Occasional viruses in France

Some other viruses also occur in France, but they are more rarely observed in the field:
 
- Alfalfa mosaic virus (AMV), occurs in tobacco grown near alfalfa fields. This virus is transmitted by aphids in a non-persistent manner. Infected plants are often isolated or grouped into foci of some plants in the plot. AMV infections cause rather varied foliar symptoms on tobacco, involving various patterns having frequently a bright yellow colour. Thus, certain AMV strains produce ringspots, more or less regular arcs and arabesques of light yellow to white, sometimes necrotic, and large patches of bright yellow on tobacco leaves (figures 1-4). One can also observe enations on the lower leaf surface (figure 3b). Note that the tobacco varieties grown in France have no varietal resistance to this virus (alfalfa mosaic virus );
 

Figure 1	Figure 2	Figure 3	Figure 4

 
- Tobacco ringspot virus (TRSV): This virus is transmitted by soil nematodes, that is why virus-infected plants are often isolated or grouped into foci of limited size. Symptoms are linear patterns, or chlorotic and necrotic ringspots (hence the name of the virus), sometimes concentric (figures 5 and 6). Like for AMV, tobacco lacks varietal resistance to this virus (tobacco ring spot virus);
 

Figure 5	Figure 6

 
- and tobacco mosaic virus (TMV). This very common virus on tobacco at a time, gradually disappeared from the cultures due to its non-seed transmission and widely use of resistant varieties. Note that this virus is emerging again in several French production areas (Loire, Gers, Alsace, Midi-Pyrenees, Charentes). Add that it is spread through contact, so it is not surprising to see disease distribution in rows or in foci. The symptoms are mosaic patterns, large "vein bandings", and filiform leaves (figures 7 and 8) (tobacco mosaic virus), the symptoms are similar to those induced by CMV (cucumber mosaic virus).
 

Figure 7	Figure 8

 
Tomato mosaic virus (ToMV), which also infects tobacco in Eastern Europe and tomato in France, does not seem to affect tobacco in France.