Phytophthora kernoviae (Brasier et al.)
Significance: Phytophthora kernoviae Brasier et al., a pathogen very similar to Phytophthora ramorum, has been detected in New Zealand. This fungus-like organism, initially called "Phytophthora Taxon C", was first found during P. ramorum surveys, on rhododendrons, beech and native English Oak (Quercus robur) trees in Cornwall England (PAS, 2004). Phytophthora kernoviae is considered more pathogenic to rhododendrons than P. ramorum and is capable of causing serious damage to beech trees. Symptoms, depending on the host, include leaf necrosis, stem die-back and “bleeding cankers”. In the UK, The Department for Environment Food and Rural Affairs (DEFRA) and the Forestry Commission are now conducting regular surveys for the disease and require the destruction of all plants found to be infected. Since the first find in 2003, there have been additional detections in woodlots and gardens in and around Cornwall and South Wales. In April, 2005, the United States Department of Agriculture notified the European Union that any nursery wishing to export host plants to the United States would be required to have an annual survey to determine that the nursery is free from P. kernoviae. The following genera of propagative material (except seeds) were named as regulated: Fagus sp., Gevuina sp., Liriodendron sp., Michelia sp., Magnolia sp., Pieris sp., Quercus sp., Rhododendron sp.
Issues of Concern: According to a recent Biosecurity New Zealand press release, reported by Scoop International News (2006), Phytophthora kernoviae has recently been found in the Northland. The pathogen, identified using DNA technology, was collected in one orchard on cherimoya or custard apple (presumably Annona cherimola Mill.), and confirmed present in a soil sample collected from Trounson Kauri Park. At this stage the origin is still unknown and investigations and surveys are continuing. Biosecurity New Zealand has not been able to establish any link to imported material.
Pathways: The pathogen has been observed to move rapidly through infected rhododendrons and it is suspected that spores may be carried locally by rain splash, wind-driven rain, irrigation or groundwater. Long distance spread may be by movement of contaminated plant material, growing media, and in soil carried on vehicles, machinery, footwear or animals.
Hosts: The following hosts have been reported in the United Kingdom: European Beech (Fagus sylvatica), Magnolia stellata, rhododendrons (mainly R. ponticum), Gevuina avellana (Chilean hazelnut), Liriodendron tulipifera (tulip tree), Michelia doltsopa, Quercus ilex (holm oak), Pieris spp., Quercus robur (English oak), and Drimys winteri (winter's bark) (DEFRA, n.d.).
Brasier, C.M., P.A. Beales, S.A. Kirk, S. Denman, and J. Rose. 2005. Phytophthora kernoviae sp. nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar necrosis of ornamentals in the UK. Mycological Research Vol. 109:853-859. DEFRA, n.d. Phytophthora kernoviae. A new threat to our trees and woodlands (Pestnote). Department for Environment Food and Rural Affairs (UK). Available on the internet at http://www.defra.gov.uk/planth/pestnote/kern.pdf PAS. 19 November 2004. New species of Phytophthora in Cornwall England. http://www.pestalert.org/viewArchNewsStory.cfm?nid=322&keyword=phytophthora%20taxon%20 Scoop Independent News. Biosecurity New Zealand investigates new fungus in Northland. http://www.scoop.co.nz/stories/SC0603/S00060.htmPosted Friday, 24 March 2006, Press Release: Biosecurity NZ. Note: Additional information on P. kernoviae has been collected and posted on the UK's Department of Environment, Food and Rural Affairs web site at http://www.defra.gov.uk/planth/pkernovii1.htm