440 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
Table III.— The quantity of reducing sugars in mg. per 10 cc. resulting from the 
hydrolysis of cane sugar , starchy and cellulose by 0.5 gm. of hyphae of A. brassicae 
in 25 cc. of solution 
Substances tested 
Hyphae grown on sweet- 
potato decoction 
Hyphae 
grown on 
cabbage 
decoction in 
the dark 
In the dark 
In the light 
0.75 per cent cane-sugar solution_ 
91.38 
82. 66 
95 58 
0.75 per cent starch paste_ 
68.80 
58.14 
61.05 
00.00 
Cellulose_____ 
00.00 
00.00 
Table IV.— The hydrogen-ion concentration of cabbage and sweet-potato decoctions 
on which A. brassicae had grown for 12 days and of the uninoculated controls 
Solutions 
Treatment 
Ph 
Cabbage decoction-- 
Do __ 
Uninoculated control, held in the dark_ 
Uninoculated control, held in the light_ - .. 
5.24 
5.01 
7.27 
7.54 
4.96 
4.96 
6.46 
6.58 
Do _ 
Inoculated, held in the dark___ 
Do _ 
Inoculated, held in the light___ 
Sweet-potato decoction- 
Do ___ 
Uninoculated control, held in the dark_ 
Uninoculated control, held in the light_ 
Do 
Inoculated, held in the dark__ 
Do -- 
Inoculated, held in the light__ 
the ice bunkers at frequent intervals. 
The addition of salt to the ice in the 
bunkers and the placing of ice in and 
over the load will help to keep the tem¬ 
perature down. Precooling the cars as 
well as the cauliflower before loading 
should prove beneficial, especially when 
shipments are made during warm 
weather. 
SUMMARY 
(1) The leaf spot of cauliflower caused 
by Alternaria brassicae has been studied, 
the pathogenicity of the casual fun¬ 
gus has been established, and the symp¬ 
toms produced on plants of different 
ages and under different conditions 
described. 
(2) A decay of the curd of cauli¬ 
flower, called “brownrot”, is also pro¬ 
duced by A. brassicae. This disease of 
the head is found only when the cauli¬ 
flower is overmature or when the head 
has been cut from the stalk. The 
disease is most destructive on cauli¬ 
flower heads in transit where they are 
decayed or discolored, so that their 
market value is greatly reduced. 
(3) A. brassicae has an optimum tem¬ 
perature for spore germination of 33° 
to 35° C. The maximum temperature 
for spore germination lies somewhere 
between 40° and 46° and the minimum 
is below 1.5°. 
(4) The optimum temperature for 
the growth of the mycelium in Petri 
dishes on Irish potato agar lies be¬ 
tween 25° and 27°. The fungus made 
some growth at 36° but none at 38°. 
No growth was evident at 2°, the low¬ 
est temperature tried, until after the 
eighth day. The minimum for growth 
is somewhere below 2°, although growth 
is very slow at this temperature. 
(5) The maximum temperature for 
infection of detached cauliflower leaves, 
artificially inoculated and held in moist 
chambers at various temperatures, was 
about 36°. The optimum for infec¬ 
tion under the same conditions lay be¬ 
tween 28° and 31°. Infection was evi¬ 
dent at 7° in five days. 
(6) The optimum temperature for 
infection of the heads inoculated and 
held at various constant temperatures 
in moist chambers was between 25° and 
30°. No infection took place at 34.7° 
or above. Infection did not become 
apparent at 1.8° for from 5 to 7 days, 
at which time the lesions appeared as 
very minute light-brown discolorations 
just visible to the unaided eye. The 
disease had developed but little at the 
end of 19 days. Infection was appar¬ 
ent in from 4 to 5 days at 7°, and 
in 19 days the decay extended into 
the tissue 1 to 2 mm. Although little 
actual decay was caused by this disease 
in two weeks below 10°, some decrease 
in the commercial value of the infected 
cauliflower resulted from the browning 
of the curds. The amount of infec¬ 
tion and the rate of development of 
the disease increase as the humidity 
of the surrounding air is raised. 
