Nov. i, 1915 
Potato Tuber-Rots Caused by Fusarium Spp . 
199 
than the parenchyma and are darker in color, sometimes almost black. 
In this stage the condition might be mistaken, and probably has been in 
the past, for stem-end ring disease caused by F. oxysporum or VeriicUlium 
albo-atrum , or for one phase of net necrosis (10,p. 14), which it more closely 
resembles. By the culture method, however, a species of Fusarium is 
invariably obtained from such tubers at the border of diseased and healthy 
tissues. The name “Fusarium eumartii ” is proposed for this fungus. 
In the more advanced stages of rot caused by F. eumartii the end of the 
tuber or the entire tuber is involved (PI. XVIII). According to the humid¬ 
ity and other environmental conditions, the rot is (1) soft and light-brown or 
(2) dry, corky to friable, and dark-brown to almost black. In general, the 
rot proceeds uniformly as a sharply differentiated layer easily removable 
when moist, but close-clinging when dry. In field material the bundles 
are often discolored as above noted, in advance of the rot. Attempts to 
isolate the organism from the tips of such bundles usually failed. In the 
experiments the rot is preceded by a moist water-soaked zone of enzymic 
activity, from the border of which no organism was obtained. No diffi¬ 
culty was experienced in isolating F . eumartii from the border of the dis¬ 
colored tissue and the watery zone. 
Considerable care is necessary to differentiate this rot from the one 
caused by the closely related F. radieicola . Sometimes the determination 
is to be decided only by the careful preparation and study of high cul¬ 
tures. The morphological differences between F. eumartii and F. radi- 
cicola are discussed on page 205. 
F. eumartii is chiefly a stem-end and wound invader, but under favor¬ 
able conditions the lenticels become infected. The fact that F. oxysporum 
was sometimes obtained in association with this fungus and the further 
fact that this disease of the tubers is reported on plants described as 
having symptoms of wilt suggest the probable relationship of F. oxy¬ 
sporum to the trouble. A field study of wilt and the relation of F. 
oxysporum to such field rots and storage rots should throw considerable 
light on the problem. 
Attempts to isolate an organism from a type of stem-end necrosis 
similar to mild cases of invasion with- F. eumartii often failed. There 
seems to be a sterile necrosis of the stem end, accompanied by browning 
of the parenchyma and bundles, which is related to the disease described 
as net necrosis (10, p. 14, pi. 2). Sometimes this type of stem-end necrosis 
can be distinguished from slight infection with F. eumartii only by the 
culture method; but when the minute ramifications of the vascular ducts 
are discolored, resulting in the characteristic phase of net necrosis, it can 
not be confused with the new type of rot. 
This rot was obtained chiefly in Pennsylvania, the following localities 
representing its known distribution: Tower City and Orwigsburg, 
Schuylkill County, Pa.; Fast Greenville, Montgomery County, Euclid, 
