reb i 5 ,1925 Root Rot of Peas Caused by Aphanomyces Euteiches 319 
several forms—earth previously inocu¬ 
lated with cultures in greenhouse ex¬ 
periments, cultures containing oospores 
planted with the seed, and zoospores 
applied at planting and at various 
times later. It seems inadvisable to 
present detailed results obtained thus 
in a single unfavorable season. Suffice 
it to say that some infection was 
obtained by all methods, but that the 
effectiveness of the method seemed to 
depend more upon the rainfall and 
temperature at and immediately after 
inoculation than upon the method. 
Zoospores poured upon the soil about 
Alaska peas breaking ground just 
before a rain on May 17 gave as high 
as 86 per cent infection, and when the 
soil was removed, exposing about 2 
inches of the stem before the spores 
were distributed, every plant became 
infected, as evidenced by examination 
of the roots. Conspicuous decay fol¬ 
lowing this infection of roots did not 
begin in any case, however, until the 
disease developed in plants growing on 
naturally infested soil. This simul¬ 
taneous development of disease in 
plats whether infested naturally or 
artifically suggests that soil tempera¬ 
ture controlled this development re¬ 
gardless of the time and manner of in¬ 
fection. All diseased plants in plats 
inoculated artifically grew to normal 
maturity and showed no conspicuous 
evidence of reduced vigor. 
In contrast with these results of 
artificial inoculation were some data 
on the effects of natural inoculation in 
a similar type of soil not far removed 
where peas had been grown repeatedly 
for 7 years. Double rows of peas-one 
rod long were planted on the infested 
soil, and extensions of these rows upon 
ground unused for peas were likewise 
planted with 400 peas to each rod. 
Unfortunately the disease had spread 
somewhat to the new land, so that 
many roots became infected, especially 
those of the susceptible variety, Sur¬ 
prize. However, the peas on the in¬ 
fested land showed early in the season 
all the symptoms of severe root rot, 
whereas those on the new land showed 
little indication of disease except at the 
ends of the rows adjoining diseased 
ground. Careful examination of plants 
in these plats during the season failed 
to reveal any other disease than that 
caused by Aphanomyces. The yields 
of some of these rows are given in 
Table IV. 
The striking contrast between the 
results of natural infection and of arti¬ 
ficial inoculation in the field plats is 
certainly not due to actual killing of 
the plants and demands explanation. 
Table IV.— Yields of dry peas in one 
rod of double row of peas upon soil 
heavily infested with Aphanomyces 
euteiches compared with yields upon 
adjoining ground where peas had not 
been grown previously . Planting was 
made April 28, 1923, 400 peas were 
planted to each rod of double row 
Infested land 
New land 
Variety 
Num¬ 
ber of 
plants 
growing 
Yield 
Num¬ 
ber of 
plants 
growing 
Yield 
Alaska_ 
333 
Grams 
250 
367 
Grams 
420 
Do_ 
369 
210 
378 
393 
Surprise_ 
237 
60 
267 
167 
Do__ 
297 
71 
292 
210 
Alaska_ 
364 
172 
346 
328 
Do_ 
360 
125 
358 
318 
Very careful and frequent examinations 
were made of the roots in all plantings. 
From these examinations it was found 
that the number of infected roots of 
the plants inoculated artificially were 
few and restricted to the region in 
which the inoculum had been applied, 
whether above, below, or near the 
seed. Under the conditions obtaining 
during this season, even the complete 
destruction of the cortex of the base of 
the stem rarely injured a plant greatly, 
provided most of the roots remained 
free from invasion. Although in arti¬ 
ficial inoculations trenches in which 
peas were planted were drenched with 
zoospore suspension at the time of 
planting, infections were few and only 
near the seed. No method of inocula¬ 
tion after the plants had started growth 
seems to have filled the soil very thor¬ 
oughly with the parasite in such condi¬ 
tion that it was ready to invade the 
plant at a large number of points at 
once when favorable conditions for 
such infection occurred. It appears 
from field observation described else¬ 
where, as well as from these experi¬ 
ments, that this disease can produce 
conspicuous injury to top growth only 
when plants are either infected under 
favorable conditions for the develop¬ 
ment of the parasite when the plants 
are small or when they suffer a large 
number of infections at a later stage of 
growth. In these artificial inocula¬ 
tions the fungus was not distributed 
deeply and thoroughly enough in the 
soil to make possible a great number of 
infections when the brief favorable 
period for infection arrived; so brief 
was the favorable period that inocula¬ 
tions of young plants made when it 
