Soft-rot Enterobacteriaceae (SRE), which belong to the genera Pectobacterium and Dickeya, consist mainly of broad host-range pathogens that cause wilt, rot, and blackleg diseases on a wide range of plants. They are found in plants, insects, soil, and water in agricultural regions worldwide. SRE encode all six known protein secretion systems present in gram-negative bacteria, and these systems are involved in attacking host plants and competing bacteria. They also produce and detect multiple types of small molecules to coordinate pathogenesis, modify the plant environment, attack competing microbes, and perhaps to attract insect vectors. This review integrates new information about the role protein secretion and detection and production of ions and small molecules play in soft-rot pathogenicity.

Pectolytic bacteria, including Pectobacterium spp. and Dickeya spp., are best isolated on crystal violet pectate (CVP), a semiselective medium containing pectin. The source of pectin is essential, because pectolytic bacteria are not able to degrade all of them. The aims of this study were to identify a new pectin source and to perfect formulations of semiselective CVP media to isolate the pectolytic bacteria Pectobacterium spp. and Dickeya spp. from different environmental compartments (plants, soil and water). The AG366 pectin, selected after screening six different formulations, was incorporated into single-layer (SL-CVP AG366 ) and double-layer (DL-CVP AG366 ) CVP media. Both media were compared with those based on Bulmer, Sigma-Aldrich and Slendid-Burger pectins, using 39 Pectobacterium and Dickeya strains. All strains formed deep cavities on AG366-CVPs, whereas nine did not produce cavities on Bulmer or Sigma-Aldrich media. Recovery rates were similar on DL-CVP AG366 , Sigma-Aldrich and Bulmer CVPs for a given taxon, and did not differ significantly between SL-and DL-CVP AG366 . Pectolytic bacteria were successfully isolated on both media from field samples of diseased potatoes, carrots, tobacco, onions, radishes and ornamentals. AG366 is thus a high-performance pectin source for the elaboration of CVP media suitable to isolate Dickeya and Pectobacterium. It is also efficient for enrichment purposes in liquid medium. The validation of AG366 as an improved source of pectin to recover the polyphagous Pectobacterium and Dickeya in different environmental compartments is essential given the current worldwide emergence and recrudescence of these bacteria.

Clavibacter michiganensis subsp. michiganensis is the causal agent of bacterial canker of tomato. The disease was first described in 1910 in Michigan, USA. C. michiganensis subsp. michiganensis (from now on called clavibacter) was initially thought to be a phloem parasite, but was later found to be a xylem-invading bacterium. The host range comprises mainly solanaceous crops such as tomato, pepper, and eggplant. Strains show great variability in virulence and are usually described as being hypervirulent, hypovirulent, or nonvirulent. Clavibacter lacks a type III secretion system, and only a few virulence factors have been experimentally determined from the many putative virulence factors. As the molecular mode of infection by clavibacter is unknown, researchers have avoided intensive work on this organism. Genetic plant mechanisms conferring resistance to clavibacter are apparently complex, and breeders have yet to develop disease-resistant cultivars.

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The current study was initiated to evaluate the efficacy of physical methods (hot water, aerated steam, electron treatment) and agents of natural origin (resistance inducers, plant derived products, microorganisms) as seed treatments of carrots for control of Alternaria dauci and A. radicina. Control of both Alternaria species by seed treatment with the resistance inducers was generally poor. Results were also Eur J Plant Pathol