836 
Journal of Agricultural Research 
Vol.XXI.No.ii 
RELATION BETWEEN ORGANISMS IN SEED POTATOES AND ORGANISMS IN 
YIELDS 
The extent to which organisms present in the seed potatoes were 
transmitted to the yields as indicated by cultures from the 1917 crop 
appears in Table IV. Plants grown from seed potatoes from which 
Verticillium albo-atrum was isolated before planting frequently developed 
wilt (PI. 140, A) and gave 29.7 per cent of Verticillium infection in the 
yields. However, not all of the plants grown from the known Verti- 
cillium-infected seed were affected by the wilt disease, consequently the 
percentage of diseased tubers in the yields was considerably lower than 
it would have been if all the plants had wilted. It was high enough, 
however, to indicate that infected seed is a very serious factor in carrying 
the disease from one year to the next. The tubers produced by one lot 
of rather badly wilted plants showed 40.2 per cent infection with V. albo- 
atrum when cultured, and another lot gave a crop containing 49 per cent 
infection. The highest percentage of Verticillium infection found in the 
tubers produced by any considerable number of plants was 92. This 
result was secured in the yield of 28 plants of the variety Up-to-Date, 
which is very susceptible to this wilt. In a number of instances indi¬ 
vidual plants of several different varieties have given yields with 100 per 
cent Verticillium infection. The average, however, as shown by the 
records, is nearer 30 to 50 per cent. Some of the plants grown on clean 
soil from tubers from which either other organisms than V. albo-atrum 
or no organisms were isolated before planting also gave a rather large 
percentage of Verticillium infection in the yields. For instance, the seed 
potatoes from which only “miscellaneous fungi” were isolated gave 13.3 
per cent Verticillium infection in the yields, and those from which no 
organisms were isolated gave 18.9 per cent Verticillium infection. This 
high wilt infection in these two lots apparently came from the spread 
of the Verticillium fungus from neighboring diseased plants in the field 
during the growing season, as will be shown more in detail in a later paper. 
Fusarium radicicola occurred in only slightly larger amounts in the 
yields produced from seed potatoes that contained this fungus than it 
did in those from seed potatoes which according to the cultures made 
were free from it when planted. For instance, the seed tubers from 
which F. radicicola had been isolated gave back 9 per cent F. radicicola 
infection in the yields, while those from which F. oxysporum alone had 
been isolated gave 8.6 per cent F. radicicola infection in the yields, and 
those from which Verticillum albo-atrum alone had been isolated gave 
4.4 per cent F. radicicola. Practically every lot of tubers cultured 
during this study has given a noticeable percentage of infection from 
F. radicicola regardless of whether this fungus was proved to be present 
in the seed potatoes or not. Thus, the indications are that it is trans¬ 
mitted to a slight extent in seed potatoes, that it may come from the 
soil and is evidently rather commonly distributed. This latter conclusion 
is in harmony with the work of Pratt (11), who secured this fungus 
in culture several times from Idaho soils never cropped with potatoes. 
