BACTERIAL EEAFSPOT OF GERANIUM IN THE EASTERN 
UNITED STATES 1 
By N^ixm A. Brown 
Pathologist , Laboratory of Plant Pathology , Bureau of Plant Industry , United States 
Department of Agriculture 
The florist's season for growing cuttings of geraniums (Pelargonium 
spp.) for garden and window-box planting is the season when this bacterial 
disease may be looked for, especially in crowded, ill-ventilated houses. 
Nearly every spring since 1912 and at any time during March, April, 
and May, according to the locality where the plants are grown, we have 
received diseased specimens. Very rarely has a diseased plant grown 
in the open been sent to us. Our first acquaintance with it, however, 
was at an earlier date when it occurred on the grounds of the United 
States Department of Agriculture in Washington (PI. 1, A). In New 
Jersey and Maryland the disease has been especially prevalent and of a 
destructive nature, whole houses of rooted plants in some instances 
becoming unsuitable for market. It is a spot disease which makes the 
leaves unsightly and undermines the health and development of the 
cuttings. The year 1915 was evidently favorable for the disease, for it 
occurred very generally in the eastern part of the United States. 
The spots are definitely outlined, usually irregular but occasionally 
circular in shape, and of a brown color. The spotting may begin either 
at the margin of the leaves or on the blade and may occur on either old 
or young leaves, although the older leaves or those nearest the soil are 
usually the worst affected. The youngest infected areas are watery 
looking, then become a reddish brown, later the tissue dries and becomes 
dark brown. When the disease is advanced the portion of the leaf 
between the spots turns dark and becomes dry and wrinkled. The 
spots, however, still show plainly in the dead area. The bacteria, which 
are motile, occur in great numbers in the spots. They are easily isolated 
from the young spots, as the epidermis can be sterilized with mercuric 
chlorid (1 to 1,000) for three to five minutes without much penetration. 
Isolations were made from material received from Maryland (PI. 1, B), 
and water suspensions of subcultures were sprayed on young geranium 
plants growing in the greenhouse. The plants were kept in a moist 
infection cage for two days. In another cage, which was also kept 
moist, were other geranium plants of the same age which were sprayed 
with sterile water. Typical spots appeared on the inoculated (sprayed) 
leaves in 9 days, and in 17 days the plants were badly spotted (PI. 3, B). 
The controls did not show any spotting. Bacteria were abundant in 
the spots. The organism was reisolated and other geranium plants 
were infected with it by spraying. In four days spots began to show on 
the leaves of these sprayed plants. The temperature was higher at this 
time, being So 0 F. during most of the daytime. 
1 Accepted for publication May io, 1922. 
Journal of Agricultural Research, 
Washington, D. C. 
add 
Vol. XXIII, No. 5 
Feb. 3. 1923 
Key No. 276 
(361) 
