Crops
Athelia rolfsii ( Sclerotium rolfsii)
Very polyphagous and rather subservient to hot and humid production areas, Athelia rolfsii is particularly aggressive on the crown of tomatoes ( southern blight ). When it is rife, a brown to black wet lesion appears and surrounds the part of the stem present in the soil, then gradually rises several centimeters at the foot of the affected plants (figure 1). If the climatic conditions are favorable, a vigorous and thick white mycelium covers it rather quickly and also reaches the part of the lesion above the ground (figure 2) . On this mycelium, rounded sclerotia, first white then beige to brown, are formed. 1-3mm long, they resemble the seeds of Brassicaceae. The mycelium also invades the root system and causes it to rot completely. Affected plants end up wilting, sometimes in a more or less reversible way at first, often suddenly. They die quickly thereafter.
Fruits in contact with the ground show a yellowish lesion, then wet rot causing tissue collapse. The wrinkled epidermis ends up splitting. Mycelium and sclerotia soon cover the lesions (Figure 3) . Like fruits, the leaves touching the ground can be attacked, large wet spots partially damaging the leaf blade.
The mycelium of this basidiomycete fungus is able to actively progress on the surface of the soil and thus pass from one plant to another . It does so in a saprophytic way from the nutrient bases that constitute plant debris of all kinds. This mycelium is relatively characteristic because it has loops of anastomosis .
Fruits in contact with the ground show a yellowish lesion, then wet rot causing tissue collapse. The wrinkled epidermis ends up splitting. Mycelium and sclerotia soon cover the lesions (Figure 3) . Like fruits, the leaves touching the ground can be attacked, large wet spots partially damaging the leaf blade.
The mycelium of this basidiomycete fungus is able to actively progress on the surface of the soil and thus pass from one plant to another . It does so in a saprophytic way from the nutrient bases that constitute plant debris of all kinds. This mycelium is relatively characteristic because it has loops of anastomosis .
A. rolfsii is relatively rare in France. Its damage is sometimes observed in a few vegetable or ornamental production areas of the Côte d'Azur, the Pyrénées-Orientales and the Basque Country. On the other hand, it is particularly frequent and damaging at all stages of tomato development in many market garden soils in the French overseas departments and territories.
For further information on this fungus, you can consult the sheet Athelia rolfsii ( Sclerotium rolfsii ).
For further information on this fungus, you can consult the sheet Athelia rolfsii ( Sclerotium rolfsii ).
Figure 1
Figure 2
Figure 3