1923] 



JENNISON — POTATO BLACKLEG 



25 



Some experiments on the pathogenicity of the potato black- 

 leg parasite performed at later dates furnish further proof of the 

 pathogenicity of the strains under observation, and will be re- 

 ported here. A brief survey of the results obtained in one of 

 these experiments (II of 7/21/17) appears in tabular form be- 

 low (table n). Tubers of the Russet Burbank variety were 

 used. They had been kept in storage nearly a year. The tubers 

 were washed and disinfected in the manner described previously. 

 A number of selected tubers were then cut into seed pieces, each 

 weighing 2 to 3 ounces. Three seed pieces were then inoculated 

 with each of the several strains of the organism at hand. Two 

 were planted in pots, the third being placed in a moist chamber 

 kept at room temperature (20-24° C.) 



TABLE II 



PATHOGENICITY OF STRAINS OF B. 



ATROSEPTICUS EMPLOYED 



Strain 



Pathogenicity to seed pieces 



Pathogenicity to seed pieces 



No. 



planted in soil 



kept in moist chamber 



160.1 



Positive (sprouts involved) 



Negative (no infection, piece dry) 



170.3 



Positive (no sprouts) 



Negative (^no infection, piece dry) 



180.2 



Positive (no sprouts) 



Positive (black rot) 



183.2 



Positive (no sprouts) 



Positive (black rot) 



187B.1 



Positive (no sprouts) 



Negative (no infection) 



191. 



Negative (sprouts) 



Negative (non-pathogenic) 



193. 



Positive (sprouts) 



Positive (black rot) 



194. 



Negative ( sprouts) 



Positive (black rot) 



195. 



Negative (sprouts) 



Negative (no infection) 



196. 



Positive (no sprouts) 



Positive (black rot) 



197. 



Negative (one sprout) 



Positive (black rot) 



201. 



Positive (no sprouts) 



Negative (no infection) 



Evidently all the strains used were still virulent. 



Among other things this experiment shows that the black- 

 leg organism may destroy infected seed pieces before sprouts 

 develop. In other cases the infectious material may be rendered 

 inocuous or even killed by drying and by other agents. These 

 conclusions are emphasized by experiments performed and re- 

 ported above. 



An experiment begun in August, 1917, showed that the strains 

 previously listed were pathogenic to potato tops; that is, all in- 

 troduced artificially gave rise to typical blackleg lesions in the 

 stems and in leaf petioles. 



A series of experiments was planned during the summer of 

 1917 in order to throw light on the question of whether potatoes 

 planted in a soil contaminated with the blackleg parasite would 



