Click on images for larger versions Figure 2. Lesion originating from insect feeding injury Symptoms Plants may be affected with black rot at any stage of growth. Seedling infection first appears as a blackening along the margin of the cotyledon. Later, the cotyledon shrivels and drops off, but only after the bacteria have passed into the young leaves and stem. Affected seedlings turn yellow to brown, wilt, and collapse.
Diseased areas enlarge and progress toward the base of the leaf, turn yellow to brown, and dry out.
The veins of infected leaves , stems, and roots turn black as the pathogen multiplies. On cauliflower, black rot commonly appears on the leaves as numerous, minute brown specks. The infected lower leaves of cabbage and cauliflower are usually stunted, turn yellow to brown, wilt, and drop prematurely. Occasionally, diseased plants have a long bare stalk topped with a small tuft of leaves. In extreme cases, heading may be prevented.