Jan. 15, 1917 
Blackleg Disease of Potato 
99 
2 or 3 inches long, were thoroughly moistened with this watery extract 
of the diseased tissues and at once planted in boxes of soil which had 
previously been thoroughly wet down. A part of the remaining watery 
extract was then poured over each box. These artificially infected tubers 
put up shoots very rapidly and on August 15, 22 days after the planting, 
one stalk began to show the characteristic signs of the disease. On the 
18th two others were also plainly affected. Examination showed only 
motile, rod-shaped organisms in the diseased tissues. Poured plates were 
made from these stems and 9 subcultures were obtained, all of which 
. proved to be pathogenic to potato tubers and stems, producing typical 
blackleg when inoculated into the latter. Some preliminary work, 
especially in the line of fermentation studies, was done with all of these, 
but one strain, designated as “IIIA,” was selected for detailed study. 
On August 12, 1908, a potato stem about 18 inches long was received 
from the University Farm, Orono, Penobscot County, which showed a 
soft, colorless decay which apparently was progressing very rapidly. The 
general appearance was decidedly different from the picture presented 
in typical cases of blackleg. The stem was affected nearly its entire 
length and there were no signs of blackening. The disease was confined 
almost entirely to the parenchyma cells of the pith within the vascular 
ring. Apparently the water conducting system had not been materially 
affected, as there was no yellowing, or other abnormalities of the foliage and 
very little signs of wilting, although one or two other stalks in the same 
hill had begun to fall over. 
The affected portion had been reduced to a pulpy, watery mass; appar¬ 
ently the middle lamella had been destroyed between the cells which 
latter, had collapsed into irregular, shapeless masses. The liquid between 
the cells was filled with large numbers of motile bacteria. From plates 
made from this stem 5 subcultures were obtained, all of which proved to 
be pathogenic to potato tubers and stems. However, in all inoculation 
tests extending over a period of eight years, typical cases of blackleg were 
produced, differing materially from the appearance of the original stem. 
One strain, marked “SE,” was studied as a representative of this type. 
In August, 1910, another series of four cultures, of which “IIP” was 
selected as a representative, were isolated from a typical blackleg stem 
received from Presque Isle, Aroostook County. 
Thus, it will be seen that the organisms which were used for the detailed 
studies were obtained from somewhat widely separated localities, repre¬ 
senting two typical cases of blackleg and a third which looked like a radi¬ 
cally different type of stem disease, characterized by a more rapid and 
much more extensive decay of the stem without the development of any 
blackening or discoloration. As will be seen later, these proved to be, 
except for slight variations in size, all of the same type as B . solanisaprus 
which was not unexpected in view of the fact that Harrison has found this 
organism of wide distribution in Canada and there is considerable reason 
