Addition of pepino mosaic potexvirus to the EPPO Alert List
Pepino mosaic potexvirus was first described in Peru by Jones et al. in 1980 on pepino (Solanum muricatum), a South American crop producing large aubergine-like edible fruits. This new virus was found in the Canete valley in coastal Peru causing a yellow mosaic in young leaves of pepino. Affected pepino plants were also contaminated by the Andean strain of potato S carlavirus. Pepino mosaic potexvirus has filamentous particles with an average length of 508 nm. The experimental host range is narrow. The virus could be mechanically transmitted to 30 species out of 32 of Solanaceae species tested (including potato, tomato and tobacco), to Tetragonia expansa (Aizoaceae, no systemic infection) and to Cucumis sativus (Curcurbitaceae, no systemic infection). It failed to infect 13 species in 6 other families. The virus caused mild mosaic or symptomless infection in 12 wild potato species and in several potato cultivars, but severe systemic necrotic symptoms on potato cultivars Merpata and Revolucion. Only systemic symptomless infection was obtained in tomato. At this time, no natural infection was found in potato fields in Peru (apparently tomato crops were not studied). During this first study it was shown that pepino mosaic potexvirus is transmitted by plant contact and not by Myzus persicae. The virus was not detected again in Peru nor in any other country, until it appeared very recently in the Netherlands and United Kingdom on tomato crops.
Situation in the Netherlands
In January 1999, pepino mosaic potexvirus was discovered in glasshouse tomato plants for the first time in the Netherlands. Affected plants showed yellow spots on the leaves, mild interveinal chlorosis and in some cases minor leaf malformations. Fruits sometimes showed discoloration. The virus was found by approximately 50 tomato growers but not in nurseries. In most cases, growers kept their crops until the end of the season and a normal quantity of fruits was harvested. Fruit discoloration sometimes caused lower grading. According to the Dutch NPPO, for 95 % of the growers, financial loss was estimated to be less than 0.5 %, for the remaining 5 %, losses reached a maximum of 5%. In the information given by the French Embassy, it is however noted that some growers (without further details) who had 70 % of their tomatoes infected had to replace their crops by cucumbers. As potexviruses are usually not transmitted by insects or seeds, persons handling the crops are probably the main factor in spreading the disease within a glasshouse and also between glasshouses. Measures have been taken by the Dutch NPPO to eliminate pepino mosaic potexvirus. Glasshouses where infection was found have been thoroughly cleaned. Strict prophylactic measures will be applied to glasshouses and nurseries. In addition, tomato plants will be visually inspected and samples tested by ELISA. The Dutch NPPO has carried out a Pest Risk Analysis (PRA) for the European Union area, and its conclusion was that pepino mosaic potexvirus did not merit classification as a quarantine pest. So far, the origin of its introduction into the Netherlands is not known.
Situation in United Kingdom
In United Kingdom, in January 1999, samples of tomatoes grown under glasshouse originating from the Netherlands and showing unusual symptoms were sent to CSL by a grower in Kent (south-east England). In September 1999, a second grower in Somerset (south-west England) sent tomato samples with similar symptoms. These tomatoes were grafted plants, grown from Dutch seeds which had been supplied by a UK propagator. Pepino mosaic potexvirus was detected in these samples. Symptoms were characterized by distorted leaf development, with bubbling of the leaf surface and chlorosis. First signs of the disease were an apparent lighter green, spiky or nettle-like 'head' of the plants which had filiform leaves reminiscent of hormone damage. Lower leaves on the plant appeared darker; occasionally yellow chlorotic angular spots were seen. Affected plants were very stunted and distorted. In United Kingdom, growers reported a very rapid development of the disease, spreading along plant rows as well as foci in other parts of the glasshouse. It is felt that the virus can cause significant crop losses if early action is not taken to eliminate infection. The virus can readily be transmitted by contaminated tools, hands, clothing, and direct plant-to-plant contact. It is also transmitted by propagation (grafting, cuttings). Seed transmission (although investigated) appears unlikely. If this virus occurred on outdoor crops, it is likely that it would be transmitted by animals, volunteer plants and possibly weeds. Preliminary inoculation studies to potato cultivars showed that pepino mosaic potexvirus does produce mosaic symptoms on leaves of cultivars Maris Peer, Pentland Dell (Jones et al. had only observed symptomless systemic infection on these cultivars) and Charlotte (not previously tested). Molecular data showed that UK and Dutch isolates are identical but present some sequence differences from the Peruvian type strain from pepino. It may be recalled that the pepino type strain did not cause symptoms on tomato (only symptomless systemic infection). The NPPO of UK took measures to eradicate the virus. At one site, the whole crop was destroyed and in the other, the affected area and its surroundings were removed. Tomato crops will continue to be monitored by the official authorities. The UK NPPO has carried out a brief PRA, and suggested that pepino mosaic potexvirus should be added to the EPPO Alert List and that further discussions should take place on whether quarantine measures are justified.
