Growers who purchased unrooted cuttings this season received a pest alert indicating Ralstonia solanacearum had been found on cuttings originating from Guatemala. USDA test results confirmed this. It is important to note that there are different strains of Ralstonia solanacearum. The one found on the cuttings is a tropical strain of Ralstonia solanacearum that is NOT R3B2 which is a quarantine pathogen under the Agriculture Bioterrorism Protection Act of 2002; however, this tropical strain is still a big concern. Letters were sent to growers and immediate efforts have been made to destroy plants, find the source of infection and test plants. Infected plants included: Osteospermum, Nemesia, Bacopa , Sunpatiens, New Guinea Impatiens, Petunia, Calibrachoa, SuperCal, Heliotrope, Verbena, Lobelia and Portulaca. Ralstonia can infect over 200 host plants!
What to look for to detect R solanacearum infection: The first symptom often noticed is a wilted leaf or wilted leaves on one side of the plant or part of a leaflet. If you cut the stem below the wilt, you may notice the discoloration of the vascular system. Suspected plants should be tested for disease presence.
This is a good time to remind growers that on-site test kits are easy to use and are available for several diseases important to floriculture crops (viruses, fungi and bacteria), including Ralstonia solanacearum. (The kit will tell you whether you have R. solanacearum, but will not identify the strain of the bacterium). Growers should consider stocking up on a few test kits for the spring growing season. Test kits will confirm or allay your disease suspicions, allow you to detect diseases early, provide you the option to treat only when necessary and use the proper management for the disease. As a result you will maintain good crop quality.
Easy to use ImmunoStrips (dip-stick tests) are available from Agdia.com in batches of 5 or 25 tests to detect viruses such as impatiens necrotic spot virus (INSV), calibrachoa mottle virus (CbMV), tobacco mosaic virus (TMV), tomato spotted wilt virus (TSWV), and cucumber mosaic virus (CMV). There is also a combination kit for CMV & INSV & TSWV & TMV. ImmunoStrips are also available for several important bacterial pathogens such as Xanthomonas campestris pv . pelargonii, Ralstonia solanacearum and Clavibacter michiganensis subsp. michiganensis. The test strips do not identify Ralstonia to the race/biovar level. Positive samples should be sent to a diagnostic laboratory for further testing.
How the test kits work: Tests are based on antibodies that are designed to recognize antigens specific to each pathogen (e.g. INSV). Any antigen present in the plant sample is extracted by grinding in the extraction solution. The extracted antigen is then allowed to react with antibodies that capture specific antigens (when present), resulting in a color change that appears as a line on the strip.
Early detection and success using test kits are only as accurate as the sample taken. For example, if a plant has symptoms of INSV, a quick test will confirm your suspicions. Collect a sample from the part of the plant showing symptoms, including green or chlorotic tissues adjacent to the necrotic area. Even, when plants are systemically infected, INSV does not spread evenly throughout the plant, so careful selection of tissues is crucial to the success of the test.
Tina Smith, UMass Extension with input from Margery Daughtrey, Long Island Horticultural Research & Extension Center
Resources
On-line instruction video for using the Agdia kits
Fact Sheet: Southern Bacterial Wilt – UMass Extension
Bacterial Wilt - Ralstonia solanacearum, Penn State Extension
Ralstonia - Understanding and Recognizing a Serious Bacterial Pathogen – Griffin Greenhouse Supplies
