PARASITISM OF SCEEROT1UM ROLFSII ON IRISH 
POTATOES 1 
By H. A. Edson and M. Shapovaeov, Pathologists , Office of Cotton, Truck, and Forage 
Crop Disease Investigations, Bureau of Plant Industry, United States Department of 
Agriculture 
INTRODUCTION 
According to various published statements Scleroiium rolfsii Sacc. 
attacks a great number of hosts. 2 It has been frequently reported on 
the Irish potato, though a clear and full description of the symptoms of 
its effect upon this host has not yet been given. Sometimes the disease 
has been designated as blight, in other cases as wilt, and very little has 
been said about the tuber-rot. The type of the decay, as distinguished 
from other tuber decays, has not been satisfactorily defined, and the 
mode of the destruction of the host cells has not been followed in detail. 
In view of this scarcity of information the writers feel justified in present¬ 
ing certain of their observations and experiments relative to this subject. 
NATURAL INFECTION 
Both the vine and the tuber of the Irish potato may be attacked by 
this fungus. The disease of stem and foliage may manifest itself in 
several different forms which vary with the age of the plant and with 
the environmental conditions. If very young plants are attacked and 
the soil moisture is abundant, they are most likely to show damping-off 
symptoms. Older plants may suffer from a rootrot or a stemrot or 
from both w T ith subsequent wilting and drooping of the leaves and the 
stems, which ultimately lie prostrate on the ground. (PI. i, A.) 
Natural infection in the field was observed in the South in advanced 
stages in several States. The symptoms produced were in general those 
of wilt or stemblight. The disease had evidently made its attack at 
or near the surface of the soil, causing a decay of the stem at that point 
and for a little distance above and below. Frequently the stem was 
consumed below to such an extent that little of the underground tissues 
except a few strands of vascular fiber remained attached if the tops 
were lifted. Wefts of mycelium or the sclerotia of the fungus could be 
seen clinging to the stem or extending radially from the plant in and on 
the surface of the soil. 
ARTIFICIAL INOCULATION 
To obtain further evidence in regard to the symptoms of the disease 
certain field experiments were conducted with artificially inoculated 
tubers. These experiments were carried on in 1919 and 1920 at Arlington 
1 Accepted lor publication July 2, 1921. 
a Taubenhaus, J. J. recent studies on sclerotium RotFsn sacc. In lour. Agr. Research, v.iS, 
no. 3, p. 127-138, 1 fig., pi. 3-6. 1919. Literature cited, p. 137-13& 
Journal of Agricultural Research, 
Washington, D. C. 
ar-x 
Vol. XXIII, No. r 
Jan 6. 19.-3 
O-261 
( 41 ) 
