Nov. i, 1915 
Potato Tuber-Rots Caused by Fusarium Spp . 
185 
author is convinced that in many cases the only sure way to determine 
the cause is by cultural studies. In general, specimens of the types of 
rot developed spontaneously in the field or storage are more character¬ 
istic than those produced by inoculation and developed under uniform 
conditions. 
The powdery dry-rot with pink-mycelium-lined cavities caused by F. 
trichothecioides is quite characteristic and not easily confused with the 
others; the same is true of the rot produced by F. discolor , var. sulphu- 
reum, with its ocherous yellow mycelium, buttherot caused by F. coeruleum t 
in its typical form with external dark-blue mycelium masses and internal 
blue coloration of the tissues, may be easily confused with some of those 
herein described unless mature spores are found on the specimen or high 
cultures are obtained. On some tubers more than one of the wound- 
parasitic types of Fusarium are present; in others, the diagnosis is com¬ 
plicated by the secondary action of bacterial and fungous saprophytes. 
While the author can in typical cases determine the cause of Fusarium 
rot without the preparation of cultures, the latter is not infrequently the 
safer method. Our inability to differentiate surely the various rots ma- 
croscopically complicates the attempt to differentiate them as types 
caused by specific organisms. 
METHOD OF TESTING PARASITISM 
The method employed to demonstrate the wound-parasitic nature of 
species of Fusarium will be outlined in detail before proceeding with the 
discussion of the several types of tuber-rot and the inoculations with the 
causal organisms. 
Sound tubers as free from skin diseases as possible were selected from 
the following varieties of potatoes: Burbank, Netted Gem, Early Rose, 
Idaho Rural, Jersey Peachblow, People's, and Pearl grown at Jerome, 
Idaho, in 1913 and 1914 and each year kept in cold storage at Washing¬ 
ton, D. C., until needed; Irish Cobbler grown in Maine in 1913 and kept 
in storage through the winter; Green Mountain grown at Arlington, Va., 
in 1914 and used soon after harvesting. 
The selected tubers were washed and disinfected in a solution of 0.5 
per cent of formalin, in the majority of the experiments for half an hour, 
and rinsed in distilled water. Some tubers taken at random were 
wounded with a large platinum needle, dipped in distilled water, imme¬ 
diately wrapped in waxed paper, and placed in disinfected Altmann incu¬ 
bators. Other tubers were similarly wounded, dipped in distilled-water 
spore suspensions of the organism to be tested, wrapped, and placed 
with the controls. 
By this method there are chances for secondary invaders, but the used 
organism is primarily the predominating one. In addition to the con¬ 
trol tubers, in every case reisolation, identification in pure culture, and 
