Bacterial canker disease is considered to be one of the most destructive diseases of tomato (Solanum lycopersicum), and is caused by the seed-borne Gram-positive bacterium Clavibacter michiganensis ssp. michiganensis (Cmm). This vascular pathogen generally invades and proliferates in the xylem through natural openings or wounds, causing wilt and canker symptoms. The incidence of symptomless latent infections and the invasion of tomato seeds by Cmm are widespread. Pathogenicity is mediated by virulence factors and transcriptional regulators encoded by the chromosome and two natural plasmids. The virulence factors include serine proteases, cell wall-degrading enzymes (cellulases, xylanases, pectinases) and others. Mutational analyses of these genes and gene expression profiling (via quantitative reverse transcription-polymerase chain reaction, transcriptomics and proteomics) have begun to shed light on their roles in colonization and virulence, whereas the expression of tomato genes in response to Cmm infection suggests plant factors involved in the defence response. These findings may aid in the generation of target-specific bactericides or new resistant varieties of tomato. Meanwhile, various chemical and biological controls have been researched to control Cmm. This review presents a detailed investigation regarding the pathogen Cmm, bacterial canker infection, molecular interactions between Cmm and tomato, and current perspectives on improved disease management.
Background Paenibacillus polymyxa is a plant-growth promoting rhizobacterium that could be exploited as an environmentally friendlier alternative to chemical fertilizers and pesticides. Various strains have been isolated that can benefit agriculture through antimicrobial activity, nitrogen fixation, phosphate solubilization, plant hormone production, or lignocellulose degradation. However, no single strain has yet been identified in which all of these advantageous traits have been confirmed.Results P. polymyxa CR1 was isolated from degrading corn roots from southern Ontario, Canada. It was shown to possess in vitro antagonistic activities against the common plant pathogens Phytophthora sojae P6497 (oomycete), Rhizoctonia solani 1809 (basidiomycete fungus), Cylindrocarpon destructans 2062 (ascomycete fungus), Pseudomonas syringae DC3000 (bacterium), and Xanthomonas campestris 93-1 (bacterium), as well as Bacillus cereus (bacterium), an agent of food-borne illness. P. polymyxa CR1 enhanced growth of maize, potato, cucumber, Arabidopsis, and tomato plants; utilized atmospheric nitrogen and insoluble phosphorus; produced the phytohormone indole-3-acetic acid (IAA); and degraded and utilized the major components of lignocellulose (lignin, cellulose, and hemicellulose).Conclusions P. polymyxa CR1 has multiple beneficial traits that are relevant to sustainable agriculture and the bio-economy. This strain could be developed for field application in order to control pathogens, promote plant growth, and degrade crop residues after harvest.
BackgroundBacillus velezensis is an endospore-forming, free-living soil bacterium with potential as a biopesticide against a broad spectrum of microbial pathogens of plants. Its potential for commercial development is enhanced by rapid replication and resistance to adverse environmental conditions, typical of Bacillus species. However, the use of beneficial microbes against phytopathogens has not gained dominance due to limitations that may be overcome with new biopesticidal strains and/or new biological knowledge.ResultsHere, we isolated B. velezensis strain 9D-6 and showed that it inhibits the in vitro growth of prokaryotic and eukaryotic pathogens, including the bacteria Bacillus cereus, Clavibacter michiganensis, Pantoea agglomerans, Ralstonia solanacearum, Xanthomonas campestris, and Xanthomonas euvesicatoria; and the fungi Alternaria solani, Cochliobolus carbonum, Fusarium oxysporum, Fusarium solani, Gibberella pulicaris, Gibberella zeae, Monilinia fructicola, Pyrenochaeta terrestris and Rhizoctonia solani. Antimicrobial compounds with activity against Clavibacter michiganensis were isolated from B. velezensis 9D-6 and characterized by high resolution LC-MS/MS, yielding formulae of C52H91N7O13 and C53H93N7O13, which correspond to [Leu7] surfactins C14 and C15 (also called surfactin B and surfactin C), respectively. We further sequenced the B. velezensis 9D-6 genome which consists of a single circular chromosome and revealed 13 gene clusters expected to participate in antimicrobial metabolite production, including surfactin and two metabolites that have not typically been found in this species - ladderane and lantipeptide. Despite being unable to inhibit the growth of Pseudomonas syringae DC3000 in an in vitro plate assay, B. velezensis 9D-6 significantly reduced root colonization by DC3000, suggesting that 9D-6 uses methods other than antimicrobials to control phytopathogens in the environment. Finally, using in silico DNA-DNA hybridization (isDDH), we confirm previous findings that many strains currently classified as B. amyloliquefaciens are actually B. velezensis.ConclusionsThe data presented here suggest B. velezensis 9D-6 as a candidate plant growth promoting bacterium (PGPB) and biopesticide, which uses a unique complement of antimicrobials, as well as other mechanisms, to protect plants against phytopathogens. Our results may contribute to future utilization of this strain, and will contribute to a knowledge base that will help to advance the field of microbial biocontrol.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1380-8) contains supplementary material, which is available to authorized users.
