In early April 2010, 30 samples of Petunia spp. were taken by phytosanitary inspectors from 22 production sites in Slovenia in the frame of surveying host plants for the presence of Potato spindle tuber viroid (PSTVd). Samples were taken in accordance with the plan of the survey for the year 2010 and were tested for the presence of PSTVd by real-time RT-PCR according to the EPPO protocol (1). At the time of sampling, there were no disease symptoms on the plants. Samples consisted of fully developed leaves collected from as many as five plants. Total RNA was isolated from 50 ± 5 mg of leaf tissue with an RNeasy Plant Mini Kit (Qiagen, Chatsworth, CA). One sample of cv. Surfinia Purple from a production site from the coastal region and another of cv. Surfinia Hot Pink 05 from a production site near Ljubljana, both multiplied through cuttings, were positive by real-time RT-PCR, confirming the presence of PSTVd or Tomato chlorotic dwarf viroid (TCDVd). To identify the viroid, RT-PCR with primer pairs of Shamloul et al. (3) and Di Serio (2) were performed with isolated total RNA of each positive sample. RT-PCR products were obtained only with primer pairs of Shamloul et al. (3). To obtain the full sequence, additional RT-PCR was done for each sample with semi-universal pospiviroid primers Vid-RE/FW (4). RT-PCR products obtained with primer pair of Shamloul et al. (3) and primer pair Vid RE/FW were sequenced (Macrogen, Seoul, Korea). Sequence analysis confirmed the identity of a viroid as TCDVd. Both isolates consisted of 360 nucleotides and were 100% identical to an isolate from tomato deposited in NCBI GenBank under Accession No. AF162131. They showed 98% identity with sequences from petunias (GQ396664, EF582392, EF582393, and DQ859013). The infected Petunia spp. stocks were destroyed. Although the infection of Petunia spp. with TCDVd is symptomless, the infected plants could be a source of infection for tomato and potato. TCDVd infection can cause severe damage on potato and tomato, similar to that caused by infection with PSTVd, to which it is closely related. To our knowledge this is the first finding of TCDVd in Petunia spp. in Slovenia.
References: (1) Anonymous. EPPO Bull. 34:257, 2004. (2) F. Di Serio. J. Plant Pathol. 89:297, 2007. (3) A. M. Shamloul et al. Can. J. Plant Pathol. 19:89, 1997. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.
