• Conservation, sources d'inoculum
  

Didymella lycopersici is preserved between two tomato crops on plant debris and organic matter in the soil . In the latter, its survival is increased in the presence of humidity, organic matter and fairly low temperatures. It was found on seeds , in the form of mycelium and pycnidia. The data concerning its conservation on Solanaceae are quite controversial: eggplant, potato, pepper, black nightshade would show a certain sensitivity following artificial inoculations, which would make these plants alternative hosts ensuring the conservation of this fungus. It is also found in the environment of greenhouse plants and / or on equipment (stakes, stakes, pottery etc.) used for cultivation and having been in contact with diseased plants. The pycnidia are mainly at the origin of the primary contaminations , via the conidia ; the role of perithecia and ascospores appears to be much more limited.

• Penetration and invasion

The first contaminations take place following a wet period , directly through the cuticle, via the stomata or via wounds . This fungus then quickly invades the tissues that it alters.

Two types of conceptacles, brownish to black, are formed in the tissues. The first, the most frequent are pycnidia subepidermal ostiolées ( anamorph form of the fungus, figures 1 to 3); they are the source of conidia colorless , mostly unicellular but also bicellular (figure 4). The perithecia , materializing the teleomorph , are more rarely formed in nature (diameter between 120 and 210 µm). These give rise to ascospores also hyaline and bicellular (5.5-6.5 x 16-18 µm). The spread of this fungus is mainly through its conidia which are dispersed by splashing occurring during rain or irrigation sprinkler . They are also affected by the tools, hands and clothes of workers during cultivation operations. The ascospores , when Perithecia form, are spread by wind . Seeds can also contribute to the sustainability and dissemination of this fungus.

• Conditions favorable to its development

The moisture is the factor that most influences the development of D. lycopersici . Indeed, the disease is particularly damaging following rains, prolonged morning dews, sprinkling. Water stagnating on the leaves stimulates the germination of spores, the penetration of germinal filaments, and subsequently the formation of fruiting bodies. This fungus grows relatively well at temperatures between 13 and 29 ° C, the optimum is at around 20 ° C . It rather likes old plants and those that have received reduced nitrogen or potassium manure. Its growth is markedly reduced from 30 ° C.