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Comparative Effect of Low Temperature on Virulence and Twitching Motility of Ralstonia solanacearum Strains Present in Florida

February 2012 , Volume 102 , Number  2
Pages  185 - 194

Ana M. Bocsanczy, Ute C. M. Achenbach, Arianna Mangravita-Novo, Jeanne M. F. Yuen, and David J. Norman

First, fourth, and fifth authors: Department of Plant Pathology, University of Florida, IFAS, Mid-Florida Research and Education Center, 2725 Binion Rd., Apopka 32703; second author: Development Lead North-East Europe, Syngenta Agro GmbH, Am Technologiepark 1-5 63477 Maintal, Germany; and third author: Sanford-Burnham Medical Research Institute at Lake Nona 6400 Sanger Road, Orlando, FL 32827. First and second authors contributed equally.

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Accepted for publication 15 September 2011.

Ralstonia solanacearum causes bacterial wilt on a wide range of plant hosts. Most strains of R. solanacearum are nonpathogenic below 20°C; however, Race 3 Biovar 2 (R3B2) strains are classified as quarantine pathogens because of their ability to infect crops, cause disease, and survive in temperate climates. We have identified race 1 biovar 1 Phylotype IIB Sequevar 4 strains present in Florida which were able to infect and produce wilt symptoms on potato and tomato at 18°C. Moreover they infected tomato plants at rates similar to strains belonging to R3B2. We determined that strains naturally nonpathogenic at 18°C were able to multiply, move in planta, and cause partial wilt when inoculated directly into the stem, suggesting that low temperature affects virulence of strains differently at early stages of infection. Bacterial growth in vitro was delayed at low temperatures, however it was not attenuated. Twitching motility observed on growing colonies was attenuated in nonpathogenic strains at 18°C, while not affected in the cool virulent ones. Using pilQ as a marker to evaluate the relative expression of the twitching activity of R. solanacearum strains, we confirmed that cool virulent strains maintained a similar level of pilQ expression at both temperatures, while in nonpathogenic strains pilQ was downregulated at 18°C.

Additional keywords: comparative study, select agent.

© 2012 The American Phytopathological Society