Evidence for natural resistance in Juniperus communis to Phytophthora austrocedri
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Evidence for natural resistance in Juniperus communis to Phytophthora austrocedri Sarah Green 1
&
Eleanor R. James 1 & Dave Clark 1 & Toni-Kim Clarke 1 & Carolyn E. Riddell 1
Received: 20 May 2020 / Accepted: 12 November 2020 # Crown 2020
Abstract Phytophthora austrocedri is a recently invasive pathogen causing widespread mortality of the ecologically important native conifer, Juniperus communis, in northern Britain. Observations of disease symptoms at severely infected woodlands revealed the presence of individual, apparently healthy trees in areas of high mortality. This study was undertaken to test the hypothesis that these ‘survivor’ trees have greater resistance to P. austrocedri. Rooted cuttings were obtained from seventeen putatively resistant J. communis clones at two heavily infected natural woodlands. Inoculation of excised stems from three putatively resistant clones with P. austrocedri provided initial data to support the hypothesis of resistance. A larger trial was conducted in which whole J. communis plants representing seventeen putatively resistant clones and a known susceptible clone were inoculated with two isolates of P. austrocedri. This trial revealed variation in resistance, with at least six clones exhibiting a high degree of resistance to the pathogen. One surprising finding given the lack of genetic diversity in UK P. austrocedri isolates was that one of the clones was resistant to one isolate and susceptible to the other, warranting further investigation. The next steps are to ascertain whether this natural resistance in J. communis is heritable and exploitable for population recovery. Keywords Invasive pathogen . Native species . Survivor . Tolerance
Juniperus communis is a dioecious evergreen conifer distributed to 30 °N throughout northern Asia, North America and Europe (Thomas et al. 2007). In Britain, J. communis is one of only three native conifer species and is listed as a priority species in the UK Biodiversity Action Plan (http://jncc.defra. gov.uk/ukbap and http://archive.jncc.gov.uk/page-5171) due to its high ecological value as a constituent of woodland ecosystems. Over the last twenty years, however, populations of J. communis in Britain have come under serious threat from the invasive oomycete pathogen, Phytophthora austrocedri (synonym: Phytophthora austrocedrae Gresl. & E.M. Hansen, sp. nov.) which is now well established across much of where J. communis occurs in northern England and Scotland (Donald et al. 2020), infecting roots and stems in at least 63 separate J. communis populations (F. Donald, Personal Communication), and resulting in extensive mortality (Green et al. 2015). The pathogen was first
* Sarah Green [email protected] 1
Forest Research, Northern Research Station, Roslin, Midlothian, UK
described in 2007 from southern Argentina where it is killing the native cypress Austrocedrus chilensis (Cupressaceae) across a significant portion of its habitat in Patagonia (Greslebin et al. 2007). The forest epidemics in Britai
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