A commercial field of celery (Apium graveolens var. dulce) cvs. Conquistador and Sabroso was planted with sets between 1 June and 10 July 2004 in Pierce County in western Washington (WA). In late August, many plants were stunted and showed chlorotic line patterns. One symptomatic plant and five nonsymptomatic plants were transferred to a greenhouse and grown at 22°C with supplemental lighting to extend day length to 16 h; foliage was trimmed back. The symptomatic plant and three nonsymptomatic plants developed a distinctive chlorotic line pattern when new foliage emerged in February. Two plants remained nonsymptomatic. Young foliage was tested by ELISA with the general potyvirus monoclonal antibody (Agdia, Inc., Elkhart, IN). All symptomatic plants yielded a positive result and the two nonsymptomatic plants were negative. Celery mosaic virus (CeMV) was previously reported to be widespread in WA (3), but primers specific for CeMV did not yield amplicons in reverse transcription (RT)-PCR from RNA isolated from symptomatic leaf tissue (RNeasy Plant Mini Kit: QIAGEN, Valencia, CA). General potyvirus primers (1) were used to amplify ≈1,700 nucleotides from the 3′ terminus of the virus genome adjacent to the poly-A tail. Six amplicons from each of three independent reactions were cloned into pCR2.1 (Invitrogen, Carlsbad, CA) and sequenced (GenBank Accession No. FJ010827). Comparison with the nucleotide sequence database revealed 98 and 97% identity to Australian isolates of Apium virus Y (ApVY) (family Potyviridae) from parsley (GenBank Accession No. AF207594) and poison hemlock (Conium maculatum) (GenBank Accession No. AY049716) (4) and 91% identity to North American isolates of ApVY from celery and Ammi majus reported from California (GenBank Accession No. EU515126) and Florida (GenBank Accession No. EU255632), respectively. To our knowledge, this is the first report of a natural infection of celery by ApVY in WA. No other potyvirus sequences were identified in RT-PCR products from symptomatic celery. In 2008, in an effort to locate local samples of CeMV, poison hemlock plants were randomly collected in Benton, Walla Walla, and Whitman counties of eastern WA. No symptoms were observed and no CeMV was detected by RT-PCR in any of these plants. No ApVY was detected in 10 of 10 poison hemlock collected from Walla Walla County, but based on sequence analysis of RT-PCR amplicons, two of two plants collected from Benton and Whitman counties were infected with ApVY. In contrast to the WA isolates from celery, sequences from these poison hemlock plants (GenBank Accession No. FJ010828) were 98% identical to previously reported North American isolates of ApVY (GenBank Accession Nos. EU515126 and EU255632) and only 91% identical to Australian isolates (GenBank Accession Nos. AF207594 and AY049716). To our knowledge, this is the first report of ApVY in WA and the first report of a natural infection of poison hemlock in the United States. The celery and poison hemlock isolates reported in this study were from different geographic regions of the state and were only 91% identical. As is the case for other potyviruses (2), weeds such as poison hemlock may serve as a reservoir of ApVY in eastern WA where many plants of the family Apiaceae are grown commercially.
References: (1) J. Chen et al. Arch. Virol. 146:757, 2001. (2) W. E. Howell and G. I. Mink. Plant Dis. Rep. 61:217, 1977. (3) W. E. Howell and G. I. Mink. Plant Dis. 65:277, 1981. (4) J. Moran et al. Arch. Virol. 147:1855, 2002.