Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2009
Publication Date: 9/21/2009
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-93-10-1076A
Citation: Ling, K., Verhoeven, J.J., Singh, R.P., Brown, J.K. 2009. First Report of Tomato Chlorotic Dwarf Viroid in Greenhouse Tomatoes in Arizona. Plant Disease. 93:1075. Interpretive Summary: Tomato chlorotic dwarf viroid (TCDVd) was first reported to infect greenhouse tomatoes in Canada in 1999. Since 2006, this viroid was identified in a large greenhouse tomato facility in Arizona and the grower suffered a significant economic loss. This highly contagious disease poses a great threat to the $400 million greenhouse tomato industry in the United States. Although TCDVd has been identified in foreign laboratories in imported tomato and/or ornamental tissues originated from the US, this is the first report of a natural occurrence of TCDVd in a large commercial tomato greenhouse in the United States. Identification of the presence of two different genotypes of TCDVd along with mixed-infection of Pepino mosaic virus made accurate determination of the etiology difficult. The complexity of the etiology will cause additional challenges to the US greenhouse tomato industry to effectively manage this emerging disease.
Technical Abstract: Tomato chlorotic dwarf viroid (TCDVd) was first identified on greenhouse tomato (Solanum lycopersicum) in Canada in 1999. Since then, it has also been reported on tomato in Colorado, US and Japan and on ornamental plants in or from Europe and North America. In 2006, tomato plants in a large greenhouse facility with continuous tomato production in Arizona exhibited viroid-like symptoms, i.e., plant stunting and chlorosis of the young leaves. Besides the commonly occurring Pepino mosaic virus (PepMV), all other known viruses were ruled out by serological, PCR or Reverse transcriptase PCR (RT-PCR) tests in multiple independent laboratories. However, RT-PCR with two sets of universal pospiviroid primers (PospiI-FW/RE and Vid-FW/RE) yielded amplicons of the expected size (approximately 196 and 360 bp) consistently from the diseased samples. Sequencing of the amplicons revealed the presence of two genotypes. The first genotype had a 360 nt genome and 100% sequence identity to the type TCDVd from Canada. The second genotype consisted of 361 nt, differed from the first by 9 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 and a much lower sequence identity (92%) to a US isolate previously identified in Colorado. The origin of TCDVd was not clear. It could have been introduced from a neighboring greenhouse where the disease was observed before 2006. It may also be introduced from infected seed since TCDVd has recently been shown to be seed-transmitted in tomato. To our knowledge, this is the first report of natural occurrence of TCDVd in Arizona.