Aug. 15, 1924 
Bacterium Marginatum on Gladioli 
175 
herbarium of the Bureau of Plant 
Industry, United States Department 
of Agriculture. 
SUSCEPTIBILITY 
This disease has been observed on 
practically all the varieties of the 
gladiolus commonly grown by florists 
but most of the inoculation tests and 
close observations have been on the 
varieties America and Mrs. Francis 
King. 
OVERWINTERING AND DISSEMINA¬ 
TION 
It has been demonstrated that the 
organism may be carried over from 
season to season on the corms. The 
causal organism has been found in a 
living and virulent condition on corms, 
stored under usual conditions, 9 months 
after being harvested. Corms as badly 
marred as those shown in Plate 3, 
with the husks so disintegrated that 
the pitted body of the corm is exposed, 
would probably be discarded by most 
growers. Other corms having small, 
inconspicuous spots on the outer husks 
might pass as healthy. These spots 
may or may not extend through the 
several layers of husks to the corm. 
Infected husks are probably as great, 
if not a greater, source of infection than 
infected corns, for the reason that at 
planting time or later in cultivating, 
broken or loose pieces becoming in¬ 
corporated with the soil, may come in 
direct contact with the plants. 
Great numbers of the parasite are 
often found on the husk parts through 
which the growing bud must push and 
some of the infecting material, carried 
along with the growing leaves, may 
eventually succeed in producing leaf 
infections which become foci for other 
infections. Meanwhile on the parent 
corm the husks are disintegrating and 
the body of the corm is changing to a 
shrunken mass on which the old pits 
are still distinguishable but not in¬ 
creased in size or depth. 
Observation of many plants indicates 
that the new corm, though in such inti¬ 
mate contact, is not ordinarily directly 
infected by the diseased parent corm. 
Many healthy plants have been grown 
in the greenhouse from diseased corms. 
The husks were removed and the corms 
planted rather deeply in clean sandy 
soil. These plants were not repotted 
nor was the soil disturbed in any way. 
In practically every case healthy plants 
and clean, new corms were produced. 
Similar corms planted outdoors- in a bed 
where the disease had occurred for sev¬ 
eral years and cultivated in the usual 
way, invariably became infected. It 
was observed that the loose soil was 
dashed on the plants by every rain¬ 
storm and considerable soil left sticking 
to the lower leaf parts and that infection 
occurred most abundantly on the parts 
spattered with soil. This, as well as 
some other experiments, indicates that 
the infection came from infected soil. 
Inoculation experiments have shown 
that the corms are most easily infected 
when the husks are young and still full 
of moisture. Unless the bacteria come 
in contact with the husks during this 
susceptible period the parasite seems 
unable to penetrate deeply enough to 
reach the body of the corm. 
Favorable temperature and moisture 
of the soil are also doubtless factors in 
the initial infection and in the contin¬ 
ued activity of the bacteria. It has 
been noted that plants in the moister 
parts of fields and beds have heavier in¬ 
fection than surrounding plants in bet¬ 
ter drained soil. 
The part played by insect trans¬ 
mission of the disease also needs to be 
considered. In a few cases of corms 
planted in unsterilized garden soil, 
mites have been found in connection 
with the lesions of the husks and corms. 
The mites had made perforations in 
the dark husk spots and small burrows 
in the corm spots. Except for the holes 
these lesions were typical for Bacterium 
marginatum and this organism was 
isolated from both husk and corm spots 
that definitely showed mite attacks. 
If mites are able to penetrate normal 
gladiolus tissues, they probably aid in 
distributing the infection. 
DISINFECTION EXPERIMENTS 
Disinfection experiments have not 
been extensive but it is believed that 
corms can be treated so as practically 
to control the disease. 
The following experiment was made, 
using badly pitted corms, variety Mrs. 
Francis King: 
The corms were first soaked for 15 
minutes in water, then the water was 
poured off and the corms were pro¬ 
tected so as to retain moisture for 
several hours. This process softened 
the hardened exudate, which otherwise 
might have interfered with the action 
of the disinfectant. Four lots were 
then treated for one-half hour as 
follows— 
(a) Mercuric chloride, 1-1000. 
(b) Copper sulphate, 1 ounce to 
1 gallon of water. 
(c) Formalin, 1-40. 
(d) Formalin, 1-80. 
