Bacterial Spot Bacterial Diseases on Tomato

Optimum Temperature: 24°C- 30°C

Causal Organism: Xanthomonas campestris pv. vesicatoria

Symptoms:
- The bacterial spot pathogen may produce lesions on all aboveground parts of the plant- leaves, stems, flowers and fruit.

- It is difficult to reliably distinguish bacterial spot from bacterial speck based on visual symptoms, especially in the early stages.

- Initial leaf symptoms are small, circular-to-irregular, dark lesions, which may be surrounded by a yellow halo.

- The lesions tend to concentrate on the leaf edges and tip and may increase in size to a diameter of 3-5 mm.

- Infected leaves may develop a scorched appearance. When spots are numerous, foliage turns yellow and eventually dies, leading to defoliation of the lower portion of the plant.

- Lesions on pedicels may cause flower abortion, resulting in lost yield and split sets of fruit.

- Fruit lesions are initiated only on green fruit, most likely because infection occurs through fruit hairs, which are present only on immature fruit.

- On fruit, the first symptoms are small, dark brown-to-black, raised spots.

- The lesions also may have a white halo, similar to the bird's-eye spotting seen with bacterial canker.

- As the fruit ages, the white halos disappear.

- In contrast, bacterial canker fruit lesions retain their white halo.

- Bacterial spot lesions may increase in size to 4-6 mm in diameter and become brown, greasy-looking and sometimes scabby.

Inoculum and Spread:
- The major sources of infection for these bacteria are thought to be seed and infected crop debris.

- Like the bacterial speck pathogen, they also may be present on volunteer tomato plants and on the surfaces of contaminated equipment (farm machinery, racks, greenhouse structures, tools).

- The bacteria are spread primarily by splashing water and wind-driven rain or mists produced during storms.

- In the field, spread by equipment or workers is probably of lesser importance than it is in the greenhouse, unless wounds are being opened up at the same time, as in a pruning operation or when plants are injured by a cultivator.

- Bacteria enter the plant through natural openings (stomates and hydathodes) or wounds caused by wind-driven soil, insects or mechanical damage (handling, wind whipping, high pressure sprayers).

Source: http://www.omafra.gov.on.ca/