CLUB-ROOT OF CRUCIFERS 
This is the best known of the slime-mold diseases of plants. It is a 
distinctly metaplastic disease, causing a marked overgrowth of the affected 
organs. It is widely prevalent both in the Old and in the New World. 
It affects most of the common cruciferous crops, especially cabbage, 
cauliflower and turnips. 
SYMPTOMS 
The roots are the only organs of the host that show lesions. The 
specimens provided exhibit the symptoms at different stages in the develop- 
ment of the disease and on different hosts. (See illustration specimens 
of the disease on various hosts.) Examine carefully the specimens pro- 
vided and OBSERVE :— 
1. The relatively small size and the much more fibrous and 
branched character of the roots of the healthy plants as compared with the 
diseased roots. 
2. The much swollen and enlarged roots of the diseased plants; 
occasional healthy roots arising from the stems above the lesion. Why? 
Determine by diameter measurements how many times the diseased root 
have been enlarged. Roots enlarged in this manner are said to be hyper- 
trophied. — 
3. That the hypertrophy occurs either in the region of the root 
next to the stem or out in the feeding-roots. 
4. That the hypertrophy involves the root in its entire diameter. 
It is not simply an outgrowth on the side of the root. 
5. The specimens of club-root on the different hosts in the illus- 
tration jars. (See also Vermont Bul. 185, pl. II-V.) Determine whether 
there is any uniformity in the shape of the swellings which may be regarded 
as characteristic of this disease. 
6. That the surface of the hypertrophied roots, especially in 
the old specimens, is much cracked and checked; to what due? These 
cracks allow the entrance of decay-producing fungi and bacteria. The 
succulent tissues quickly become soft and rotten and have a foul odor. 
The club-root pathogene itself does not cause the tissues to soften. 
7. That the root beyond the hypertrophy, the branches and fine 
feeders, seem to be normal and healthy. 
8. The abruptness with which the hypertrophy ceases at the 
base of the stem; this is a disease of the roots. 
Nodules, tubercles and galls due to other causes are often produced on 
roots of plants, as for example: the nematode-gall caused by minute 
worms; legume-tubercles and crown-gall of trees caused by pathagenic 
bacteria. (See illustration specimens in jars.) 
Make a DRAWING of a ‘“‘clubbed”’ root along side of a healthy one. Main- 
tain relative proportions. 
Where the roots are badly clubbed, the plants fail to head, or form loose 
worthless heads. Affected plants often wilt or “flag” during the heat of 
the day but recover at night. These symptoms exhibited by the tops 
can be well observed only in the field. 
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