684 
Journal of Agricultural Research 
Vol. XXVIII, No. 7 
The roots commonly turn pink and gradually decay until eventually the entire 
root system may disappear. A semiwatery decay affecting all the tissues of 
the succulent scales starts from the base upward. In early infections this 
decay may continue so as to almost completely destroy the bulb by harvest. 
In other cases incipient infections at harvest continue to advance during storage 
and transit, finally leaving dry, shrivelled mummies. In the case of red onions 
it is common for the anthocyan pigment in the outer epidermis to turn green in 
color for a considerable distance in advance of the actual decay, indicating a 
change in reaction of the cell sap. Fusarium infection of the bulb is often asso¬ 
ciated with insect wounds, and since this organism is primarily a wound para¬ 
site the coincidence of severe epiphytotics of the disease and maggot injury is 
common. 
THE CAUSAL ORGANISM 
SOURCE OF PURE CULTURE 
The culture of Fusarium used in the following experiments was isolated from 
typically diseased specimens of White Portugal onion sets collected in storage 
at Morton Grove, Ill. Spore dilution plates were first made, and from a sub¬ 
sequent transfer a pedigreed strain from a single spore was secured. This strain 
was used for all of the experimental studies. 
MORPHOLOGICAL AND CULTURAL CHARACTERS OF THE ORGANISM 4 * 
The morphological and cultural characters of the organism as determined 
from cultures on various media are as follows: 
Fusarium cepae ( Hanzawa ) emend. Microconidia usually not numerous. 
Macroconidia gradually attenuate toward the apex, distinctly pedicellate and 
uniformly curved throughout; typically 3-septate, 35 by 4 (21 to 47 by 3 to 5) 
microns; from small to medium sporodochia (up to 1.5 mm. in diameter), often 
converging into pionnotes; chlamydospores intercalary and terminal and com¬ 
monly present in conidia; aerial mycelium typically scant; when present, short, 
white to gray; color of conidia from light brown 6 when grown in the dark, to 
ochraceous salmon or light ochraceous buff when grown in diffuse light; no 
sclerotia have been observed on any medium; color of substratum quite variable, 
on slightly acidified hard potato agar plates in diffuse light, from dark vinaceous 
purple to vinaceous purple; another series on same medium under same condi¬ 
tions color from chocolate to Hessian brown. 
Measurements of spores on the various media are as follows: 
On hard lima bean agar culture, 9 days old, conidia from pionnotes: Mostly 
3-septate, range 21 to 44X3 to 5a, average 35.6 X4/*. 
On hard lima bean agar,culture 20 days old, conidia from pionnotes: Mostly 
3-septate, range 30 to 47X4 to 4.6/*, average 40X4.3/1. 
On potato stem plug, culture 21 days old, conidia from small sporodochium: 
Mostly 3-septate, range 26 to 42X3 to 5/*, average 34X3.9/*. 
On raspberry cane plug, culture 24 days old, conidia from small sporodochium: 
Mostly 3-septate, range 30 to 38X3 to 5/*, average 34.5X4/*. 
On oat agar, culture 10 days old, conidia from large sporodochium: 75 per cent, 
3-septate, range 33 to 44X3 to 4.5/*, average 35.7X3.7/*; 24 per cent, 4-septate, 
range 35 to 45X3.2 to 4.8/*, average 39.2X3.6/*. 
On hard oat agar, culture 250 days old, chlamydospores (in conidia): Abun¬ 
dant, 0-septate, range 7.6 to 10.5X5 to 8.8/*, average, 8.2X7.9/*. 
< The writers are indebted to Miss Helen Johann for many helpful suggestions in connection with these 
studies. 
6 Designations of color are made according to Itidgway (7). 
