Scientific name: Ralstonia solanacearum

Native range: worldwide

Geranium plant infected with R. solanacearum race 3 biovar 2. Photo by Margery Daughtrey, Cornell University, bugwood.org

At Risk

Primary hosts of R. solanacearum race 3 biovar 2 includes members of the Solanaceae family and geraniums (Pelargonium spp.). Imported ornamental plants and cuttings, especially geraniums, are considered a significant risk for introducing this bacteria to the U.S. and may be required to have documentation certifying their freedom from this pathogen before import is allowed.

Distribution

Ralstonia solanacearum race 1 occurs in the southern U.S. Most races and biovars are restricted to similarly warm climates. However, R. solanacearum race 3 biovar 2 is considered cold hardy in temperate climates. Ralstonia solancearum race 3 biovar 2 can be found throughout most of the world including Mexico, but does not occur in the U.S.

Biology

Ralstonia solanacearum is a bacterium that can infect over 200 different plants, with the Solanaceae (potato family) containing the highest number of susceptible species. Infections can cause wilting and death of susceptible plants. Introduction to a new area occurs through propagative plant material such as infected seed potato tubers and ornamental cuttings. In addition to surviving in plant material the bacteria can also persist in soil or planting media as well as irrigation and waste water, and spread to other fields occurs by surface runoff water and infested soil that is moved on equipment.

Identification

Infected plants show wilting of part or all of the plant, followed by leaf yellowing then death of the leaf between the veins and stunted growth. The stem interior becomes discolored and dark streaks may be visible. A sticky or slimy substance containing the bacteria may ooze from freshly cut infected stems, and is especially visible if placed in water. A cross section of an infected potato tuber may show a ring of brown discoloration and light pressure may produce an ooze. On intact tubers, soil may stick to ooze around the eyes.Look-Alikes

Wilted, yellowing leaves can be due to environmental factors as well as other diseases, including other strains of R. solanacearum. Root rots caused by many fungi can also cause leaf wilting, yellowing of leaves, and stunted growth. In geraniums, bacterial leaf blight caused by Xanthomonas hortorum pv. pelargonii causes leaves to wilt and yellow, similar to R. solanacearum R3bv2, but this disease also causes round tan - brown spots on the leaves. In potato, tuber symptoms of bacterial ring rot caused by Clavibacter michiganensis subsp. sepedonicus can look similar to those caused by R. solanacearum R3bv2.

Tomato bacterial wilt caused by R. solanacearum showing entire plant wilted, near death. Photo by Don Ferrin, Louisiana State University Agricultural Center, Baton Rouge, LA., bugwood.org. Brown discoloration of stem tissues caused by R. solanacearum. Photo by Clemson University, USDA Cooperative Extension Slide Series, bugwood.org. Bacterial ooze from tuber. Photo by H. David Thurston, Cornell University, Ithaca, NY

Regulatory Status: Regulated

There are multiple races and biovars of R. solanacearum and most are not regulated. However, one specific strain, called race 3 biovar 2 (R3bv2), is considered an extreme threat to the United States. If R. solanacearum race 3 biovar 2 was discovered in Minnesota, actions would be taken to prevent spread and to eradicate the pathogen.

What Can Be Done?

The MDA is monitoring for R. solanacearum through a variety of methods including surveys. Visit the University of Minnesota website for information about diagnosing plant problems. The University of Minnesota Plant Diagnostic Clinic is available to test samples of unknown plant problems. Contact the MDA via Arrest the Pest if you suspect you have found Ralstonia solanacearum R3bv2 in Minnesota.