Main symptoms

Symptoms usually appear 15 to 25 days after aphid infection; this depending on environmental conditions (light intensity) but also on the stage of infection and varietal sensitivity.

First, chlorotic spots appear on the lamina of the older leaves (figure 1), then on the intermediate leaves (figure 2). Gradually, these spots spread and turn distinctly yellow. Eventually, there is an almost generalized interveinal yellowing; a still green area of ​​tissue persists along the veins (Figure 3). Affected leaves, especially those on the lower crown, may present a necrotic area at the edge of the leaf blade (Figure 4). In addition, they are thicker and break when folded, which helps distinguish this virus from premature physiological senescence. In addition, this disease has sometimes been confused with a deficiency in magnesia.

Early infections lead to a significant reduction in the weight of the "apple" of salads (up to 50%). The phenological stage of the plant at the time of infection and the relative sensitivity of the variety influence the extent of the damage. Depending on the latter, a more or less severe dressing of the salads will be necessary to consider their marketing.

In infected seed carriers, interveinal jaundice is very characteristic on the bracts; moreover, the quantity of seeds produced is reduced.

No variation in the degree of aggressiveness of strains has been demonstrated in lettuce, except in the United States where a particular isolate, BWYV-ST9 with satellite RNA, causes more severe symptoms. Mixed BWYV + LMV or BWYV + CMV infections cause much greater damage. The synergy of the effects of BWYV and LMV in lettuce may be the cause of internal necrosis of the veins in certain varieties of iceberg-type batavia.