Xanthomonas vesicatoria is a bacterium that causes bacterial leaf spot on peppers and tomatoes.
Life cycle and appearance of Bacterial spot
Xanthomonas vesicatoria survives on volunteer tomato plants in the field and on diseased plant debris. The bacteria are also seed-transmitted. Disease development is favoured by temperatures between 24 and 30 °C and high precipitation due to rain, fog or overhead irrigation. Infection is through stomata and wounds. The dispersal is in windblown water drops, mechanical means such as clipping and handling and aerosols. Many isolates are resistant to copper-containing pesticides.
Xanthomonas vesicatoria in tomato causes small, water-soaked spots on leaves which are first round and become more angular as they grow. The centre of the lesions may fall out as they become drier. Under humid conditions, the spots may merge with lesions on the petioles and stems and form long dark streaks. On fruits, first small black specks are seen on green fruits. The specks grow into brown spots that look like scab. These spots may be surrounded by a halo.
In pepper, the spots on the leaves are also round and small to start with and slightly raised from the leaf surface. They occur on the abaxial (underside of) leaf surfaces and may enlarge into dark brown lesions with a light brown centre. As with powdery mildew infection, pepper plants shed the leaves that are severely infected. Humid conditions are conducive for lesion expansion. On the stems, long, narrow cankers appear, which become rough and light brown. On fruits the spots are first small, circular and green but they turn brown, become raised and look like cracked scab.