N. L. Robertson,
K. L. Brown, and
L. M. Winton, USDA-ARS, Subarctic Agricultural Research Unit, Palmer, AK; and
P. S. Holloway, Department of Plant, Animal, and Soil Sciences, University of Alaska-Fairbanks
Peonies (Paeonia sp.) are highly valued for their large showy flowers in home gardens and commercially in the cut flower industry. In 2007, scattered peony (Paeonia lactiflora ‘Sarah Bernhardt’) plants cultivated on small plots at the University of Alaska Experimental Station in Fairbanks displayed distinct leaf ringspot patterns. Symptoms were more severe during the cooler months of the growing season (June and September), with symptom remission in the intervening warmer months. Leaf samples from six symptomatic plants were collected in July and from 20 symptomatic plants in September and assayed for viruses. Leaf samples (1 g) were assayed with a general protocol for plant virus extraction and partial purification with differential centrifugation followed by protein detection on stained sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1). No distinct proteins indicative of viral coat protein(s) were detected. Tomato spotted wilt virus (TSWV) and Tobacco rattle virus (TRV), known pathogens of peony, were then specifically targeted. Total RNA was extracted from each sample with an RNeasy Plant Mini kit (Qiagen Inc., Valencia, CA) and used as the template for reverse transcription (RT)-PCR with random primers. TSWV was not detected by RT-PCR with tospovirus group-specific primers (Agdia, Inc., Elkhart, IN). A nested set of primers designed from the TRV 16-kDa protein gene on RNA1 (4) amplified an ~600-bp fragment from one of the symptomatic plants. This DNA was directly sequenced (GenBank Accession No. FJ357572) and BLAST searches in GenBank revealed as much as 95% nucleotide (nt) identity with TRV accessions J04347 and X03685. Additional primer pairs specific for TRV (2) amplified overlapping fragments with expected sizes of ~818, ~515, and ~290 bp from the 29- and 16-kDa protein genes on the 3′-end of RNA1 that were directly sequenced. Assembly of these sequences in Sequencher 4.8 (Gene Codes Corp., Ann Arbor, MI) resulted in a 1,422-nt sequence (Accession No. FJ357571) and Clustal X analysis (3) showed 93 to 94% nt identity to TRV isolates, -ORY (AF034622), -PpK20 (AF314165), -Pp085 (AJ586803), and -SYM (D00155). Mechanical inoculation of partially purified virions from the confirmed TRV-infected peony plant to Nicotiana benthamiana gave no symptoms to occasional ringspots, faintly curled leaves, and chlorotic blotches on N. tabacum ‘Samsun’, and local lesions on Chenopodium amaranticolor. TRV infection of these hosts was confirmed by RT-PCR. With electron microscopy, rod-shaped particles similar to TRV with a distinct central canal characteristic of TRV were seen occasionally only from inoculated N. benthamiana. On the basis of the biological and molecular data, we have determined the virus in the peony to be an isolate of TRV, tentatively named TRV-Peony. TRV was confirmed in only one other peony based on a sequenced 290-nt PCR fragment with 95% identity with the sequence from the other TRV-infected peony. Lack of TRV detection in the other symptomatic peonies was possibly due to low viral concentrations and interfering plant substances. Documentation of TRV in peonies is especially important to help avoid distribution of virus-infected vegetative propagation material. To our knowledge, this is the first report of TRV in this host in Alaska, but also of this virus in Alaska.
References: (1) L. C. Lane. Methods Enzymol. 118:687, 1986. (2) D. J. Robinson. J. Phytopathol. 152:286, 2004. (3) J. D. Thompson et al. Nucleic Acids Res. 24:4882, 1997. (4) F. Van Der Wilk et al. Eur. J. Plant Pathol.100:109, 1994.