Bacterial wilt is a disease with a high negative economic impact in tropical and sub-tropical regions of the world. It is caused by a soil-borne bacterium, Ralstonia solanacearum.
This bacterium causes wilting in several crops belonging to the solanum (tomato) family such as potatoes, tomatoes, tobacco, bell pepper and eggplant.
It also causes wilting in bananas, peanuts, ginger and geraniums. The bacterium can be introduced into a field by infected transplants, soil on vehicles, ploughs, machinery, tools or other sources, and in contaminated water.
Once a field is contaminated, the bacteria spreads through water (rain and irrigation), tillage and other practices that move soil, including the movement of people and animals during planting, cultivation and harvest.
Symptoms
The most obvious symptom is the sudden wilting of plants. This often occurs during flowering and green fruit production. The plants wilt during the heat of the day and recover at night.
Eventually, they collapse and do not recover, even when water is provided.
Diagnosis
When the outer tissues are cut away from an infected plant with a knife, the inner stems will show a brown discolouration of the vascular system (water conducting elements), especially at the soil line.
The presence of bacteria in wilted plants can be confirmed by placing a cut stem, taken from near the soil line, into a clear container of water.
If the plant has bacterial wilt disease, white strands will stream out from the bottom of the stems into the water. This test, known as bacterial streaming, is diagnostic of bacterial wilt.
Control
Bacterial wilt is difficult to control because the bacterium can survive in soil for long periods of time. It can infect and survive in association with a wide range of crops and weeds.
Effective management of bacterial wilt therefore requires an integrated approach.
