No known vector.

Method	Instructions	NAPIS Survey Method
Visual	Collect bark lesions, shoot, twigs, or leaves from symptomatic trees.	3031 - General Visual Observation
Water Sample	Water/Soil sampling with rhododendron leaf baits.	3014 - General Water Sample

For Visual:
Trees (trunk/logs): for bleeding cankers, the inner bark in the area directly around the oozing sap is cut until a canker margin is evident. Pieces of phloem and xylem are removed and placed in a sealed container.

Shoots/twigs: a piece of stem including the leading edge (junction between diseased and healthy tissue) is removed and placed in a sealed plastic bag, with a small piece of
damp tissue to prevent desiccation.

Leaves: 4-6 leaves showing a suitable range of symptoms are removed and placed in a sealed plastic bag. If possible, all samples of plant material should be sent to the laboratory to arrive by the next day. Overheating or desiccation of samples prior to dispatch should be prevented.

See CPHST Pest Datasheet for water baiting information.

No specific signs are present.

Phytophthora kernoviae causes various symptoms on infected host plants. These symptoms can be classified into 3 main types: formation of bleeding lesions, dieback of branch and shoot tips and various foliage, and, quite often, shoot necroses. Like P. ramorum, P. kernoviae causes bleeding stem cankers on members of the Fagaceae and foliar blight and shoot dieback on other hosts. As a rule, bleeding lesions are observed on the European beech, Tulip tree (Liriodendron tulipifera), and English oak (Quercus robur). The bleeding lesion form of disease is the most dangerous. Mature trees of the above mentioned species are affected with cankers appearing at the stem bottom. Their size varies from several centimeters to 3 or more meters in length (along the trunk). Lesions can be hollow as lagoons and, sometimes, affected tissues are colored with black stripes separating the healthy part from the discolored affected one. Discoloration of the phloem and xylem tissue is caused by development of P. kernoviae mycelium.

On foliage hosts, leaf spotting, blight, and shoot dieback develop. The pathogen sporulates on foliage hosts and is dispersed by rain to bole hosts such as beech (Fagus sylvatica) and oak (Quercus spp.), where cankers develop (Aleksandrov and Arbuzova, 2012; Dick and Parke, 2012).

ID/Diagnostic: Multiple

1. Serological: An ELISA test is available for Phytophthora at the genus level for primary screening. A positive does not indicate P. kernoviae.

ID must be confirmed by other methods.

2. Molecular:
PPQ CPHST has validated work instructions available upon request for a real-time PCR (qPCR) for confirmation of P. kernoviae.

Please contact:
Ashlee Barth - USDA-APHIS-PPQ-CPHST
(301) 313-9277
ashlee.k.barth@aphis.usda.gov

Symptoms in infected hosts are very similar to those of P. ramorum, which infects some of the same hosts. However, P. kernoviae has clear morphological distinctions from P. ramorum (Aleksandrov and Arbuzova, 2012). Compared to P. ramorum, which often occurs in similar habitats in the UK, P. kernoviae is homothallic instead of heterothallic, is papillate instead of semi-papillate, does not produce chlamydospores, and has a longer pedicel length (Dick and Parke, 2012).

P. kernoviae may be distinguished from other homothallic Phytophthora species with caducous, papillate sporangia with medium-length pedicels by its lower optimal temperature (cfr. P. botryosa, and P. hevea); higher optimum temperature (cfr. P. nemerosa), often tapered oogonial stalks (cfr. P. meadii, P. botryosa, P. nemerosa), often asymmetric sporangia (cfr. P. meadii, P. megakarya, P. nemerosa), and longer pedicels (cfr. P. boehmeriae) (Brasier et al., 2005; Dick and Parke, 2012).

Widmer (2010) developed a diagnostic key to differentiate P. kernoviae from other Phytophthora species that infect the foliage of Rhododendron.

Brasier et al. (2005) describe distinct morphological characteristics of P. kernoviae. Phytophthora kernoviae is homothallic and produces amphigynous antheridia and caducous and conspicuously papillate sporangia (Brasier et al, 2005). Phytophthora boehmeriae is the only known species that has the same characters. However, P. kernoviae can be easily separated from P. boehmeriae by shape of oogonial stalks (tapered vs. not tapered) and sporangia (often asymmetric vs. spherical/ovoid) and pedicel length (medium vs. short) (USDA, 2008).

Schlenzig (2011) developed a duplex PCR method, based on the internal transcribed spacer (ITS) regions of the ribosomal DNA, that can simultaneously detect P. kernoviae and P. ramorum. Hughes et al. (2011) developed a TaqMan real-time PCR assay for detection of P. kernoviae that is also based on internal transcribed spacer (ITS) sequence.

Tomlinson et al. (2010) developed a method for nucleic-acid-based detection of P. kernoviae. This method involves extraction of DNA on the nitrocellulose membranes of lateral-flow devices, loop-mediated isothermal amplification (LAMP) of target DNA using labeled primers, and detection of the generically labeled amplification products by a sandwich immunoassay in a lateral-flow-device format. This method is suitable for on-site use.