Biology, epidemiology

• Conservation, sources d'inoculum
  

The Stemphylium have potential saprophytic allowing them to easily maintain one season to another, on and in the soil, on plant debris of any kind (leaflets, stems, floral senescent parts) of the tomato and many alternative hosts , cultivated or not. S. solani and, to a lesser degree, S. floridanum are capable of attacking several cultivated Solanaceae (eggplant, pepper ) or wild ( Solanum carolinense, S. lycocarpum ) which will allow them to survive and / or d 'ensure the production of the primary inoculum. Note that the strains of S. solani affecting cotton are aggressive on tomato, potato and blue lupine in Brazil (cotton strains are all the same genetically different from tomato strains). S. floridanum is described on Allium, safflower, gladiolus and chrysanthemum. It is not excluded that these different hosts can serve as reservoir plants for inoculum. S. vesicarium and S. botryosum f. sp. lycopersici can also count on their perithecia to be preserved from one season to another, their ascospores being able to ensure the primary contaminations.

• Penetration and invasion

The conidia of these fungi germinate on the leaflets and enter directly through the cuticle or via various wounds . Their mycelium then quickly invades the tissues, and spots are already visible 5 days after the first contaminations.

• Sporulation and dissemination

Once the mycelium is installed, conidiophores and conidia form on the underside of the leaf blade:
St. vesicarium (figures 1The 2); St. floridanum (Figures 3 and 4); St. nightshade (Figures 5 and 6).
The conidia are then dispersed mainly by wind and air currents, but also by splashing water following rains or irrigation by sprinkling. Remember that plants can transmit the disease if infections occur in the nursery.

• Conditions favorable to its development

The development of these Stemphylium spp. is favored by climatic conditions humid , in particular the presence of water on plants (rain, dew, sprinkling, condensation in greenhouses) and by high temperatures. Their thermal optima are between 23 and 27 ° C , depending on the species.