Biology Reference
In-Depth Information
11.
Adaptation of Alien Diseases
to Hosts and Vectors
“Migrations of virulent and fungicide-resistant strains in the past two decades
have caused a worldwide resurgence of the potato (and tomato) late blight
disease....This resurgence supports the view that introduced pathogens and
new variants of old ones present a real and immediate threat for plants as well
as for animals and humans.”
—F
RY AND
G
OODWIN
(1997)
The sudden oak death fungus (
Phytophthora ramorum
) was discovered and
described in the Netherlands and Germany, where it parasitized
Rhodo-
dendron
and
Viburnum
shrubs. In 1995, however, the fungus appeared in
central California (Rizzo et al. 2002), where it began to attack and kill a
wide variety of broad-leafed trees and shrubs, especially tanoak (
Lithocar-
pus densiflorus
), various live and deciduous oaks (
Quercus
spp.), and
madrone (
Arbutus menziesii
). By summer 2001, the disease had spread
along the coastal region from Monterey County to Mendocino County,
causing the death of tens of thousands of trees. The range of trees and
shrubs affected also widened, and by summer 2002, 17 species had been
identified with infections.These included members of five genera of trees
belonging to families other than the Fagaceae, to which the oaks belong.
The fungus attacks the roots of the species most subject to being killed.
California bay laurel (
Umbellularia californica
), in which the leaves, but not
the roots, are infected, appears to play a major role in the dispersal of
spores of the fungus.
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