Bacterial wilt

Bacterial wilt known as Ralstonia solanacearum biovar 3, formerly known as Pseudomonas solanacearum (SMITH) and Burkholderia solanacearum). Bacterial Wilt also known as Southern bacterial wilt or sleeping disease. It is a serious soil borne disease that is endemic to the tropical, subtropical and the warm, temperate areas of the world. Bacterial wilt lives in the soil and infect the plants through the roots or stem. They move into the large vascular bundles and later cause a decay of the pith which may produce large cavities in the stem. The wilting is caused by gradual blocking of the movement of water in the stem. Bacterial wilt is most active in temperatures above 24°C.

Conditions for the development of bacterial wilt

• • During warm, moist conditions the pathogen develops rapidly.
• • Optimum temperature : 28°C to32°C.
• • Pruning and trellising wounds as well as insect wounds can also cause infection.
• • The disease can be spread through implements, shoes and hoofs.
• • Run off water can contaminate streams and rivers in the lower areas.

Symptoms of bacterial wilt

• Surface symptoms usually occur 2 to 8 days after infection of the plant
• Initial wilting usually occurs during the warmer times of the day and plants recover when the temperature drops in the afternoon.
• Wilting becomes permanent when the disease progresses.
• Initially only one or two leaves of the plant start to wilt.
• A rapid overall wilting of the plant can occur 2 to 3 days later where after the plant may die.
• The disease usually appears in patches but it can spread to wider areas if a susceptible host is planted repeatedly visited by insects.
• If the stem of a wilted plant is cut across near the ground, the pith has a darkened, water soaked appearance and there is a greyish, slimy exudate when the stem is pressed.
• Bacterial wilt causes no spotting of the fruits.
• Bacterial wilt differs from fusarium and verticillium wilt , which do not cause sudden wilting or decay of the stems of older plants.
• Quite often adventitious roots start to develop

Roots

• Below ground symptoms appear as various degrees of root decay
• Initially, one or a few roots may show a brown rot.
• The entire root system may show a brown rot.

Systemic symptoms

• The vascular system in the stem of a plant in the early stages of the disease appears yellow or light brown in the transverse or longitudinal section.
• Becomes a darker brown as the disease progresses.
• The pith and cortex also becomes brown.
• If the lower part of an infected stem (10 cm) is cut crosswise and placed in a glass of water, tiny drops of a white milky ooze exude from the stem. These are millions of bacteria flowing from the wound.

Controlling bacterial wilt

• There is no effective chemical control of this disease. Once the soil is infested, it is very difficult to remove the pathogen and therefore it is important to prevent the disease from spreading.
• Do not over irrigate as it creates favourable conditions for the pathogen to develop.
• The bacterium is very sensitive to moisture levels in the soil and cannot survive under dry conditions.
• The bacterium is also very sensitive to high pH levels in the soil and low soil temperatures.
• Buy seedlings only from reliable nurseries.
• When producing seedlings at home, use sterilized soil and clean water.
• Plant resistant/tolerant cultivars.
• Do not use contaminated irrigation water e.g. water from an irrigation dam with an inflow from a contaminated field.
• Sanitation: All implements and equipment should be washed with water and a solution of 3.5 % to 5% sodium hypo chloride (household bleach).