The bacterium ‘Dickeya solani’, an aggressive biovar 3 variant of Dickeya dianthicola, causes rotting and blackleg in potato. To control this pathogen using bacteriophage therapy, we isolated and characterized two closely related and specific bacteriophages, vB_DsoM_LIMEstone1 and vB_DsoM_LIMEstone2. The LIMEstone phages have a T4-related genome organization and share DNA similarity with Salmonella phage ViI. Microbiological and molecular characterization of the phages deemed them suitable and promising for use in phage therapy. The phages reduced disease incidence and severity on potato tubers in laboratory assays. In addition, in a field trial of potato tubers, when infected with ‘Dickeya solani’, the experimental phage treatment resulted in a higher yield. These results form the basis for the development of a bacteriophage-based biocontrol of potato plants and tubers as an alternative for the use of antibiotics.
Here we discuss the advantages of the majority of this versatile and diverse group of microorganisms for plant health and growth as demonstrated by their contribution to disease-suppressive soils, their antifungal and antibacterial activities, their ability to produce volatile compounds and their capacity to enhance plant biomass. Although much is still to be discovered about the colonization strategies and molecular interactions between plant roots and these microorganisms, they are destined to become important players in the field of plant growth-promoting rhizobacteria for agriculture.
Xanthomonas axonopodis pv. dieffenbachiae (Xad) is the causal agent of anthurium bacterial blight and listed as an A2 quarantine organism by EPPO. However, the name Xad covers a variety of strains. Here, 25 Xad strains and 88 phylogenetically related strains, including Xanthomonas type strains and representatives of other pathovars, were examined using a polyphasic taxonomic approach. Multilocus sequence analysis of seven genes showed that strains isolated from Dieffenbachia, Philodendron and Anthurium cluster into three phylogenetic groups (PG I, II and III), while the type strain of X. axonopodis clustered into a fourth group (PG IV). PG I included the type strains of X. citri subsp. citri, X. citri subsp. malvacearum, X. fuscans subsp. fuscans and X. fuscans subsp. aurantifolii. PG II included the type strains of X. euvesicatoria, X. perforans, X. alfalfae subsp. alfalfae and X. alfalfae subsp. citrumelonis. PG III included the type strains of X. phaseoli. Each PG was shown to represent a single species, based on average nucleotide identity values, DNA-DNA hybridization data and phenotypic characteristics. Therefore, strains named as Xad belong to PG I, PG II and PG III, and not to X. axonopodis (PG IV). Taxonomic proposals are made: emendations of the descriptions of X. citri, X. phaseoli and X. axonopodis, to encompass the strains of PG I, PG III and PG IV, respectively; and reclassification of X. perforans and X. alfalfae as X. euvesicatoria and emendation of the description of X. euvesicatoria to encompass all strains of PG II.
The spotted wing Drosophila (Drosophila suzukii) is an invasive and serious economic pest to small and stone fruits and its control is difficult. RNA interference (RNAi) or double-stranded RNA (dsRNA)-mediated gene silencing is rapidly becoming a widely used functional genomics tool in insects and holds great potential for insect pest control. This study investigates whether RNAi is functional in D. suzukii and whether oral delivery of dsRNA can elicit gene silencing and insecticidal activity. Firstly, microinjection of dsRNA targeting two essential genes (alpha COP and shrb) into the haemolymph of adult flies was performed, confirming that the RNAi system is functional and that gene silencing results in mortality. Secondly, dsRNA targeting alpha-COP and two extra essential genes, rpl13 and vha26, was mixed with artificial diet and fed to the larval and adult stages of D. suzukii. With naked dsRNA, no clear silencing and mortality were scored. However, combining dsRNA with a transfection reagent led to a significant increase in gene silencing and insect mortality. The best results were obtained with ds-Vha26. The results are discussed in relation to future optimization of the production, formulation, combinations and delivery of dsRNA
Chitin is a promising soil amendment for improving soil quality, plant growth, and plant resilience. The objectives of this study were twofold. First, to study the effect of chitin mixed in potting soil on lettuce growth and on the survival of two zoonotic bacterial pathogens, Escherichia coli O157:H7 and Salmonella enterica on the lettuce leaves. Second, to assess the related changes in the microbial lettuce rhizosphere, using phospholipid fatty acid (PLFA) analysis and amplicon sequencing of a bacterial 16S rRNA gene fragment and the fungal ITS2. As a result of chitin addition, lettuce fresh yield weight was significantly increased. S. enterica survival in the lettuce phyllosphere was significantly reduced. The E. coli O157:H7 survival was also lowered, but not significantly. Moreover, significant changes were observed in the bacterial and fungal community of the lettuce rhizosphere. PLFA analysis showed a significant increase in fungal and bacterial biomass. Amplicon sequencing showed no increase in fungal and bacterial biodiversity, but relative abundances of the bacterial phyla Acidobacteria, Verrucomicrobia, Actinobacteria, Bacteroidetes, and Proteobacteria and the fungal phyla Ascomycota, Basidiomycota, and Zygomycota were significantly changed. More specifically, a more than 10-fold increase was observed for operational taxonomic units belonging to the bacterial genera Cellvibrio, Pedobacter, Dyadobacter, and Streptomyces and to the fungal genera Lecanicillium and Mortierella. These genera include several species previously reported to be involved in biocontrol, plant growth promotion, the nitrogen cycle and chitin degradation. These results enhance the understanding of the response of the rhizosphere microbiome to chitin amendment. Moreover, this is the first study to investigate the use of soil amendments to control the survival of S. enterica on plant leaves.
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