Biology, epidemiology

- Conservation, sources d'inoculum

Although the biology of Pythium tracheiphilum is not well understood, it may be thought that it is likely to live in a state saprophytic at the expense of organic matter. It seems capable of attacking or being hosted by a number of different hosts of lettuce, which also ensure its multiplication and conservation: various Lactuca , sunflower, artichoke, cardoon, salsify, fennel , peas and some weeds, including groundsel. Artificial inoculations, carried out on cucumber, cauliflower, tomato and peas, demonstrated that this pseudo-fungus could attack these hosts. The strains encountered in the field would not have the same pathogenic power with respect to these hosts. It can be maintained in the soil thanks to resistance structures , such as its oospores (figure 1) and to a lesser degree its sporangia (figure 2).


- Penetration and invasion

It penetrates the epidermal tissues certainly through wounds , then it gains the vascular system which it gradually invades, in particular the xylem. We observe in the latter the presence of mycelial filaments.


- Sporulation, dissemination

Subsequently, it produces sporangia and oospores inside the damaged tissues or on their surface. It is perfectly suited to the aqueous phase of soils. Water largely ensures its dissemination. Aerial dispersions are reported in the USA as a result of spattering of contaminated soil particles occurring during sprinkler irrigation or heavy rains. They lead to large leaf necrosis which is not observed in France.


- Conditions favorable to its development

Like many pythiaceae, its development is mainly favored by the presence of water. A high soil moisture (90% of field capacity), reduced gas exchange constitute an ecological advantage for this oomycete. The temperature influences less growth because of contamination are possible between 5 and 43 ° C . He still appreciates temperatures around 20-24 ° C. Young plants, succulent tissues, are more sensitive, which is confirmed by the often early attacks of this Pythium .