Viroids - potato
Contributors to this section: CIP, Lima, Peru (Carols Chuquillanqui, Segundo Fuentes, Ivan Manrique, Giovanna Muller, Willmer Pérez, Reinhard Simon, David Tay, Liliam Gutarra); CIP, Nairobi, Kenya (Ian Barker); FERA, UK (Derek Tomlinson, Julian Smith, David Galsworthy, James Woodhall).
Spindle tuber of potato
Potato Spindle Tuber Viroid (PSTVd)
EPPO A2 quarantine organism.
Foliage: Symptom expression is influenced by the host species, host cultivar, strain of PSTVd, environmental conditions and method of inoculation (Harris, 1980; Pfannenstiel, 1980).
Stem and blossom pedicels are slender, longer than normal and remain erect. Leaflets are slightly reduced with fluted margins, tend to curve inward and overlap the terminal leaflet. Angles between stems and petioles are more acute than normal (Hooker, 1981; Wale, 2008). Infected plants are stunted and their leaves are dark green and rugose.
Tubers: Tubers may be elongated, with pointed ends and reduced in size (Jeffries, 1998). Tuber eyes appear to be more numerous and have characteristics of indentation or enhanced edges (Wale, 2008)
Lycopersicon esculentum (tomato), Persea americana (avocado), Solanum tuberosum (potato), Ipomoea batatas (sweet potato), Solanum melongena (aubergine or eggplant), Solanum (nightshade), Solanum nigrum (black nightshade).
Asia, Europe, North America, Central America, South America, Oceania.
Biology and transmission
PSTVd is readily transmitted through botanical seed, pollen or ovules (Grassmick, 1986) and contact, but mainly by machinery in the field (Wale, 2008).
PSTVd is easily mechanically transmitted. It was found that transmission could occur when infectious sap contaminated cutting knives used for tuber propagation, with contamination of young tuber sprouts with infectious sap resulting in the highest percentage of infection. Heterologous encapsidation of PSTVd in particles of PLRV has been reported and may explain the observed insect transmission. This has important implications for epidemiology and spread of PSTVd in potato fields (Querci et al., 1997).
Detection/indexing method in place at CIP
- At CIP, the viroid is detected by NASH.
- In seed certification schemes, no virus infections must be tolerated during the growing season. Stocks of in vitro cultures used for propagation should be from pathogen-free plants and maintained under conditions designed to prevent infection and contamination.
Procedure followed at the centers in case of positive test
- In CIP if pathogen is detected the imported germplasm must be cleaned by thermotherapy.
References of protocols at EPPO, NAPPO or other similar organization
OEPP/EPPO. 1978. Data sheets on quarantine organisms No. 97; Potato spindle tuber viroid. Bulletin OEPP/EPPO Bulletin, 8:2.
OEPP/EPPO. 2004. Potato spindle tuber pospiviroid. Diagnostic protocols for regulated pests. PM7/33(1). Bulletin OEPP/EPPO Bulletin 34:257-269.
References and further reading
Grasmick ME, Slack SA. 1986. Effect of potato tuber spindle viroid on sexual reproduction and viroid transmission in true potato seed. Canadian Journal of Botany 64:336–340.
Harris PS, Browning IA. 1980. The effects of temperature and light on the symptom expression and viroid concentration in tomato of a severe strain of potato spindle tuber viroid. Potato Research, 23(1):85–93
Hooker WJ. (ed.). 1981. Compendium of Potato Diseases. American Phytopathological Society. St. Paul, Minnesota, USA. 125 pp.
Pfannenstiel MA, Slack SA, 1980. Response of potato cultivars to infection by the potato spindle tuber viroid. Phytopathology, 70(9):922–926
Querci M, Owens RA, Bartolini I, Lazarte V, Salazar LF, 1997. Evidence for heterogeneous encapsidation of potato spindle tuber viroid in particles of potato leafroll virus. Journal of General Virology, 78(6):1207–1211.
Wale S, Platt HW (Bud), Cattlin N. 2008. Diseases, Pests and Disorders of Potatoes. A Color Handbook. Manson Publishing, London, UK. 176 pp.
Seed Health General Publication Published by the Center or CGIAR
Jeffries C. 1998. FAO/IPGRI Technical Guidelines for the Safe Movement of Germplasm. No. 19. Potato. Food and Agriculture Organization of the United Nations, Rome/International Plant Genetic Resources Institute, Rome.