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Background: The species Pectobacterium carotovorum includes a diverse subspecies of bacteria that cause disease on a wide variety of plants. In Morocco, approximately 95% of the P. carotovorum isolates from potato plants with tuber soft rot are P. carotovorum subsp. carotovorum. However, identification of this pathogen is not always related to visual disease symptoms. This is especially true when different pathogen cause similar diseases on potato, citing as an example, P. carotovorum, P. atrosepticum and P. wasabiae. Numerous conventional methods were used to characterize Pectobacterium spp., including biochemical assays, specific PCR-based tests, and construction of phylogenetic trees by using gene sequences. In this study, an alternative method is presented using a gene linked to pathogenicity, in order to allow accuracy at subspecies level. The pmrA gene (response regulator) has been used for identification and analysis of the relationships among twenty nine Pectobacterium carotovorum subsp. carotovorum and other Pectobacterium subspecies., Results: Phylogenetic analyses of pmrA sequences compared to ERIC-PCR and 16S rDNA sequencing, demonstrated that there is considerable genetic diversity in P. carotovorum subsp. carotovorum strains, which can be divided into two distinct groups within the same clade., Conclusions: pmrA sequence analysis is likely to be a reliable tool to identify the subspecies Pectobacterium carotovorum subsp. carotovorum and estimate their genetic diversity.

Pectobacterium carotovorum subsp. carotovorum, Pectobacterium astrosepticum and Pectobacterium chrysanthemi are the soft rot tuber of potatoes pathogens (Solanum tuberosum). The aim of this study was to determine the occurrence of these pathogens in Moroccan regions producing potatoes. Fifty three isolates of Pectobacterium were isolated on medium Crystal Violet Pectate. The comparison of their bacteriological characteristics with standard strains allowed us to conclude that all the isolates belonged to the Pectobacterium. With regard to phenotype characteristics, the variability that was found included 32 typical Pectobacetrium carotovorum subsp. carotovorum, 3 typical Pectobacterium atrosepticum, and 18 atypical Pectobacterium carotovorum subsp. carotovorum. Three strains of the atypical group; showed that the biochemical properties overlap among the Pectobacterium carotovorum and Pectobacterium chrysanthemi. These data were needed molecular characterization. However, the PCR amplification of total genomic DNA of 53 isolates with the two primers Y1/Y2 and P143/P145 yielded an amplified fragment of the expected size (434 bp) only with Y1/Y2, indicated that all the isolates collected and tested belonged to the Pectobacterium carotovorum species. On the basis the pathogenicity tests, these strains revealed that they were pectinolytic, and showed differences in aggressiveness against potato and leaves of tobacco.

Pectobacterium carotovorum are economically important plant pathogens that cause plant soft rot. These enterobacteria display high diversity world-wide. Their pathogenesis depends on production and secretion of virulence factors such as plant cell wall-degrading enzymes, type III effectors, a necrosis-inducing protein, and a secreted virulence factor from Xanthomonas spp., which are tightly regulated by quorum sensing. Pectobacterium carotovorum also present pathogen-associated molecular patterns that could participate in their pathogenicity. In this study, by using suspension cells of Arabidopsis thaliana, we correlate plant cell death and pectate lyase activities during coinfection with different P. carotovorum strains. When comparing soft rot symptoms induced on potato slices with pectate lyase activities and plant cell death observed during coculture with Arabidopsis thaliana cells, the order of strain virulence was found to be the same. Therefore, Arabidopsis thaliana cells could be an alternative tool to evaluate rapidly and efficiently the virulence of different P. carotovorum strains.