Nov. i, 1915 
Potato Tuber-Rots Caused by Fusarium Spp. 
195 
from that produced by F. coeruleum and other species * * *. In tubers with the 
jelly-end rot F. orthoceras is often, but not always, associated with such fungi as F. 
radicicola, Mycosphaerella solani , Sporotrichum fiavissimum Lk., Rhizoctonia, and also 
with bacteria. 
Concerning F. radicicola , he says (p. 258): 
It is often isolated from Irish potato, especially from dry tubers affected with stem- 
end dry rot. Sometimes it is associated with other organisms, but frequently seems 
to invade the tuber from the stolon before a cork layer has been formed * * *. Its 
presence in the sweet potato suggests that it might require a higher optimum tempera¬ 
ture than its related species, such as F. solani and F. martii. 
F. radicicola , F. oxysporum , F. moniliforme Sheldon, and Rhizoctonia 
sp., together with various saprophytic fungi and bacteria, were isolated 
by the writer from jelly-end rots from Watsonville and Moorland, Cal. 
F. orthoceras , Mycosphaerella solani , and Sporotrichum -fiavissimum were 
not obtained from such tubers. 
F. radicicola was most frequently obtained from typical “jelly-end” 
tubers from California and Idaho. Its ubiquitous nature and its be¬ 
havior in all of the inoculation experiments support the view that it is 
one of the fnost important causes of this disease. The relation of this 
species to other tuber rots is discussed in the paragraph on dry-rot. 
The prevalence in California of wilt caused by species of Fusarium and 
the frequency with which F. oxysporum was isolated from jelly-end rot 
suggests the fundamental relationship of this species to the disease. F. 
oxysporum was isolated and identified 24 times from jelly-end rot and 
stem-end dry-rot tubers from California alone. While often associated 
with bacteria and fungus saprophytes, in most of these cases it was 
the only organism secured from the respective tubers which could be 
regarded as the cause of the condition. It was freqently present in pure 
culture at the border of rotting and healthy tissues. Whether unaided 
it produces jelly-end rot under field conditions is not known. A potato 
tuber Jtrom California was diagnosed as ring disease and placed in the 
incubator. After a period of two months at an average temperature of 
18.36° C. a typical jelly-end rot had developed. F. oxysporum was the 
only organism secured from the interior of this tuber at the border of 
healthy tissue. The inoculation experiments with F. oxysporum sup¬ 
port the view that it is capable of producing jelly-end rot. F. radicicola 
and F. oxysporum were also isolated, though not necessarily in associa¬ 
tion, from rot areas on the side of tubers resulting from wounds and 
lenticel invasion. 
DRY-ROT 
F. radicicola as a cause of stem-end dry-rot was first obtained in 
August, 1913, from some tubers submitted from Grassfield, Va. Its 
widespread occurrence in stem-end dry-rotting tubers may be judged 
from the following distribution: Hermiston, Oreg.; Watsonville and 
Sonora, Cal.; Fallon, Nev.; Ocean Springs, Miss.; Jerome, Idaho; Honeove 
