Potato spindle tuber viriod (PSTVd)
English names: Potato spindle tuber, Bunchy top of tomato
Nordic names: Kartoffeltenknoldviroid (DK)
Estonian name: Kartuli värnaviroid
Major host plants
Potatoes and tomatoes are the main hosts. PSTVd has also been identified on ornamental solanaceous plants (e.g. Brugmansia sp., Solanum jasminoïdes), which normally are asymptomatic. Wild solanaceous hosts can act as potential reservoirs of the disease.
Mild strains of PSTVd cause no obvious symptoms, while severe strains in sensitive cultivars can cause the following symptoms:
Symptoms in the field may be difficult to recognise before plants mature. Plants are stunted. Foliage is very upright and is often a darker green than normal. Axillary buds may proliferate to give symptoms similar to those of witches' broom. Tubers are small, elongated, cylindrical, spindle or dumb-bell-shaped, with prominent eyes evenly distributed over the tuber. Sprouting is slower than in healthy tubers. Typical tuber symptoms develop after some generations.
Stunted plants with yellowing and leaf curling. Stems are bunching with small compacted apical leaves. Fruits are smaller, sometimes slightly misshapen, with yellowing on the top of the fruit.
Symptoms become more pronounced in warm conditions and under high light intensity.
Though the pathogen is considered absent in potatoes from the EU, there have been outbreaks of PSTVd in tomato crops in BE, DE, FR, NL and UK. The disease has been found too in symptomless ornamentals a number of times.
A map can be downloaded from EPPO's website. See instructions here.
The disease is mechanically transmitted by contact between healthy and diseased plants, cutting knives, equipments etc. The viroid appears to reach greatest concentration in the leaf hairs. Within tomato plants, it moves rapidly and systemically from an inoculated leaf to actively growing tissue via the phloem. In potato plants, the pathogen occurs in highest concentrations in the upper leaves and tubers.
The viroid is spread over short distances within crops by mechanical transmission. Over long distances, it is most likely to be carried by seeds and potato tubers.
Detection and inspection
For identification, laboratory tests are required.
Pest status and importance
In Europe, PSTVd is likely to cause direct damage primarily in warm dry areas of Southern and Central Europe. However, in the cooler Northern countries, the disease could establish as a latent infection in seed-potato stocks, with severe consequences for export potential. In potato, yield losses of up to 64% in size and number of tubers have been recorded. Quality may be negatively affected as well.
Source of information
See further information here:
Author: Jorma Rautapää
Editor: Dorthe Vestergaard