Disease has been implied as an important selective
force acting in plant populations. This study was
conducted to determine the effects of stripe rust (Puccinia
striiformis) on the population dynamics of wheat (Triticum
aestivum) cultivar mixtures.
Five wheat cultivars were grown in pure stands and all
possible mixtures at three and two locations in 1987 and
1988, respectively. In 1989, four replacement series and
their component pure stands were grown in two locations.
All treatments were exposed to or protected from two stripe
rust races. Disease severity and yield were determined on
a per-cultivar basis for mixtures and also for pure stands.
In all but one mixture, disease severity relative to
the pure stands was reduced between 6 and 97%. Disease
severity changes could be separated into two effects:
First, selection for the more resistant or susceptible
genotype reduced or increased disease in mixtures as
compared to their pure stands by up to 47 and 11%,
respectively. Second, epidemiological effects of host
diversity reduced disease severity on individual cultivars
below that of their pure stands. Disease severity on a
genotype was often frequency-dependent. However,
interactions among plant genotypes sometimes appeared to
alter susceptibility and obscured the relationship. Non-diseased
and diseased mixtures yielded 0 to 8% and 8 to 15%
more than pure stands, respectively. overall, mixture
yields were more influenced by plant-plant interactions
than by disease.
Population dynamics over time were studied by applying
variable disease pressure to populations of four wheat
cultivars for one-to-three generations in two locations.
Fitnesses of genotypes were calculated by regressing the
legit of a genotype's frequency on generation. Fitnesses
were affected by disease and location and appeared constant
over time. However, genotype frequency-changes were
negatively correlated with planting frequencies, suggesting
that fitnesses were frequency-dependent. Analysis of data
from longer-term studies in the literature indicated that
three generations may not have been sufficient to detect
frequency-dependence. Stable equilibria may more likely
exist for mixtures of genotypes that are closely related
and adapted to the environment in which they are grown than
for randomly selected genotypes. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36262 |
| Date | 25 October 1991 |
| Creators | Finckh, Maria Renate |
| Contributors | Mundt, Christopher C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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