Biology, epidemiology

- Conservation, sources d'inoculum

Thielaviopsis basicola persists ( Chalara elegans ) in the soil for a very long time, thanks to its chlamydospores (figure 1). It is able to colonize organic matter and infect many host plants, whether cultivated or not, which will help to multiply and conserve it. Indeed, more than 120 species have been identified belonging to at least 15 different botanical families. Among the vegetable crops, one can quote the bean, the pea, the cucumber, the melon, the watermelon, the carrot, the eggplant, the tomato ... These hosts do not have the same sensitivity to this fungus and therefore multiply it. More or less good. It is well known that strains of Thielaviopsis basicola show different pathogenic powers.

In nurseries, dust from contaminated soil is an important source of inoculum. It is also preserved on the material used for the production of the plants. In Australia, it was found, before sowing, in certain peat-based substrates.


- Penetration and invasion

The chlamydospores , to a lesser extent the endoconidia (Figure 2), germinate near the roots and penetrate directly through the skin or through wounds . The fungus quickly colonizes the tissues of the cortex and the vessels that it causes to rot. In damaged tissues, it produces numerous chlamydospores. It also forms on the surface of the roots, along with a multitude of endoconidia.


- Dissemination

Chlamydospores and endoconidia are easily disseminated by water and soil dust . It is likely that the soil, present on the tools used to work the soil, contributes to the propagation. The same goes for contaminated salad plants.


- Conditions favorable to its development

Thielaviopsis basicola is best known to be serious on various plants when growing conditions are difficult. This is the case during cold and wet springs . Under these conditions, the root development of plants is reduced, or even stopped, and he takes the opportunity to severely crack down. It therefore appreciates wet soils, but especially cold. Its optimum temperature is normally around 17-23 ° C . The Australian strains reported would have a higher thermal optimum, ranging between 23-26 ° C, reflecting an adaptation to the sub-tropical conditions of the affected region. The soil pH influences the behavior of this fungus; at acidic pH (around 5.6) it is normally less active. Adding calcium to the soil can increase its development.