312 ■ Maine Agricultural Experiment Station. 1917. 



the stem with great rapidity. The attacked plants usually pre- 

 sent a characteristic appearance in the field. If the progress of 

 the disease is slow they are more or less unthrifty and under- 

 sized, and have a more compact, upward growing habit than 

 normal, turning first lighter green then yellow and finally dying. 

 If the progress of the disease is rapid the plant may fall over 

 suddenly without much previous signs of disease. 



A soft rot of the tubers is also produced. Infection takes 

 place in the hill by means of the disease following along the 

 stolons from the stem to the base of the tuber. 



Blackleg has been observed in Germany, France, Belgium, 

 Holland, England, Ireland, Canada and the United States. It 

 was first reported in the United States in 1906 and in Maine 

 in 1907. Evidence is given to show that it was introduced into 

 and widely disseminated in the United States by means of in- 

 fected seed potatoes. 



Most writers on the subject have emphasized the economic 

 importance of the disease. While blackleg is by no means un- 

 important, judgments based on observations made in Maine 

 would indicate that its destructiveness has been overestimated. 

 This more particularly applies to the losses occasioned by tuber 

 decay caused by the blackleg organism, which have undoubtedly 

 been confused with those primarily due to other causes. 



At the same time the evidence is conclusive that in Maine 

 the disease does not live over winter in the soil and that infected 

 seed tubers are the sole source of infection and means of dis- 

 tribution of blackleg. 



Successful methods of control have been worked out, which 

 depend upon the elimination of all diseased or imperfect seed 

 tubers and then disinfecting the remainder with corrosive sub- 

 limate or formaldehyde. 



The aim of the bacteriological investigation was to secure 

 cultures of all named pathogenic organisms previously described 

 in Europe and America as the cause of blackleg and, in com- 

 parison with like cultures obtained from diseased plants in Maine, 

 subject them to the same tests, at the same time, under identical 

 conditions. This work resulted in the conclusion that Bacillus 

 atroscpticiis van Hall, Bacillus solanisaprus Harrison and Bacil- 

 lus melanogenes Pethybridge and Murphy were identical with 

 each other and with the organisms obtained from diseased plants 



