Nov. i, 1915 
Potato Tuber-Rots Caused by Fusarium Spp. 
187 
much alike, detailed accounts of the appearances presented are of doubtful 
value and are eliminated. With every rot-producing species of Fusa¬ 
rium included in the experiments the effect was essentially the same—at 
minimum temperatures, a slow dry-rot; at maximum, a very wet rot, 
with the tubers completely softened in two or three weeks. Sometimes 
in the former a mycelium-lined cavity is developed, surrounded by a 
zone of tissue appearing water-soaked—i. e., a zone of enzymic activity; 
in other tubers at higher temperatures the same organism proceeds to 
soften the tuber in a stratiform manner, the several layers reaching 
across the tuber. Bad-smelling rots did not occur with the species of 
Fusarium. Such rots associated with Fusarium spp. were found to be 
mixed infections. When Fusarium spp. per se rot potatoes, an odor 
suggesting ammonia and trimethylamin is developed. 
Rots caused by species of Fusarium are commonly spoken of as either 
“dry-rots” or “ wet-rots.” The former are a result of comparatively slow 
development at low temperatures. The experiments show that any 
of these organisms capable of causing a rot work more rapidly in an 
environment of optimum temperature accompanied by high humidity, 
the tubers developing a wet-rot (see p. 196). Upon drying out, the 
condition would be termed a “dry-rot.” The two forms grade insen¬ 
sibly into each other, so that neither term is specific. The examination 
of potato tissues rapidly softening as a result of inoculation with pure 
cultures of Fusarium spp. indicates that the middle lamella is dissolved 
considerably in advance of the fungus; the hyphae ramify between the 
cells, but do not appear to enter them at once. Ultimately the con¬ 
tents of the cells are liberated, and the starch grains become more or 
less corroded. 
It should be noted that the experimental data, revised and grouped 
under the respective organisms, were obtained through a series of experi¬ 
ments covering a period of more than a year. For example, the data 
on F. oxysporum (see p. 191) were extracted from eight different experi¬ 
ments which included several other species and show at a glance the 
comparative effect of original and reisolated strains on different varieties 
of potatoes at sundry temperatures. 
In the notes on the artificial inoculations recorded under the respective 
organisms the history of the various strains is first outlined, followed by 
a brief consideration of the results in text and tabular form. 
CERTAIN FIELD AND STORAGE ROTS OF POTATO TUBERS 
AND THEIR CAUSE 
TUBER-ROT CAUSED BY FUSARIUM OXYSPORUM AND FUSARIUM HYPER- 
OXYSPORUM 
In a study of a wilt and dry-rot of Solarium tuberosum , Smith and 
Swingle (14) attributed both manifestations to a species of Fusarium. 
After a consideration of the incomplete nature of previous descriptions 
