First report of Blueberry scorch carlavirus in Europe: addition to the EPPO Alert List
In northern Italy, Vaccinium corymbosum (highbush blueberry) has been planted during the last thirty years and has gained some economic importance for the fresh fruit market. During summer 2004, several plants from a field in the south of Piemonte showed symptoms of Blueberry scorch carlavirus (BlScV). Electron microscopy, ELISA and RT-PCR confirmed the presence of this virus. This is the first record of Blueberry scorch carlavirus in Europe. Considering the damage that this virus can cause to V. corymbosum, the EPPO Secretariat decided to add Blueberry scorch carlavirus to the EPPO Alert List.
Blueberry scorch carlavirus
Why: Blueberry scorch carlavirus (BlScV) is causing damage to Vaccinium crops in North America, and it has recently been found in Europe (in the north of Italy in 2004).
EPPO region: Italy (Piemonte).
North America: Canada (British Columbia), USA (Connecticut, New Jersey, Massachusetts, Oregon, Washington). In late 1970s, the Sheep Pen Hill disease was observed in New Jersey and later considered as being caused by a particular strain of Blueberry scorch carlavirus. The virus was first characterized in highbush blueberries (V. corymbosum) in Washington in 1980. In 2000, an outbreak was reported in British Columbia (Canada), as well as in two new US states in 2001 (Connecticut and Massachusetts).
On which plants: Vaccinium corymbosum (highbush blueberry). The virus was detected in samples of V. macrocarpon (cranberry) and V. ashei (rabbiteye blueberry) but apparently no symptoms were observed. The potential for infection of other American Vaccinium species needs to be investigated (e.g. V. angustifolium, V. membranaceum, V. ovatum, V. parvifolium and ornamental Vaccinium). Data is also lacking on the susceptibility of species naturally occurring in Europe (e.g. V. myrtillus, V. uliginosum, V. vitis-idaea).
Damage: Symptoms vary largely according to virus strains and cultivars. Some cultivars may show complete necrosis of flowers, partial necrosis of leaves, twig dieback, leading eventually to plant death. Others may show a total absence of symptoms. Marginal chlorosis of leaves is also observed on some cultivars. On cultivars expressing symptoms, there is often a latent period of up to two years between infection and symptom expression. Symptoms may be confused with other causes (bacterial or fungal diseases, frost injury or nutrition deficiency) and therefore testing is required to identify the virus.
Transmission: Blueberry scorch carlavirus is transmitted by aphids in a non-persistent mode and a known vector is Ericaphis (Fimbriaphis) fimbriata. Aphid transmission is considered as the most important means of transmission in the field. Within a field, some infected plants may not express symptoms and therefore act as reservoirs for further transmission. Over long distances, the virus is essentially moved by the use of infected plants for planting. So far, mechanical transmission of the virus between Vaccinium plants has never been observed.
Pathway: Plants for planting of Vaccinium.
Possible risks: Vaccinium (including species from North America, such as V. corymbosum) are increasingly grown in Europe for fruit production. A negative impact of such a virus on naturally growing Vaccinium in Europe, especially in fragile environments, could be envisaged but is very difficult to estimate. The aphid vector, E. fimbriata, is not known to occur in Europe, but it cannot be excluded that other aphid species occurring in Europe might transmit the virus. Some control methods are recommended in North America (e.g. roguing of infected plants, aphid control, use of virus-free planting material). Heat therapy and meristem tip culture are reported to eliminate the virus, and could be used in certification schemes. As in North America recent outbreaks and crop losses are reported, it seems desirable to limit the spread of this disease in Europe and to consider the pathogen in European certification schemes for the production of healthy planting material of Vaccinium.
EPPO RS 2005/101
Panel review date - Entry date 2005-07
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