Dec. 10, 1913 
Foot-Rot of the Sweet Potato 
257 
Most of the inoculations were made in the greenhouse, principally 
because they were performed in the winter. One set, however, which 
was conducted in the field, gave results so similar to those in the green¬ 
house that it was not possible to distinguish between them in any essen¬ 
tial details. The plants for inoculation were obtained from sound pota¬ 
toes carefully selected for the purpose. They were grown in pots of 
sterilized soil and kept far enough apart to prevent accidental infection 
from watering and overlapping of the vines. Only strong, vigorously 
growing plants were inoculated, all others being thrown out. That 
there was probably no accidental infection is shown by the fact that 
not a single check in the whole series of inoculations became diseased. 
Inoculations in the Field 
Experiment No. i. —On August 26, 10 sweet-potato plants, the vines being about 
3 feet long, were inoculated 1 on the Potomac Flats near Washington, D. C., by insert¬ 
ing pycnospores and hyphae of organism No. 102 (culture No. 1 of Aug. 15) into the 
lower part of the stem. Ten plants pricked with a sterile needle were used as checks. 
Results.—On September 18 all the inoculated plants were infected, 2 the plants 
turning yellow, and the lower leaves dropping off. The periphery of the stem for 3 
to 5 inches above the ground was black, and pycnidia were abundantly formed thereon. 
The stems were blackened throughout, but attempts to isolate the fungus from the 
fibro-vascular bundles gave negative results. None of the checks were diseased. The 
infected plants were all lifted on October 10, taken to the laboratory, and examined. 
Pycnidia were present on all. On October 12 cultures were made from seven of these 
plants, and the organism recovered 3 in each case. 
Inoculations in the Greenhouse 
Experiment No. 2.—On August 26, 1912, 10 young sweet-potato plants in pots 
were inoculated with organism No. 100 (culture No. 8 of Aug. 15) by inserting 
pycnospores and hyphae into the stem at the soil line. Five plants pricked with a 
sterile needle were left as checks. 
Results.—On September 16 four plants, on November 14 one, and on November 
25 three, or a total of eight plants, were infected. None of the checks were diseased. 
Pycnidia were formed on all the diseased plants and the organism recovered from 
three. The experiment was terminated December 2, 1912. 
Experiment No. 3.—On November 13 ten young sweet-potato plants in pots were 
inoculated as in experiment No. 2 with organism No. 101 (culture No. 9 of Oct. 31). 
Six plants pricked with a sterile needle were left as checks. 
Results.—On December 14 one plant, on December 18 three, on December 21 one, 
on December 26 one, on December 30 two, and on January 10 two, or a total of ten 
plants, were infected. Pycnidia were present on eight plants when lifted and devel¬ 
oped on the other two after two days in a moist chamber. All the checks remained 
healthy. The experiment was terminated January 17, 1913. 
1 All inoculations recorded in this article, unless otherwise stated, have been made from cultures grown 
on sterile moistened corn meal and only when spores were exuding from the pycnidia. 
2 By “ infected” is to be understood the stage when the plant began to wilt and die. It was generally 
quite evident some days earlier that the plants were infected, although they were not so recorded until 
this stage was reached. 
3 No attempt has been made to recover the organism from all diseased plants. Occasionally, however, 
the fungus was recovered from infected plants in order to compare it with the original strain, or for the 
purpose of inoculating it into other plants. 
