Characterization of Dickeya strains isolated from potato grown under hot-climate conditions

Dickeya strains isolated in Israel in 2006-2010 were characterized by dnaX sequence analysis, pulsed-field gel electrophoresis (PFGE), biochemical assays and pectolytic activity, and found to be homogeneous: most of them could be classified as Dickeya solani'. Of the 34 strains isolated from imported seed tubers or potato plants grown from imported seed, 32 were typed as D.solani' and only two were characterized as Dickeya dianthicola. Biovar typing indicated that all D.solani' strains were biovar 3. Dickeya solani' strains were most closely related to Dickeya dadantii subsp. dieffenbachiae according to PFGE and dnaX analyses and both species exhibited high pectolytic activity. Expression levels of two putative virulence genes, pelL (encoding a pectic enzyme) and dspE (encoding a type III effector) were significantly induced in D.solani' strains isolated from potato plants or tubers grown in hot climates such as the Negev region in Israel, compared to those isolated from seed tubers imported from the Netherlands, France or Germany. Results of this study support the hypothesis that D.solani' strains isolated in Israel are also clonal; however, they appear to be more virulent than strains isolated in Europe.