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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 common to its genus. 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] Pstv also causes Tomato bunchy top and is seed transmitted in tomato.[7] it contains single stranded RNA without protein coat.
| Potato spindle tuber viroid | |
|---|---|
Virus classification 
| |
| (unranked): | Viroid |
| Family: | Pospiviroidae |
| Genus: | Pospiviroid |
| Species: | Potato spindle tuber viroid
|
Discovery
editIt was discovered by Theodor Otto Diener, who is a plant pathologist at the U.S Department of Agriculture's Research Center in Beltsville, Maryland, and discovered it in 1971. He named it viroid because it is 1/80th size of a virus.[3]
Strains and their symptoms
editDifferent 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
editPSTVd 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 |
 |
Course of infection
editSystemic movement within the infected host is through the phloem.[D 1]
References
edit- ^ 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.
- ^ "ARS Research Timeline - Tracking the Elusive Viroid". 2006-03-02. Retrieved 2007-07-18.
- ^ a b Discovery of Viroids Archived 2016-03-03 at the Wayback Machine
- ^ Zimmer, Carl (September 25, 2014). "A Tiny Emissary From the Ancient Past". New York Times. Retrieved September 26, 2014.
- ^ Sanger, H.L. (1982). "Biology, Structure, Functions and Possible Origin of Viroids" (PDF). Nucleic Acids and Proteins in Plants II : Structure, Biochemistry and Physiology of Nucleic Acids. 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.
- ^ a b c "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.
- ^ Mink, G. I. (1993). "Pollen and Seed-Transmitted Viruses and Viroids". Annual Review of Phytopathology. 31 (1). Annual Reviews: 375–402. doi:10.1146/annurev.py.31.090193.002111. ISSN 0066-4286. PMID 18643763.
- Ding, Biao (2009). "The Biology of Viroid-Host Interactions". Annual Review of Phytopathology. 47 (1). Annual Reviews: 105–131. doi:10.1146/annurev-phyto-080508-081927. ISSN 0066-4286. PMID 19400635.
- ^ p. 114, "Long-Distance Trafficking In the first experimental investigation on viroid systemic movement within an infected plant, Palukaitis (99) showed that PSTVd moved from a photoassimilate-source leaf into sink organs in a pattern consistent with phloem transport. This was supported by in situ localization of PSTVd in the phloem (144)."
Bibliography
edit
- Agrios, George N., 1936- Plant pathology (3rd edition) San Diego: Academic Press, 1988.
- Singh, R.P; Fletcher J.D.; "Background of disease (potato spindle tuber) and method of control", Agriculture and Agri food Canada, Crop & Food Research New Zealand Retrieved November 15, 2007
- DEFRA Plant Health
- "Pathogen and plant damage (potato spindle tuber)" Retrieved November 15, 2007, from George N. Agrois, Plant Pathology (3rd Ed) San Diego: Academic Press,(1988).