Cucumber mosaic virus  (CMV)  

(Cucumovirus, Bromoviridae)

CMV is a cucumovirus transmitted by aphids in the non-persistent mode. It has been reported on all continents and in all climates , but its incidence may vary from region to region. It is one of the main viruses of cucurbits in temperate and Mediterranean regions. CMV is more rarely encountered on these crops in tropical or sub-tropical regions, although it is present in the environment, and in particular in weeds. Very common in field culture, it is also found under shelter. CMV causes losses that are greater the earlier the infections. Watermelon is usually not affected much.

In France , the frequency of CMV infections in cucurbits varies greatly depending on the species, year or region . A survey carried out from 2004 to 2008 in the main French production areas showed that CMV was present in 20% of 2,660 samples analyzed, mainly on cucumber (34% of samples tested), melon (32%), and much less frequently. on zucchini (7%) and squash (5%). Over the 5 years of observation, the frequency of CMV varied from 6% (2006) to 37% (2004) suggesting the existence of cycles for this virus. More generally, it seems that CMV is less frequent today in France, in particular in the South-East, than it was twenty years ago. However, CMV remains common in the southwest of France.

CMV is often found in mixed infection with other viruses. Synergies leading to stronger symptoms have been reported in mixed infections between CMV and different potyviruses.

CMV was first isolated from cucumber in 1916 in the USA. It is the type species of Cucumoviruses . CMV is widespread worldwide and has one of the most extensive host ranges in both monocots and dicots. More than 1000 plant species are sensitive to CMV, and in particular many market garden species (tomato, pepper, lettuce, spinach), fruit (cherry, banana) and weeds. CMV is transmitted by many aphid species in a non-persistent fashion.

A large number of strains of CMV have been described. Depending on their biological (symptomatology, thermosensitivity), serological and molecular characteristics, CMV strains are assigned to two main groups (I and II), group I itself being divided into IA and IB.

CMV has a divided genome made up of three single-stranded RNAs of positive polarity. Some isolates have additional satellite RNA that can alter symptom expression.

The viral particles are paraspheric about 29 nm in diameter (Figure 1).

Figure 1

Many viruses cause mosaics in cucurbits, which often makes visual diagnosis difficult. However, the symptoms of CMV in zucchini are quite characteristic and allow rapid identification of the virus. Commercial kits diagnostic ELISA are available as well as primers for molecular diagnosis. Recently, rapid detection kits have been developed: they make it possible to reveal the presence of CMV in a few minutes in the field.