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Genetic Diversity and Host Range Variation of Ralstonia solanacearum Strains Entering North America

First, fifth, and sixth authors: Department of Plant Pathology, University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Rd., Apopka 32703; second author: Crop Protection Department, University of Puerto Rico, P.O. Box 9030, Mayaguez, Puerto Rico 00681; third author: Plant Molecular and Cellular Biology Program, Plant Pathology Department, University of Florida, Gainesville 32611; fourth author: United States Department of Agriculture--Agricultural Research Service (USDA-ARS)-USHRL, Fort Pierce, FL 34945; and seventh author: USDA-ARS USVL, Charleston, SC.

Each year, large volumes of ornamental and food plant propagative stock are imported into the North America; occasionally, Ralstonia solanacearum is found systemically infecting this plant material. In this study, 107 new R. solanacearum strains were collected over a 10-year period from imported propagative stock and compared with 32 previously characterized R. solanacearum strains using repetitive polymerase chain reaction (rep-PCR) element (BOX, ERIC, and REP) primers. Additional strain comparisons were made by sequencing the endoglucanase and the cytochrome b561 genes. Using rep-PCR primers, populations could be distinguished by biovar and, to a limited extent, country of origin and original host. Similarity coefficients among rep-PCR clusters within biovars were relatively low in many cases, indicating that disease outbreaks over time may have been caused by different clonal populations. Similar population differentiations of R. solanacearum were obtained when comparing strain sequences using either the endoglucanase or cytochrome b561 genes. We found that most of the new biovar 1 strains of R. solanacearum entering the United States were genetically distinct from the biovar 1 strains currently found infecting vegetable production. These introduced biovar 1 strains also had a broader host range and could infect not only tomato, tobacco, and potato but also anthurium and pothos and cause symptoms on banana. All introductions into North America of race 3, biovar 2 strains in the last few years have been linked to geranium production and appeared to be clonal.

Additional keywords:bacterial wilt, FAME.