Biology, epidemiology

The epidemiology of Golovinomyces cichoracearum var. cichoracearum (obligate parasitic fungus) is not well known about salad.


- Conservation, sources d'inoculum

Golovinomyces cichoracearum var. cichoracearum can persist from year to year in several ways:
- thanks to its globular cleistothecia (perithecia without ostiole) which ensure its sexual reproduction; they sometimes form on the oidized leaves. They are not found very commonly, but they are nonetheless a form of conservation in winter. Usually, asci in cleistothecia form in the fall. It is not until the following spring that the ascospores will be projected;
- through other hosts . The species Golovinomyces cichoracearum var. cichoracearum is very polyphagous. It is capable of attacking a very large number of hosts, more than 200 species belonging to 25 different families. In fact, this species would contain more or less specialized forms infecting different plants. The parasitic specialization of strains associated with lettuce is not very well known; they should be able to maintain and multiply on alternative hosts, crops or weeds. Lactuca serriola and other wild lettuces are capable of harboring it.


- Penetration and invasion

Infection of the host is carried out from a primary inoculum consisting of either ascospores or conidia . These, once in contact with the host, germinate quickly in two hours if the surrounding conditions are favorable (18 to 25 ° C, 95 to 98% relative humidity). They form an appressorium, then enter directly into the epidermal cells, developing haustoria. The latter play the role of suckers allowing the removal of the elements necessary for the growth of the mycelium of the fungus.


- Sporulation and dissemination

Within 4-6 days of infection, short conidiophores (Figure 1) arise on secondary hyphae formed on the surface of the leaf blade and produce conidia (Figures 2 and 3). Sporulation is very abundant. Conidia are quite fragile and only live for a few hours, or even a few days, when conditions are favorable. They are very light and are therefore easily transported and dispersed by the wind (up to 200 km according to some authors) and, incidentally, by rain or sprinkler irrigation, during splashing. Disseminations are greatest at night, between midnight and 4 a.m.


- Conditions favorable to its development

Golovinomyces cichoracearum var. cichoracearum seems able to grow at temperatures between 4 and 32 ° C . Its thermal optimum is around 18-25 ° C. The presence of free water on the leaves does not seem conducive to its development.

The brightness influences its growth. It appreciates diffused light, while direct sunlight thwarts its extension. It is partly for this reason that it is found more on the lower leaves, inside the plant cover, where the ambient microclimate is particularly mild. Young plants would be less sensitive. Golovinomyces cichoracearum var. cichoracearum can complete a complete cycle in 4 days, if the surrounding conditions are favorable.