970 
Journal of Agricultural Research 
Vol. XXXI, No. 10 
Table IX .—Results from the treatment of 2-year-old peach roots with disinfecting 
chemicals, after which they were planted in soil infected with freshly broken-up 
crown galls and then grown for two years 
Treatment given 
Number 
of trees 
dying 
Number 
of trees 
with 
galls 
Number 
of trees 
free from 
galls 
Per¬ 
centage 
of trees 
with 
galls 
Bordeaux paste 3-6-4___ _ ____ 
14 
23 
14 
62 
Bordeaux mixture 4-6-50__ _ 
6 
20 
4 
83 
Bordeaux mixture 12-15-50. _ _ 
12 
7 
11 
38 
Ortho lime-sulphur (concentrated)_ _ 
5 
All died. 
Ortho l-10-___‘__J__ 
2 
14 
9 
60 
Ortho 1-20. __ _ __ 
2 
7 
11 
38 
Ferrous sulphate (Bordeaux paste) a _ __ 
7 
3 
18 
14 
Check_*_1_ ........ 
0 
40 
10 
80 
• This was made by the formula of J. W. Tourney, (7, p. 26): 1 part ferrous sulphate, 2 parts copper sul¬ 
phate, and 3 parts quicklime. 
SUMMARY 
Forty different species (often several varieties per species) of Pru- 
nus and Amygdalus have been tested by making artificial inocula¬ 
tions with the crown-gall organism, Pseudomonas tumefaciens. 
There are apparently great differences in susceptibility among these 
species and often among varieties of the same species. This is espe¬ 
cially true in such diversified species as P. domestica. 
Resistance, from the data given sometimes seem to be a specific 
and at other times a varietal characteristic. In Prunus domestica 
some of the varieties tested have shown strong resistance, giving infec¬ 
tion from 15 per cent or less of the inoculations. In the wild Species 
P. pumilaj P. besseyi , P. mume , P. umbellata , and P. alleghamensis, 
the species as a whole is apparently strongly resistant. Further 
tests may, however, demonstrate that this resistance is a varietal 
characteristic. 
The inoculation by punctures is a test more severe than would be 
found under natural conditions. The species in Table III probably 
would be completely resistant under nursery conditions. Possibly 
those showing less than 25 per cent of infection might also be classed 
as practically resistant. 
Species of Amygdalus showed a high percentage of infection when 
the inoculations were made with gall fragments at the time of plant¬ 
ing the pits. The one-year-old trees of various species inoculated 
by placing gall fragments around the roots showed a lower percentage 
of infection than those trees inoculated through punctures on the 
twigs. 
Seven years of experimental inoculation on Prunus mume has 
demonstrated its high resistance. From 4,950 inoculations only 
307 galls developed, or about 6 per cent of infection. Some of the 
introductions of this species are more susceptible than others; they 
show about 13 per cent of infection, which is comparatively low- 
Preliminary inoculation tests on seedlings of Prunus umbellata indi¬ 
cate a considerable variation as regards susceptibility to crown gall 
(Table IV). Seven out of eleven of them gave less than 15 per cent 
infection. The results suggest the possibility of finding a strongly 
resistant strain of this species. 
