Coleus (Coleus blumei) is an ornamental plant that is susceptible to infection by several viroids of the genus Coleviroid, which is a member of the family Pospiviroidae. Coleus blumei viroid (CbVd) -1 was first reported in commercial yellow coleus fields in Brazil in 1989 (1). In addition, CbVd-2, CbVd-3, and CbVd-4 have only been detected from coleus in Germany in 1996 (4). CbVd-5 and CbVd-6 were recently identified in China (2). In March 2010, leaves were collected from 50 symptomless coleus plants from a commercial nursery in Hainan Province, China. Total RNA was extracted from the leaves (3). Reverse transcription (RT)-PCR using CbVd-2 specific primers (forward: 5′-AGCTTACCTGGGTTCCCT-3′ and reverse: 5′-CTCTCCTCTATTTACTCTCTTCTC-3′) corresponding to positions 76 to 93 and 52 to 75 on the CbVd-2 reference sequence, respectively (GenBank Accession No. NC003682). Amplification of a 301-bp product was obtained from one sample. This PCR product was then cloned into pMD18-T (Takara, Dalian, China). Twelve positive clones were sequenced and the results were subjected to BLAST analysis. Sequence analysis showed that two sequences (GenBank Accessions Nos. HQ727542 and HQ727544) shared 99% identity with the reference sequence of CbVd-2 (NC003682), and four sequences (HQ727541, HQ727543, HQ727545 and HQ727547) had 99.34% identity with the reference sequence of CbVd-2 (NC003682). The proposed secondary structures of these variants have approximately 75% paired nucleotides. Results suggested the presence of CbVd-2, which is a member of the Coleviroid genus, Pospoviroidae family. To our knowledge, this is the first report of CbVd-2 from commercial coleus in China.
References: (1) M. E. N. Fonseca et al. Fitopatol. Bras. 14:94, 1989. (2) W. Y. Hou et al. Arch. Virol. 154:993, 2009. (3) S. F. Li et al. Ann. Phytopathol. Soc. Jpn. 61:381, 1995. (4) R. L. Spieker et al. J. Gen. Virol. 77:2839, 1996.