RHIZOCTONIA STEM-ROT 
This disease affects a great variety of plants. It appears to have an 
extensive range, occurring both in the new and the old world, in the tem- 
perate zones and in the tropics. 
SYMPTOMS 
The symptoms vary considerably depending upon the host affected. 
Studies here will be confined to seedlings, potatoes and carnations. 
On seedlings. The disease on seedlings is often known as damping-off. 
The base of the stems are affected, sometimes also the roots. Examine 
the diseased seedlings provided and OBSERVE :— 
1. The form, size and color of the lesions. 
2. Their location on the stem with respect to the surface of the 
soil. 
3. The depth to which the lesion penetrates (cut across the stem 
through the lesion). Are any of the stems girdled? 
4. A rotting of the roots in some seedlings. 
5. In some cases, the reddish brown mycelial strands or mats of 
the pathogene in the lesions. 
The symptoms of this disease in seedlings may be those resulting 
from a stem-rot or root-rot. They vary slightly with the seedling-host 
affected. (See Illinois Bul. 189:308—337.) 
Make sKETCHES to show the symptoms of the disease as exhibited 
in the seedlings provided. 
On potatoes. A striking field-symptom is a marked unevenness in 
the stand. Many hills are wanting or the shoots are small and weak. 
If on digging up the seed-tubers, where plants have failed to come up, 
diseased sprouts are found, it is an almost certain evidence of this disease. 
Examine the specimens of diseased sprouts provided and see Maine Bul. 
230, fig. 62-67. OBSERVE :— 
6. The dark-colored canker-like lesions; their size, location on 
the sprouts and depth to which they penetrate. 
7. That some of the sprouts may get above ground before they 
are rotted off. They may even develop weak plants which grow slowly 
and persist for a time. 
8. That many of the sprouts which are rotted off send up new 
sprouts from a node below the lesion. These may in time become 
diseased and even rot off or they may produce nearly normal tops. 
Make a series of SKETCHES to show the various symptoms and effects 
exhibited by diseased potato sprouts. 
Study the older stalks of diseased plants provided. oBSERVE:— 
; 9. The necrotic lesions at the base of the stem just below the 
soil-level. In some specimens the stem is nearly rotted off. 
10. The effect of the disease as exhibited in the tops, especially 
the production of clusters of small tubers about the base of the stem at 
a surface of the soil and the production of aerial tubers in the axils of the 
eaves. 
11. The rosette-symptoms exhibited by the tops of some affected 
plants. (See Ohio Bul. 139, fig. 4; and 145, fig. 1.) 
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