1923] 



JENNISON — POTATO BLACKLEG 15 



tilators to prevent the atmosphere from becoming saturated. 

 As nearly as practicable the temperature should be kept at 

 about 38° F. in order to check sprouting. Butler (19) has 

 shown that potatoes kept at 40° F. will sprout after about 200 

 days, while at 35° F. sprouting is delayed indefinitely. Shapova- 

 lov and Edson ('19) showed that potato tubers which are in a 

 wilted or softened condition when cut, due to the development of 

 sprouts or improper storage, are very much more likely to be in- 

 fected by fungous or bacterial parasites which exist in or may be 

 introduced into the soil. 



The seed pieces to be used for planting should be sorted and 

 only sound, rot-free tubers used. Previous to cutting they 

 should be treated in a 0.1 per cent corrosive sublimate (HgCl 2 ) 

 solution or in a 1 : 240 formaldehyde dip. If the former is used, 

 the tubers should be immersed for iy 2 hours, then more of the 

 dissolved mercuric chloride added at the rate of 1.5-2.0 grams 

 (depending upon the amount of dirt accompanying the tubers) 

 for each bushel treated. Avoid treating excessively dirty pota- 

 toes in the corrosive sublimate, and make up a fresh solution 

 after having treated 50 bushels. If the formaldehyde solution 

 is used the tubers should be immersed in the dip for about iy 2 

 hours. Undoubtedly, a less lengthy immersion would be suffi- 

 cient to kill all contaminating blackleg germs present. When 

 the pathogen is lodged internally treatments sufficient to kill 

 it would probably kill the buds also. 



When and where practicable, planting should be done late 

 enough to avoid having the crop sprout and struggle along in 

 a cold, damp soil, since it has been shown that these conditions 

 facilitate the development of the blackleg parasite. While it 

 has not been conclusively proved that the blackleg parasite does 

 not overwinter in the soil at times, it is nevertheless advisable 

 to practice rotation of the crop, since some of the worst enemies 

 of the potato accumulate in the soil and persist therein for long 



periods of time. 



Tests made by the writer show that the blackleg bacillus is 

 resistant to considerable extremes of cold. Test-tubes contain- 

 ing about 15 gms. of soil were thoroughly autoclaved and the 

 sterility of the soil carefully tested before inoculation. Finally, 

 a series of cultures thus prepared were inoculated with a freshly 

 invigorated strain of the organism and placed out of doors for 24 



