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Strawberry is economically important and widely grown but susceptible to a large variety of phytopathogenic organisms. Among them, Xanthomonas fragariae is a quarantine bacterial pathogen threatening strawberry productions by causing angular leaf spots. Using whole transcriptome sequencing, gene expression of both plant and bacteria in planta was analyzed at two time points, 12- and 29-days post inoculation, in order to compare pathogen and host response between the stages of early visible and of well-developed symptoms. Among 28’588 known genes in strawberry and 4’046 known genes in X. fragariae expressed at both time points, a total of 361 plant and 144 bacterial genes were significantly differentially expressed, respectively. The identified higher expressed genes in the plants were pathogen-associated molecular pattern receptors and pathogenesis related thaumatin encoding genes, whereas the more expressed early genes were related to chloroplast metabolism as well as photosynthesis related coding genes. Most of X. fragariae genes involved in host interactions, recognitions and pathogenesis, were lower expressed at late-phase infection. This study gives a first insight on the interaction of X. fragariae with its host. The strawberry plant changed its metabolism consistently with the progression of infection.

Strawberry is economically important and widely grown, but susceptible to a large variety of phytopathogenic organisms. Among them, Xanthomonas fragariae is a quarantine bacterial pathogen threatening strawberry productions by causing angular leaf spots. Using whole transcriptome sequencing, the gene expression of both plant and bacteria in planta was analyzed at two time points, 12 and 29 days post inoculation, in order to compare the pathogen and host response between the stages of early visible and of well-developed symptoms. Among 28,588 known genes in strawberry and 4046 known genes in X. fragariae expressed at both time points, a total of 361 plant and 144 bacterial genes were significantly differentially expressed, respectively. The identified higher expressed genes in the plants were pathogen-associated molecular pattern receptors and pathogenesis-related thaumatin encoding genes, whereas the more expressed early genes were related to chloroplast metabolism as well as photosynthesis related coding genes. Most X. fragariae genes involved in host interaction, recognition, and pathogenesis were lower expressed at late-phase infection. This study gives a first insight into the interaction of X. fragariae with its host. The strawberry plant changed gene expression in order to consistently adapt its metabolism with the progression of infection.

Xanthomonas fragariae is a quarantine organism in Europe, causing angular leaf spots on strawberry plants. It is spreading worldwide in strawberry-producing regions due to import of plant material through trade and human activities. In order to resolve the population structure at the strain level, we have employed high-resolution molecular typing tools on a comprehensive strain collection representing global and temporal distribution of the pathogen. Clustered regularly interspaced short palindromic repeat regions (CRISPRs) and variable number of tandem repeats (VNTRs) were identified within the reference genome of X. fragariae LMG 25863 as a potential source of variation. Strains from our collection were whole-genome sequenced and used in order to identify variable spacers and repeats for discriminative purpose. CRISPR spacer analysis and multiple-locus VNTR analysis (MLVA) displayed a congruent population structure, in which two major groups and a total of four subgroups were revealed. The two main groups were genetically separated before the first X. fragariae isolate was described and are potentially responsible for the worldwide expansion of the bacterial disease. Three primer sets were designed for discriminating CRISPR-associated markers in order to streamline group determination of novel isolates. Overall, this study describes typing methods to discriminate strains and monitor the pathogen population structure, more especially in the view of a new outbreak of the pathogen.

Xanthomonas arboricola pv. fragariae was described in 2001 as the causal agent of strawberry bacterial leaf blight. We report here the first draft whole-genome sequences of fiveX. arboricolapv. fragariae isolates from Italy and France.

Xanthomonas fragariae is a worldwide spread plant bacterial disease causing angular leaf spots, and thus reducing the yield of production for strawberry fruits. Three isolates with variable geographic and time origins were sequenced with long-read technology (PacBio) to generate finished genomes of virulent strains and observe their variability in content.

Molecular diagnostics of plant pathogens are crucial to prevent disease spread and to enhance food quality and security. A comparative genomics approach using genomes of different Xanthomonas species and pathovars was applied to identify highly specific targets in the genome of Xanthomonas fragariae, the causal agent of angular leaf spot of strawberry, listed under quarantine regulations in Europe. A reliable and sensitive loop-mediated isothermal amplification (LAMP) assay was designed using a unique marker providing a highly specific and rapid detection, making this technique convenient for on-site detection. Specificity of the designed assay was tested on 37 culture collection strains of X. fragariae, 82 strains of other Xanthomonas species and pathovars and 11 strains of other bacterial genera isolated from strawberry leaves. A detection limit of 10^2 fg was achieved, approximating 20 genome copies per reaction. When performing analyses with crude plant material, a consistent lower detection efficiency of 10^2 CFU ml−1 was achieved. The LAMP assay designed in this study was adapted to work on crude plant material without any prior extensive extraction steps or incubation period. Moreover, it does not require advanced analytical knowledge or a fully equipped laboratory. Results were produced within 7 to 20 min depending on the pathogen concentration, thus providing a high throughput and user-friendly method for detection and screening of plant material in support of quarantine regulations.