Phytophthora Austrocedrae - Forestry Journal

Feature: Phytophthora austrocedraeAsexual spores called sporangiaand their associated motilezoospores are the main meansof spread for Phytophthoras.Characteristic elliptical-shapedsporangium of Phytophthoraramorum with zoospores beingsqueezed out is shown here.(Picture courtesy Forestry Commission).(Far left) Close-up of foliar blightand dieback symptoms on Japaneselarch caused by Phytophthoraramorum. (Picture courtesy ForestryCommission).Famous last words on Phytophthora austrocedrae eradicationFor those in the arb sector more interested to know what happenedat the site in Scotland where Phytophthora austrocedrae wasfound on Nootka cypress, the following is a short summary basedon report GBR-24/2 submitted to the FAO’s International PlantProtection (IPPC) and report EPPO RS 2011/135 submitted to theEuropean and Mediterranean Plant Protection Organisation by theUK plant health authorities in May 2011.Dieback was noted on two C. nootkatensis and threeChamaecyparis lawsoniana (Lawson’s cypress). The affected treesshowed similar symptoms to previous findings of Phytophthoralateralis on Lawson’s cypress with some having fresh basal lesions.One tree had branch dieback. The trees yielded positive forPhytophthora when tested with a Lateral Flow Device (LFD).Samples testing positive for Phytophthora were tested further usingPhytophthora-specific PCR (polymerase chain reaction)* primerson DNA extracted from the bark. Resulting gene sequences wereanalysed to determine the Phytophthora species. One isolatefrom C. nootkatensis gave 100% and 99% sequence matchesto P. austrocedrae. Cultures from the material yielded an isolateconfirmed as P. austrocedrae based on culture morphology(shape and structure of mycelium and spores) and DNA analysis.On the same site there were also two positive identifications forPhytophthora cambivora and a single positive identification for P.lateralis all on C. lawsoniana.In addition to tree destruction, phytosanitary measures were put intoplace to avoid any further spread of P. austrocedrae. These includedprohibiting the removal of plant material from infected sites(including composted material), thorough cleaning of all machineryand equipment used to fell and dispose of the infected material,warning notices for members of the public and disinfectant footmats placed at all exit points.The IPPC report documents the status of P. austrocedrae under ISPM(International Standards for Phytosanitary Measures) No 8 as ‘undereradication’. Nature of immediate or potential danger is describedby the report as “none”.“The outbreak is contained and the plants have been destroyed,”says the report. Famous last words?*Polymerase chain reaction (PCR) is a technique used in molecular biology toamplify pieces of DNA (gene sequences) and allow exact identification of microbialplant pathogens through gene sequence identification and matching.References: www.ippc.int/index.php?id=1110879&no_cache=18http://archives.eppo.org/EPPOReporting/2011/Rse-1106.pdfNEWS IN BRIEFcouncil in Kent has ordered a landmark 95ft Wellingtonia tree to be cut down to make way for a housing development. The tree, inA a pub garden in Tonbridge and estimated to be about 100 years old, is currently protected by a Tree Preservation Order. The localTonbridge Civic Society and as well as local residents have protested to Tonbridge and Malling Borough Council that the tree should besaved. But their protests have been overruled by the council who argued that the economic advantages of the new 20-house developmentoutweigh the environmental benefit of protecting the tree.An arboricultural assessment had discovered some bark damage, but it was concluded that this was more likely caused by an animalrather than an infection.For the protesters, local councillor Janice Browne said there was, “no admissible justification” for the felling of the tree. She added: “A treeof this value should not be removed to facilitate site redevelopment.”The most severe criticism has come from Ron Levy of the Redwood World website. He commented: ”It is a relatively rare type of tree thathas become a landmark tree and is now part of the local amenity. Despite its considerable age, it is a youthful and vigorous example of itstype, so it begs the question as to how it is possible that a tree preservation order can be disregarded just because it better suits the plansof the developer to cut it down? This would appear to make tree preservation orders utterly pointless, since it seems to me that the all thedeveloper had to do was simply point at some missing bark and claim the tree is diseased and their application to fell was granted.”Family activities to discover the intrepid world of plant hunting, expert carvers creating big play trail pieces and over 100 exhibitors jointhis year’s Treefest at Westonbirt, the National Arboretum in Gloucestershire. The event takes place from Saturday 25 to Monday 27August at the Forestry Commission-managed arboretum. Visitors can watch as carvers take inspiration from fairytales and nature to createlarge wooden sculptures that will become part of the new play trail in Silk Wood. Wood for the sculptures is sourced as part of the routinemanagement of Westonbirt arboretum’s tree collectionSimon Hough, the Forestry Commission’s recreation manager at Westonbirt Arboretum commented: “Over 20,000 visitors came to ournew-look Treefest last year and we had some great feedback about the event – particularly around the family activities, live music andexhibitors. We know many visitors want to see big carving, so this year Treefest will have three expert carvers creating pieces to stay on siteafter the event. We hope visitors will enjoy watching these sculptures take shape across the weekend.”For tickets and further information visit www.forestry.gov.uk/westonbirt-treefest.35