Minnesota Plant Diseases. 



345 



Club-root of cabbage, radish, turnip and other cruciferous 

 plants (Plasmodiophora brassicae Wor.). This disease is not un- 

 common in Minnesota but the exact extent of its distribution 

 is not known. The cause of the disease is not a true fungus 

 but is a slime mold or fungus animal. It forms no fungus 

 threads but produces spores somewhat similar to those of the 

 true fungi. The spores gain entrance to the host plant, usually 

 in the root region though the parasite may also exist in the leaf. 



Fig. 179.— Club-root of turnips. 1. Strap-leaf. 2. Aberdeen. 3. Rutabaga. 4. Snowball. 

 5. Golden Ball. 6. Cowhorn. 7. Kashmyr. After Halsted. 



It lives within the host in a truly parasitic manner, destroying 

 the cells in which it dwells. It causes, however, great stimula- 

 tion of the tissues of the host, so that the latter produces wart- 

 like growths on its roots. The roots, moreover, become much 

 distorted, hence the common name of club root. The host 

 plant is much weakened by the attack and usually fails to head 

 out. The roots soon decay and thus the animal organisms, 

 which have already formed great numbers of spores, return to 



