Phytophthora alni species complex (Brasier & S.A. Kirk, 2004) Husson, Ioos & Marçais, 2015, nothosp. nov. Alder Phytophthora

California Pest Rating for

Phytophthora alni species complex (Brasier & S.A. Kirk, 2004) Husson, Ioos & Marçais, 2015, nothosp. nov. Alder Phytophthora
Pest Rating: A


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Posted by tn

2 thoughts on “Phytophthora alni species complex (Brasier & S.A. Kirk, 2004) Husson, Ioos & Marçais, 2015, nothosp. nov. Alder Phytophthora”

    Dr. Tyler Bourret
    UC Davis Plant Pathology

    December 3, 2021


    I am excited about the proposed pest ratings on the Phytophthora alni species complex and P. bisheria.

    I just wanted to share a couple insights from my perspective as a Phytophthorologist.

    First, I know that the APHIS group is in the process of emending the name P. bisheria to P. bishii. So P. bishii is likely to be the more official name of that species going forward. I recommend at least listing both variants in the pest rating just for the sake of clarity.

    Second is the “P. xalni species complex.” For whatever reason, the researchers who have worked on the three taxa formerly named P. alni have omitted P. xcambivora from their studies, despite the fact that P. xcambivora is at least as closely related to P. xalni as P. xmultiformis. In fact, I personally think that P. xcambivora is a better candidate for the other parent of P. xalni than P. xmultiformis, but that’s beside the point.

    I agree that P. xcambivora is the only species in this group documented in California – I can find no evidence that P. xalni, P. xmultiformis or P. uniformis are here. So the species listed in the pest rating are the right ones, and I agree that an A is appropriate!

    The only issue I have is with the definition of the P. xalni species complex. If the complex is defined phylogenetically (which it doesn’t necessarily have to be), then P. xcambivora is also a member of the complex, whether it is narrowly or widely defined. I attached a tree I adapted from a recent Plant Disease article ( to show what I mean by these “complexes”. This is really a minor nomenclatural issue, but I just wanted to bring it to your attention. There is nothing inherently wrong with defining the complex as you did in the pest rating proposal, it is just not the way I would personally define the complex.

    Thanks, keep up the excellent work!

    -Tyler Bourret

    To: Dr. Bourret

    Thank you for your comments and your support for this proposed rating for Phytophthora xalni. I am aware of the new name for Phytophthora bisheria and I will include it in my comments for that pest rating proposal.

    Thank you for the newly published information on P. cambivora. As you noted, it is already in California and under regulation. It was reviewed and rated by Dr. John Chitambar, former Primary State Plant Pathologist (now retired) in 2017, and it has B rating.
    -Heather Scheck, Primare State Plant Pathologist


    December 3, 2021
    From: the California Oak Mortality Task Force, & The Phytophthoras in Native
    Habitats Work Group, — Committees of the California Forest Pest Council, Contact: Janice Alexander,

    To: Heather J. Scheck, Primary Plant Pathologist/Nematologist, CDFA
    Comment on: Proposed California Pest Rating Proposal for Phytophthora alni species complex (Brasier
    & S.A. Kirk, 2004) Husson, Ioos & Marçais, 2015, nothosp. nov.; Alder Phytophthora
    Current Pest Rating: None Proposed Pest Rating: A
    The California Oak Mortality Task Force and the Phytophthoras in Native Habitats Work Group,
    committees of the California Forest Pest Council, support this California Department of Food and
    Agriculture (CDFA) proposal to assign an “A” rating to the Phytophthora alni species complex.
    An “A” rating is defined as “An organism of known economic importance subject to state (or
    commissioner when acting as a state agent) enforced action involving eradication, quarantine
    regulation, containment, rejection, or other holding action.” We believe this rating is
    appropriate since this pathogen complex has never been detected in California and if it were to
    become introduced it would threaten California’s natural resources, horticultural and agricultural
    Thank you for taking this action to protect California plant health.
    Chairperson, California Oak Mortality Task Force RPF #2885
    California Department of Forestry and Fire Protection, Forest Entomology and Pathology 118 S
    Fortuna Blvd
    Fortuna, CA 95540

    To: Chair Lee, COMTF
    Thank you for your comment and support
    – Heather Scheck, Primary State Plant Pathologist

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