LONGEVITY OF PYCNOSPORES OF THE CHESTNUT- 
BLIGHT FUNGUS IN SOIL 
By F. D. Heald and M. W. Gardner, Agents, Investigations in Forest Pathology, 
Bureau of Plant Industry 
INTRODUCTION 
That “spore horns'’ of the blight fungus Endothia parasitica (Murr.) 
And. are dissipated by rains has been recognized since the first studies on 
the chestnut bark disease. That the pycnospores are washed down the 
tree and are responsible for reinfections has been especially noted by 
Collins (1912). 1 This fact was also emphasized by Metcalf and Collins 
(1911), as may be noted from the following quotation: 
When the spores of the fungus are present, especially in the form of threads, or 
“horns ,’* they are readily washed down the branches and trunk by every rain, and 
are thus carried down to or toward the base of the tree. 
During the winter and spring of the year 1913 investigation of the 
dissemination of the chestnut-blight fungus by the writers disclosed the 
fact that during every rain, even at seasons when spore horns were not 
produced, pycnospores in great numbers were washed down the trunks 
of diseased trees. (Heald, 1913b; Heald and Gardner, i9i3a-b.) This 
naturally led to the question as to what became of these millions of 
pycnospores washed into the soil. 
Several possibilities suggested themselves. One of these was that the 
spores might germinate in the soil water and thus be readily killed by 
desiccation or other unfavorable conditions. Another was that, though 
the spores would not germinate, their period of viability might be very 
short even in wet soil, or that possibly they might retain their viability 
until it was terminated by unfavorable conditions such as freezing or 
drying out of the soil. 
On the other hand, it was possible that the spores might remain viable 
not only during the time that the soil was wet but that they might endure 
for extended periods such unfavorable conditions as those produced by 
freezing or desiccation. 
As to the possibility of pycnospores germinating in soil water, the 
tests so far carried out with various soil extracts have yielded inconclusive 
results. Pycnospores will germinate in certain soil extracts and not in 
others, the percentage of germination ranging from o to 65. 
Our tests on the longevity of pycnospores in sterile tap water may be 
cited here as having some bearing on their persistence in wet soil. The 
few tests made have shown that 61 to 93 per cent retain their viability 
for four weeks. Only one trial was made to determine their power to 
endure freezing in sterile tap water. A very large percentage, 96, sur¬ 
vived a period of six days of freezing, and 10 per cent survived a second 
period of eight days of freezing. Further investigation along all of these 
lines is planned. 
Regarding the resistance of pycnospores to desiccation in soil, more 
conclusive results have been obtained. The purpose of the tests recorded 
1 Bibliographic citations in parentheses refer to “Literature cited,” p. 75 . 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D, C. 
(67) 
Vol. II, No. 1 
Apr. 15, 1914 
G—18 
