Characterization of D ickeya strains isolated from potato grown under hot‐climate conditions

D ickeya 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 ‘ D ickeya 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 D ickeya dianthicola . Biovar typing indicated that all ‘ D . solani ’ strains were biovar 3. ‘ D ickeya solani ’ strains were most closely related to D ickeya 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 N egev region in Israel, compared to those isolated from seed tubers imported from the N etherlands, F rance or G ermany. Results of this study support the hypothesis that ‘ D . solani ’ strains isolated in I srael are also clonal; however, they appear to be more virulent than strains isolated in E urope.