• Conservation, sources d'inoculum
  

Botrytis cinerea is sometimes found on seeds . It is able to maintain itself in the soil on the most diverse plant debris and in several forms: conidia (figure 3), mycelium or sclerotia (figure 4). The latter persist in the soil for several years. The saprophytic potentials of B. cinerea allow it to be easily preserved on organic matter. It is polyphagous and capable of attacking and colonizing several hundred cultivated plants or weeds which contribute to its conservation and constitute potential sources of inoculum, this is the case for the majority of market garden plants. On these plants as on its sclerotia, it sporulates abundantly. Primary contaminations are therefore often aerial and in this case involve conidia which are very easily transported by the wind. These spores germinate in a few hours (5 hours at 20 ° C) on wet leaves and / or in the presence of an ambient humidity of at least 95%. The germination of conidia is strongly affected at temperatures above 30 ° C.

• Penetration and invasion

Once the germ tube is formed, it penetrates the tissues and gives rise to mycelium which destroys the walls of the cells and their contents. Penetration takes place either directly through the cuticle or from various wounds , in particular on the stem via disbudding and leaf stripping wounds. The infections take place approximately after about fifteen hours . B. cinerea also settles on the tomato via the stems of the bunches and the wounds resulting from their uprooting. It can also invade all senescent, necrotic and / or dead tissues such as petals, necrotic sepals, old leaflets. It sometimes colonizes tissues already damaged by other pathogens or pests. It quickly spreads to tissues, which it rots in a few days thanks to the hydrolysis of peptic substances.

• Sporulation and dissemination

On all its hosts as well as on plant debris, it produces a gray mold (figure 1) made up of mycelium and numerous long and branched conidiophores (figure 2). At their ends emerge conidia ovoid to spherical which ensure the dissemination of B. cinerea (figure 3). The sporulation can start 3 days after the initial contamination. The release is carried out mainly through the wind and drafts , to a lesser degree of rain and water splash. It is also ensured by the workers during cultivation operations. The mycelium is at the origin of contamination by contact of diseased tissues with healthy tissues. B. cinerea can eventually produce small, flat sclerotia on damaged tissue which also allows its preservation (Figure 4). Under favorable conditions, the duration of a cycle is quite short, of the order of 4 days.

• Conditions favorable to its development

Like many aerial fungi, it is particularly fond of humid environments. A relative humidity of around 95% and temperatures ranging between 17 and 23 ° C are conditions very conducive to his attacks. These parameters are found especially under shelters, but also in the open field during rainy periods or following sprinkler irrigation. Plants that are etiolate or overgrowth are particularly vulnerable. This is particularly the case when the shelters are closed in order to conserve heat: the plants then tend to develop rapidly. Their vegetation, becoming quite luxuriant and having succulent tissues, therefore becomes very sensitive to B. cinerea . Note that the attacks of this fungus are more particularly serious in the earliest crops, new greenhouses often more airtight, greenhouses equipped with a heat shield, plastic shelters. Under these, the quality of the coating would influence the development of certain diseases, and of B. cinerea in particular. In fact, less damage was observed with EVA, compared to PVC and polyethylene. Under EVA, it seems that we have better light transmission, lower humidity and less formation of water drops on the walls. Finally, the agrotextiles sometimes used to protect plants from insects lead to an increase in humidity, aggravating the damage.

Note that some varieties are more sensitive than others to gray mold.