Ralstonia solanacearum race 3 biovar 2 is a bacterial pathogen not known to occur in the US. It causes a wilt disease in several important agricultural crops such as potatoes, tomatoes, peppers and eggplant. The disease it causes is known as Southern wilt, bacterial wilt, and brown rot of potato.
Introductions in greenhouse production geraniums occurred in several states in 2003, introduced from Kenya, and 2004, introduced from Guatemala, which were subsequently eradicated.
APHIS requires that all geraniums imported from countries with Ralstonia solanacearum race 3 biovar 2, must be certified as tested and found free of the bacterium and meeting production facility sanitation requirements. For more information, look for the document, “Minimum Sanitation Protocols for Offshore Geranium Cutting”, to be posted to this website. Additionally, a program review and planning meeting was sponsored by PPQ in Riverdale, Maryland in June of 2003. A record of that meeting appears on this website.
Disease Spread and Greenhouse Sanitation
Ralstonia solanacearum can be transmitted through soil, contaminated irrigation water, equipment, or personnel. For example, it may be spread by transplanting and propagating infected plants, taking cuttings without disinfecting grafting knives between plants, pinching buds of plants, and especially by subirrigating geraniums. The pathogen does not readily spread from plant-to-plant through the splashing of water, casual contact, or aerially. Spread can be controlled in greenhouses by the application of sound sanitation practices.
Wilting symptoms in geraniums caused by Ralstonia species are similar to wilting symptoms caused by other pathogens such as Xanthomonas campestris pv. pelargonii, the agent of bacterial blight. The primary geranium symptom of infection by R. solanacearum race 3 biovar 2, is wilting of leaves and/or abnormal yellowing of lower leaves, while Xanthomonas campestris pv. pelargonii can also produce leaf spots. Bacterial streaming may be seen if stem sections from Ralstonia infected, symptomatic plants are placed into water. If infected with Ralstonia, vascular discoloration of the stem is common, and roots may sometimes turn brown. However, with Xanthomonas campestris pv. pelargonii, vascular discoloration is less pronounced or absent, and roots remain white. See the image gallery links on the menu for examples of symptoms.
Ralstonia solanacearum is thought to have originated in the temperate highland regions of Peru. Ralstonia solanacearum race 3 biovar 2 is present in Europe, Asia, South and Central America, and Australia. (Races are defined by host range and biovars by biochemical reaction tests).
Ralstonia solanacearum race 3 biovar 2 is listed on the Agriculture Bioterrorism Act of 2002 as a select agent with special requirements for US laboratory research and accountability. Introductions into the US from infected geraniums are not thought to be intentional, but are the result of unsanitary greenhouse practices in the foreign source facility. For more information on permit regulations regarding select agents, see the PPQ Permit Unit website.