Feb. 15, 1925 
Inoculation of Coniferous Stems 
339 
Under the conditions of the writer’s 
experiments, the Pythium debaryanum 
lines showed a smaller virulence range 
than did the same ones when used in 
soil inoculation experiments by Hartley 
(, 2 ). There are two possible explana¬ 
tions for this: (1) Some lines may have 
formerly been considered nonparasitic 
because of their inability to live sapro- 
phytically in the soil until the seeds 
had germinated, and (2) lines really 
weak may have seemed strongly para¬ 
sitic in the writer’s tests because of the 
heavy inoculum. The same may be 
true also of other genera. 
For unexplained reasons, Corticium 
vagum exhibited far more variability 
than it did in Hartley’s {2, 3) experi¬ 
ments. 
Few of the Fusarium species exhib¬ 
ited decidedly high or constant par¬ 
asitic ability, but as a whole the genus 
appears able to cause considerable 
damage. 
The other tested fungi besides 
Pythium debaryanum, Corticium vagum, 
Botrytis cinerea and Fusarium spp. are 
probably unimportant in the field 
because of the infrequency of their 
occurrence in coniferous nurseries 
even though some lines tested in these 
experiments were rather virulent. 
The fact that the virulence and 
variability of the parasites depend to 
a certain extent on the medium used as 
inoculum, suggests that the virulence 
of the parasites in the soil, or at least 
their ability to maintain themselves 
saprophytically there until seeds had 
germinated, is largely dependent upon 
the amount and quality of the available 
food supply. 
In order definitely to establish the 
relative susceptibility of the various 
hosts, tests should be conducted in 
which all the hosts are inoculated in the 
same experiment. However, it is to be 
expected that the hosts would be of 
approximately equal virulence in these 
experiments because Hartley ( 3) re¬ 
ported Pinus resinosa, P. banksiana, 
and Picea engelmanni as highly sus¬ 
ceptible to damping-off under field 
conditions. It is probable that the 
fungi which proved themselves only 
moderately parasitic under the 
extremely artificial conditions of these 
experiments would do little or no 
damage under nursery conditions. 
SUMMARY 
(1) Direct inoculations of stems 
without bringing the inoculum in 
contact with the soil were conducted 
in the greenhouse of the United States 
Department of Agriculture at Wash¬ 
ington, D. C. with seedlings of Pinus 
resinosa , P. banksiana , and Picea 
engelmanni. Over one hundred dif¬ 
ferent fungous lines, most of which 
were Pythium debaryanum, Corticium 
vagum, and Fusarium spp., were 
tested. 
(2) The virulence and variability of 
the different fungi depend to some 
extent on the substratum on which they 
are grown. 
(3) The most virulent parasites in 
these experiments were Pythium deba¬ 
ryanum. Botrytis cinerea, Rheosporan- 
gium aphanidermatus and Fusarium 
sporotrichioides. 
(4) The time elapsing between inoc¬ 
ulation and the appearance of damp¬ 
ing-off was especially short for the 
virulent swift-growing fungi. 
LITERATURE CITED 
(1) Davenport, C. B. 
1904. STATISTICAL METHODS; WITH SPECIAL RE¬ 
FERENCE TO BIOLOGICAL VARIATION. Ed. 2, 
223 p. New York. 
(2) Hartley, C„ Merrill, T. C., and 
Rhoades, A. S. 
1918. SEEDLING DISEASES OF CONIFERS. JOUr. 
Agr. Research 15: 521-558, illus. 
(3) -. 
1921. DAMPING-OFF IN FOREST NURSERIES. U. S. 
Dept. Agr. Bui. 934, 99 p., illus. 
(4) Rathbun, A. E. 
1921. METHODS OF DIRECT INOCULATION WITH 
damping-off fungi. Phytopathology 11: 
80-84, illus. 
(5) -. 
1922. root rot of pine seedlings. Phytopathol¬ 
ogy 12: 213-220, illus. 
( 6 ) -. 
1923. damping-off of taproots of conifers. 
Phytopathology 13: 385-391. 
(7) Rosenbaum, J. 
1917. studies of the genus phytophthora. 
Jour. Agr. Research 8: 233-276, illus. 
(8) Spaulding, P. 
1914. THE DAMPING-OFF OF CONIFEROUS SEED¬ 
LINGS. Phytopathology 4: 73-88, illus. 
