Re: Sudden Oak Death linked to rhododendrons
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.
Richard Starkeson,
Berkeley, California
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