Main symptoms

In general, the diseased lettuce contrasts in the plot by their puny size (figure 1) and their partial head. The lower leaves can wilt during the hottest times of the day, sometimes turning yellow and necrosis during severe attacks.

The uprooting of several low-growing plants shows root damage which is sometimes impressive. The roots show yellowish lesions that turn brown quickly (Figures 2 and 3). We note in places, as on the pivot, a superficial suberization and longitudinal cracks (figures 4 and 5). They also tend to swell (Figure 6). Their surface thus becomes rough and cracked; there are furrows, ridges, corky ridges on the root system.

The pivot is often very affected; it is strongly suberized and enlarged and becomes brittle (figure 7). Ultimately, only a small portion of the taproot and a few newly formed adventitious roots at the crown level remain on the plants, with many damaged roots having disappeared.

The "non-infectious corky root", associated with nitrogen toxicity, is characterized by a pink to red coloration of the roots and the central cylinder.