Re: Sudden Oak Death linked to rhododendrons
Moira wrote:
> Thanks Richard for the information about this
Phytophthora.
>
> It is obvious we have an immense amount to learn about the
etiology of
> disease and that so far we are only touching the fringes
of the
> subject. One thing which becomes increasingly evident is
that while
> many disease organisms have been with us for a very long
time there is
> also a great deal of evolution going on throwing up new
strains and even
> completely new diseases. In human medicine we have for
instance in
> recent times seen several very terrible viruses come
apparently from
> nowhere, but I have no doubt bacterial and fungal diseases
are likewise
> evolving, if not quite so spectacularly.
>
> One thing which seems odd about this particular
Phytophthora is that its
> host range apparently consists of just two not
particularly closely
> related genera. One wonders what is the common factor
which makes both
> susceptible. It is also strange that only a small number
of different
> oaks are (so far at least) affected.
>From information at the Sudden Oak Death sites, it appears
to be almost totally destroying the 3 species of oak, all
native to California. So far, European oaks have not
contracted it.
As I grow almost 300 species and hybrid rhododendrons
adjacent to native Garry oak stands, I am following this
with great interest.
Further information on this Phytophthora:
It is a new species first isolated on ornamental
rhododendrons in Germany and The Netherlands in 1993 and is
genetically distant to most of the other 60 species within
the genus Phytophthora. The closest relative in the genus
is P. lateralis, a virulent pathogen of Port Orford Cedar.
P. lateralis is known to be present in natural stands of
P.O. Cedar in the Pacific Northwest and occasionally on P.O.
Cedar stock in nurseries in Europe.
Perhaps there is another host species which is contaminating
both rhododendrons and oaks. Perhaps it is a native fungus
that went through a mutation due to environmental changes or
proximity of a new host species. Certainly there is a free
exchange of rhododendron material between California and the
Port Orford Cedar habitat in Oregon, not to mention Port
Orford Cedars. (I am drawing this connection myself which
is not supported by information at the sites.)
Diane Pertson
> This is the first time I have heard of a species of fungus
being
> positively identified by its DNA. This seems like a great
tool for
> clearing up questions of identity and relationships of
and I can see it
> being made much use of by mycologists.
>
> Moira
> --
> Tony & Moira Ryan <theryans@xtra.co.nz>
> Wainuiomata (near Wellington, capital city of New Zealand)
>
