Ling K-S, Verhoeven J Th J, Singh R P, Brown J K
USDA-ARS, U.S. Vegetable Laboratory, Charleston, SC 29414.
Plant Protection Service, P.O. Box 9102, 6700 HC Wageningen, the Netherlands.
Plant Dis. 2009 Oct;93(10):1075. doi: 10.1094/PDIS-93-10-1075B.
Tomato chlorotic dwarf viroid (TCDVd), a member of the genus Pospivroid, family Pospiviroidae, was first identified on greenhouse tomato (Solanum lycopersicum) in Canada (2). Since then, it has also been reported elsewhere, e.g., on tomato in Colorado (4). During 2006 in Arizona, tomato plants in a large greenhouse facility with continuous tomato production exhibited viroid-like symptoms of plant stunting and chlorosis of the young leaves. Symptomatic plants were often located along the edge of the row, indicating the presence of a mechanical transmissible agent. Approximately 4% of the plants in this greenhouse were symptomatic in 2008. Symptoms were distinctly different from those caused by Pepino mosaic virus (PepMV), a virus that was generally present in this greenhouse and also in our test samples. Other commonly occurring tomato viruses were ruled out by serological, PCR, or reverse transcription (RT)-PCR tests in multiple laboratories. RT-PCR with two sets of universal pospiviroid primers, PospiI-FW/RE and Vid-FW/RE (4), yielded amplicons of the expected sizes of 196 and 360 bp in three samples collected from symptomatic plants. Direct sequencing of the amplicons revealed that the genome was 360 nt and 100% identical to the type TCDVd from Canada (GenBank Accession No. AF162131) (2). Mechanical inoculation with leaf tissue extract from four samples to plants of the tomato 'Money-Maker' resulted in the same viroid-like symptoms and TCDVd was confirmed in these plants by RT-PCR and sequencing. In both 2007 and 2008, 18 samples were tested using primers PSTVd-F and PSTVd-R (1), which are capable of amplifying the full TCDVd genome. Analysis of the sequences from the amplicons revealed two genotypes of TCDVd. The first genotype (GenBank Accession No. FJ822877) was identical to the type TCDVd and found in 11 samples from 2007 and one from 2008. The second genotype (GenBank Accession No. FJ822878) was 361 nt, differing from the first by nine nucleotide substitutions, 2 insertions, and 1 deletion. This second genotype was found in 7 and 17 samples from 2007 and 2008, respectively, and showed the highest sequence identity (97%) to a Japanese tomato isolate (AB329668) and a much lower sequence identity (92%) to a U.S. isolate previously identified in Colorado (AY372399) (4). The origin of TCDVd in this outbreak is not clear. The genotype identified first could have been introduced from a neighboring greenhouse where the disease was observed before 2006 and where this genotype also was identified in 2007. The second genotype may have been introduced from infected seed since TCDVd has recently been shown to be seed transmitted in tomato (3). To our knowledge, this is the first report of natural occurrence of TCDVd in Arizona. References: (1) A. M. Shamloul et al. Can. J. Plant Pathol. 19:89, 1997. (2) R. P. Singh et al. J. Gen. Virol. 80:2823, 1999. (3) R. P. Singh and A. D. Dilworth. Eur. J. Plant Pathol. 123:111, 2009. (4) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.
番茄褪绿矮缩类病毒（TCDVd）是马铃薯纺锤块茎类病毒科马铃薯纺锤块茎类病毒属的成员，最初在加拿大的温室番茄（Solanum lycopersicum）中被鉴定出来（2）。从那时起，在其他地方也有相关报道，例如在科罗拉多州的番茄上（4）。2006年在亚利桑那州，一个持续种植番茄的大型温室设施中的番茄植株表现出类病毒样症状，即植株矮化和幼叶黄化。有症状的植株通常位于行的边缘，表明存在一种机械传播的病原体。2008年，这个温室中约4%的植株出现了症状。这些症状与由佩佩诺花叶病毒（PepMV）引起的症状明显不同，PepMV是一种在这个温室以及我们的测试样本中普遍存在的病毒。多个实验室通过血清学、PCR或逆转录（RT）-PCR检测排除了其他常见的番茄病毒。使用两组通用的马铃薯纺锤块茎类病毒引物PospiI-FW/RE和Vid-FW/RE（4）对从有症状植株上采集的三个样本进行RT-PCR，得到了预期大小为196和360 bp的扩增子。对扩增子进行直接测序显示，基因组为360 nt，与来自加拿大的TCDVd标准株（GenBank登录号AF162131）100%相同（2）。用四个样本的叶片组织提取物对番茄“金冠”植株进行机械接种，导致了相同的类病毒样症状，通过RT-PCR和测序在这些植株中确认了TCDVd。在2007年和2008年，使用能够扩增完整TCDVd基因组的引物PSTVd-F和PSTVd-R（1）对18个样本进行了检测。对扩增子序列的分析揭示了TCDVd的两种基因型。第一种基因型（GenBank登录号FJ822877）与TCDVd标准株相同，在2007年的11个样本和2008年的1个样本中发现。第二种基因型（GenBank登录号FJ822878）为361 nt，与第一种基因型有9个核苷酸替换、2个插入和1个缺失的差异。这种第二种基因型分别在2007年的7个样本和2008年的17个样本中发现，与日本番茄分离株（AB329668）的序列同一性最高（97%），与之前在科罗拉多州鉴定的美国分离株（AY372399）的序列同一性则低得多（92%）（4）。此次疫情中TCDVd的来源尚不清楚。首先鉴定出的基因型可能是从2006年之前观察到该病且在2007年也鉴定出该基因型的相邻温室引入的。第二种基因型可能是从受感染的种子引入的，因为最近已证明TCDVd可在番茄中通过种子传播（3）。据我们所知，这是亚利桑那州自然发生TCDVd的首次报道。参考文献：（1）A. M. Shamloul等人，《加拿大植物病理学杂志》19:89，1997年。（2）R. P. Singh等人，《普通病毒学杂志》80:2823，1999年。（3）R. P. Singh和A. D. Dilworth，《欧洲植物病理学杂志》123:111，2009年。（4）J. Th. J. Verhoeven等人，《欧洲植物病理学杂志》110:823，2004年。
