A NEW STRAIN OF RHIZOCTONIA SOLANI QN THE 
POTATO , . 
By J. Rosenbaum, Mycologist, and M. Shapovalov, Agent, Cotton, Truck, and 
Forage-Crop Disease Investigations, Bureau of Plant Industry, United States Depart¬ 
ment of Agriculture . 1 
INTRODUCTION 
t 
Investigators heretofore have spoken of strains of Rhizoctonia solani 
Kuhn when referring to cultures isolated from different hosts as well as 
to different isolations from the same host. Thus, Duggar 2 states 
(P- 423 ): 
The potato is the most interesting of the host plants with respect to the parasitism 
of Rhizoctonia by reason of the many types of disease induced under diverse condi¬ 
tions. The conditions may be in part climatic and, in part perhaps, dependent upon 
the pathogenicity of the particular strain of the fungus ... 
He further states (p. 442): 
Strains do occur, however, evidence of which may persist for some time in the 
general appearance of the cultures. 
Edson 3 says— 
Much confusion exists regarding the identity of the various forms, and there is like¬ 
wise great diversity of opinion as to the pathogenic properties of the members of the 
group. 
Thus, while it is recognized that differences do exist, it has not been 
shown that it is possible to distinguish the different strains, especially 
from cultures obtained from the same host, either from their morphology 
or their growth on various media. Thus, Peltier 4 makes the following 
statement: 
. . . hence, on the measurement of the mycelial cells of Rhizoctonia Solani t as on 
the study of the growth on media, no conclusions can be based in regard to the dis¬ 
tinguishing strains of this difficult species. 
The purpose of this paper is to present evidence that two strains of 
R. solani are found on the potato (Solanum tuberosum ), and, further, that 
it is possible to distinguish these with accuracy from the macroscopic 
growth on various media, as well as by the more accurate morphological 
comparisons. 
1 The writers are indebted to Dr. H. A. Edson, of the Office of Cotton, Truck, and Forage-Crop Disease 
Investigations, for advice and suggestions during the progress of this work. 
2 Duggar, B. M. Rhizoctonia crocorum (Pers.) DC. and R. solani Kuhn (Corticium vagum B. & C.), 
with notes on other species. In Ann. Mo. Bot. Gard., v. 2, no. 3. p. .403-45*. 9 fig- 1915- Bibliography,, 
p. 452-458. 
1 Edson, H. A. Seedling diseases of sugar beets and their relation to root-rot and crown-rot. In Jour. 
Agr. Research, v. 4. »o. 2, p. 151. 1915. 
« Peltier, G. L- Parasitic Rhizoctonias in America. Ill. Agr. Exp. Sta. Bui. 189, p. 372. 1916. 
Journal of Agricultural Research, 
Washington, D. C. 
ib 
V0I.IX, No. 12 
June 
Key No. G—114 
(4*3) 
