BEAN BLIGHT 
This is the common bacterial disease of beans. It apparently affects 
all varieties of Phaseolus. vulgaris L., the field- and garden-bean, as well 
as the Lima bean, Phaseolus lunatus L. 
SYMPTOMS 
This disease affects all parts of the host above the ground, leaves, 
stems, pods and seeds. 
On the leaves. Examine the leaves provided and OBSERVE :— 
1. The location, size, color and general appearance of the lesions 
on both sides of the leaf. 
2. The zonate character of the spots. How do you account 
for each zone, especially the opaque, green water-soaked zone which shows 
best when the leaf is held to the light; also the pale green outermost zone? 
Draw to show these characters and indicate fully in the labeling, the 
color and appearance. 
On the stems. The affected stems show no distinct lesions since only 
the vascular system, as arule, is usually involved. Diseased stems finally 
shrivel following the wilting of the leaves. This symptom is not common. 
On the pods. Examine the pods provided and oBSERVE :— 
3. The location, size, color and water-soaked appearance of 
the lesions. Pod-lesions are sometimes red-bordered. (See illustration 
specimens.) 
4. Depth to which the lesions penetrate. Determine by cutting 
across the pod through a lesion. Draw to show form and depth of the 
lesion. Label fully as to color and character. 
On the seed. Examine the lesion with a hand-lens and OBSERVE :— 
5. The discolored, roughened surface. To what is this due? 
What relation do the lesions on the seed bear to the pod-lesions? Make a 
DRAWING showing the character of the lesions on the seed. 
Examine the passe-partouts provided and compare the symptoms of 
this disease with those of the anthracnose, a fungous disease of the bean 
which is also very prevalent. Make prawincs of a pod, seed and leaf 
affected with anthracnose, showing how the symptoms of that disease 
differ from those of the bean blight. 
ETIOLOGY 
The cause of this disease is Bacterium Phaseoi E. F. Smith (=Pseudo- 
monas Phaseol: EFS.), a monotrichic bacterium which produces yellow 
colonies on agar. 
Life-history. This organism is a restricted parasite, normally passing 
its entire life within the bean. It probably has no true saprogenic phase 
in its life-history. 
The Primary Cycle is initiated in the spring from the cotyledons 
of diseased seedlings. 
Pathogenesis. Diseased seed have been soaked a short time in water. 
Peal the seed-coat from the lesion. Make two mounts, one from the 
diseased seed-coat and one from the diseased cotyledon, chopping and 
crushing the tissues. OBSERVE:— 
6. The minute, short rod-shaped bacteria to be detected only 
with the high-power. Are they inside or outside the cells? DRaw. 
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