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Biology, epidemiology

- Conservation, sources d'inoculum

Botrytis cinerea is sometimes found on seeds . This fungus is able to maintain itself in the soil on the plant debris most diverse , this in several forms: conidia, mycelium, sclerotia (figure 1). The latter persist in the soil for several years. When they are present near the leaves in contact with the soil, they germinate and mycelium gains them. The potential saprophytic of Botrytis cinerea allows 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. Contaminations are therefore often aerial; in this case they involve conidia which are very easily transported by the wind. These spores germinate on the leaves in the presence of water.

- Penetration and invasion

Subsequently, the germinal tube of conidia or the mycelium of sclerotia penetrate the tissues, especially the leaf parenchyma, destroying the cell walls and their contents. Penetration takes place either directly through the cuticle or from various wounds. Botrytis cinerea also invades all necrotic and / or dead tissues such as those observed following damage due to frost, water stress leading to "tip-burn", sunburn . It also colonizes tissues already damaged by various pathogens such as Sclerotinia minor or Sclerotinia sclerotiorum , Rhizoctonia solani , Bremia lactucae or by pests. It quickly spreads to tissues which it causes to rot in a few days, thanks to the hydrolysis of peptic substances. Other secondary microorganisms, especially bacteria, gain access to these tissues, also contributing to their degradation.

- Sporulation and dissemination

On all its hosts, as well as on plant debris, it produces mycelium and numerous long, branched conidiophores (Figures 2 and 3). At their ends emerge conidia ovoid to spherical (figure 4), which ensure the dissemination of Botrytis cinerea . This takes place mainly through wind and drafts, to a lesser extent rain and splash. It is also ensured by the workers during cultivation operations. The mycelium is the source of contamination by contact of diseased tissue with healthy tissue. Botrytis cinerea also forms on damaged tissues small sclerotia flat which ensure its preservation.

- Conditions favorable to its development

Like many aerial fungi, it is particularly fond of environments humid . A relative humidity of around 95% and temperatures between 17 and 23 ° C are very favorable conditions for its attacks. They are found in shelters, but also in the open field, during rainy periods or following sprinkler irrigation. Plants that are overgrown or withered are particularly vulnerable. Certain substances released during the senescence of the seedlings promote its development. Agro-textiles are sometimes used to protect plants from insects. The damage of Botrytis cinerea is more consequent under these covers, because of a higher hygrometry. Under plastic tunnel, the quality of the coating would influence the development of certain diseases and Botrytis 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 of shelters.

Last change : 04/29/21
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Figure 4