338 
Journal oj Agricultural Research 
Vol. XXX, No. 4 
the above figure and the ones given in 
Table VI because more lines were 
used on P. resinosa than on P. bank- 
siana . Isolation from a coniferous 
host did not increase virulence of 
Botrytis cinerea. 
In only 6 per cent of the tested cases 
was Botrytis more virulent when 
grown on corn-meal agar than when 
grown on rice mush. The virulence 
was, however, equal in 41 per cent of 
tlie cases. The different lines exhib¬ 
ited more variability when grown on 
agar than when grown on mush (fig. 2). 
Four lines showed the same virulence 
when the inoculum was placed at the 
ground level as when it was placed on 
platforms. 
Miscellaneous Fungi 
Table VI gives the results of inocu¬ 
lating Pinus resinosa and P. banksiana 
with miscellaneous fungi by the plat¬ 
form method. 
All lines of Phomopsis juniperovora 
showed some evidence of parasitic 
ability. There is some slight evidence 
that Pinus banksiana is slightly more 
susceptible than P. resinosa to this 
species. Hartley (2) and his associates 
previously found the species unable to 
cause damping-off in soil inoculations. 
There is a possibility that the reason 
for this is the inability of the fungus to 
maintain itself in the soil saprophy- 
tically until the seed has sprouted. 
Cephalothecium roseum showed some 
slight evidence, which needs confirma¬ 
tion, of ability to cause damping-off of 
both species. Thielavia basicola, Pes- 
talozzia funereal and an unidentified 
Verticillium sp. caused no damping-off. 
TIME ELAPSING BETWEEN INOCU¬ 
LATION AND APPEARANCE OF 
DAMPING-OFF 
As stated above, all experiments 
were continued for four days. Figure 
2 gives a set of graphs comparing the 
daily damping-off of Pinus resinosa 
seedlings when inoculated with various 
groups of fungi grown on rice mush 
and corn-meal agar. The percentages 
for each day are based upon the number 
of seedlings living at the end of the 
preceding day. 
Pythium debaryanum, Rheosporan- 
gium aphanidermatus , Phomopsis juni¬ 
per ovor a and the more virulent Cor- 
ticium vagum lines caused the collapse 
of some seedlings within 24 hours from 
the placing of the inoculum, while 
Botrytis cinerea caused almost one- 
third of the seedlings to damp-off 
during the same period. With the 
exception of Phomopsis, these same 
fungi caused about the same percentage 
of P. banksiana seedlings to damp-off 
by the end of the first day. There was 
a slight amount of damping-off caused 
by Fusarium spp. during the same 
period. By the end of the first day 
P. debaryanum caused a somewhat 
larger percentage of the Picea engel- 
manni seedlings to damp-off. 
At the end of the fourth day for most 
of the Fusarium and Corticium groups 
the percentage of damping-off was 
increasing (fig. 2). This probably 
means that the experiments were closed 
before some of these lines had showed 
their maximum parasitic ability. This 
fact may explain in part why in these 
experiments Corticium seemed less 
virulent than formerly ( 3). Most of 
the other fungi seemed to have reached 
their maximum parasitic ability by the 
end of three days. 
Botrytis cinerea, Rheosporangium 
aphanidermatus, and Pythium debary¬ 
anum all grow very rapidly on artificial 
media. This may explain in part why 
damping-off symptoms appeared so 
soon on seedlings inoculated with them. 
However, Phomopsis grows slowly. 
The first three genera are also all very 
virulent parasites. It is rather sur¬ 
prising in view of their reputation for 
toxicity that the more parasitic of the 
Fusarium spp. were so much slower 
than Pythium in producing a visible 
effect on the seedlings. 
Ten Fusarium lines and a few Cor¬ 
ticium lines which always gave nega¬ 
tive results were omitted from the 
graphs. No damping-off was notice¬ 
able in the controls until the end of 
three days. 
DISCUSSION OF RESULTS 
Lines of Pythium debaryanum, Rheo¬ 
sporangium aphanidermatus, Corticium 
vagum, Botrytis cinerea, and a few of 
the numerous species of Fusarium 
were all able to cause considerable 
damping-off. Pythium debaryanum, 
the very similar Rheosporangium, and 
Botrytis cinerea seem able to damp-off 
approximately the same percentage 
of the inoculated seedlings. How¬ 
ever, in view of the fact that Hartley 
and his assistants (2) found Botrytis 
causing damping-off only in the labor¬ 
atory and never in the nursery bed, 
and have never found Rheosporangium 
occurring naturally in coniferous seed¬ 
lings, less importance is attached to 
inoculation results with them. They 
are very active parasites and are 
potentially capable of causing great 
damage, if present under nursery 
conditions. 
