CROWN-GALL STUDIES OF RESISTANT STOCKS 
FOR PRUNUS 1 
By Clayton O. Smith 
Research Associate in Plant Pathology , Citrus Experiment Station } College of 
Agriculture , University of California 
INTRODUCTION 
Of all nursery troubles in California on the stocks used for the stone 
fruits, the disease commonly known as crown gall is probably the 
most prevalent. Observations in the nursery often reveal a high 
percentage of infection with crown gall, especially in sandy soils, on 
peach and almond roots, and to a less extent on myrobalan plum 
and apricot. 
Investigation (8 ) 2 has shown that the nursery stocks in general 
use for the stone fruits in California are susceptible to artificial 
inoculation with the crown-gall organism, Pseudomonas tumefaciens 
Sm. and T. Cannery pits of peach and apricot, rather than pits of 
the more primitive species, are usually planted for such nursery 
stock. Inoculations of the peach ( Amygdalus persica) produce about 
80 per cent infection, and the almond {Amygdalus communis) is 
probably as susceptible. Inoculations of the myrobalan plum {Prunus 
cerasifera ) result in 75 to 95 per cent of galls. The apricot (P. ar- 
meniaca) is somewhat more resistant, infections resulting from about 
74 per cent of the inoculations. 
The general characteristics of the crown-gall disease caused by 
Pseudomonas tumefaciens have been carefully studied {6), but a 
satisfactory and practical control is yet to be found. The most 
promising line of attack is in the use of more resistant stocks, species, 
or varieties of Prunus or Amygdalus which in experiments or practice 
have shown themselves substantially free from infection, and which 
are also suitable for growth. 
The genus Prunus is rich in species and varieties which might be 
employed for stock purposes. Little is known concerning their 
adaptability as roots for the stone fruits or their resistance to crown 
gall; these questions are under investigation at the present time. 
This paper gives a preliminary report on the inoculation of a number 
of species and varieties of Prunus and Amygdalus. 
SOURCE OF MATERIAL 
PRUNUS FORMS 
The species listed in Tables I and II have been obtained from 
supposedly reliable sources. Scions and pits of many of the eastern 
varieites were obtained from the Arnold Arboretum. The United 
States Department of Agriculture has sent us material from its 
1 Received for publication Feb. 19, 1925; issued January,1926. Paper No. 89, University of California 
Graduate School of Tropical Agriculture and Citrus Experiment Station, Riverside, Calif. 
2 Reference is made by number (italic) to “Literature cited,” p. 971. 
% 
Vol. XXXI, No. 10 
Nov. 15, 1925 
Key No. Calif.-41 
Journal of Agricultural Research, 
Washington, D. C. 
( 957 ) 
