYMV) (family Caulimoviridae, genus Badnavirus) from canna was first reported from Japan (4) and later in the United States (1,3). Most recently, CaYMV was reported from Italy and the Netherlands (2). Samples were tested for CaYMV by PCR using CaYMV-specific primers, CaYMV-3 (5′- GAC TTC CTG GGT GCA ACA AT -3′) and CaYMV-4 (5′- TCT GTG CAA TCT TGG CGT AG -3′) (2), which produced a 565-bp amplicon. All samples tested gave the amplicon of expected size. The amplicon from one leaf sample from each of the cultivars was cloned and sequenced. Sequence comparisons with those available in the GenBank confirmed that the sequence obtained was that of CaYMV (95% sequence identity). Increased awareness of the prevalence of CaYMV in nurseries and avoiding the propagation and distribution of infected plants are necessary to minimize the further spread of this virus in canna. References: (1) B. E. L. Lockhart. Acta Hortic. 234:69, 1988. (2) M. T. Marino et al. Online publication. New Disease Reports. http://www.bspp.org.uk/NDR/july2007/2007-08.asp , 2007. (3) M. T. Momol et al. Online publication. doi:10.1094/PHP-2004-0809-01-HN. Plant Health Progress, 2004. (4) S. Yamashita et al. Ann. Phytopathol. Soc. Jpn. 51:642, 1985.

Streptocarpus flower break virus (SFBV) belongs to the genus Tobamovirus and was described from naturally infected streptocarpus plants in 1995 (2). The complete genomic sequence was recently reported (1). Prominent symptoms include flower breaking while foliar symptoms are often lacking. In March 2007, four streptocarpus plants (cv. Indigo Dream) from San Diego County, CA were tested for the presence of SFBV by ELISA and reverse transcription (RT)-PCR. Symptoms suggestive of a virus infection were not present on these mother plants at the time of sampling. ELISA with SFBV-specific antiserum showed that all samples were infected with SFBV. The ELISA results were verified by RT-PCR followed by cloning and sequencing. Two sets of primer pairs were used in separate RT-PCR tests. One was a degenerate tobamovirus group-specific primer pair and the second primer pair was specific to SFBV (1). The tobamovirus group-specific primer pair consisted of Tob Uni1, 5′-ATT TAA GTG GAG GGA AAA CCA CT-3′ and Tob Uni2, 5′-GTY GTT GAT GAG TTC GTG GA-3′. The SFBV-specific primers were SFBVcpF: 5′-AAA ATG TCG TAC GTG GTG GT and SFBVcpR: 5′-ACC CAC AGA ACT TCC TTC AA-3′ (1). PCR amplicons of the expected size (686 bp for the tobamovirus group-specific primer pair and 562 bp for the SFBV-specific primer pair) were obtained for each primer pair. The positive PCR test using the SFBV-specific primer pair confirmed the presence of SFBV. To further verify the identity of the virus, the amplicons obtained with each primer pair were separately cloned and sequenced. At least two clones for each amplicon were sequenced in both directions. Sequence comparisons with those available in GenBank showed 98% sequence identity with the corresponding genomic region (GenBank Accession No. NC_008365) of SFBV (1). To our knowledge, this is the first report of SFBV in the United States and it highlights the need for testing for this virus to ensure propagation and distribution of virus-free material. References: (1) C. Heinze et al. Arch. Virol. 151:763, 2006. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 101:311, 1995.