INVESTIGATIONS OF POTATO WART. 5 
also a demonstration of the practicability of changing over to new 
varieties in localities threatened by the introduction of the wart para- 
site. This cooperative report is issued to bring together all available 
information regarding the reaction to wart and the suitability of Ameri- 
can potato varieties for purposes of potato-wart quarantine. Further- 
more, in order to present the studies upon additional host range which 
were carried on by the United States Department of Agriculture, in their 
proper relation to the varietal investigations with potatoes, a summary 
of all planting tests with miscellaneous solanaceous species in wart- 
infested soil has been appended. The susceptibility of tomato varie- 
ties to wart was discovered in 1919 7 and extensively confirmed in 1920. 
The need for further information as to the importance of this host 
from the standpoint of quarantine administration led to the adoption 
in 1921 of a cooperative agreement between the Federal Horticultural 
Board and the Pennsylvania State Department of Agriculture for 
testing on a large scale all obtainable tomato varieties. 
As already stated, most of the named varieties of potatoes and 
all the seedlings employed in these tests were furnished by the Office 
of Horticultural and Pomological Investigations of the Bureau of 
Plant Industry. One collection was received from the Agricultural 
Experiment Station of Prince Edward Island, and a number of local 
varieties have been obtained from growers. In the first year of the 
tests 29 immune varieties were received from England through the 
courtesy of Sir Lawrence Weaver, of the Board of Agriculture and 
Fisheries. Duplicates of some of these, together with a number of 
additional stocks, were imported in 1920 by J. G. Sanders, of the 
Pennsylvania State Department of Agriculture. By an arrangement 
between the Federal Horticultural Board and William Stuart, of the 
Office of Horticultural and Pomological Investigations, new varieties 
received by that office from abroad are grown for one year in quar- 
antine before bein^ tested in Maine or elsewhere. This arrange- 
ment has resulted in including several varieties received from Scot- 
land and Holland in the wart-reaction trials at Freeland, Pa. Finally, 
a collection of German varieties was received from E. Schaffnit, of 
Poppelsdorf, Bonn, in 1921 and carried through two years, and a 
collection of eight French varieties, furnished by E. Foex, of the 
Station de Pathologie Vegetale, France, was available for testing in 
1922. The results of the trials covering four years are assembled 
and summarized in Table 1. 
The American varieties are placed in groups according to Stuart's 
classification. 8 It should be noted, however, that in material of so 
diverse a germinal complexion as the potato the varietal similarities 
which constitute the basis of a horticultural classification can not 
afford an index to genetic relationships adequate in all cases to 
predict in advance of actual testing the wart reaction of a variety 
from the known behavior of horticulturaily similar types. This is 
well illustrated by the behavior of the varieties of the Early Michigan 
and the Green Mountain groups. In the former group, Early Har- 
vest, Ehnola, Extra Early Sunlight, and White Albino are regarded 
as immune, while Early Sunrise and Early White Albino are suscep- 
tible (PI. I). Among the varieties belonging to section 2 of the 
Green Mountain group, which have faintly colored sprouts, Charles 
7 Lyman, G. R., and others. Op. cit. 
8 Stuart, William. Group classification end varietal descriptions of some American potatexvs. U. S. 
Dept. Agr. Bid. 176, 59 p., 19 d1. 1915. 
