THE RHIZOCTONIA DISEASE OF POTATOES. 21 3 



pitted were used. Three of each lot were disinfected with for- 

 maldehyde before planting in the pots of sterilized soil. The 

 untreated tubers in each case produced potatoes covered with 

 sclerotia, some of them seriously deformed, some russeted and a 

 part showed the "little potato" characteristics of the disease. 

 The disinfected tubers produced a crop nearly free from 

 sclerotia and free from other characteristics of the disease 

 except for some slight russeting of the tubers. 



A number of different tests were made where a consider- 

 able number of medium sized sclerotia were removed from 

 the surface of potatoes and soaked for one hour in i to i,ooo 

 and I to 2,000 corrosive sublimate and i to 240 and i to 480 

 of 40 per cent formaldehyde. In no case did any of these 

 sclerotia germinate on being transferred to plates of potato 

 agar after first being rinsed in distilled Avater, Avhile untreated 

 sclerotia soaked in pure water for an equal length of time grew 

 vigorously in every instance. 



Lime has been recommended for treating soil for Rhizoc- 

 tonia but this was not found to be successful by Rolfs. To 

 test this in the greenhouse under control conditions 12 pots of 

 sterilized soil were planted with clean tubers. Lime was added 

 to 6 of them at the rate of 3,000 pounds per acre. Previous to 

 planting a mass of the fungus from a pure culture was placed 

 in the soil in each plot just below the seed tuber. Two different 

 strains of Rhizoctonia were used, one isolated the year before 

 and one recently obtained. 



Two of the tubers in the lime pots failed to grow and en- 

 tirely decayed. The remainder produced a crop no better than 

 that where the lime had not been applied. In all cases the new 

 tubers were small, deformed, blackened or browned at the stem 

 end, and more or less russeted. The potatoes were more seri- 

 ously affected where the more recently isolated strain of the 

 fungus was introduced into the pots. 



Economic Importance of the Rhizoctonia Disease of 

 Potatoes. 



A large part of the foregoing discussion has been based 

 upon observations made on one field with one variety of pota- 

 toes. Also most of the greenhouse experiments were made with 