Pepino mosaic potexvirus - a new virus of tomato introduced into Europe
Why: Pepino mosaic potexvirus came to our attention because it was very recently found in Europe for the first time on glasshouse tomatoes, in the Netherlands and in UK. In addition, UK and Sweden suggested that it should be added to the EPPO Alert List. More information was requested by France.
Where: Originally described in Peru on pepino. Found in January 1999 in the Netherlands (in approximately 50 tomato glasshouses) and in United Kingdom in 2 tomato glasshouses (in the south of England).
On which plants: Originally described on pepino (Solanum muricatum). It affects glasshouse tomatoes (Lycopersicon esculentum) in the Netherlands and UK. Experimental host range includes mostly Solanaceous plants, including potato and tobacco (no data on Capsicum annuum, Solanum melongena). On potato, symptoms could be obtained with the 'pepino type strain' on S. tuberosum cvs. Merpata and Revolucion and with the 'tomato strain' on cvs. Maris Peer, Pentland Dell and Charlotte (but so far, the disease has never been seen in potato crops).
Damage: In Peru, it caused a yellow mosaic in young leaves of pepino. In the Netherlands, affected tomato plants showed yellow spots on the leaves, mild interveinal chlorosis and in some cases minor leaf malformations. Fruits sometimes showed discoloration. It appears that losses were not very significant (only 5% of the growers reported economic losses of less than 5%). In UK, affected tomatoes showed distorted leaf development, with bubbling of the leaf surface and chlorosis. Affected plants were very stunted and distorted. It appears that the disease spreads very rapidly and that the virus can cause significant crop losses, if early action is not taken to eliminate infection.
Transmission: Pepino mosaic potexvirus is transmitted by contact: contaminated tools, hands, clothing, direct plant-to-plant contact, and propagation (grafting, cuttings). Seed transmission is unlikely, as it is generally not observed in potexviruses. The same applies to insect transmission.
Note: Molecular studies showed that the Dutch and UK isolates were identical, but slightly different from the 'pepino type strain'. The pepino type strain only caused systemic symptomless infection on tomato.
Pathway: Plants for planting (including vegetative parts used for propagation) of tomatoes, vegetables?, growing media ? Although, seed transmission appears unlikely more studies are needed to clarify this issue.
Possible risks: Tomato is a major crop in the EPPO region both indoor and outdoor. So far, the disease has only been found under glass but eradication would probably be much more difficult if it was found on outdoor crops. Other Solanaceous crops may be at risk, and in particular potato, as it has been shown that certain cultivars expressed symptoms during inoculation tests. However, natural infections have never been observed in potato crops.
EPPO RS 2000/003
Panel review date - Entry date 2000-01.
Sources
Jones, R.A.C.; Koenig, R.; Lesemann, D.E. (1980) Pepino mosaic virus, a new potexvirus from pepino (Solanum muricatum). Annals of Applied Biology, 94, 61-68.
Information from the French Embassy in the Netherlands (based on Agrarisch Dagblad 25, 28 and 30 September 1999)
NPPO of NL, 1999-12.
NPPO of UK, 1999-12.
EPPO RS 2000/003