Main symptoms

Symptoms vary greatly depending on climatic conditions, stage of infection and variety of salad (Figure 1). In France, as we specified previously, the symptoms are often limited to a slight marbling or a discreet mosaic, this when the plants are cultivated during the summer, in the Mediterranean area. Symptoms often tend to subside as the plant grows. During periods of strong temperature contrasts, the growth of young plants can be greatly reduced and yellow mottling and necrosis can be observed on the leaves (Figure 2).

The effects of CMV on lettuce are so weak that susceptibility ratings in cultivated varieties could only be established on the basis of percent weight loss at harvest. Isolates belonging to both serotypes were isolated from lettuce, but no difference in aggressiveness between them was demonstrated.