Main symptoms

Thanatephorus cucumeris , like Pythium spp., Causes seedling mortalities linked to a constriction of the stem located at ground level, more or less brown and of rather dry consistency (figure 1).

This fungus is most feared for the symptoms it causes on adult plants. The first symptoms are especially visible as the harvest approaches on the leaves in contact with the ground . Their expression may be somewhat different depending on the types of salad. On lettuce and escarole , we can observe:
- numerous reddish to brown changes of dry consistency, both on the petioles, the midrib and on the leaf blade (Figures 2 and 3). On the latter, their evolution seems faster and the tissues give the impression of "melting";
- browner lesions located on the limbus momentarily respecting the main vein (figures 4 and 5).

These spots spread quickly and rot tissue sets in (Figure 6). It is more or less humid depending on the climatic conditions. It first affects the lower leaves which may wilt and turn yellow . Subsequently, it gains the leaves of the heart and sometimes even the stem. The collar can be subsequently belted.

On or near the damaged tissues, there are sometimes discreet whitish to brown filaments (Figures 3 and 7) running along the stem, veins and leaf to leaf. Poorly defined, brown masses are sometimes located along the veins (Figure 8).

Figures 9 and 10 show damage caused by Thanatephorus cucumeris on chicory.

It should be noted that Botrytis cinerea and bacteria ( Pectobacterium carotovorum susp. Carotovorum , Pseudomonas marginalis ) can colonize tissues already damaged by Thanatephorus cucumeris and help accelerate tissue decay.