Sclerotinia sclerotiorum , widely distributed in the world and affecting many species, is also reported on tomato ( white mold ). It attacks both flat or staked field crops as well as those produced under cover. This species is present in France and is also prevalent on lettuce.
 

Like Botrytis cinerea , this fungus is an opportunistic parasite that readily colonizes wounds and senescent plant tissue.
 

It is therefore not surprising that it is rife with field crops in flat, moist soil conditions and at a time when well-developed plants have vegetation that covers the stems and fruits. All organs near or in contact with the ground can be affected by wet and soft rot. The lesions on the stem are moist and the tissues take on a fairly typical beigeish tint and milky appearance. They extend and eventually encircle the stem. A white cottony mycelium ends up developing more or less abundantly on the damaged tissues (figure 1), as well as large black masses, rather elongated and of variable size: sclerotia.
On this type of crop, a focus of rot is often formed within the plant cover, the disease being transmitted by contact from diseased organs to healthy organs. Leaflets, like fruits, are also affected by a wet and soft rot which causes the first to disintegrate and the second to liquefy (see chapter Fruit stains ). As before, mycelium and sclerotia may be present on affected organs.
 

Symptoms caused by S. sclerotiorum can be observed in cultivation under cover. Very often, only cankers on the stem are observed following airborne contaminations. They are due to ascospores of the fungus resulting from its sexual reproduction. The alterations on the stem start, as for Botrytis cinerea , senescent tissues or various wounds. Remember that pruning wounds are privileged entry points from which wet and soft changes develop. The lesions present, as in the open field, a beige tint and gradually become covered with a white cottony mycelium (figure 2). Sometimes orange droplets exude from it. Masses, initially white and gradually melanating, of hard consistency, form either on the stem (figure 3) or inside it (figure 4): these are the sclerotia (figure 5) of this fungus, conservation organs ensuring its sustainability in the soil.
 

Note that the perfect form of Sclerotinia sclerotiorum is sometimes visible on the surface of moist soil. It is characterized by the formation of small "trumpets", the apothecia, which are at the origin of the ascospores responsible for airborne contamination.