Athelia rolfsii ( Sclerotium rolfsii ) attacks all organs of the tomato located in or near the soil , whether the plants are very young (in nurseries) or adults.

The collar is particularly vulnerable. A lesion quickly transforming into rot sets in and gradually girdles it over several centimeters. Affected tissues are moist and turn brown more or less intensely. If the climatic conditions and / or the soil are sufficiently humid, a dense whitish mycelium covers the diseased parts fairly quickly. Smooth, rather spherical structures (1 to 3 mm in diameter), first white, then tawny to reddish brown, are gradually visible within the mycelium; these are the sclerotia of Athelia rolfsii . The latter have an appearance comparable to mustard seeds. Subsequently, the fungus also invades the roots which it causes to rot quite quickly.

The destruction of the crown and the root system of plants is the cause of secondary wilting more or less reversible ; some tomato plants regain their usual turgor during the night. In many cases, this recovery is only fleeting and plants wilt again as temperatures rise during the day. During the hot weather, withering is brutal and complete and all the vegetation ends up drying out completely .

A. rolfsii is also able to damage fruits and leaves that come into contact with the soil or already affected organs. The fruits show slight changes yellowish at first, quickly becoming wet and soft , widening, while the skin splits (Figures 1 and 4). Eventually, they can liquefy under the combined action of secondary invaders. Of large wet spots are sometimes observed on the leaflets in contact with the ground. They spread quickly and eventually cause them to rot completely. As on the crown, mycelium and numerous sclerotia gradually cover the rotten tissue.

Remember that this fungus grows particularly on young plants with tender tissues. It is therefore not surprising to see some attacks in the weeks following planting, especially if the conditions at the time are hot and humid.

Diseased plants generally have a distribution in foci . In some particularly humid areas, the mycelium spreads on the ground to pass from one plant to another.