THE NATIONAL NURSERYMAN 
129 
l 
SOME OF THE RESULTS OF THREE YEARS’ EXPERI¬ 
MENTATION WITH CROWN GALL. 
The following is a summary of the lecture given at the an¬ 
nual meeting of the American Association of Nurserymen at 
West Baden, Ind., June 15, 1905, by George G. Hedgcock, 
Pathologist of the U. S. Department of Agriculture: 
WHAT APPLE CROWN GALL IS. 
The disease ordinarily called crown gall on the roots of the 
apple tree is most prevalent on grafted trees at the union of 
the root and scion, and is more often found on the lower end 
of the scion. Only a small per cent, of budded trees are 
ordinarily diseased, but as high as 50 per cent, of some of the 
varieties are diseased in grafted trees. The disease is more or 
less prevalent in all localities, wherever the apple trees are 
grown from root-grafts. In the course of the investigation 
no nursery investigated has been found free from this disease. 
FORMS OF CROWN GALL. 
Apple crown gall has two forms, one of which is devoid of 
small roots in the region of the gall, the other has few, to 
many small roots arising from the gall or its vicinity. A third 
form now under investigation is here assumed to be a distinct 
disease, and consists of numerous small roots arising from a 
slightly thickened tap-root, in which there is no distinct gall 
formation. This is designated as the “Hairy Root” disease 
of the apple. The “Hairy Root” disease is not included in 
the data from which the following results were drawn. Care 
should be taken also not to confuse with crown gall in the 
nursery, two other gall diseases of the apple tree, one due to 
the woolly aphis, the other to the presence of very tiny worms 
known as nematodes in the root cells. The galls produced 
by these two parasites are smaller and softer than true crown 
gall, and are more numerous and more apt to be found on 
side roots. There is also a soft gall often found on apple 
seedling roots, and occasionally on grafted trees, which differs 
slightly from the harder form common on grafted trees and 
which may be due to a different cause. 
INOCULATION EXPERIMENTS. 
Careful examination for two years conducted both in the 
greenhouse and in the nursery give the following results from 
inoculations made with the common hard type of apple crown 
gall, devoid of “Hairy Roots.” Apple seedlings grown in the 
greenhouse from seeds sterilized with concentrated sulphuric 
acid, planted in a soil which had been sterilized in a soil auto¬ 
clave at a steam pressure of 15 pounds to the square inch, 
watered with boiled river water, were used for experimentation. 
Such seedlings remained free from disease throughout the 
experiment, both in control and in inoculated plots. A 
portion of these were inoculated by inserting a piece of living 
gall in a wound upon the root, and wrapping it with a thread, 
others were inoculated by mixing minced galls with the soil. 
Carefully selected apple seedlings from the nursery were 
inoculated in the same manner in both field and greenhouse. 
The average result of all such inoculations for two years are 
10 per cent, diseased in the inoculated and 14 per cent, dis¬ 
eased in the control portions of the plots. No reasons for the 
excess in the control can be given. 
Extensive inoculations of root-grafts for two years gave in 
1903 an average of 44 per cent, of diseased trees in the in¬ 
oculated portion, and 39 per cent, in the control parts of the 
plots. In 1904, with an equally large number of trees, 9 per 
cent, were diseased in the inoculated and 15 per cent, in the 
control portion of the plots. An average for the two years 
gives 27 per cent, diseased in both the inoculated and the 
control portions. About 10,000 apple grafts were used in 
these experiments. No evidence can be deduced from the 
results that the disease is contagious, since the inoculation was 
thoroughly made with a large quantity of minced galls at the 
time of planting. 
EFFECT UPON THE APPLE TREE. 
It has been claimed that the disease kills the apple tree in 
three years in the case of young trees. An experiment with 
300 trees to determine the effect of the galls on the growth of 
diseased trees, at the end of one year showed no difference in 
the appearance of the diseased from healthy trees. Of 175 
diseased trees, five were dead at the end of the year; of 125 
healthy trees of the same age, seven were dead. Trees grown 
in the nursery under the same conditions, selected from the 
same grade, with equally developed roots were used, the only 
difference being that each of the diseased trees possessed a 
well developed gall on the root. Outside of experiments by 
the Department considerable data has been collected, which 
indicate that the disease does not greatly shorten the life of the 
young tree, unless the galls completely encircle it above the 
root system, and in such cases that deeper planting of diseased 
trees will probably enable them to form a system of roots 
above the encircling gall and thus prolong their life. An 
orchard of 50 crown gall trees near Brussells, Ill., at the end 
of eight years contained 40 healthy vigorous trees, eight 
having died, and two were dying, with a root rot, which may 
or may not have gained entrance through the gall. No re¬ 
plants had been made at any time during the growth of the 
orchard. These are now under observation, orchards con¬ 
taining 14,000 crown gall trees. Experiments on the nature 
of the disease in 1905 include 110,000 apple root-grafts and 
10,000 seedlings. 
CROWN GALL OF RASPBERRY AND STONE FRUITS. 
The crown gall of the peach, plum, cherry, raspherry, al¬ 
mond, and apricot have been proven by careful inoculation 
to be one and the same disease on each of these plants. It is 
very contagious when inoculated into wounds upon the roots 
of the plants. Peach and raspberry are most susceptible to 
inoculation from galls taken from any of these plants. On 
the other hand, inoculations upon the apple and pear from 
galls of the above plants failed, and those from galls of the 
apple and pear upon the raspberry and stone fruits were 
equally unsuccessful. The pear gall is similar to that of the 
apple and does not appear to be contagious from results 
obtained. 
HOP GALL. 
The crown gall of the hop is evidently caused by the pres¬ 
ence of a slime-mould resembling Plasmodiophora brassicae in 
the tissues of the galls. The crown-gall and root-galls of the 
rose and grape are not certainly infectious. It is not advisable 
to use cuttings or off-shoots from diseased plants of the rose, 
raspberry or grape, owing to the presence of the disease in the 
tissues of these plants above the ground. A study of all these 
galls is in progress. 
A REQUEST FOR COOPERATION. 
There is a great diversity of reports as to the tendency of 
different varieties of apple to form crown gall when grafted. 
The Department is anxious to secure in the next few months 
as much data as possible from all parts of the United States as 
to the per cent, of crown gall upon common varieties of apple 
on both grafted and budded trees, and it is requested that 
leading nurserymen and fruit growers send a confidential re¬ 
port of such percentages to the Mississippi Valley Laboratory 
at St. Louis. All data which may be furnished in connection 
with this inquiry will be considered confidential; that is, 
when any publications or announcements pertaining to crown- 
gall are made the names of the nurserymen furnishing infor¬ 
mation will in no case be given, but each will receive a full 
report of the investigation when issued. Blanks for data and 
full directions will be furnished upon application to Geo. G. 
Hedgcock, at the Mississippi Valley Laboratory, St. Louis. Mo. 
