Disease guide

Ralstonia solanacearum.
Five races have been reported.

Worldwide (subtropical and tropical areas)

Symptoms begin as drooping of the lower leaves, followed soon after by wilting of the entire plant. No foliar yellowing is associated with this wilt disease. When the stem is cut a slimy, gray exudate oozes from the cut end. A longitudinal section of the stem reveals a yellow to light brown vascular discoloration which later turns darker brown and/or hollow as the disease progresses. A quick aid to diagnosis is to place a freshly cut stem piece in water. A white, milky stream of bacteria will ooze from the cut stem.

This bacterium has a host range of greater than 200 plant species, which it can infect and survive on. It can also survive in the soil where it infects roots through natural wounds caused by the formation of secondary roots, or through wounds caused by transplanting, cultivation practices or nematode feeding. Chewing insects may also transmit the bacterium. It can be spread in irrigation water, in soil on cultivation equipment and in diseased transplants. Warm (29-35°C, 84-95°F) weather and high soil moisture levels favor the development of this disease.

The use of disease-free transplants, soil fumigation, weed control and crop rotation can all reduce the incidence of this disease. Grafting onto resistant rootstocks or using tolerant varieties can be effective in minimizing losses from bacterial wilt.