Main symptoms

The first plants affected by the ( lettuce large vein virus Mirafiori lettuce big vein virus , MLBVV) are quickly spotted in crops because they have an abnormally more upright habit, depending on the type of lettuce; moreover, the salads appear puffy, even disheveled (figures 1 and 2). Ultimately, plants are most often not marketable. When infected at an early stage, they can remain stunted. All types of lettuce are affected, but nuances of symptoms can be distinguished.

On butter, batavia, iceberg and romaine lettuce, we note above all a lightening of the chlorophyllic tissues located along the veins, giving the impression that the latter are widening (large vein symptoms = Big-vein, figure 3).

On the other hand, on oak leaf and Lollo lettuce, it is the stunted appearance of the plants and the deformation of the leaves that is most remarkable (figure 4).

Low temperatures favor the expression of symptoms. They are accentuated when the air temperature is around 14-16 ° C. They are attenuated or disappear if the air temperature rises to 22-24 ° C and above, and this whatever the temperature of the soil at the level of the roots. The succession of cold or milder climatic periods may explain the presence on salads of normal leaf layers alternating with layers with deformed leaves.