Sudden Oak Death Research Project:
Susceptibility to Phytophthora ramorum in a
key infectious host: landscape variation in host genotype, host
phenotype, and environmental factors
Genetic diversity of
a host
population and its spatial structure can strongly influence
host-pathogen interactions and disease spread. Very few studies
have characterized the genetic composition of a plant host population as
a pathogen was spreading through its range, and no studies have
extensive, direct genotyping of host individuals in natural settings in
which a pathogen is spreading.
In this study,
DNA-based genetic markers (AFLP) were employed to characterize the genome of
Umbellularia californica (California Bay), one of the most abundant
and epidemiologically important foliar hosts for Phytophthora ramorum.
The goal of this research was to describe the spatial genetic structure
and diversity of U. californica within the Sonoma Mountain and
Sonoma Valley region.
Laboratory
susceptibility trials were conducted on detached leaves and assessed
field disease levels for 97 host trees from 12,225 m2 plots. Genotype
and phenotype characteristics were assessed for each tree.
Effects of
plot-level environmental conditions (understory microclimate,
 amount of
solar radiation and topographic moisture potential) on disease
expression were also evaluated.
Susceptibility varied
significantly among U. californica trees, with a fivefold
difference in leaf lesion size. Lesion size was positively related to
leaf area, but not to other phenotypic traits or to field disease level. Genetic diversity was structured at
three spatial scales, but primarily among individuals within plots. Lesion size was
significantly related to amplified fragment length polymorphism (AFLP) markers,
but local environment explained most variation in field disease level.
Thus, substantial
genetic variation in susceptibility to P. ramorum occurs in its
principal foliar host U. californica, but local environment
mediates expression of susceptibility in nature.
Anaker, B.L., Rank, N.E., Huberli,
D., Garbelotto, M., Gordon, S., Whitkus, R., Harnik, T., and Meentemeyer, R.K. 2008.
Susceptibility to Phytophthora ramorum in a key
infectious host: landscape variation in host genotype,
phenotype, and environmental factors. New Phytologist
177: 756-766.
(PDF)
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