Pea Diseases 167 



Diseases of the Pea 



Indoor peas may become subject to several dis- 

 eases. 



ScLEROTiNiA TOt (fig. 33), See Lettuce drop, p. 

 150. 



Thielavia Root Rot 



Caused by Thielavia hasicola Zopf. 



Symptoms. Plants severely infected with Thiela- 

 via have practically no root system, for the latter is 

 destroyed by the fimgus as rapidly as they are 

 formed. All that is left is a charred, blackened stub. 

 The diseased host constantly attempts to produce 

 new roots above the injured part, but these in turn 

 become infected. Such plants linger for a long time, 

 but fail to set pods which are of any value. 



The Organism. The mycelium of Thielavia hasi- 

 cola is hyaline, septate, and branched. The Myce- 

 lium becomes somewhat gray with age. Three kinds 

 of spore forms are produced — endospores, chlamy- 

 dospores, and ascospores. The endospores are so 

 called because they are formed inside a special thread 

 of the mycelium. This is the spore form that com- 

 monly occurs in pure cultures of artificial media 

 and on the host. The endospore case is formed on 

 terminal branches with a somewhat swollen base 

 and a long tapering cell. The endospores are formed 

 in the apex of this terminal cell and are pushed out 

 of the ruptured end by the growth of the unfrag- 



