846 
Journal of Agricultural Research 
Vol.XXI.No. 11 
The presence of discoloration in the stem-end vascular region of potato 
tubers is not a trustworthy index of the presence of disease-producing 
organisms therein and ought not to be relied upon exclusively as a guide 
for the separation of diseased from healthy tubers for planting purposes. 
For instance, 45 per cent of the tubers which were “browned” in the 
vascular region when cultured gave organisms which cause disease in 
potatoes, and 55 per cent gave either no organism or miscellaneous 
fungi of no apparent importance; 22 per cent and 5 per cent of those 
which were “yellowed” and “not discolored,” respectively, gave organ¬ 
isms parasitic on potatoes, the others of these lots giving nothing of 
consequence. , 
Verticillium albo-atrum occurred in all sizes of potato tubers, though 
somewhat more extensively in the small ones than in those of medium 
size. Fusarium oxysporum and F. radicicola did not seem to occur con¬ 
siderably more in one size of potato tuber than in another. The medium¬ 
sized tubers gave a larger proportion of miscellaneous organisms than 
the smaller ones. 
Verticillium albo-atrum is transmitted to a considerable extent from 
seed potatoes to yields. From 30 to 50 per cent of the tubers grown 
from known infected seed potatoes were invaded by the same organism 
when harvested and cultured. Fusarium radicicola and F. oxysporum 
were transmitted to only a slight extent from seed potatoes to yields 
and were apparently not infrequently present in soils which had not 
been planted to potatoes for several years. 
The stem-end seed pieces did not seem to give more disease either in 
the plants or in the tubers produced therefrom than the eye-end seed 
pieces of the same infected tubers. The differences are at least so slight 
that it apparently is not advisable in attempting to avoid wilt in seed 
potatoes to rely much on the practice of discarding the stem ends and 
planting only the eye ends of tubers suspected of containing wilt 
organisms. 
Verticillium albo-atrum is widely distributed in Oregon, having been 
recorded from 16 counties, and is the most important potato wilt- 
producing organism in the western part of the State. It causes appre¬ 
ciable losses each year, not only in commercial fields but especially in 
seed plots, because the presence of this fungus greatly lessens the value 
of the potatoes for seed purposes. It annually is responsible for the 
failure of a considerable number of fields to pass inspection for certifi¬ 
cation. The yields of affected plants are reduced on the average of 
from 30 to 50 per cent. 
Fusarium oxysporum is also widely distributed in the State, having 
been noted in 11 counties, though it is seemingly of little importance, 
at least in the western portion. In only a few cases have any consider¬ 
able number of plants been found attacked by this organism in any 
western Oregon fields examined. 
