POTATO-STEM LESIONS 
By H. A. Bdson, Pathologist, and M. Shapovalov, Agent, Cotton, Truck, and Forage 
Crop Disease Investigations , Bureau of Plant Industry, United States Department 
of Agriculture 
INTRODUCTION 
The brown canker-like areas occurring on the underground portions of 
the potato (, Solatium tuberosum) plants in various parts of the country 
have been attributed by many writers to the attacks of Rhizoctonia solani 
Kuhn. (Rolfs, 1 Morse, and Shapovalov, 2 Drayton, 3 and others.) On the 
other hand, Dink 4 has found that similar lesions on potato stems in 
Nebraska may be due to species of Fusarium. Observations during the 
last few years, as well as numerous isolations and inoculation experi¬ 
ments, show quite conclusively that although Rhizoctonia and Fusarium 
may constitute the two principal genera of fungi responsible for the 
injuries in question, yet at the same time there are undoubtedly several 
other organisms hitherto not connected with this trouble which are 
capable of producing similar and even macroscopically identical stem 
lesions. The relative importance and frequency of the individual mem¬ 
bers of this group may vary throughout the country with the changing 
soil, season, and climate. 
EXPERIMENTAL WORK 
ISOLATIONS 
A great number of isolations were made in the summers of 1916 and 
1917 from the material collected on various farms in northern Maine. 
Both severely injured stems and stolons and those showing only small 
individual lesions served as material for this work. The majority of the 
cultures yielded Rhizoctonia solani and Fusarium oxysporum , then fol¬ 
lowed F. discolor , Boirytis sp., Alternaria solani , Alternaria sp., Clono- 
stachys sp., Acrostalagmus sp., Sclerotinia sp. and a number of Hypho- 
mycetes which failed to show parasitism in subsequent inoculation ex¬ 
periments. Different lesions on the same plant frequently yielded differ¬ 
ent fungi and, in several instances two parasites developed in cultures 
1 Rolfs, F. M. potato failures, a preliminary report. Colo. Agr. Exp. Sta. Bui. 70, 20 p., 12 pi. 
1902. 
- POTATO FAILURES. A SECOND REPORT. Colo. Agr. Exp. Sta. Bui. 91, 33 p„ 5 pi. 1904. 
* Morse, W. J. t and Shapovalov, M. the rhizoctonia disease of potatoes. Maine Agr. Exp. 
Sta. Bui. 230, p. 193-216, fig. 61-73. 1914. Literature cited, p. 216. 
* Drayton, F. L. the rhizoctonia lesions on potato stems. In Phytopathology, v. 5, no. 1, p. 59- 
63, fig. 5, pi. 6. 1915. Literature cited, p. 63. 
4 Link, G. K. K. a physiological study of two strains of fusarium in their causal relation to 
Tuber rot and wilt of potato. In Bot. Gaz., v. 62, no. 3, p. 169-209, 13 fig. 1916. Literature cited, 
p. 207-209. 
Journal of Agricultural Research, 
Washington, D. C. 
ox 
213) 
Vol. XIV, No. s 
July 29,1918 
Key No. G-149 
