Feb. 15,1925 Root Rot of Peas Caused by Aphanomyces Euteiches 323 
are known to have enjoyed this freedom 
from disease must be examined. In a 
conspicuous instance of such immunity 
examined recently, the subsoil of the 
field was found to be sand, which af¬ 
forded admirable drainage. It may be 
that a limited amount of land will be 
found outside of irrigated territory on 
which peas may be grown intensively 
for a long time without trouble from 
root rot. However, most soil which has 
drainage and texture open enough to 
secure immunity to disease will proba¬ 
bly be found too dry and infertile to 
produce large yields from a plant with 
a comparatively small root system like 
the pea. 
Since there is a large amount of valu¬ 
able land now incapable of producing 
profitable crops of peas because of in¬ 
festation with root rot, the question is 
often asked how long the fungus re¬ 
mains in the soil, and if a rotation can 
be devised that will make possible the 
utilization of this land i i the future. 
Since there is no experimental evidence 
which will aid in answering these ques¬ 
tions, it is necessary to seek the 
experience of growers who have aban¬ 
doned land for pea growing because of 
disease for varying periods of years. 
Experience of this kind is always open 
to question because one can not be 
sure that this root rot and not some 
other disease was the cause of the crop 
failure, both before and after the 
period in which the land was used for 
other crops. Notwithstanding such 
doubts, there appear to be two well- 
attested instances in Wisconsin in 
which fields failed to produce healthy 
peas after being used six years for other 
crops following a complete failure from 
rootrot. The writer has seen two fields 
of peas ruined by root rot after an inter¬ 
val of four years following a failure and 
another field in the same locality pro¬ 
ducing healthy peas nine years after a 
failure, presumably from this disease. 
In contrast with this Wisconsin experi¬ 
ence, healthy fields of peas have been 
found in sandy soil in Delaware where 
peas failed four years earlier from dis¬ 
ease which may have been root rot. 
From these instances and other experi¬ 
ences which might be cited it seems 
that in the heavier soils the parasite 
may persist for at least six years after 
it has once become abundant. In light 
soils its period of survival may be 
shorter. Probably no other fungus 
parasite of peas survives so long as 
this, and its duration in any locality 
can best be determined by repeated 
experimental plantings on infested 
ground during a series of years. 
RESISTANT VARIETIES 
Observation of the behavior of vari¬ 
eties of peas grown on diseased soil 
in several places has given rise to the 
opinion, more or less current among 
growers, that some varieties of peas 
show resistance and will produce a 
better crop than others. Inasmuch 
as Wilber Brotherton has been study¬ 
ing resistance under field conditions on 
an extensive scale and will report re¬ 
sults in the near future, no attempt 
will be made here to consider the 
merits of commercial varieties. An 
attempt has been made to supplement 
Brotherton’s studies by seeking to de¬ 
vise laboratory methods whereby dis¬ 
ease resistance can be tested more 
rapidly than in field trials, and also to 
learn in so far as possible the nature 
of the resistance which varieties may 
possess. 
The attempt to test varieties in the 
greenhouse under controlled conditions 
has not yet developed a method that 
is satisfactory. In the greenhouse in 
winter there is an apparent oblitera¬ 
tion or reduction of differences in be¬ 
havior compared with that observed in 
the field not unlike that which oc¬ 
curred in an earlier study (5, p. 471) 
of resistance of peas to a species of 
Fusarium. This work is still in prog¬ 
ress and may be reported more fully 
later. 
It may be said here, however, that no 
variety of peas, whether of the garden 
or of the field varieties, has been 
found immune to the fungus. The 
hardiest variety of field pea which 
produces a crop on soil so infested that 
few plants of garden varieties survive 
to maturity suffers almost if not 
quite as great a loss of cortex from 
its roots as its more susceptible 
neighbors. In spite of this loss it 
maintains growth and matures seed. 
This difference in behavior, termed re¬ 
sistance, seems to be due to several 
characters which resistant plants pos¬ 
sess to a greater degree than those 
which perish. There is some evidence 
indicating that the fungus traverses the 
cortex of some varieties much more 
slowly than that of others, thus destroy¬ 
ing roots less rapidly. Finally, when 
cortex is destroyed the remaining vascu¬ 
lar cylinder of some plants seems to 
be able to exclude bacteria and fungi in 
the soil and to function quite efficiently 
thus denuded of absorbing tissue. 
Whatever the importance of these 
several factors in resistance men¬ 
tioned above, it will be seen at once 
that the growth of resistant peas 
