22 Diseases of Greenhouse Crops 



Parasitic Soil Fusaria 



Next in importance to Rhizoctonia is a group of 

 fungi which belong to the genus Fusarium. Soils 

 infected with these species of fungi become unfit 

 for tomatoes, sweet peas, etc., thereby causing great 

 financial losses to the greenhouse man. Individual 

 difficulties will be taken up in studying each of these 

 crops separately. As an illustration of a typical 

 Fusarium sick soil let us consider the wilt of sweet 

 pea. The cause of this trouble is a soil inhabiting 

 fungus, Fusarium lathyri Taub. 



Symptoms. The first symptom of the disease is a 

 sudden flagging of the leaves, accompanied by gen- 

 eral wilting and collapse of the seedling. Usually 

 upon sowing the seeds a fair percentage germinate 

 and reach the height of about 8 to lo inches before 

 they are attacked by the fungus (fig. 7, b.). If the 

 collapsed seedlings are allowed to remain on the 

 ground, the stems will soon be covered with the 

 sickle shaped spores. Eventually the decayed tis- 

 sue rots and is soon invaded by small fruit flies 

 which now begin to distribute the fungus from place 

 to place by carrying its spores. 



The Organism. The mycelium of Fusarium 

 lathyri is hyaline, septate and branched. At an early 

 age the mycelial cells round up into countless num- 

 bers of chlamydospores. Old cultures are practically 

 one mass of these resting bodies. The spores are of 

 two sorts, the macroconidia which are sickle shaped, 



