Fusarium spp. are among the most important pathogens of Douglas-fir
(Pseudotsuga menziesii) seedlings in bareroot nurseries. Currently the most effective
disease control method is soil fumigation with methyl bromide. As methyl bromide is
phased out, however, other disease management strategies may become more important.
We explored two alternative approaches to management of Fusarium diseases in
Douglas-fir seedlings. The first approach was to transfer certain components of conifer
forest soil, where Fusarium usually does not occur, to nursery soil, where Fusarium is
often abundant. Specifically, we tested two hypotheses: (1) conifer forest soil contains a
greater proportion of bacteria antagonistic in vitro to Fusarium than does nursery soil,
and (2) pine needles, humic acid, ectomycorrhizal fungi, or bacteria obtained from forest
soil will protect Douglas-fir seedlings against disease caused by soilborne Fusarium spp.
if added to nursery soil. We did not find conclusive evidence to support either
hypothesis. The second approach was to investigate the potential for biological control
of seedborne Fusarium. Previous workers have shown, and we have confirmed in our
studies, that Fusarium present on a small percentage of Douglas-fir seeds before cold
stratification may spread during stratification; we recovered Fusarium from nearly all
stratified seeds, representing three seedlots, plated on three culture media. When these
seeds were planted in pasteurized soil, however, seedborne Fusarium did not cause
significant disease in seedlings. Biological control of seedborne Fusarium during
stratification may be important both to reduce the contribution of seedborne Fusarium to
nursery soil and to protect germinants from soilborne Fusarium. We hypothesized that
Pseudomonas chlororaphis isolate RD31-3A, a fluorescent pseudomonad previously
shown to control Fusarium on Douglas-fir, would reduce the spread of Fusarium during
stratification and protect seedlings from damping-off when seeds were planted into soil
infested with pathogenic F. oxysporum. High populations of RD31-3A were recovered
from seeds after stratification, and bacterial treatment reduced the spread of Fusarium
without affecting seed germination or subsequent seedling dry weights. RD31-3A did
not, however, protect seedlings from soilborne F. oxysporum. Nevertheless, seed
treatment with bacteria during stratification may be an efficient way to deliver biological
control agents to conifer seeds. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34474 |
| Date | 02 December 1996 |
| Creators | Hoefnagels, Mari��lle Henriette, 1965- |
| Contributors | Linderman, Robert G. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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