Ralstonia solanacearum.( Bacterial wilt)

Description of plant pathogen

Associated with very soggy soil and high temperature, this disease is more problematic in the summer and in regions of warmer weather. The bacteria can remain in the soil for several years. Wilting of the plant occurs from top to bottom, from the beginning of flowering, but leaves remain green. The lower part of the stem becomes brownish and exudation of a bacterial pus occurs when doing the "test-of-glass", which consists of placing a piece of the plant stem suspect in a glass of water: if so, there to a bacterial exudation of pus in water.

Bacterial wilt of tomato in field, caused by Ralstonia solanacearum. Bacterial wilt of tomato in field, caused by Ralstonia solanacearum. 

Symptoms

In tomato, bacterial wilt first appears as flaccidity in the younger leaves.  Under ideal environmental conditions, a complete and rapid wilt develops with advanced stages appearing within two to three days and plant death soon follows.  If environmental conditions are not optimal and the disease develops slowly, leaf epinasty may occur, and adventitious roots may appear on the stem. 

When sectioned, the stem vascular system initially appears yellow or light brown.  As the disease progresses, the stem becomes a darker brown, and eventually the pith and cortex become brown.  Water-soaked lesions may appear on the stem in the event of massive invasion of the cortex.

In potatoes Symptoms may appear at any plant age and include wilting and yellowing of leaves and stunting of plants.  Disease may be severe in young, succulent plants and may appear as rapid wilting of leaves and collapse of stems.  Initially, only one stem may wilt.  If conditions are optimal, all the leaves in a hill may wilt quickly but remain green.  Stems may appear streaked as infected vascular bundles become visible.  Tuber vascular tissue is usually a distinct grayish brown, and the discoloration may expand into the pith or cortex.  Tuber eyes turn grayish brown, and a sticky exudate may form at the eyes or where the stolon is attached to the tuber.  Eventually, infected tubers left in the ground will turn into a slimy mass surrounded by a thin layer of outer tissue and periderm.

Control\Management

1. Integrated  management of bacterial wilt by using healthy seed and planting in clean soils. Planting in R. Solanacearum- free soil.
2. Plant resistance is one of the most effective means of controlling R. Solanacearum.
3. Removal of rotted tubers. After harvest, sort out the left over diseased tubers must also be removed from the field and destroyed using the same procedure as for haulms.
4. Weeding before planting the potato and any other crop used in rotation.
5. Sanitation and cultivation practises aiming to avoid or limit pathogen survival and dissemination.
6. Roguing volumteer potato plants.
7. Removal of potato haulms  and roguing wilted potato plants.