July 21, 1923 
Bacterial Spot of Lima Bean 
151 
soil, in 8-inch pots and when the first two or more leaves had developed 
they were inoculated with an atomizer spray of a water suspension of a 5 
to 10-day old culture of the organism. The plants were then placed in 
a warm, damp chamber for 24 hours, after which they were removed to a 
greenhouse bench where the temperature was about 22 0 C. 
Practically the same method of inoculation was used in the field. 
Plants free from the disease were selected, inoculated with atomizer 
spray, and then covered with a glass moist chamber over night or in 
humid cloudy weather they were left uncovered. In all these experi¬ 
ments the plants were inoculated before the blossoms began to appear. 
Both inside and out of doors typical lesions began to develop in from 
2 to 7 days after the plants were inoculated. 
Control plants were always sprayed with sterile water and incubated 
under the same conditions as inoculated plants, but in no case did the 
disease develop in them. 
RELATIONS TO HOST TISSUE 
Inoculation experiments have shown that wounds are unnecessary for 
infection. Razor sections of recently infected leaf tissues showed inva¬ 
sion to be in the parenchyma. Young lesions in leaves were fixed in 
Gilson’s solution, imbedded in paraffin, sectioned, and stained with 
Ziehl’s carbol-fuchsin. A study of diseased material prepared in this 
way showed that the organism enters through the stomata and works 
its way into the underlying tissue between the cells. TKelhiddle lamella 
was destroyed and the cells were crowded apart by the increasing num¬ 
bers of bacteria. In the later stages the walls may be tom or collapse 
and the bacteria invade the cell cavities. The infected areas dry out 
and become sunken on the lower surface. No vascular invasion was 
observed. 
OVERWINTERING AND CONTROL 
Up to this time practically no experimental work has been done in 
relation to the overwintering of the bacterial spot organism and the 
methods for controlling the disease. It has been noted, however, that 
the disease attacks the pod and seed which suggests the possibility of 
the organism living overwinter with the seed. In 1917, when severe pod 
infection developed, only a few infected pods matured. These were 
picked, and the seed was planted the following spring in the greenhouse, 
but no infection appeared on any of the plants. 
It should not be inferred from this one experiment, however, that dis¬ 
eased seed is not a source of primary infection. Since a pathogenic 
strain of the organism has been isolated from diseased leaves kept for 
two years in a herbarium, it seems quite possible for the organism to live 
over winter in the diseased seed as well, and possibly in the diseased 
leaves in the field. It has been noted also that the disease appeared 
year after year in the same garden in the first young leaves, but rarely 
became serious until later in Hie summer when both old and young leaves 
were attacked. This condition is not universal, since gardens have been 
found free from the disease early in the season and several gardens under 
our observation have remained free from it throughout the entire year. 
Until further work on overwintering and dissemination has been done, 
it seems inadvisable to recommend any specific control measures. Since 
the causal organism of bacterial spot attacks the seed, seed disinfection 
