692 
Journal of Agricultural Research 
Vol. XXVIII, No. 7 
then subdivided into three equal lots as follows: Lot 1, consisting of 10 inoculated 
and 10 uninoculated bulbs, was placed in wire baskets in an incubator held at 
21° to 22° C.; lot 2 was held at 13° to 18°; and lot 3 was held at 5 to 
14°. The inoculated bulbs in lot 1, when examined 30 days later, were com¬ 
pletely decayed, the succulent tissue having almost disappeared, leaving the 
outer dry scales in their original position. In lot 2 the decay was nearly as 
complete, desiccation not having progressed quite so far. At 5° to 14° the 
decay extended only through the immediate center of the bulbs. The controls 
remained healthy in all cases. 
Experiment 2: One hundred and sixty white sets (f to 1J inches in diameter) 
were divided into four lots of 20 inoculated and 20 uninoculated bulbs each. 
They were placed at 32°, 20° to 21°, 11° to 16°, and 8° C., respectively. After 
19 days the inoculated bulbs at 32° were completely decayed and desiccated; 
at 20° to 21° the rot was well advanced but the tissue was more watery than 
at 32°; at 11° to 16° the inoculated bulbs were only slightly decayed but were 
sprouting profusely; while at 8° the decay was very slight. After 37 days the 
inoculated bulbs at 11° to 16° had all rotted, with two exceptions, after having 
produced sprouts of an average length of 5 inches. After 62 days the inoculated 
bulbs at 8° showed slight decay, usually only adjacent to the wound. The 
striking effect of inoculation upon this lot was the stimulation of premature 
sprouting in spite of very slight decay. All the inoculated bulbs had sprouts 
2-to 6 inches long while of the controls only four had short sprouts, although 
they were wounded in the same way as the inoculated bulbs. The controls in 
all the lots remained healthy without exception. 
■These experiments indicate that at the higher temperatures (30° C.) there is 
a very rapid “dry rot” of the onion bulb when inoculated through a basal wound. 
The desiccated condition of the tissue is probably brought about by the in¬ 
creased evaporation due to high temperature and somewhat lower relative hu¬ 
midity. As the temperature is reduced the progress of the rot is slower until 
at 8° there is very slight decay but excessive sprouting. The latter is an im¬ 
portant factor in onion storage, since sprouting makes the bulb worthless for 
market purposes, and thus Fusarium infection may be indirectly responsible for 
considerable losses on onions held at low temperatures. It is also of interest 
to note that the fungus is active at a lower temperature in the case of the dor¬ 
mant bulb than in that of the growing plant. 
SUMMARY 
Fusarium bulb rot of onion is a disease of increasing importance in the United 
States. A comprehensive survey of Fusaria associated with the disease in vari¬ 
ous parts of the world has been started by Dr. G. K. K. Link. The present 
paper is a study of the disease as caused by a single strain which appears to be 
the chief causal agent of the disease in the Middle West. A description of the 
disease under mid-western conditions is given. 
The organism, Fusarium cepae Hanzawa, belongs to the section Elegans and 
is very close to Fusarium hyperoxysporum Woll., F. redolens Woll., and F. oxys- 
porum Schlecht. Its morphological and cultural characters are recorded. 
On potato agar the fungus grows over a range of from 4° to 35° C. Optimum 
growth takes place between 25° and 28°. 
On Richard’s solution the fungus grows over a range in P H from 2.2 to 8.4; 
best growth occurs at P H 6.6. The fungus thus grows well within that range 
of acidity or alkalinity ordinarily encountered in the host tissue or in the soil. 
Inoculations were readily secured through wounds in plants growing from 
sets in the greenhouse. A much smaller percentage of infections was secured 
