Re: Sudden Oak Death linked to rhododendrons
Richard Starkeson wrote:
>
> Tony & Moira Ryan wrote:
>
> > It remains to be seen whether the disease whiich has been found on
> > Rhododendrons in Europe will in fact eventually spread to oaks.
> >
>
> I think the prospect is unlikely. In California, the only place it has yet
> caused disease in oaks, it has only affected 3 oak species, all native to
> California, and left all other oak species untouched. (Unfortunately, it seems
> to be totally wiping out the three affected species, wherever it has spread,
> leaving large tracts of dead trees). Although this species of Phytophthora has
> been known on european rhododendrons since 1993, it has not been found affecting
> any european oaks. DNA analysis seems to show that the Phythopthora affecting
> the California Oaks has the exact same structure as that of the particular
> Phytophthora species that was found in the european rhododendrons. This is
> different from other Phytophthora species that also affect rhododendrons.
>
> >
> > I don't know if anybody is clear in which direction the disease is
> > spreading.
> > If originally a European disease I suppose it could have suffered a
> > mutation after crossing the Atlantic increasing its pathogenicity and
> > allowing it to increase its host range..
> >
> > Conversely, if it has come in the other direction there is no particular
> > reason to believe it has changed and maybe it is only a matter of time
> > before European oaks begin to fall victim.
>
> It is indeed an interesting puzzle. It is unlikely to have come from Europe to
> California via rhododendrons, as there is there is almost no importation of
> rhododendrons from Europe to California. Perhaps it came from asia, imported
> with new rhododendron collections. Or perhaps it came from another host
> species, and has only recently migrated to both oaks and rhododendrons.
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.
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)
