Final diagnosis


Bremia lactucae (mildew)

On this young plant, the well-evolved spots have an intense yellow color and eventually necrosis. <b> <i> Bremia lactucae </i> </b> (downy mildew)
The spots expand and merge if conditions are very favorable. Ultimately, large areas of the limbus are affected. <b> <i> Bremia lactucae </i> </b> (downy mildew)
On this leaf, we can clearly see the possible development of late blight spots on young seedlings. They are initially pale green, then they gradually take on a yellow tint. There is also a discreet white down on the surface of the blade. Their outline is generally delimited by the ribs. <b> <i> Bremia lactucae </i> </b> (downy mildew)
This young lettuce shows several chlorotic spots on the lower leaves. <b> <i> Bremia lactucae </i> </b> (downy mildew)
The lower and middle leaves of this lettuce are covered with yellow and / or necrotic spots. <b> <i> Bremia lactucae </i> </b> (downy mildew)
The yellow spots are more visible on the upper surface of the leaf blade. They can be located in the limbus or at its periphery. <b> <i> Bremia lactucae </i> </b> (downy mildew)
By detailing this spot more closely, we note that it is angular and elongated and that it seems delimited by the veins. <b> <i> Bremia lactucae </i> </b> (downy mildew)
On the lower surface of the leaf blade, the spots are more diffuse and less marked. <b> <i> Bremia lactucae </i> </b> (downy mildew)
By turning the diseased leaves, one can easily observe the fruiting bodies of this oomycete which appear in the form of a more or less white down. <b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew)
The sporulation of <b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew) is clearly visible under this salad leaf.
This salad has several yellow spots distributed especially on the lower leaves. <b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew)
<b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew) on this salad base.
Mildew spots often initially have a pale green to yellow tint, and are rather delimited by veins. <b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew)
As the mildew develops, the spots gradually necrotize and take on a brownish tint. <b> <i> Bremia lactucae </i> </b> (salad mildew, downy mildew)
The more chlorotic spots are also delimited by the veins. <b> <i> Bremia lactucae </i> </b> (downy mildew)
Intense sporulation covers the spots on the underside of the leaf blade. <b> <i> Bremia lactucae </i> </b> (downy mildew)
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Under certain conditions, downy mildew sporulation can occur abundantly on both sides of the leaf blade as is the case on these young leaves. <b> <i> Bremia lactucae </i> </b> (downy mildew)
The shrub sporangiophores of <b> <i> Bremia lactucae </i> </b> (downy mildew) emerge through the stomata. They have rather spherical sporangia at the end of sterigmas.
<b> <i> Bremia lactucae </i> </b> (downy mildew) produces shrubby sporangiophores with mainly dichotomous branching, carrying at the end of sterigmas rather circular sporangia whose diameter ranges from 12 to 30 µm in diameter.
<b> <i> Bremia lactucae </i> </b> (downy mildew) is a heterothallic fungus; two sexual types exist (B1 and B2). Their meeting leads to the formation of spherical oogons with a thick wall. These structures are rarely found in nature on plant debris.
In damaged tissue, brown oospores are sometimes observed 27–30 µm in diameter. They ensure the sexual reproduction of this heterothallic fungus. <i> <b> Bremia lactucae </b> </i> (downy mildew)