Beech; Rhododendron

No known vector.

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 CAPS 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).

1. Serological: An Enzyme-Linked ImmunoSorbent Assay (ELISA) Reagent Set for Phytophthora (AGDIA, Cat# SRA 92600/1000) at the genus level for primary screening. A positive does not indicate P. kernoviae.

Identification must be confirmed by other methods.

2. Molecular: Real-time polymerase chain reaction (qPCR) is approved for species identification (see Notes). To request a copy of these protocols, email the S&T Beltsville laboratory at APHIS-PPQCPHSTBeltsvilleSampleDiagnostics@aphis.usda.gov and use the subject line "Diagnostic protocol request".

Diagnostic Resources:

IDphy: molecular and morphological identification of Phytophthora, a tool that supports morphological and molecular identification of Phytophthora spp. including P. austrocedrae, developed by PPQ in collaboration with Phytophthora experts.

https://idtools.org/id/phytophthora/index.php

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.

3/13/2020: The qPCR protocol uses the Cepheid SmartCycler thermocycler machine. In 2019, the manufacturer discontinued this machine. The S&T Beltsville laboratory is currently adapting the protocol for a different machine. Diagnostic labs may use the protocol for the Cepheid SmartCycler if their machine is in good condition. For the 2020 survey season, please contact the diagnostic laboratory you use for screening to confirm their capacity before you begin collecting samples.