42 
BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 
Pythium can cause the "germination-loss" type of damping-off in 
Douglas fir as well as in species of Pinus. Of the seeds sown in the 
control plat 43 produced seedlings which appeared above the soil, 
while only two seedlings appeared from an equal number of seeds 
sown in the inoculated plat. 
Altogether, 38 strains, excluding reisolations, have been tested on 
one or more of the 3 pine species. Strains from both the Pacific 
coast and the eastern United States and from a number of hosts 
other than pines were among those used. With the exception of two 
or three strains from a pine nursery in Michigan, the use of which 
was followed by so little damping-off as to leave their parasitism 
uncertain, all of the strains proved parasitic under favorable condi- 
tions, though some were more virulent than others. The positive re- 
sults in the 14 successful experiments are based on the comparison 
of a total of approximately 1,160 inoculated pots with 195 control 
pots. 
Table III. — Inoculation experiments with Pythium deoariianum in pots of steri- 
lized soil. 
Pythium strain. 
Num- 
ber 
of 
pots. 
Inoculation 
method. 
Results. 
Series, experiment number, 
and host. 
No. 
Initial strain 
from which it 
wasreisolated. 
Emerged 
(per 5-pot 
unit). 
Damp- 
ing-off 
after 
germi- 
nation 
(per 
cent). 
Sur- 
vival 
(per 5- 
pot 
unit). 
Series A.— Initial inocula- 
tions: 
[218 
5 
5 
5 
5 
5 
5 
5 
5 
5 
6 
5 
5 
5 
5 
5 
5 
Agar cultures 
broadcast 
atoneside 
of pot. 
No inoculum 
do 
Agar cultures 
at single 
point in 
each pot. 
No inoculum 
Agar cultures 
broadcast 
atoneside 
of pot. 
No inoculum. 
do....... 
do 
Agar cultures 
broadcast 
at one side 
of pot. 
do 
do 
No inoculum 
( b ) 
1 
74 
82 
41 
55 
16 
18 
90 
82 
82 
14 
3 
13 
78 
14 
78 
100 


28 

81 
89 



72 
67 
67 

72 


No. 58, Pinus banksiana. . 
Controls. 
..do 
74 
82 
[295 
30 
No. 58, Pinus ponderosa.. 
[Controls. 
[258 
55 
3 
..do 
Controls. 
..do 
2 
90 
82 
No. 62, Pinus banksiana. . 
..do 
338a 
82 
4 
347a 
1 
348 a 
4 
* 
^ontrola 
[338 
[Controls. 
78 
SeriesB.— Reisolatedstrains: 
No. 62, Pinus banksiana. . 
No. 295 (in P. 
ponderosa, 
expt. 58). 
4 
78 
a A different soil used in these pots from that used wit h strain 258 and the first three control units. 
6 All inoculations with fragments of agar cultures scattered broadcast at one side of the pot, including 
about one-fourth of its area. Nothing was added to the controls in experiment 62, but sterile agar was 
added to the controls in experiments 66, 67, and 68. 
