Botrytis cinerea is the fungus responsible for the gray mold which is common on tomatoes, as it does on many other vegetable crops. Very often, humid and cold climatic conditions accompany its extension. Although it is found in the open field, it is under cover that its damage to the stem is particularly feared.
 

It has significant saprophytic potential that allows it to colonize many senescent or injured plant tissues. The tomato during its growth has such tissues in particular:

- the dehiscent cotyledons in the nursery which are at the origin of the development of lesions surrounding the stem of future plants (figures 1 and 2). The latter will reveal cankers at the time of planting and therefore problems of recovery;

- injured leaflets, young or old, chlorotic and senescent and see the chapter Spots on leaflets and leaves );

- senescent floral parts (in particular the petals) still in place or fallen on other parts of the plants;

- and of course, various natural injuries or related to the management of plants (leaf stripping, disbudding ).
 

These nutrient bases, placed in a humid environment, allow this opportunistic fungus to settle and rapidly colonize various tissues, and in particular those of the stem. These quickly become wet and take on a brown tint. They end up necrosis and drying out, their coloring then varying from beige to a more or less dark brown. Eventually, lesions, or even cankers, more or less extensive, are visible on the stems, mainly localized at the level of pruning and disbudding wounds (Figures 3 and 4). They gradually extend, sometimes over several centimeters, and eventually encircle the stem. In many cases, the distal part of the plant eventually wilts and withers. A cut in the stem shows that the vessels and sometimes the marrow are damaged.
 

Let us add that the lesions are usually covered with a very characteristic grayish to beige mold (Figure 4). This consists of the very numerous arbuscular conidiophores of the fungus, which produce innumerable conidia (Figure 5).
 

Other photos of the symptoms caused by B. cinerea on Leaf and Fruit (see also the chapter Fruit stains ) are available.

For additional information on this fungus, you can consult the sheet Botrytis cinerea .