Main symptoms

In the nursery, damping off is rarely caused by Botrytis cinerea . However, this fungus, sometimes present on seeds that have matured in rainy conditions and in the environment of the seedlings, is responsible for lack of emergence and seedling mortality. These, once collapsed, are sometimes covered by a white, sterile mycelial weft, called " web disease ". This is the case in too dense seedlings; it sometimes attacks seedlings by settling from senescent cotyledons or low leaves in contact with moist soil. The lesions formed are reddish-brown and soft in consistency. Generally speaking, damping-off is rather caused by several species of Pythium spp. and by Thanatephorus cucumeris .

During cultivation and at the approach of harvest, its attacks can materialize by sudden wilting of plants (figure 1), isolated or in foci, following an alteration of the vascular system. As we said previously, it likes old senescent leaves which are found under the vegetation cover (figures 2 and 3) and in contact with the ground after the head. It overwhelms them quickly, producing a wet rot , brown to brown . This rot spreads to the other adjacent healthy leaves and to the crown (figure 4) which is more or less deeply damaged. The vessels are thus affected (figure 5) and the plants can wilt and / or wither gradually or suddenly depending on the climatic conditions (figures 6 to 8).

More aerial attacks on young leaves apple also occur (Figure 9). Of damp, brown spots (10 to 12) extend rather the edge of the lamina. They give rise fairly quickly to a rot of the same nature which is generalized in apples (figure 14). This can be the case with salads harvested too late. In China, damage to the lettuce stalk is also observed.

Significant attacks can take place at the time of flowering of the seed carriers. The senescent floral parts constitute nutritive bases very favorable to the installation of Botrytis cinerea on the inflorescences, causing their rotting and the contamination of some harvestable seeds.

Whatever parts of the lettuce are affected, the affected tissues become covered with a gray mold very characteristic (Figures 14 and 15) consisting of the conidiophores and conidia of the fungus. Black sclerotia (2 to 5 mm in diameter) (Figure 16) are occasionally visible on the same tissues. A dirty white cottony mycelium can sometimes be seen to form, which can be confused with that of Sclerotinia spp.