Cephalosporium stripe of wheat (Triticum aestivum),
caused by the soilborne fungus Cephalosporium gramineum,
results in significant yield reductions in dryland winter
wheat crops of the U.S. Pacific Northwest. The
development of resistant cultivars offers the best hope
for disease control. Breeding for resistance is hampered
by the long trial times inherent in screening adult
plants, and by cultivar x environment interactions in
field tests. The principal objective of this research was
to develop and test a procedure for screening wheat
seedlings in controlled environments for resistance to
Cephalosporium stripe.
Wheat seedlings were raised hydroponically in growth
chambers, and the fungus was increased in large
fermentation tanks. The seedlings were inoculated at
about 12 days post-germination. Disease severity was
assessed approximately seven days later using a
chlorophyll meter to measure the symptoms of chlorosis and
striping.
In three trials, five soft white cultivars from the
Pacific Northwest and four hard red cultivars from the
Southern Great Plains with known levels of field
resistance were tested with a Pacific Northwest fungal
isolate. With one exception, chlorophyll readings ordered
the cultivars appropriately, with moderately resistant
cultivars ranking above susceptible cultivars. Three
other moderately resistant cultivars from the Pacific
Northwest also appeared in one or two trials, and were
ranked properly by chlorophyll level.
Chlorophyll levels of uninoculated plants were
assayed to determine if differences in chlorophyll content
were innate in the cultivars. The chlorophyll levels of
uninoculated and inoculated seedling treatments were only
significantly correlated when the cultivar Madsen, which
ranks high both in resistance and in chlorophyll content,
was included. In adult plants, flag-leaf chlorophyll
level corresponded to intensity of Cephalosporium stripe
symptoms where disease was present, and was independent of
known field resistance in undiseased cultivars.
The seedling screening technique was used to
investigate pathogenic variability in C. gramineum. In
two experiments, a total of eight cultivars from the
Pacific Northwest and the Southern Great Plains were
tested with three fungal isolates from each region. No evidence of virulence/vertical resistance was found.
There was also no significant adaptation of isolates to
greater virulence on cultivars from the same region. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33687 |
| Date | 21 July 1997 |
| 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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