Bacterial wilt

Scientific name: Ralstonia (Pseudomonas) solanacearum
Causal organisms: Bacteria

Host plants

Potato, tomato, tobacco, eggplant, banana and plantain are the major hosts but peanut, bell pepper, cotton, sweet potato, cassava, castor bean, ginger and other solanaceous weeds are also affected

Affected plant stages

Vegetative and reproductive stages

Affected plant parts

Whole plant

Symptoms

Bacterial wilt is very destructive especially during hot and wet seasons. Plants wilt and die suddenly.

Bacterial wilt of potato

The infested leaves wilt during the (sunny) day and sometimes recover during cool hours. The wilting is similar to the result of lack of water. During the rapid development of the disease, the entire plant wilts quickly without yellowing. Other symptoms could be wilting of only a part of the stem, or one side of the leaf/ stem, or the stem wilts or dries up completely and the remainder of the plant remains healthy. The infested tuber releases the bacteria on its 'eyes'. Cutting the diseased tuber will show a browning and a death of the vascular ring and the immediate surrounding tissues of up to 0.5 cm each side of the ring. On the cut surface, a creamy fluid usually appears on the vascular ring.

Bacterial wilt of tomato/eggplant

The initial symptom is a wilting of the terminal leaves, which after 2 - 3 days becomes permanent when the whole plant wilts due to the active development of the disease. Then the whole plants wilt and die suddenly. In the case of a slow development of the disease, the plant stunts and produces large numbers of adventitious roots on the stem.

Bacterial wilt diagnosis in the field can be done easily. Cut a piece of the stem 2 - 3 cm long from the base. Suspend the cut stem in clear water in a glass container. Hold the stem with an improvised tong to maintain it in a vertical position. Within a few minutes, the smoke-like milky threads are discharged from the cut stem.

Moko disease

An initial symptom of an infected banana is that one of the youngest three leaves turns pale-green or yellow in color and breaks down at the junction of the petiole and the pseudostem. All the other leaves follow to collapse around the pseudostem after one week. An infected finger or fruit shows dry and rotted pulp that is colored brown or black, and the presence of bacterial discharges.

Conditions that favor development

1. Crop residues left in the field that were infected by Ralstonia solanacearum
2. Injured roots caused by farm tools or by soil pests
3. Warm temperature and high moisture
4. High soil pH
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5. Poor and unfertile soil
6. Nematodes present in the soil

Preventive control

1. Remove and destroy all infected plants immediately
2. Control nematodes
3. Rotate crops other than solanaceous crops. Rice, corn, beans, cabbage, and sugarcane are found to be resistant to bacterial wilt
4. Since the bacteria can be transmitted through farm tools, wash or expose them to heat before using in another field
5. For banana, remove and chop the plants surrounding the infected mat or within the radius of 6 meters from the infected plant to prevent further spread of the disease

References

• Brooklyn Botanic Garden. (2000): Natural disease control: A common-sense approach to plant first aid. Handbook # 164. Brooklyn Botanic Garden, Inc. 1000 Washington Avenue, Brooklyn, NY.
• PCARRD. (1988): Philippine recommends for banana. Technical Bulletin Series No. 66, DOST, Philippines.
• Ploetz, R.; et. al. Editors. (1998): Compendium of tropical fruit diseases. APS Press, The American Phytopathological Society. Saint Paul, Minnesota, USA.
• Thurston, D. (1998): Tropical plant diseases. Second Edition. APS Press. The American Phytopathological Society. St. Paul, Minnesota, USA.
• Wagner, Georg. (2004): Vegetables' pests. Personal Communication. Schopperplatz 14, 4082 Aschach / Donau.