Main symptoms

On batavia, the agent of the necrotic rings of lettuce ( Lettuce ring necrosis agent , LRNA) initially causes rings, spots of orange to brown color and of a slightly oily appearance (figures 1 to 5). These symptoms are first visible on the underside of the limbus (Figures 1 to 3).

On thin-leaved batavias, these alterations evolve fairly quickly into papery necrosis (figure 6).

On butter lettuce, yellow spots, punctate or angular, appear initially, sometimes giving the upper surface of the leaf a marbled appearance (Figures 7 to 11). Rings, orange spots may also develop.

In fact, such orange rings are visible on all types of lettuce, first in the leaf axils and along the veins. They can generalize to the entire limbus. It is always the lower leaves or intermediate crowns that show symptoms (Figures 9 to 11). While careful observation can identify the first symptoms at the 15-20 leaf stage, it is usually at the pre-apple stage that growers begin to assess the extent of damage.