Biology, epidemiology

- Conservation, sources d'inoculum

The conservation of Microdochium panattonianum from one year to another is carried out essentially on the plant debris present in the soil of the crop or its environment. Authors report maintenance in the soil for 4 years. In some production areas where wild lettuce ( Lactuca serriola susceptible ) survive, they can contribute to its sustainability. It could also be harbored by other weeds, notably Sonchus aster . Short-term storage of this fungus on seeds has been reported; it currently seems to be called into question.

In fact, it is above all " microsclerotia " (35 to 65 µm in diameter), forming in the cells of damaged tissues, which are at the origin of the first contaminations. These microsclerotia present on the soil can be projected onto the lower leaves of lettuce, during rain or sprinkler irrigation. Subsequently, they germinate on the moist leaf blade and give rise to a short appressorium. Of conidiophores can also form on the sclerotia in the soil surface. The conidia produced also provide primary contaminations. They come to be deposited on the leaves thanks to the wind and the projections of water.


- Penetration and invasion

The presence of free water on the limbus is essential for contaminations which take place directly through the cuticle or, more rarely, via the stomata . Microdochium panattonianum gradually colonizes the tissues (intra and intercellular colonization) which quickly necrose and fill with microsclerotia . These last reach the ground at the same time as the decomposed tissues. The incubation period lasts on average from 4 to 12 days depending on the climatic conditions.


- Sporulation and dissemination

The high humidity allows the fungus to sporulate abundantly on the spots. The presence of free water is necessary first; thereafter, a relative humidity of 100% is sufficient. The numerous conidia formed under the cuticle (figures 1 to 3) are the cause of secondary contaminations. These are favored by rain, sprinkler irrigation, the wind which carries microdrops over distances varying according to its power. Market gardeners during cultivation operations and the tools they use can also contribute to the spread of the disease.


- Conditions favorable to its development

Microdochium panattonianum is a fungus which particularly likes environments humid following periods of fog, dews and especially rains or sprinkling irrigations. At the same time, it appreciates fairly low temperatures; its thermal optimum is around 17-19 ° C . Symptoms may still appear near 2 ° C. Germination of conidia would no longer be possible above 28 ° C. The fungus would be destroyed following exposure to 40 ° C for 10 minutes.