July ai, 1923 
Bacterial Spot of Lima Bean 
143 
on the upper or grooved side of the petiole, and may extend throughout 
its length. When it attacks the base of the leaf stalks, the leaves shed 
prematurely. 
The disease is not confined to the leaves but also occurs in the stems 
and pods. On the stem the lesions vary in size from 1 mm. to several 
centimeters long (PI. 2). The lesions on the stems as well as on the 
petioles extend into the vascular tissue, but no evidence was found to 
indicate that the organism progressed very far through the vessels. A 
straw or light wine-colored exudate appears on the stem lesions in the 
moist chamber and occasionally in the field, which dries down and forms 
a thin glistening crust. In several cases the peduncles were found 
attacked and even completely girdled. In such cases, and when the 
pedicels are attacked, the blossoms and young pods shed. Brown spots 
have been observed on the blossoms of diseased plants, but the organ¬ 
ism has never been isolated from them. 
On the pods the disease begins as small brown spots surrounded by a 
water-soaked halo. The lesions may occur both on the side of the pod, 
and also along the sutures where they become streaks (PI. 3, A). They 
may extend through the walls of the pod and attack the seed, in which 
case the veins of the seed coat around the invaded area often exhibit a 
reddish color and occasionally a white sticky exudate underneath the 
seed coat. In some cases spongy excrescences were found protruding 
from the inner walls of the pod beneath the surface lesions. A crust 
of exudate was found on some of the pod lesions in the field. When 
diseased pods were kept over night in a moist chamber, drops of a straw- 
colored exudate appeared on the lesions (PI. 3, B). These drops later 
dried down to form a thin crust. 
Isolations made from stems, leaves, and pods, such as here described, 
have produced typical lesions when applied to healthy plants and reiso¬ 
lations have yielded the typical organism. 
SEASONAL OCCURRENCE 
Since the bacterial spot of lima bean has been under observation a 
variety of conditions has been found to exist. In 1917 the disease 
appeared on the first leaves and progressed steadily throughout the 
season until frost killed the plants. In 1918 no observations were 
made. Again in 1919 the disease appeared early in the season, but 
its development was checked in July with the onset of dry weather and 
the subsequent growth of the plants was free from the disease. On the 
other hand, the blight caused by B. phaseoli was common in lima beans 
at Madison, especially in the phytopathological garden where the lima 
beans were planted beside common beans. Practically the same con¬ 
ditions obtained in 1920. In 1921 the disease did not appear until 
later in the summer, but once started, it continued to develop until 
frost. By this time the plants were very ragged. It thus appears that 
frequent rains and favorable temperature are necessary for dissemina¬ 
tion of the organism and development of the disease. 
ECONOMIC IMPORTANCE 
Under field conditions as observed in 1917 bacterial spot is an im¬ 
portant disease of the foliage. Practically no pods were set in the 
phytopathological garden after August 15 because of the severe infec- 
