TRANSMISSION OF SOME WILT DISEASES IN SEED 
POTATOES 1 
By M. B. McKay 
Associate Plant Pathologist, Oregon Agricultural Experiment Station 
Among the diseases of the potato plant (Solarium tuberosum L.), the 
wilt diseases are the most widely known and are reported to cause the 
greatest loss the whole country over. There are several fungi which 
cause wilt of potato plants, but the most important and most frequently 
mentioned are Fusarium oxysporum Schlecht. and Verticillium albo-atrum 
Reinke and Berthold. These parasites have been known for many years 
as a cause of disease in potatoes, and although many important facts 
concerning their nature and control have been learned by the different 
investigators who have studied them, there still remain points of interest 
and value concerning which there is a lack of adequate and definite 
knowledge and which will require much additional work to be completely 
cleared up. The investigations reported here were begun in order to 
secure some knowledge of the importance of these wilt diseases in Oregon 
and to determine the extent to which the fungi causing them are trans¬ 
mitted from year to year in seed potatoes. Fusarium radicicola Wollenw. 
has during this work been frequently isolated from the stem-end vascular 
region of potato tubers that in appearance could not be distinguished 
from those affected by a known wilt fungus. It has been necessary, 
therefore, to include this fungus in this study even though it is not known 
to be a cause of wilt of potato plants. Incidentally, also, some data have 
been collected on the natural occurrence of these organisms in the soil. 
This work was begun in 1916 and continued to the end of 1920. It has 
been conducted mainly in the vicinity of Corvallis, though field observa¬ 
tions have shown that the organisms studied performed in very much 
the same way throughout western Oregon. However, the results secured 
probably could not apply in their entirety to the eastern part of the 
State where the soil, climatic, and other conditions are very different. 
The work was begun with the supposition that Fusarium oxysporum was 
the organism chiefly responsible for potato-wilt in this region, but as the 
investigation has progressed it has been found that Verticillium albo-atrum 
is much the more serious of the two and that the former organism is 
relatively unimportant in western Oregon. Some of the tests begun for 
the purpose of determining the length of rotation necessary to avoid wilt 
infection from the soil can not be completed before a few more seasons 
of study. The work on the transmission of the organisms in seed potatoes 
has been terminated, however, and the results secured are given here. 
1 Published with the permission of the Director of the Oregon Agricultural Experiment Station. 
Journal of Agricultural Research, 
Washington, D. C. 
t) 
(821) 
Vol. XXI, No. 11 
Sept. 1, 1921 
Key No. Oreg.-6 
