Ralstonia solanacearum

(Bacterial wilt or Brown rot)

• Causal agent and transmission

The causal agent responsible for bacterial wilt is the bacterium Ralstonia solanacearum (synonym Pseudomonas or Burkholderia solanacearum).

It is a phytopathogenic bacterium, distributed worldwide, which has been discovered over the five continents. Typical of the subtropical and warm temperate regions, it has been found more recently in cooler climates, notably in Europe and in the highlands of Southern America and Africa.

The bacterium penetrates the plant either through natural wounds on the roots (axil or point of emergence of the secondary roots) or through artificial wounds caused by man (trans- planting, pruning, pinching off, harvesting equipment) or caused by nematodes (Meloidogyne spp.). The bacterium will then be able to colonise the vascular system, where it will actively multiply and rapidly spread throughout the plant.

• Significance 

Ralstonia solanacearum has a very wide host range; it affects more than 53 botanical families comprising over 200 plant species. Economically important crop hosts include banana, tobacco, groundnut, potato, tomato, cassava, etc. Among the Solanaceae, other crops or ornamentals can also be affected: aubergine, pepper, petunia, etc.

This bacterium can also be hosted by tolerant plants, i.e. ones in which there is no visible manifestation of the disease; they include weeds such as bittersweet nightshade (Solanum dulcamara) and black nightshade (Solanum nigrum).