688 
Journal of Agricultural Research 
Vol. XXVIII, No. 7 
this Fusarium bulb rot is associated with onion maggot injury. It is obvious 
from the experimental evidence just given that mechanical injury to the base of 
onion bulbs due to insects or other causes will greatly facilitate infection by 
Fusarium cepae . 
INOCULATIONS IN THE FIELD 
Inoculation experiments were continued out of doors at Madison, Wis., in 
1922 on soil which had never previously grown onions. The soil was inoculated 
at the time of planting (April 22) by the addition of a spore suspension of the 
organism. Plats of uninoculated soil were planted as controls. Bulbs were 
grown from bottom sets of White Portugal, Red Wethersfield, and Yellow Strass- 
burg varieties, and from seed of Crystal Wax Bermuda, Crimson Globe, Silver 
Globe, Golden Globe, and White Portugal varieties of onion. Plantings from 
seed of White Welsh onion (Allium fistulosum) and leek (Allium porrum) were 
included. The development of the disease followed closely that observed previ¬ 
ously under natural field conditions. Approximately equal numbers of plants 
from inoculated and uninoculated plats were examined on August 8. The results 
are given in Table III. It is significant to note that infection took place in the 
case of every variety of common onion (Allium cepae) tried. Varieties represent¬ 
ing each of the three color types (white, yellow, and red) were included and no 
marked differences in varietal susceptibility were noted. The Welsh onion and 
leek are apparently decidedly resistant. 
Table III. — Results of field inoculations with Fusarium cepae upon different 
varieties of common onion and upon Welsh onion and leek 
Method of 
propagation 
Variety 
Number 
of bulbs 
examined 
at end of 
season 
Per cent 
showing 
Fusarium 
bulb rot 
Condition 
of 
controls 
/Red Wethersfield, White Portugal, Yellow Strassburg.. 
215 
22 
Healthy. 
xrow 
IRed Wethersfield.:. 
150 
15 
Do. 
Crystal Wax Bermuda. 
300 
a 2 
(a) 
Red Globe. 
175 
12 
Healthy. 
White Globe.. 
295 
18 
Do. 
From seed.... 
Yellow Globe.... 
75 
8 
Do. 
White Portugal..... 
300 
7.5 
(&) 
White Welsh. 
400 
0 
Healthy. 
Leek. 
400 
0 
Do. 
° No Fusarium rot in checks; results were obscured by the abundance of soft rot in both inoculated plants 
and checks following early maturity of this variety. 
6 One bulb was diseased and Fusarium isolated therefrom. 
INOCULATIONS IN STORAGE 
Although the fungus was found constantly associated with the decay of onion 
bulbs, the first attempts to reproduce the disease by artificial inoculation of 
mature bulbs were unsuccessful. Insertion of spores into wounds at the base of 
the bulbs did not result in infection under ordinary storage conditions, although 
the disease was known to progress in naturally infected bulbs in the same environ¬ 
ment. Holding of the bulbs continuously at a high relative humidity was 
undesirable because this condition brought about almost immediate sprouting. 
It was found, however, that the typical bulb rot could be produced if the bulbs 
were inoculated as indicated above and held* for 48 hours in the saturated atmos¬ 
phere of moist chambers at room temperature and then placed in wire baskets 
under ordinary laboratory conditions. Thirty onion sets thus inoculated and 
incubated at 22° C. were completely decayed after 30 days while the same number 
of controls showed only slight desiccation and remained perfectly healthy. The 
experiment was successfully repeated with large bulbs of both the white and red 
types. In the case of the small sets the decayed tissues dried out rapidly and a 
“dry rot” was produced. With the larger bulbs the greater amount of succulent 
tissue yielded a somewhat more “watery decay” and the greater amount of 
moisture brought about the production of more aerial mycelium which was most 
pronounced as a white fluffy mass at the base of the bulb. (See PI. 2, B.) 
