Soil Sickness Due to Parasites 45 



a guide to the trucker and gardener, we shall consider 

 two typical soil diseases, one which produces root 

 rot, the other wilt only. 



ROOT ROT 

 Caused by Rhizoctonia solani Kuhn. 



This fungus is of great economic importance be- 

 cause of its widespread distribution. It is capable 

 of producing a damping off on a variety of seedlings, 

 as well as of attacking older and mature plants. 



Symptoms. The symptoms of Rhizoctonia wilt 

 do not differ materially from those produced by 

 Pythium de Baryanum. On older plants however 

 Rhizoctonia produces cankers or deep lesions which 

 are very characteristic (fig. 6 a). These are formed 

 on the roots as well as on the base of the stem. 

 The lesions are reddish brown and extend into the 

 cortical or vital layer as well as into the woody tissue. 

 There is perhaps no other parasitic fungus which is 

 so widespread and capable of attacking such a vari- 

 ety of hosts as Rhizoctonia. The work of Peltier 1 

 shows that the following truck crops are susceptible 

 to Rhizoctonia: Beet, bean, cabbage, cauliflower, 

 celery, cowpea, cucumber, cress, eggplant, horse- 

 radish, lettuce, muskmelon, okra, pepper, radish, 

 squash, sweet potato, garden pea, parsnip, potato, 

 and tomato. 



The Organism. In 1828 Duhamel described Rhi- 



* Peltier, G. L., Illinois Agr. Expt. Sta. Bui. 189: 283-391, 1916. 



