Biology, epidemiology

• Conservation, source d'inoculum

Phytophthora capsici soil is a fungus capable of living in a state saprophytic at the expense of organic matter. It is likely to be maintained in the soil thanks to specific structures of varying resistance: oospores resulting from its sexual reproduction, chlamydospores (whose role is not known), and to a lesser extent sporangia and mycelium . Note that the oospores would keep from 2 to 12 years.

This chromist attacks a wide range of hosts (more than fifty species) which also ensure its multiplication and conservation. Among the latter, let us quote vegetables such as chilli, tomato, eggplant, beans, of course several cucurbits (pumpkin, pumpkin, cucumber, melon, watermelon ... ), but also weeds. The sporangia germinating directly or the flagellated zoospores resulting from the latter are at the origin of the primary and secondary contaminations.

• Penetration, invasion

The zoospores once encysted, germinate and infect the tissues. These are quickly invaded and destroyed.

• Sporulation, disseminatio

This chromist produces numerous sporangia on affected tissues, especially on fruits. P. capsici , like all Phytophthora , is particularly suited to aqueous media, in particular in the soil. Thus, water ensures in particular its dissemination, via flows, the pollution of water reserves, canals, even streams and rivers . Its sporangia would also be dispersed by the wind like the chromist agents of late blight. Tillage implements carrying contaminated soil particles, transporting material, infested plants and certain substrates can also contribute. It should be remembered that aerial dissemination can occur during rains or sprinkler irrigation, following splashing.

• Conditions favorable to its development

attacks P. capsici are particularly serious in very humid, poorly draining and / or over-irrigated soils, and in rainy and hot periods, with temperatures between 24 and 32 ° C. Its thermal amplitude of development would be between 8 and 37 ° C.

Heavy rainfall or too much irrigation increases the risk of the disease developing. In addition, compacted, fine-textured, poorly draining soils present favorable conditions for root rot.

The succession of wet and dry periods would stimulate the release of zoospores. Moreover, the receptivity of its hosts is not said to be constant as they grow, seedlings and young tissues often being more sensitive.