Mycosphaerella graminicola (anamorph Septoria tritici) causes Septoria tritici blotch, a
globally important disease of winter wheat. Resistance and pathogenicity generally vary
quantitatively. The pathogen reproduces both sexually and asexually, and the pathogen
population is highly genetically variable. Several unresolved questions about the
epidemiology of this pathosystem are addressed by this research. Among them are
whether cultivar-isolate specificity exists, how partial host resistance affects pathogen
aggressiveness and sexual reproduction, and how host genotype mixtures influence
epidemic progression and pathogenicity.
At its release in 1992, the cultivar Gene was highly resistant to M. graminicola, but that
resistance had substantially dissolved by 1995. Six of seven isolates collected in 1997
from field plots of Gene were virulent to Gene seedlings in the greenhouse, while 14 of
15 isolates collected from two other cultivars were avirulent to Gene. Gene apparently
selected for strains of M. graminicola with specific virulence to it.
In a two-year experiment, isolates were collected early and late in the growing season
from field plots of three moderately resistant and three susceptible cultivars, and tested on
seedlings of the same cultivars in the greenhouse. Isolates were also collected from plots
of two susceptible cultivars sprayed with a fungicide to suppress epidemic development.
Isolate populations were more aggressive when derived from moderately resistant than
from susceptible cultivars, and more aggressive from fungicide-sprayed plots than from
unsprayed plots of the same cultivars.
Over 5,000 fruiting bodies were collected in three years from replicated field plots of
eight cultivars with different levels of resistance. The fruiting bodies were identified as
M. graminicola ascocarps or pycnidia, or other. In all three years, the frequency of
ascocarps was positively correlated with cultivar susceptibility, as measured by area
under the disease progress curve, and was also positively associated with epidemic
intensity.
For three years, four 1:1 mixtures of a moderately resistant and a susceptible wheat
cultivar were planted in replicated field plots. Isolates from the plots were inoculated as
bulked populations on greenhouse-grown seedlings of the same four cultivars. Mixture
effects on disease progression varied among the years, and were moderately correlated
with mixture effects on pathogenicity. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32370 |
| Date | 19 March 2002 |
| Creators | Cowger, Christina |
| Contributors | Mundt, Christopher C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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