510 
Journal of Agricultural Research 
Vol. XXIX, No. 10 
tract. Where germination did occur, 
however, the growth was greater than 
in the control. In the second and 
third experiments the percentage of 
germination of A. niger was increased 
over the control in both white and 
colored scale extracts, and growth was 
practically the same in all three ex¬ 
tracts. 
It may be indicated, therefore, that 
whereas Aspergillus sp. 4660 is de¬ 
cidedly inhibited b\^ the water extract 
from colored scales, A. niger is only 
moderately retarded, if at all. Hence 
no rparked varietal resistance to the 
latter organisms would be expected in 
the colored types. This is in accord 
with the general observation. 
ent symptoms and have been respec¬ 
tively designated gray mold neckrot, 
mycelial neckrot, and small sclerotial 
neckrot. All three organisms are in 
the main wound parasites and usually 
enter through the neck of the bulb. 
The first two species are active pro¬ 
ducers of decay, commonly invading the 
entire bulb. The third form is less 
aggressive and is more often confined to 
the outer scales. 
The marked resistance of colored 
varieties of onion to Botrytis has long 
been recognized by onion growers and 
dealers. The greater susceptibility of 
white forms to B . allii is noted by 
Munn (I). Selby also mentions this 
fact (#), although it is not clear with 
Table II. — The effect of water extracts from dry outer scales of White, Yellow, 
and Red Globe varieties of onion on the germination and growth of certain species 
of Aspergillus and Helminthosporium as compared with Colletotrichum circinans 
Organism 
Experi¬ 
ment 
No. 
1 
! 
Germination in— 
Length of germ tubes in— 
Con¬ 
trol 
White 
scale 
extract 
Yellow 
scale 
extract 
Red 
scale 
extract 
Con¬ 
trol 
White 
scale 
extract 
Yellow 
scale 
extract 
Red 
scale 
extract 
Per cent 
Per cent 
Per cent 
Per cent 
Microns 
Microns 
Microns 
Microns 
Colletotrichum circinans _ 
1 
99 
80 
0 
2 
414 
224 
0 
0 
f 1 
38 
97 
0 
8 
11 
55 
0 
40 
Aspergillus niger _ __ 
49 
90 
90 
100 
1 3 
0 
89 
88 
52 
0 
203 
190 
195 
1 
88 
98 
1 
0 
47 
38 
1 
0 
A . sp. 4660.... ... 
1 2 
42 
80 
1 3 
0 
1 3 
6 
97 
2 
0 
21 
85 
10 
0 
Helminthosporium sp_ 
1 ! 
84 
100 
0 
2 
j 
Helminthosporium sp. is a small- 
spored form which commonly causes 
dark-colored blotches on the outer 
scales of White Globe onions, but has 
never been noted on the colored forms. 
The toxic effect of colored scale ex¬ 
tract is quite as distinct as with any 
other organism studied, while the white 
scale extract is apparently beneficial. 
It is probable, therefore, that the toxins 
in the red and yellow bulbs serve to 
restrict this organism largely to the 
white varieties. 
RELATION OF PIGMENT TO DEVEL¬ 
OPMENT OF BOTRYTIS AND TO 
NECKROT RESISTANCE 
Of the three species of Botrytis 
associated with the neckrot of onion, 
one, Botrytis allii, has been fully des¬ 
cribed by Munn (I). The remaining 
two species will be described in another 
paper by the senior writer, and will be 
referred to here as Botrytis sp. 110 and 
Botrytis sp. 108a. Although these 
forms commonly occur together, in¬ 
dividually they cause somewhat differ- 
which species of Botrytis he deals, 
since he undoubtedly was in error in 
referring to the causal organism as 
Sclerotium cepivorum . Botrytis sp. 110 
and Botrytis sp. 108a are the common¬ 
est in the Wisconsin and Illinois onion¬ 
growing sections, and the writers’ criti¬ 
cal field observations are confined large¬ 
ly to these forms. In 1920 and 1923 
white, red, and yellow onions were 
planted on old onion soil at Racine, 
Wis. The crops were placed in storage 
and the development of mycelial neck¬ 
rot during that period noted. 
The White Globe variety developed 
56 per cent of mycelial neckrot in 1920 
and 44 per cent in 1923. The Red 
Globe variety developed less than 
1 per cent in both periods. Yellow 
Globe developed 6 per cent in 1920, 
but was not included in the 1923 test. 
Yellow Strasburg, not included in the 
test of 1920, developed less than 1 per 
cent in 1923. 
The marked resistance of the colored 
varieties is thus evident. In both of 
these experiments comparative sus¬ 
ceptibility to Botrytis sp. 108a was also 
