Abstract
Outbreaks of acute oak decline (AOD) have been documented in England from 2006. Both species of native oaks (Quercus robur and Quercus petraea) are affected. To complement isolation efforts for identification of putative causative biotic agents and increase our understanding of bacteria associated with oak tissue, five sites in England were chosen for this study. Samples of outer bark, inner bark, sapwood and heartwood were taken from healthy oak and trees with symptoms at varying stages of the syndrome. Furthermore, larval galleries attributed to infestation with Agrilus biguttatus were included. After DNA extraction and amplification of the V3–V5 fragment of the bacterial 16S rRNA genes by pyrosequencing, the dataset was analyzed to identify patterns in bacterial communities in oak tissue samples with and without AOD symptoms at each site. The composition of bacterial communities differed greatly according to the site from which the samples were obtained. Within each site, the composition of the bacteria associated with symptomatic tissue varied between advanced stages of the syndrome and healthy tissue. Key players in healthy and symptomatic tissue were identified and included members of the Gammaproteobacteria related to Pseudomonas sp. or Brenneria goodwinii and members of the Firmicutes.
Highlights
Acute oak decline (AOD) appears to be a complex, secondary disease of native oak (Quercus robur and Q. petraea), and is increasingly found on turkey oak (Q. cerris) in the UK
We demonstrated that strong site-specific signatures exist for oak associated bacteria studied in
The number of phylotypes ranged from several hundreds to below hundred. From this variability we could identify two taxa mainly associated with tissue from healthy trees. Apart from this variability we could identify two taxa mainly associated with tissue from healthy belonging to the Gammaproteobacteria
Summary
Acute oak decline (AOD) appears to be a complex, secondary disease of native oak (Quercus robur and Q. petraea), and is increasingly found on turkey oak (Q. cerris) in the UK. Spatial structuring at the plant part level [6,7,13] suggests the adaptation of specific taxa to available microniches within a plant’s phyllosphere, whereas on a larger scale, geographical distance [14] shapes phyllosphere communities as shown for Tamarix trees. High-throughput sequencing technologies were used to identify thousands of sequences per sample and attempt to reveal the various taxa and their relative abundance interacting in healthy and diseased trees, including any rare or uncultivable microbial species. The 16S rRNA gene, the most comprehensive taxonomic marker available to date [37,38] was selected for metabarcoding To our knowledge this is the first study of the bacterial microbiome associated with oak bark and internal tissue. We expected that the microbiomes would differ according to the health status of trees
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