Potato spindle tuber viroid

The Potato spindle tuber viroid ("PSTVd") was the first viroid to be identified.[1][2][3][4] PSTVd is a small, single stranded circular RNA molecule[5] closely related to the chrysanthemum stunt viroid. Present within the viroidal RNA is the Pospiviroid RY motif stem loop. The natural hosts are potatoes (Solanum tuberosum) and tomatoes (Solanum lycopersicum). All potatoes and tomatoes are susceptible to PSTVd and there is no form of natural resistance. Natural infections have also been seen in avocados and infections in other solanaceous crops have been induced in the laboratory. Until 2017 PSTVd was thought to be unable to infect Solanum sisymbriifolium.[6] Then in May seeds exported by a Dutch company were noticed to be infected.[6] These seeds were shipped from the company, but had been originally bred to their specifications in two Asian countries.[6]

Potato spindle tuber viroid
Virus classification
(unranked): Virus
Realm: incertae sedis
Kingdom: incertae sedis
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family: Pospiviroidae
Genus: Pospiviroid
Species:
Potato spindle tuber viroid

Strains and their symptoms

Different strains of PSTVd exist and symptoms range from mild to severe. Mild strains produce no obvious symptoms. Symptoms in severe strains are dependent on environmental conditions and are most severe in hot conditions. Symptoms may be mild in initial infections but become progressively worse in the following generations. Common symptoms of severe infections include color changes in the foliage, smaller leaves and spindle-like elongation. Sprouting also occurs at a slower rate than in unaffected potatoes. Infected tomatoes are slower to show symptoms which include stunted growth with a ‘bunchy top’ caused by shortened inter-nodes. Leaves become yellow or purple and often become curled and twisted. Necrosis eventually occurs in the veins of the bottom and middle leaves and the top leaves decrease in size. Fruit ripening is also affected leading to hard, small, dark green tomatoes.

Long distance spread of PSTVd usually occurs via infected seeds but transmission via aphids (Myzus persicae) also occurs but only in the presence of PLRV (potato leaf roll virus). Mechanical transmission also occurs once it has been introduced to an area.

Primary and secondary structure of PSTVd

PSTVd comprises 359 nucleotides.

Primary Structure
  1   CGGAACUAAA CUCGUGGUUC CUGUGGUUCA CACCUGACCU CCUGAGCAGA AAAGAAAAAA
 61   GAAGGCGGCU CGGAGGAGCG CUUCAGGGAU CCCCGGGGAA ACCUGGAGCG AACUGGCAAA
121   AAAGGACGGU GGGGAGUGCC CAGCGGCCGA CAGGAGUAAU UCCCGCCGAA ACAGGGUUUU
181   CACCCUUCCU UUCUUCGGGU GUCCUUCCUC GCGCCCGCAG GACCACCCCU CGCCCCCUUU
241   GCGCUGUCGC UUCGGCUACU ACCCGGUGGA AACAACUGAA GCUCCCGAGA ACCGCUUUUU
301   CUCUAUCUUA CUUGCUUCGG GGCGAGGGUG UUUAGCCCUU GGAACCGCAG UUGGUUCCU
Secondary Structure
Putative secondary structure of the PSTVd viroid. The highlighted nucleotides are found in most other viroids.

References
  1. Diener TO (August 1971). "Potato spindle tuber "virus". IV. A replicating, low molecular weight RNA". Virology. 45 (2): 411–28. doi:10.1016/0042-6822(71)90342-4. PMID 5095900.
  2. "ARS Research Timeline - Tracking the Elusive Viroid". 2006-03-02. Retrieved 2007-07-18.
  3. Discovery of Viroids Archived 2016-03-03 at the Wayback Machine
  4. Zimmer, Carl (September 25, 2014). "A Tiny Emissary From the Ancient Past". New York Times. Retrieved September 26, 2014.
  5. Sanger, H.L. (1982). Nucleic Acids and Proteins in Plants II : Structure, Biochemistry and Physiology of Nucleic Acids (PDF). Berlin, Heidelberg: Springer Berlin Heidelberg. p. 383. doi:10.1007/978-3-642-68347-3_12. ISBN 978-3-642-68349-7. Retrieved 13 March 2019.
  6. "First finding of Potato spindle tuber viroid (PSTVd) in seeds of Solanum sisymbriifolium, originating in Asia - June 2017". Netherlands Food and Consumer Product Safety Authority. 2017-06-28. Retrieved 2020-11-30.

Bibliography
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