Biology, epidemiology

epidemiology of Little Verticillium dahliae is known about the on lettuce. It seems unlikely that its behavior is different from that which it shows on other crops, especially vegetables.


- Conservation, sources d'inoculum

This fungus is a poor competitor at ground level. Despite this, its conservation is ensured by its microsclerotia (figure 1) which perpetuate it for up to fifteen years in the soil. Its large polyphagia allows it to attack many cultivated host plants (pepper, eggplant, tomato, cucurbits, cauliflower, tobacco, cotton, potato) or weeds (black nightshade, amaranth ...) which promote its multiplication and its conservation.


- Penetration, invasion

Contamination occurs either by direct penetration of the mycelium, or through various root injuries. In addition, they can be favored by attacks by root-knot nematodes and Pratylenchus spp. Once in place, this fungus gains the vascular system of plants, which it gradually colonizes. These react to this vascular invasion by forming gum or tyloses which prevent its vascular progression. These defense mechanisms contribute to the wilting of salads. Verticillium dahliae produces microsclerotia and fragile whorled conidiophores in tissue forming ovoid conidia (Figure 2).


- Dissemination

It is possible by soil, by agricultural equipment soiled by contaminated soil and by plant debris. Soil dust containing microsclerotia and / or conidia is easily disseminated by air currents, as well as by splashing water and soil insects.


- Conditions favorable to its development

There appear to be a number of strains with varying thermal requirements. Their thermal optima would be between 20 and 32 ° C. Short photoperiods and low illumination sensitize plants to the disease which would be more severe in neutral to alkaline soils. The monoculture of sensitive plants or too short or poorly chosen rotations contribute to increasing the incidence of this disease in certain plots.