Twenty-two isolates of Pectobacterium carotovorum were collected from soft-rotted potato tubers originating from different production areas in Morocco, and their phenotypic and genetic characteristics were investigated. All of the isolates were identified as P. carotovorum by API 20E (identification kit) system, and yielded a 434-bp DNA fragment of the pectate-lyase-encoding pel gene in PCR experiments. Collected strains were also evaluated for their susceptibility to 11 different antibiotics: Sulfamethoxazole/ trimethoprim (SXT), Ceftazidime (CAZ), Ciprofloxacin (CIP), Cefotaxime sodium (CTX), Imipenem (IPM), Gentamicin (CN), Amikacin (AK), Colistin sulphate (CT), Netilmicin (NET), Ampicillin (AMP) and Cephalothin (KF). Of the total P. carotovorum strains isolated, 5 were resistant to only two antibiotics: Ampicillin and Cephalothin. Evaluation of genetic diversity was performed on all isolates by molecular typing with Enterobacterial Repetitive Intergenic Consensus (ERIC-PCR). Results showed the isolates to be distributed on 2 major clusters subdivided into many subclusters. The genetic diversity within the potato strains of P. carotovorum subspecies is shown. No correlation between ERIC-PCR analyses, suscebtibility patterns, geographic areas and year isolated was observed. These results may indicate that the tuber could be the main source of contamination. In conclusion, the ability to distinguish Pectobacterium carotovorum strains from diseased potato with PCR based assay will be useful for strain relatedness studies of this pathogen in Morocco.
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.
BackgroundThe 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.ResultsPhylogenetic 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.ConclusionspmrA sequence analysis is likely to be a reliable tool to identify the subspecies Pectobacterium carotovorum subsp. carotovorum and estimate their genetic diversity.
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