Main symptoms

On the young plants resulting from infected seeds, one discerns very quickly, on the leaves, thinning of veins (figure 1), a mosaic, even an embossing of the blade (figures 2 and 3), sometimes some necrotic punctures . As a result of these early infections, plant growth can be severely reduced. Ultimately, the salads are stunted, do not spice up and are therefore not marketable.

Plants infected later show a light green to yellow mottling and leaf deformation (Figure 4), including curling of the outer leaves. The development of salads can be more or less reduced. In some cases of late infections, the expression of symptoms may be very limited; only the dull appearance of the salads reflects their contamination by LMV.

Symptoms are particularly noticeable in actively growing plants; they are generally more characteristic and more pronounced in butter, romaine or leaf lettuce varieties than in batavia or iceberg types (Figure 5).

You should be aware that the symptoms of LMV can be very variable, depending on the type and variety of salad grown, the strain of virus involved, the stage of development of the plant at the time of infection. and surrounding conditions. For example, on some salad varieties and in the presence of particular strains of LMV, yellow patches or yellowing of the veins may appear on the older leaves (Figure 6). Punctiform necrosis or in larger areas, usually located at the edge of the blade, are also visible under contrasting temperature conditions (Figures 7 and 8).

On seed carriers, seed production is all the more affected as the variety is susceptible and the infection early.