SEPTORIA LEAF-SPOT OF CELERY 
This disease is often called late blight in contradistinction to the 
early blight or Cercospora leaf-spot. Both of them will affect the plant 
while it is still in the seedling-stage, but the Septoria leaf-spot is usually 
most severe later in the season. Both diseases are very destructive to 
the celery-crop. 
SYMPTOMS 
This disease is found on all parts of the plant above the surface of the 
soil. 
On the leaves. Examine specimens of both dried leaves and those 
preserved in liquid. OBSERVE:— 
1. The numerous spots scattered over the leaf, both on the upper 
and lower surface. Do the lesions extend through the leaf? 
2. That the spots are irregular in outline and often coalesce 
with neighboring spots. Do the spots have any definite zones surrounding 
them as found in lesions on strawberry or beet leaves? 
3. That each spot is marked with a large number of black 
papilla-like bodies,—the fruit-bodies of the pathogene. 
Make a pRaWING of a diseased leaf. 
On the stems provided, OBSERVE :— 
4. The small brown sunken areas, which also show the black 
fruit-bodies. DRAW. 
On the seed. If specimens of diseased seed-capsules are not provided, 
see Zeitschrift far Pflanzenkrankheiten 20:7.1910; or Michigan Special bul. 
77:4. COPY. 
ETIOLOGY 
The pathogene is Septoria Petroselina Desmazieres var. Apiz Briosi 
and Cavara. 
Life-history. Only the conidial form of the pathogene is known. 
In this form it is able to survive the winter, hence a sexual stage, if it does 
exist, is probably of little importance in the perpetuation of the fungus. 
The Primary Cycle has its beginning with infection by the conidia 
which are present in the debris of last-years crop, or with those which 
are found on the seed. 
Pathogenesis. Crush in water several of the small black pycnidia 
from old leaves, cover and OBSERVE :— 
5. The thin long cylindrical spores, slightly curved and tri- 
septate. (Staining with iodine may be necessary to make the septation 
evident.) 
These spores are blown about or spattered to the outer, lowest leaves 
of the celery, where they germinate, sending germtubes through either the 
upper or lower epidermis. The mycelium which is usually intercellular, 
soon forms pycnidia. 
Cut thin cross-sections of a diseased spot or use prepared slides and 
under the high-power, OBSERVE :— 
6. The large thick-walled pycnidium, which ordinarily is nearly 
globose but in the sections may be flattened or dented. Does it set 
deeply into the tissues? 
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