182 
Journal of Agricultural Research 
Vol. XXX, No 
small sclerotial neck rot. As with B. 
allii, it usually enters through wounds 
at the neck but attacks the succulent 
scale tissues less rapidly than does B. 
allii. 
Two strains of Botrytis dnerea Pers. 
were also included. One strain was 
isolated by the writers from cyclamen, 
the other was secured from G. B. Ram¬ 
sey, who had isolated it from tomato. 
The parasitic behavior of this species 
has been described most recently by 
Brown ( 1 ). Its method of invasion 
on other plants is very similar to that 
described by Munn (5) for B. allii , ex¬ 
cept that B. dnerea may penetrate the 
leaf cuticle. Inoculation experiments 
with these strains on onion bulbs 
yielded only negative results. 
FUSARIUM 
Two strains of Fusarium (Fusarium 
cepae Han. and Fusarium sp. 45) iso¬ 
lated from onion and determined by 
inoculation to be capable of causing the 
common Fusarium bulb rot were used. 
For comparison, the wheat-scab organ¬ 
ism, Fusarium graminearum Schwabe 
{Gibber ella saubinetii (Mont.) Sacc.) was 
included. The onion Fusaria are par¬ 
enchyma invaders. They enter princi¬ 
pally through wounds at the base of the 
bulb and cause a semiwatery decay ( 8 ). 
The exact relation of parasite to host 
tissue has not been studied. 
ASPERGILLUS 
Two forms of Aspergillus were used. 
The black mold fungus (Aspergillus 
niger Van Tiegh.) is a common storage 
fungus, especially upon the southern 
Bermuda crop {6). The organism de¬ 
velops on the dead outer scales or be¬ 
tween the succulent scales of the bulb, 
and the invasion of sound healthy 
scales is comparatively meager. Upon 
injection into wounds on the bulb it 
does not cause decay. It appears to 
have no marked preference between 
colored and white varieties of the Ber¬ 
muda types. 
A second species of Aspergillus, 
isolated from Italian garlic by E. D. 
Eddy, was used for comparison. This 
produces yellow spores and dark- 
brown sclerotia in abundance. Charles 
Thom of the Bureau of Chemistry, 
United States Department of Agri¬ 
culture, to whom the culture was 
referred, is at present working upon the 
classification of this and related forms, 
and for the purposes of this discussion 
it will be referred to by his number, 
4660. When spores and mycelium 
were injected into wounds in onion 
bulbs, a rapid decay resulted. In 
contrast to A. niger, then, it appears 
to be an active parasite of the onion 
bulb. 
GERMINATION AND GROWTH IN 
ONION JUICE 
It has already been shown (7) that 
ordinarily spores and mycelium of 
C. circinans neither grow nor survive 
in the undiluted juice expressed from 
onion scales. This is probably due for 
the most part to the residual, nonvola¬ 
tile toxin which remains in the ex¬ 
tracted cell sap. It is obvious there¬ 
fore that the fungus hyphae would not 
invade the lumen of the host cell with¬ 
out some change in the contents of 
the latter being produced in advance 
of them or at least not without being 
protected by the plasma membrane of 
the host. It appears that changea 
in the host cell do occur in advance of 
the onion smudge organism ( 6 ). It 
was of interest to determine whether 
the extracted juice was similarly toxic 
to other bulb parasites. Spores of 
each of the fungi mentioned were 
placed in drops of expressed onion 
juice which was diluted to various 
degrees with distilled water. The 
results are recorded in Table V. 
It was found that, with one excep¬ 
tion, none of the spores germinated in 
undiluted juice. Very little germina¬ 
tion occurred in a dilution of 1 to 1. 
It was generally true of all these fungi 
that germination and growth increased 
with greater dilution. This points to 
the presence of toxins, rather than lack 
of nutrient as the principal inhibitory 
factor, inasmuch as dilution decreases 
the amount of available food. In the 
dilution of 1 to 10 it is noteworthy that 
all three species of Colletotrichum 
were still completely inhibited, while 
the species of Botrytis and Fusarium 
which are pathogenic to onions germi¬ 
nated and grew. In these two genera 
the nonpathogenic species tried were still 
almost completely inhibited. It is inter¬ 
esting also to compare the two species 
of Aspergillus. A. sp. 1+660, which is a 
vigorous bulb-decaying organism, grows 
well in the 1 to 10 dilution, while A. 
niger, a superficial fungus, is entirely 
inhibited. The differences in the be¬ 
havior of the various species becomes 
less marked in the higher dilutions. 
It is significant that of the onion 
parasites, the organisms causing the 
most rapid decay (Botrytis allii, Fusa¬ 
rium cepae , Fusarium sp. 45, and 
Aspergillus sp. 4660) show germination 
and growth in the 1 to 10 or in lower 
dilutions, while the least aggressive 
parasites (Colletotrichum circinans and 
