A FORM OF POTATO DISEASE PRODUCED BY 
RHIZOCTONIA 
ByGhEN B. Ramsey , 1 
Assistant Plant Pathologist , Maine Agricultural Experiment Station 
What appeared to be an undescribed type of potato-tuber disease was 
observed a few years ago in southern Maine for the first time. Material 
from this region has been available for study during the present winter 
(1917). While there is no reason to think that it does not occur in other 
parts of the State, the writer has not seen any noticeable cases of this 
trouble in northern Maine, although all of the summer of 1916 was spent 
in the study of potato (Solarium tuberosum) diseases in Aroostook County. 
This type of trouble was first recorded in Maine by Mbrse and Shapo¬ 
valov. 2 Moreover, after examining a considerable number of potatoes 
received from various parts of the country as illustrating different types 
of potato-scab, they were led to make the following statement relative to 
this form of potato-tuber injury mentioned above: 
A critical examination of potatoes from a large number of sources, including those 
from other States, has convinced the writers that it is fairly common. 
While several authors have mentioned scabbing, pitting, cracking, and 
ulcer formation more or less in association with Rhizoctonia, so far as the 
writer has been able to ascertain, with the exception of the publication 
mentioned above, no other references have been made in the literature to 
this type of scabbing or pitting, or, as the writer has chosen to call it, 
“dry core'’ of the potato tuber. Probably one of the nearest references 
to this type of trouble was made by Rolfs 8 in his description of an experi¬ 
ment with Rhizoctonia. He placed small amounts of hyphse from pure 
cultures of the fungus on the surface of small growing potatoes Und 
covered them with sterilized grafting wax. Fourteen days afterward two 
of these potatoes were examined, and a number of brown spots were 
found on the inoculated surfaces. Microscopic examination showed that 
the hyphae had entered the lenticels and produced small ruptures in the 
skin. Further on he states that all of the inoculated tubers developed 
rough surfaces and cracks, but nothing was mentioned that would lead 
1 Thanks are due to Dr. W. J. Morse for materials and for valuable suggestions in formulating this 
paper. 
2 Morse, W. J. ( and Shapovalov, Michael. The Rhizoctonia disease of potatoes. Maine Agr. Exp, St a. 
Bui. 230, p. 206. 1914. 
8 Rolfs, F. M. Potato failures. A preliminary report. Colo. Agr. Exp. Sta. Bui. 70, p. 11. 1902. 
(421) 
Journal of Agricultural Research, 
Washington, D. C. 
ik 
Vol. IX, No. ia. 
June 18,1917 
Key No. Me.—10 
