Sept, i, 1931 
Transmission of Some Wilt Diseases in Seed Potatoes 845 
tubers not affected by rot lead one to suspect that the appearance of the 
trouble depends more on climatic conditions than it does on the presence 
of any one of two or three organisms. 
It seems possible and perhaps probable that when moisture in the 
soil is deficient in the latter part of the growing season, as it frequently 
is in western Oregon, and the transpiration of the plant is relatively 
excessive during hot weather the plant might, as sometimes occurs in 
fruits (j), actually withdraw water from the stem end of the tuber, 
giving a sunken withered condition favorable to the entrance of various 
organisms both parasitic and saprophytic. There might then be a 
gradual progress from this condition to typical jelly endrot, and in 
each case the condition of the tuber at harvest time would perhaps 
depend on the particular conditions surrounding it during growth and 
the period of maturing. It remains, however, for future work to deter¬ 
mine what the facts in the case are. It should be stated that for the 
present no special measures for the control of this stem-end rot can be 
definitely recommended. 
SUMMARY 
The studies reported here were conducted in western Oregon, and the 
results apply to western Oregon conditions. They may not apply in 
their entirety to the rest of the State. 
In western Oregon, Verticillium albo-atrum is more important than 
Fusarium oxysporum as a cause of wilt of potato plants. Each of these 
organisms is frequently present in the stem-end vascular region of potato 
tubers produced by diseased plants, and their presence there is usually 
though by no means always indicated by distinct discoloration of that 
region. An average of 6.6 per cent and occasionally as high as 14.4 per 
cent of the tubers which gave V. albo-atrum in culture were not dis¬ 
colored. 
Fusarium radicicola also is often present in this same region of the 
potato tuber, though it is not known to be a cause of wilt of the plants; 
and the discoloration generally accompanying it cannot be distinguished 
from that usually present with the two common wilt-producing organisms, 
Verticillium albo-atrum and F. oxysporum . 
Fusarium radicicola caused heavier discoloration than Verticillium 
albo-atrum in the infected tubers, while F. oxysporum caused still heavier 
discoloration than either of the other two organisms. 
In addition to these three fungi there are also several others that 
invade the stem-end vascular region of potato tubers, and the longer 
the potatoes are kept in storage the larger is the number of tubers which 
give organisms in culture. Some of these are parasitic on potatoes and 
many others are not, so far as known, associated in any way with a 
disease of this crop. They are usually though not always accompanied 
by discoloration of the tuber tissues. 
54131°—21 -4 
