Summary
The invasive pathogen Phytophthora austrocedri is causing widespread mortality of native juniper in northern Britain. This project aims to provide the evidence base to guide juniper conservation strategies that mitigate the effects of the pathogen. Our work focuses on understanding routes of pathogen introduction, identifying sites at highest risk from pathogen establishment and determining the genetic basis of resistance in juniper allowing for an evolutionary-based approach to conservation management.
Research Objectives
The objectives of this project are to:
- determine the genetic basis underlying natural resistance in juniper populations to P. austrocedri.
- carry out comparative whole genome analyses of P. austrocedri isolates to shed light on the pathogen’s genetic background and population history.
- develop a greater understanding of the epidemiology of P. austrocedri by defining optimum conditions for growth and survival and by identifying mechanisms of spread.
- determine the wider distribution of the pathogen in Britain, linking disease severity with key site factors (soil type, wetness, climate, human activity).
Latest Update
Phytophthora austrocedri is killing juniper in many parts of Scotland and northern England. This recently introduced pathogen is a tetraploid species of hybrid origin which grows optimally at cooler temperatures (15°C), and it is these characteristics which enhance invasiveness at high latitudes.
The British lineage of P. austrocedri is genetically and morphologically distinct from the lineage causing widespread mortality of Chilean cedar in Argentina and the geographical origin of the source population, where both lineages originated, remains unknown. The good news is that juniper populations in Britain harbour heritable genetic variation in disease resistance, and exhibit both quantitative and qualitative phenotypic variation in resistance.
The fact that juniper has the genetic potential to adapt to P. austrocedri means that population recovery is possible through management for natural regeneration. Successful defence in juniper against P. austrocedri involves rapid induction of the host response with increased virulence in the pathogen linked to enhanced suppression and evasion of host defences.
Candidate genes in juniper have been identified that may be key to resistance and work is ongoing to confirm their role. Genetic clustering of British P. austrocedri isolates by geographical location points to multiple introductions of different genotypes at different juniper sites, possibly through supplementary planting, with no long distance spread of the pathogen. Once the pathogen has been introduced to a site, it has a slow natural spread in soil, requiring high moisture conditions. Juniper populations on wet sites with acid soils are predisposed to infection. Once established at a site P. austrocedri can be spread readily in soil locally, vectored by animal movements and/or human activities.
General Content
Publications arising from this project
Crowson, D., Cavers, S., Cottrell, J.E., Ennos, R.A., Green, S. 2026. Vulnerable juniper populations show adaptive potential in the face of a highly damaging invasive tree pathogen. Evolutionary Applications 19, no. 6: e70276. https://doi.org/10.1111/eva.70276.
Crowson, D. 2025. Ecological genetics of the invasive tree pathogen Phytophthora austrocedri and its native host juniper. PhD Thesis, University of Edinburgh.
Donald, F., Hedges, C., Purse, B.V., Cunniffe, N.J., Green, S., Asaaga, F.A. 2024. Utility of decision tools for assessing plant health risks from management strategies in natural environments. Ecology and Evolution, 2024;14:e11308. https://doi.org/10.1002/ece3.11308
Donald, F., Purse, B.V., Green, S. 2021. Investigating the role of restoration plantings in introducing disease – a case study using Phytophthora. Forests 12 (6), 764; https://doi.org/10.3390/f12060764
Green, S., James, E.R., Clark, D., Clarke, T-K., Riddell, C.E. 2020. Evidence for natural resistance in Juniperus communis to Phytophthora austrocedri. Journal of Plant Pathology 103, 55-59. https://doi.org/10.1007/s42161-020-00693-1
Donald, F., Green, S., Searle, K., Cunniffe, N.K., Purse, B. 2020. Small scale variability in soil moisture drives infection of vulnerable juniper populations by invasive forest pathogen. Forest Ecology and Management 473, 118324 https://doi.org/10.1016/j.foreco.2020.118324
Riddell, C.D., Dun, H.F., Elliot, M., Armstrong, A.C., Clark, M., Forster, J., Hedley, P.E., Green, S. 2020. Detection and spread of Phytophthora austrocedri within infected Juniperus communis woodland and diversity of co-associated Phytophthoras as revealed by metabarcoding. Forest Pathology https://doi.org/10.1111/efp.12602
Henricot, B., Pérez-Sierra, A., Armstrong, A., Sharp, P. M., Green, S. 2017. Morphological and genetic analyses of the invasive forest pathogen Phytophthora austrocedri reveal two clonal lineages colonised Britain and Argentina from a common ancestral population. Phytopathology 107, 1532-1540. https://doi.org/10.1094/PHYTO-03-17-0126-R
Green, S., MacAskill, G.A., Dun, H., Armstrong, A.C., Henricot, B. 2016. First report of Phytophthora austrocedri infecting Nootka cypress in Britain New Disease Reports (2016) 33, 21. http://dx.doi.org/10.5197/j.2044-0588.2016.033.021
Green, S., Elliot, M., Armstrong, A., Hendry, S.J. 2014. Phytophthora austrocedrae emerges as a serious threat to juniper (Juniperus communis) in Britain. Plant Pathology 64, 456-466. https://doi.org/10.1111/ppa.12253
Mulholland, V., Schlenzig, A., MacAskill, G.A., Green, S. 2013. Development of a quantitative real-time PCR assay for the detection of Phytophthora austrocedrae, an emerging pathogen in Britain. Forest Pathology 43, 513-517. https://doi.org/10.1111/efp.12058
Green, S., Hendry, S.J., MacAskill, G.A., Laue, B.E., Steele, H. 2012. Dieback and mortality of Juniperus communis in Britain associated with Phytophthora austrocedrae. New Disease Reports 26, 2. http://dx.doi.org/10.5197/j.2044-0588.2012.026.002
Donald, F., Green, S., Searle, K., Cunniffe, N.K., Purse, B. 2020. Small scale variability in soil moisture drives infection of vulnerable juniper populations by invasive forest pathogen. (PDF-2.5 MB) Forest Ecology and Management 473, 118324
Riddell, C.D., Dun, H.F., Elliot, M., Armstrong, A.C., Clark, M., Forster, J., Hedley, P.E., Green, S. 2020. Detection and spread of Phytophthora austrocedri within infected Juniperus communis woodland and diversity of co-associated Phytophthoras as revealed by metabarcoding. (PDF-1.2 MB) Forest Pathology
Henricot, B., Pérez-Sierra, A., Armstrong, A., Sharp, P. M., Green, S. 2017. Morphological and genetic analyses of the invasive forest pathogen Phytophthora austrocedri reveal two clonal lineages colonised Britain and Argentina from a common ancestral population. (PDF-850 KB) Phytopathology 107, 1532-1540.
Green, S., MacAskill, G.A., Dun, H., Armstrong, A.C., Henricot, B. 2016. First report of Phytophthora austrocedri infecting Nootka cypress in Britain New Disease Reports. (PDF-6.3 MB) (2016) 33, 21.
Green, S., Elliot, M., Armstrong, A., Hendry, S.J. (2015). Phytophthora austrocedrae emerges as a serious threat to juniper (Juniperus communis) in Britain. (PDF-1 MB) Plant Pathology 64, 456-466.
