Final diagnosis


Pythium tracheiphilum (Pythium wilt)

In general, affected plants grow very slowly and are ultimately stunted compared to surrounding healthy plants. <b> <i> Pythium tracheiphilum </i> </b> (lettuce stunt)
<b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt") becomes established very early in the vascular system of lettuce seedlings. These subsequently show very slow growth. This salad affected by this fungus is dwarf; it contrasts sharply with the surrounding healthy and well-developed plants.
On the other hand, the pivot of this lettuce is narrower at the level of its distal part which is browner. <b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt")
This young lettuce, cut lengthwise, shows necrotic changes located in the vessels and sometimes in adjacent tissues. <b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt")
Contiguous vessels and tissues show a darker blackish tint. <b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt")
This lettuce, affected by <i> <b> Pythium tracheiphilum </b> </i> ("lettuce stunt"), shows browned vessels.
In addition to revealing vascular browning, diseased plants have a fairly reduced root system. <b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt")
<b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt") produces globular to subglobular, intercalary or terminal sporangia, varying in diameter from 22 to 34 µm.
Its oogonia are spherical, smooth-walled, often fertilized by 1 to 2 antheridia, most often monoclines (14-17 µm). They give rise to thick-walled plerotic oospores. <b> <i> Pythium tracheiphilum </i> </b> ("lettuce stunt")