Nov. 1, 1925 
Bacterial Spot of Oowpea and Lima Bean 
851 
early stages of the leaf lesions caused by Cercospora cruenta Sacc. 
are more diffuse and less clearly defined. The older lesions are 
larger than the bacterial lesions, with a darker center and less con¬ 
spicuous border than the latter, and show some tendency, at least 
in the Blackeye variety, to be delimited by the larger veins. The 
abundant sporulation of the fungus is of course a reliable differential 
characteristic. 
ECONOMIC IMPORTANCE 
The bacterial spot disease may cause very severe foliage injury to 
cowpea seedlings and young plants, especially in wet seasons, and 
not only kills leaves but may even cause the death of many young 
plants. Tisdale has reported through the Federal plant disease 
survey that this disease caused a serious defoliation of cowpeas in 
Florida. In the cowpea crop grown for seed the pod lesions of this 
disease may cause considerable loss. In the case of lesions con¬ 
stricting and stunting the pod, the number of seeds is reduced, and 
seeds borne under lesions are stunted or shriveled, are impaired in 
germinability, and produce diseased and weakened seedlings. Leaf 
and stem infection on older plants is, as a rule, less destructive. The 
disease seems to be very destructive to lima beans, especially in its 
leaf attack 
CAUSAL ORGANISM 
ISOLATION 
The bacterial nature of the disease on cowpeas was discovered in 
the late summer of 1921. On August 26 the surface of a spotted pod 
was sterilized in a 1:1,000 solution of mercuric chloride and a lesion 
was cut out with a flamed scalpel and macerated in^ drop of sterile 
water on a flamed slide. This drop of water was plated out in potato- 
dextrose agar by the loop-dilution method, ana after three days at 
room temperature the plates were evenly seeded with similar grayish- 
white bacterial colonies. The surface was sliced off from another pod 
lesion and a portion of the underlying brown tissue of the ovary wall 
was similarly tested. The plates were evenly seeded with colonies 
similar to those from the other lesion. 
On the same date two leaf lesions were cut out with flamed scissors, 
immersed first in alcohol to wet the surfaces and then in a 1:1,000 
solution of mercuric chloride for a few minutes, rinsed in sterile 
water, and macerated in drops of sterile water on flamed slides. The 
loop-dilution plates from both lesions were evenly seeded with grayish- 
white colonies apparently identical with those in the plates from the 
pod lesions. Furthermore, 18 leaf lesions were similarly cut out, 
sterilized, rinsed, and planted in poured plates of potato-dextrose 
agar. Grayish-white bacterial growth occurred around nine of 
these. Poured plate isolations made on August 30 from leaf, pod, 
and stem lesions yielded a similar organism. Numerous transfers 
were made from typical plate colonies to dextrose-potato agar slants 
and all appeared to be similar. Successful atomizer inoculations were 
made in the field and greenhouse, and the organism was reisolated 
from the lesions produced. 
Successful isolations were made later from seedling cowpeas grown 
in sterile soil from diseased commercial seed. The organism was 
obtained from lesions on cotyledons, first leaves, epicotyl, and 
hypocotyl, and from vascular infection in the epicotyl. In 1923 the 
