Main symptoms

Thielaviopsis basicola ( Chalara elegans ) is a soil fungus responsible for extensive damage to the underground part of lettuce. It gradually colonizes the roots , initially causing discreet and small alterations of light brown color (figure 2). Subsequently, they expand and take on a dark brown to black tint along their entire length. A large part of the feeder rootlets is destroyed (Figure 3). Ultimately, a large proportion of the root system presents a black rot rather characteristic (figure 4). The large roots, a little less sensitive, wear sleeves superficially suberized color brown to black .

Of arthroconidia (chlamydospores) (Figure 5), typical of Thielaviopsis basicola , are visible in root tissues; they allow it to be identified with certainty.

Affected salads are often underdeveloped and chlorotic. They sometimes wilt on hot days.