1923] 



JENNISON — POTATO BLACKLEG bd 



General Summary 



I 



The blackleg disease of Irish potatoes in North America and 

 Europe is caused by a Schizomycete which should bear the name 

 Bacillus atrosepticus van Hall. 



The following names are to be considered only as synonyms: 

 Bacillus phytophthorus Appel, B. solanisaprus Harrison, B. me- 

 lanogenes Pethybridge & Murphy. 



The index number "5312-32120-2111" very briefly describes 

 Bacillus atrosepticus van Hall, the number being based on the 

 results of the writer's comparative studies. 1 A revised descrip- 

 tion of this organism appears on pages 43-44. 



The blackleg parasite grows best at about 26° C. It withstands 

 extremely low temperatures (-28.2 °C.) for several hours. 



This organism produces acid and a small volume of gas from 

 each of a number of sugars. The gas-producing capacity is rel- 

 atively weak, but this capacity can be built up to a certain ex- 

 tent by constant cultivation in the presence of the sugars which 

 it is able to utilize. 



The pathogen infects the vines and the tubers of the potato. 



Virulence of the parasite, as tested by artificial inoculation, 

 appears to be dependent upon a rather delicate balance of tem- 

 perature and water relations, and upon the sugar content of the 

 tissues inoculated. 



The "incubation period" varied in the experiments under ob- 

 servation and appears to be influenced by the same factors men- 

 tioned above. No definite "turning point" was observed to oc- 

 cur, as in the case of many animal diseases. 



The above conclusions are based on studies of 12 strains of the 

 potato blackleg parasite, including the 4 "species" originally de- 

 scribed as being the cause of the disease. 



The strains studied were observed to be morphologically sim- 

 ilar. That they were very much alike in their cultural charac- 

 teristics and physiology was abundantly proven by extensive 

 comparative studies (see data on p. 41). 



*See Descriptive Chart, Society of American Bacteriologists. 



