JOIIM OF AMOILTORAL RESEARCH 
Vol. XXX Washington, D. C., February 15, 1925 No. 4 
ROOT ROT OF PEAS IN THE UNITED STATES CAUSED BY 
APHANOMYCES EUTEICHES (N. SP .) 1 - 2 
By Fred Reuel Jones, Pathologist, and Charles Drechsler, Associate Patholo¬ 
gist, Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureau of 
Plant Industry, United States Department of Agriculture 
INTRODUCTION 
During the past five years, in which 
the senior writer has endeavored to 
determine the causes which produce the 
root rot of peas known widely in the 
United States, several fungous diseases 
have been distinguished which sever¬ 
ally or together appear to be responsible 
for all of the important injury which 
has been found incident to the under¬ 
ground portion of this plant. One of 
the less important of these diseases 
caused by a species of Fusarium has 
been described in a previous paper ( 8) , 3 
The most important of these diseases, 
more important, in fact, than the others 
combined, is the subject of the present 
paper. The account of the morphology 
and taxonomy of the fungus causing the 
disease and the drawings are contrib¬ 
uted by the junior author. Several 
fungous diseases of pea roots of much 
local importance have also been studied. 
Among these are two caused by species 
of Pythium, one of which in some sea¬ 
sons is almost always associated with 
Aphanomyces, an association which 
misled the senior writer in a previous 
note ( 6 ) to ascribe to the Pythium alone 
the injury due to both organisms. The 
diseases caused by species of Pythium 
remain to be described in a following 
paper. 
THE DISEASE 
DESCRIPTION 
The injury caused by a fungous para¬ 
site which invades only the subterra¬ 
nean portion of the plant must, of 
course, be sought in its early stages in 
the roots themselves. In later stages 
the top of the plant may be modified in 
response to the root injury in a way 
which may be specifically character¬ 
istic. In the case of this disease the 
injury eventually presented by the top 
of the plant is not characteristic, the 
form which it takes depending largely 
upon the stage of development at which 
the roots became thoroughly invaded 
and to a lesser extent upon the degree 
of resistance of the variety of peas. If 
the plant becomes invaded in the basal 
stem below ground as well as in the 
roots before the plant has developed 
more than three or four nodes, sudden 
wilting may result. Usually under 
field conditions invasion takes place 
later than this, and the result is a gen¬ 
eral retardation of growth, the death of 
the lower leaves progressively upward, 
and finally, when the plant is in full 
bloom, it may shrivel up completely. 
More frequently, however, the plant 
persists in a weakened condition until 
it has brought its poorly filled pods to 
maturity. 
If extensive infestation of the roots is 
delayed until the blossoming period, the 
plants may mature under favorable 
conditions without any conspicuous in¬ 
dication of injury. These several symp¬ 
toms have no common factor which dis¬ 
tinguishes plants infectqd with Apha¬ 
nomyces from those attacked by several 
other fungi. However, there is one 
test which can be applied that will often 
give a decisive indication of this dis¬ 
ease. If some of the infested plants are 
pulled, the stems of those which are 
thoroughly invaded will fail to break at 
the seed, as is the usual rule with 
healthy plants, but the vascular core of 
the taproot will pull out as a long string 
1 Received for publication May 19, 1924—issued April, 1925. 
2 Results of work done in cooperation with the Agricultural Experiment Station of the University of 
Wisconsin. 
3 Reference is made by number (italic) to “Literature cited,” p. 325. 
Journal of Agricultural Research. Vol. XXX, No 4 
Washington, D. C. Feb. 15, 1925 
Key No. G-456 
13952—25f-1 
(293) 
