ARS | Publication request: Identification of Potato spindle tuber viroid naturally infecting greenhouse tomatoes in North Carolina and its potential in seed transmission

Submitted to: Tomato Disease Workshop
Publication Type: Proceedings
Publication Acceptance Date: September 18, 2012
Publication Date: October 16, 2012
Citation: Ling, K., Li, R., Panthee, D.R., Gardner, R.G. 2012. Identification of Potato spindle tuber viroid naturally infecting greenhouse tomatoes in North Carolina and its potential in seed transmission. Tomato Disease Workshop. p27.

Technical Abstract: In spring 2012, an unusual severe disease (plant stunting, chlorosis, and small fruits) was observed on 18% of tomato plants (Solanum lycopersicum L.) in a small research greenhouse facility in western North Carolina. Over time, the disease spread to other tomato plants inside the greenhouse. Initial screenings for possible viruses were negative either using enzyme-linked immunosorbent assay (ELISA) or reverse transcription polymerase chain reaction (RT-PCR). However, real-time RT-PCR showed a positive for pospiviroid on eight tested diseased plants and one seed sample. Using a set of primers previously designed to amplify a full genomic sequence for a pospiviroid, expected size of products (360 bp) were cloned and sequenced. A consensus full viroid genomic sequence was obtained from 22 clones in this experiment. BLASTn analysis in the NCBI database showed that this sequence shared the highest nucleotide sequence identity of 96.9% to several isolates of Potato spindle tuber viroid (PSTVd). Using infected tomato tissue as inoculum, similar disease symptoms were observed on the inoculated tomato plants ‘Rutgers’ two weeks post mechanical inoculation and the presence of PSTVd was confirmed using real-time RT-PCR. The diseased tomato plants were contained, properly disposed and eradicated in this location. In the U.S., natural infection of PSTVd on tomato was first identified in California in 2010. To our knowledge, this is the first report of a natural occurrence of PSTVd on tomato in the eastern U.S. The broader geographic distribution of PSTVd on tomato and the potential latent infection in potato and a number of ornamentals emphasize the need for better testing of viroids in these plants. To determine whether PSTVd is truly seed transmissible in tomato, seedling grow-out tests using highly PSTVd-contaminated seeds are underway and the results will be discussed.