Oct. 30, 1916 
Spongospora subterranea and Phoma tuberosa 
251 
consideration. These meager descriptions and difference in size of spores, 
coupled with the pathogenicity of this fungus on the tuber, led the 
writers to designate the organism “ Phoma tuberosa , n. sp.” 
Phoma tuberosa, n. sp. 
Lesions on tubers of Solanum tuberosum; brownish to dark gray or black; 6 to 2 5 mm. 
in diameter; sunken, membraneous, with an irregular and sharply defined margin. 
Pycnidia black, generally scattered over entire surface, subcuticular, irregular, 
subglobose to spherical, majority provided with a single well-defined ostiole, some¬ 
times breaking at several points for exudation of spore mass, varying in size from 80 to 
160 by 90 to i6oju. When placed in water the pycnospores are seen to ooze out in a 
shiny string, which soon breaks up into the individual spores. Pycnospores i-celled, 
hyalin, subglobose, 3.7 to 6 by 1.8 to 3.7 ji. Hyphae septate, dark brown in the tissues 
of the host. A definite stroma absent. 
Habitat.—Wound parasite on tubers of Solanum tuberosum often associated with the 
sori of Spongospora subterranea . First found as a storage-rot in Maine. 
SUMMARY 
(1) Spongospora subterranea exists in six different potato-growing 
sections of the United States, all northern except one. 
(2) No infections resulted on the progeny of powdery-scab-infected 
seed potatoes planted in 15 different localities along the Atlantic seaboard. 
However, 8 lots of soil out of 12 shipped from as many of these localities 
to northern Maine and planted with infected seed produced a crop showing 
powdery-scab. 
(3) Periods of damp, rainy, and cloudy weather, coupled with poor 
drainage, favor the development of S. subterranea. 
(4) Infection develops earlier on the roots than on the tubers. In 1915 
jn northern Maine 57 days elapsed between planting of infected tubers in 
virgin soil and the first signs of root infection. Infection on the tubers 
appears about the stem end first. All underground portions of the 
potato plant may become infected with S. subterranea . Galls are often 
very numerous on the root system of potato plants growing in infected 
soil, while the tubers are absolutely free from infection; hence, a clean 
root system is the criterion for determining the absence of the disease. 
(5) It is not unusual to find parts of fields in northern Maine in which 
some of the progeny of over 90 per cent of the hills are infected with 
powdery-scab. Several cases were found in which from 50 to 75 per cent 
of the 1914 crop was infected. It was found that S. subterranea may be 
spread when infected tubers are planted in virgin soil. Cultural practices 
and soil water are probably the most important agents in spreading the 
disease. 
(6) Besides the potato, there are seven other solanaceous hosts of 
S. subterranea , including the tomato, as determined by the writers. 
The disease manifests itself on these hosts in the form of large destructive 
galls on the roots, these being fully as injurious as those on the potato 