A free-living diazotrophic strain, DS2T , was isolated from corn rhizosphere. Polyphasic taxonomy was performed including morphological characterization, Biolog analysis, and 16S rRNA, cpn60 and nifH gene sequence analyses. 16S rRNA gene sequence analysis indicated that strain DS2 T was closely related to the genus Azospirillum (96 % similarity). Chemotaxonomic characteristics (DNA G+C content 67.9 mol%; Q-10 quinone system; major fatty acid 18 : 1v7c) were also similar to those of the genus Azospirillum. In all the analyses, including phenotypic characterization using Biolog analysis and comparison of cellular fatty acids, this isolate was found to be different from the closely related species Azospirillum lipoferum, Azospirillum oryzae and Azospirillum brasilense. On the basis of these results, a novel species is proposed for this nitrogen-fixing strain. The name Azospirillum canadense sp. nov. is suggested with the type strain DS2 T (=NCCB 100108The genus Azospirillum was first described by Tarrand et al. , 2006). A few Azospirillum strains including A. brasilense and A. oryzae were isolated from rhizosphere of corn, growing in Western Ontario, Canada. Strain DS2 T was isolated from rhizosphere soil. It was identified as Azospirillum due to its cell shape, colony morphology, nitrogen fixation and 96 % similarity for the 16S rRNA gene sequence but the species was not identified as it did not show close similarity to any known species of this genus. Strain DS2T was screened for its growth-promoting activity and it showed significant growth promotion in two corn varieties and vegetables, under greenhouse conditions. This strain is on field trial for growth promotion in corn at two research stations in Ontario, Canada. In the present study, we characterized this strain by using a polyphasic approach, including phylogenetic analyses of the 16S rRNA, cpn60 and nifH gene sequences. Isolate DS2T was isolated on M medium (Xie & Yokota, 2005) except that biotin was not added and pH 7.2-7.4 was used. Subcultivation was done on the same medium at 30 u C for 48-72 h. The bacterium formed wet, white colonies which later turned light-pink. Cell morphology was observed using a scanning electron microscope. Cells of the bacterium were short rods 0.9 mm in width and 1.8-2.5 mm in length, with a single polar flagellum (Fig. 1). Bacterial growth at different temperatures (20-41 uC) and pH values (4-10) and with various NaCl concentration (0.5-3 %) ranges was determined in M medium. The Biolog analysis system and API 20NE bacterial identification kit were used for physiological characterization. Results of the analyses are given in the species description. A summary of the results of carbon-source utilization suitable for the differentiation of isolate DS2T from known Azospirillum species is presented in Table 1. Phosphate solubilization on NBRIP medium (Nautiyal, 1999) was not observed. Indole acetic acid production in the presence of 100 mg l 21 tryptophan in CCM (Rennie, 1981) T were determined with a gas chromatograph, usi...
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