Biology, epidemiology

Black rot agents, in particular certain Alternaria , are fungi that are widely present on plants and in their environment. They have saprophytic potentials allowing them to easily maintain themselves on and in the soil, on plant debris of all kinds (leaflets, stems, senescent floral parts, etc.), derived from tomatoes and numerous alternative hosts, cultivated or not.

The conidia of these opportunistic pathogens germinate on the fruits and enter them directly through the cuticle or via the stomata, lenticels and various wounds (punctures, microcracks and cracks, perforations, lesions following a "sunburn" or in the cold, microlesions of the cuticle… Their mycelium invades the tissues and does not take long to produce conidiophores and conidia (figures 1 and 2) which will be dispersed by wind and drafts, and sometimes splashing. water. Their extension can take place by contact of diseased fruit with healthy fruit, in the field as well as during storage. Note that ascospores (figure 3) can be formed inside perithecia present on rotten fruit. These spores are resulting from sexual reproduction in Pleospora spp., the anamorph of which corresponds to Stemphylium spp ..

Their development is favored by humid climatic conditions and optimal temperatures between 18 and 30 ° C. Wounded fruits, already affected by a primary pest and / or having reached an advanced stage of maturity are particularly vulnerable. Remember that some species are likely to produce mycotoxins.