SUMMARY Phenotypic and genetic characteristics were investi- gated of 24 isolates of Pectobacterium carotovorum, re- covered in summer 2001 from artichokes in the Sele val- ley (Campania, southern Italy). Based on biochemical tests, all isolates were identified as P. carotovorum subsp. carotovorum, except for four atypical ones. PCR-ampli- fication of a 434 bp fragment of the pectate-lyase-en- coding pel gene, gave the expected band from all iso- lates, whereas no amplicons were obtained using P. atrosepticum-specific primers. PCR-RFLP on pel gene, placed the four atypical isolates in the RFLP groups 8, 9 and 11 (ISPaVe 110A, ISPAVe 105A and ISPAVe 91B) of the subspecies carotovorum and in the RFLP group 3 of the subspecies odoriferum (ISPaVe CA). DNA-poly- morphism investigated by rep-PCR and M13-PCR showed the isolates to be distributed in two main groups, totalling 14 haplotypes. Eight different haplo- types were obtained from samples collected in the same field and three different haplotypes were found in the same plant. The rep-PCR fingerprinting of ISPaVe CA was the same as P. carotovorum subsp. odoriferum NCPPB 3839. The majority of the isolates did not show a significative differential virulence response, with the exception of ISPaVe 114B, the most-virulent, and IS- PaVe 105B, the least-virulent. Key words: rep-PCR, M13-PCR, virulence, hypersen- sitive reaction. Erwinia carotovora subsp. carotovora, recently pro- posed as Pectobacterium carotovorum subsp. carotovo- rum (Hauben et al., 1998; Gardan et al., 2003) (Pcc) is the causal agent of soft rot on a wide range of host plants (Toth et al., 2003). In Italy, typical symptoms oc- cur in artichoke mainly from July to September. Most of the external leaves are chlorotic and slightly wilted, show necrosis at the base of the petiole and soft rot of Corresponding author: S. Loreti Fax: +39.06.82070370 E-mail: stefania.loreti@entecra.it the pith. Severe wilt and collapse of the plants ensue. In summer 2001, a serious attack of soft rot of artichoke plants occurred in four production sites of the Sele val- ley (Campania, southern Italy). A preliminary molecular characterization showed a very large variability of the isolated bacterial population (Loreti et al., 2001, 2006). Twenty-four pectinolytic bacterial isolates were ob- tained on crystal violet pectate (CVP) medium by incu- bation at 27°C for 3-4 days. These isolates were charac- terized based on Lelliot and Stead (1987) tests for acidi- fication of lactose, sorbitol, melibiose and α-methylglu- coside, production of reducing substances from sucrose and growth at 36°C. Several Pectobacterium reference and type strains were included in the tests (Tab. 1). Ex- perimental infection assays were performed on potato tubers of cvs Mona Lisa, Agria and Vivaldi, as described by Vitale et al. (2004), and the data obtained from four inoculation tests were analysed statistically using the Statgraphics Plus 5.1 Program. Hypersensitive reaction (HR) assay was performed on leaves of Nicotiana tabacum L. cv. Samsung using a bacterial suspension of 10 8 CFU ml -1 . Total genomic DNA was extracted from 1.5 ml broth cultures using the Puregene DNA isolation kit (Gentra System-Flowgen, UK). Polymerase chain reaction (PCR) was done with primers Y1 and Y2, specific for P. carotovorum, and primers Y45 and Y46, specific for P. atrosepticum (Pa) (Darrasse et al., 1994; Frenchon et al., 1995). PCR-RFLP was as described by Helias et al. (1998) using reference strains of Pcc (PD 1769 and CIP 009), Pa (NCPPB 549) and P. carotovorum subsp. odor- iferum (Pco) (NCPPB 3839). All bacterial isolates were characterized by rep-PCR analyses, performed with REP and ERIC primers (Louws et al., 1994) and by M13-PCR assay (Zaccardelli et al., 2000). The amplification products (15 μl) were analysed on 1.6 % (w/v) agarose gel run in TAE buffer (0.04 M Tris, 0.001 M EDTA, 0.02 M acetic acid), stained with 0.5% ethidium bromide and photographed under UV light. Each experiment was repeated three times. Results of REP, ERIC and M13-PCR genomic fingerprinting were combined to obtain an single binary matrix. Cluster analysis was made with the NTSYSpc software (version 2.11j; Exeter Software, USA) using simple matching Journal of Plant Pathology (2009), 91 (3), 757-761 Edizioni ETS Pisa, 2009 757 SHORT COMMUNICATION PHENOTYPIC AND GENETIC VARIABILITY OF PECTOBACTERIUM CAROTOVORUM ISOLATED FROM ARTICHOKE IN THE SELE VALLEY A. Gallelli 1 , M. Galli 1 , D. De Simone 1 , M. Zaccardelli 2 and S. Loreti 1 1 CRA, Centro di Ricerca per la Patologia Vegetale, Via C.G. Bertero 22, 00156 Roma, Italy 2 CRA, Centro di Ricerca per l’Orticoltura, Via dei Cavalleggeri 25, 84098 Pontecagnano (SA), Italy