New Disease Reports
New Disease Reports (2020) 41, 18. [http://dx.doi.org/10.5197/j.2044-0588.2020.041.018]
Get pdf (706 KB)
Next > < Prev

First report of acute oak decline disease of native and non-native oaks in Switzerland

B. Ruffner 1*, S. Schneider 1, J.B Meyer 2, V. Queloz 1 and D. Rigling 1

*beat.ruffner@wsl.ch

Show affiliations

Received: 12 Mar 2020; Published: 25 Mar 2020

Keywords: Brenneria goodwinii, Gibbsiella quercinecans, Rahnella victoriana

In spring 2017, stem bleeds accompanied by necrosis of the inner bark and sapwood were reported on three trees of Quercus petraea in the region of Basel, Switzerland. In 2018 and 2019 the same symptoms were observed at seven other sites across the country on Q. cerris, Q. pubescens, Q. robur and Q. rubra (Figs. 1-2). Samples prepared from symptomatic lesions resulted in abundant bacterial growth when plated on nutrient agar. Colonies with different morphotypes were assessed by partial 16S rRNA and gyrB gene sequencing (Lane et al., 1991; Brady et al., 2008), available under GenBank Accession Nos. MT094254-MT094265 and MT108370-MT108380. Sequence comparisons indicated the occurrence of Brenneria goodwinii, Gibbsiella quercinecans and Rahnella victoriana. These three bacteria have been associated with a polymicrobial decline disease, termed acute oak decline (AOD) (Denman et al., 2014). The presence of the bacteria in bark and sapwood samples was confirmed using a multiplex Taqman qPCR assay (Denman et al., 2018).

For pathogenicity tests, bacteria were applied by stem cut inoculations (Green et al., 2009) on two-year-old Q. robur plants. Treatments consisted of single and mixed inoculations using one strain per bacterial species and sterile water as a control. Three plants per treatment were inoculated with 5 μl of a 108 cfu/ml bacterial suspension and kept in a greenhouse at a temperature of 20 to 25°C. After eight weeks the first visual symptoms developed above and below the infection cut. Brownish discoloration and small lesions with oozing exudate were observed on plants inoculated with B. goodwinii/G. quercinecans, B. goodwinii/R. victoriana and B. goodwinii/G. quercinecans/R. victoriana. Plants treated with single strain inoculations with either strain or the mixed treatment G. quercinecans/R. victoriana showed variable degrees of stem discolouration but no lesions developed. After twenty weeks, necrotic tissue samples (Fig. 3) were tested using the Taqman qPCR assay. All bacteria of the initial treatment were detected, except in one plant inoculated with all three bacteria, which was dead at the time of sampling. In control treatments, none of the bacteria was detected, and plants remained healthy. To complete Koch's postulates, bacteria were successfully re-isolated on Gassner agar.

This is the first report of AOD in Switzerland associated with B. goodwinii, G. quercinecans, and R. victoriana. As AOD is of increasing concern in Great Britain and threatens native oaks, careful monitoring of this decline disease in oak ecosystems is warranted.

Figure1+
Figure 1: Disease symptom of acute oak decline on Quercus rubra in the field.
Figure 1: Disease symptom of acute oak decline on Quercus rubra in the field.
Figure2+
Figure 2: Necrotic tissue characteristic of acute oak decline underneath a stem bleed.
Figure 2: Necrotic tissue characteristic of acute oak decline underneath a stem bleed.
Figure3+
Figure 3: Symptoms on a young oak plant inoculated with Brenneria goodwinii, Gibbsiella quercinecans and Rahnella victoriana, showing degradation of the vascular tissue.
Figure 3: Symptoms on a young oak plant inoculated with Brenneria goodwinii, Gibbsiella quercinecans and Rahnella victoriana, showing degradation of the vascular tissue.

Acknowledgements

The authors thank Quirin Kupper, Stephanie Pfister and Vivanne Dubach for their assistance in diagnostics and in the field. This work was supported financially by the Swiss Federal Office for the Environment (FOEN).

References

  1. Brady CL, Cleenwerck I, Venter SN, Vancanneyt M, Swings J, Coutinho TA, 2008. Phylogeny and identification of Pantoea species associated with plants, humans and the natural environment based on multilocus sequence analysis (MLSA). Systematic and Applied Microbiology 31, 447-460. [http://dx.doi.org/10.1016/j.syapm.2008.09.004]
  2. Denman S, Brown N, Kirk S, Jeger M, Webber J, 2014. A description of the symptoms of Acute Oak Decline in Britain and a comparative review on causes of similar disorders on oak in Europe. Forestry: An International Journal of Forest Research 87, 535-551.  [http://dx.doi.org/10.1093/forestry/cpu010]
  3. Denman S, Doonan J, Ransom‐Jones E, Broberg M, Plummer S, Kirk S, Griffiths AR, Kaczmarek M, Forster J, Peace A, Golyshin PN, Hassard F, Brown N, Kenny JG, McDonald JE, 2018. Microbiome and infectivity studies reveal complex polyspecies tree disease in Acute Oak Decline. The ISME Journal 12, 386-399. [http://dx.doi.org/10.1038/ismej.2017.170]
  4. Green S, Laue B, Fossdal CG, A'Hara SW, Cottrell JE, 2009. Infection of horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi and its detection by quantitative real-time PCR. Plant Pathology 58, 731-744. [http://dx.doi.org/10.1111/j.1365-3059.2009.02065.x]
  5. Lane DJ, 1991. 16S/23S rRNA sequencing. In: Stackebrandt E, Goodfellow M, eds. Nucleic Acid Techniques in Bacterial Systematics. New York, USA: John Wiley & Sons, 115-175. [http://dx.doi.org/10.1002/jobm.3620310616]
To cite this report: Ruffner B, Schneider S, Meyer JB, Queloz V, Rigling D, 2020. First report of acute oak decline disease of native and non-native oaks in Switzerland. New Disease Reports 41, 18. [http://dx.doi.org/10.5197/j.2044-0588.2020.041.018]

©2020 The Authors