Final diagnosis


Septoria lactucae (Septoria leaf spot)

The lower leaves of this sucrine, a particularly sensitive salad, are strewn with angular and necrotic spots. <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot")
Several angular spots, delimited by veins, light brown, are the cause of partial chlorosis of the leaf blade. <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot")
The spots, delimited by veins and brown in color, are surrounded by a chlorotic halo. <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot")
Careful observation of the limbus makes it possible to distinguish tiny black structures embedded in the tissues: these are the pycnidia of the parasitic fungus. <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot")
On this leaf in section, we can clearly see a bouquet of thread-like spores gradually emerging from a pycnidia. <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot")
Pycnid of <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot") partly submerged in leaf tissue (100 to 200 µm in diameter): a bouquet of spores is released at the level of the ostiole.
The conidia produced by the pycnidia of <b> <i> Septoria lactucae </i> </b> (septoria, "<i> Septoria </i> leaf spot") are hyaline and threadlike; they show from 1 to 3 partitions. Their dimensions are variable: 25-40 x 1.5-2 µm.