Plant Pathology Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA Phenotypic and Genetic Diversity among Pseudomonas syringae pv. phaseolicola K. K. Guven Gu ¨ ven 1, 1,2 , J. B. J. B. Jones Jones 2 , M. T. M. T. Momol Momol 3 and and E. R. E. R. Dickstein Dickstein 2 AuthorsÕ addresses: 1 Faculty of Science, Department of Biology, Anadolu University, Eskisehir TR-26470, Turkey; 2 Plant Pathology Department, Institute of Food and Agricultural Sciences, University of Florida, 1453 Fifield Hall, PO Box 110680, Gainesville, FL 32611-0680, USA; 3 North Florida Research and Education Center, University of Florida, Quincy, FL 32351, USA (correspondence to J. B. Jones. E-mail: jbjones@ufl.edu) Received May 14, 2004; accepted October 11, 2004 Keywords: Pseudomonas syringae pv. phaseolicola, polymerase chain reaction, fatty acid profiling, pulsed-field gel electro- phoresis Abstract The relationships among a worldwide collection of 56 strains of Pseudomonas syringae pv. phaseolicola, cau- sal agent of halo blight disease on bean, were investi- gated by studying the phenotypic and genetic diversity. All P. s. pv phaseolicola strains tested were pathogenic on the bean cultivar ÔCanadian WonderÕ. Carbon sub- strate utilization using BIOLOG (Biolog GN2 Micro- plate test) clustered all the phaseolicola strains together. The use of the phaseolotoxin gene cluster as a polymerase chain reaction (PCR) target detected all the P. s. pv. phaseolicola strains identified as toxin pro- ducers (Tox + ) except for one strain (NCPPB 2385) from Australia. Grouping of P. s. pv. phaseolicola by fatty acid composition suggested the existence of five clusters. A majority of the strains from the USA and Turkey were present in Cluster A while 12 of the 16 strains in group C were from Africa. PmeI and PacI enzymes were used for pulsed-field gel electrophoresis (PFGE) analysis of P. s. pv. phaseolicola. Digestion of chromosomal DNA from P. s. pv. phaseolicola with PmeI and PacI generated 29 and 28 groups, respect- ively. Determination of similarity coefficients and clus- tering by UPGMA revealed five clusters. More diversity was observed among strains with PFGE than with fatty acid profiling. The results obtained in this study suggest that although a number of strains formed small clusters based on their geographical ori- gin, a clear segregation cannot be concluded. The uni- formity of the strains in Turkey isolated in 1994 could possibly indicate a recent introduction of a population of closely related strains. Although only a limited number of strains from the USA were compared, it is interesting to note that the strains were phylogenetical- ly closely related considering that they spanned approximately 20 years. The oldest strain, NCPPB 52 from Canada, which was collected in 1941, had identi- cal PFGE patterns with several strains from South Africa and one strain in Turkey collected in the 1990s. The presence of identical PFGE groups in more than 1 year in South Africa and Germany and the phyloge- netically closely related group in the USA coupled with the fatty acid data would indicate the likelihood for local seed sources and/or endemic populations. Introduction Halo blight, caused by Pseudomonas syringae pv. phase- olicola (Burk.) Dows., is an important seed-borne dis- ease of beans (Phaseolus vulgaris L.) (Fahy and Lloyd, 1983). The disease is disseminated within the crop by rain splash and is favoured by cool temperatures and is widespread in Europe and North America. In the trop- ics, it is prevalent in the medium to high altitude (1500– 2000 m) bean-growing areas, e.g. the Andean region of South America, Mexican highlands and the highlands of East, Central and Southern Africa (Mabagala and Saettler, 1992; Taylor et al., 1996; Fourie, 1998). Pathogenic variation among P. s. pv. phaseolicola (nine races) has been reported worldwide (Patel and Walker, 1965; Taylor, 1970; Hale and Taylor, 1973; Taylor et al., 1996), with differential pathogenicity to bean cultivars. The genetic relationships among P. syringae pathovars were examined by rep-polym- erase chain reaction (PCR) (Louws et al., 1994), by ribotyping (Gonza´lez et al., 2000) and by rare cutting restriction enzymes (Cooksey and Graham, 1989; Grothues and Rudolph, 1991). Characterization of the genetic variability among strains of P. s. pv. phaseolicola was already reported by genomic finger- printing with repetitive extragenic palindromic (REP) sequence, enterobacterial repetitive intergenic consen- sus (ERIC) sequence and random amplified polymor- phic DNA (RAPD) primers (Marques et al., 2000) and multilocus enzyme electrophoresis analysis (Gu¨ven, 2001). Despite the prevalence and economic importance of the bacterium, no intensive analysis of U. S. Copyright Clearance Centre Code Statement: 0931–1785/2004/15212–0658 $ 15.00/0 www.blackwell-synergy.com J. Phytopathology 152, 658–666 (2004) Ó 2004 Blackwell Verlag, Berlin ISSN 0931-1785