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Our current research involves mapping quantitative trait loci (QTL) for adapative traits, such as bud phenology and cold-hardiness. The progeny from the three-generation pedigree were vegetatively propagated and planted at two Weyerhaeuser test sites in Washington and Oregon. The immortalized mapping population will be measured for numerous traits over time. We are beginning to measure form and growth traits and will estimate QTL affecting these traits as well. We are using an interval mapping, multiple regression method of analysis that was designed for species that are outcrossing and highly heterozygous (Knott et al. 1997*).
Traits
* Knott SA, Neale DB, Sewell MM, Haley CS (1997) Multiple marker mapping of quantitative trait loci in an outbred pedigree of loblolly pine. Theor Appl Genet 94:810-82 |
A three-generation outcrossed pedigree was used for the construction of a genetic map and also for QTL analysis. The grandparents are divergent for the date of budflush. Two F1s were then mated in 1990 to produce approximately 300 F2 progeny.
A subset (48) of the F2 progeny were immediately placed under long day conditions to expedite growth so that RFLP data could be collected. This population of 48 progeny was the basis of the initial linkage map from which markers to be used in QTL analysis were selected. Marker data collected for QTL mapping (n = 192) was included in the final linkage analysis.
Vegetative cuttings were taken from the remaining 250 progeny and outplanted at two Weyerhaeuser test sites at Turner, Oregon and Twin Harbors, Washington for long term trait analyses.
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Cuttings were taken from approximately 250 progeny for replicate planting in the field.
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The Douglas-fir Verification Experiment is designed to test previously detected QTLs for phenology in an additional set of progeny from the same two parents and also an attempt to uncouple response to three environmental cues t hat control the timing of bud flush and bud set. Five-hundred additional progeny have undergone vegetative propagation at Weyerhaeuser Company in Washington. These progeny will be measured after treatments described in the Project Summary (below) and QTLs for each treatment will be estimated. This experiment was funded in 1997 by USDA/CRSEES National Research Initiative Competitive Grants Program (NRICGP).
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| project summary |
Douglas-fir (Pseudotsuga menziesii (Mirb.) is the most ecologically and economically important forest tree species of the Pacific Northwest. It has a broad and environmentally diverse range to which it is highly adapted to se asonal cycles and their attendant environmental signals. The annual growth rhythm, as determined by the timing of bud flush in the spring and bud set in mid- to late summer, is precisely adapted to these environmental differences. Bud flush and bud set ti ming determines susceptibility to late spring or early fall frosts, respectively. In addition, early bud set in droughty environments can prevent plant moisture stress. The timing of spring bud flush is controlled primarily by low environmental stimuli; ( 1) chilling history during winter dormancy, and (2) temperature sum during quiescence. The timing of bud set is controlled by; (1) photoperiod, and (2) moisture stress.
We have constructed an RFLP linkage map for Douglas-fir using a 3-generation outbred pedigree. We used a sample of 250 clonally replicated progeny to map QTLs for the timing of bud flush and bud set in replicated field plantations. Unde r these conditions, it was not possible to separate the effects of the different environmental stimuli controlling bud phenology. In our next set of experiments, we propose to use controlled environmental conditions to determine if different sets of QTLS are responding to different environmental stimuli. The specific hypotheses that we will test are:
- Chilling sum and temperature sum requirements for spring bud flush are controlled by different sets of QTLs.
- Photoperiod and moisture stress levels required to induce bud set are controlled by different sets of QTLs.
A mapping population of 500 new clones (10,000 plants in total) will be grown in a CRAVO shade house and greenhouses where chilling sum, heat sum, photoperiod, and moisture stress can be controlled. We will use a previously mapped set o f 71 highly informative RFLP markers and a multiple-marker, interval mapping procedure to map bud phenology QTLs in the treatment populations. Following completion of the studies described in this proposal, the 10,000 plants will be transplanted to long-t erm genetic tests where we can estimate QTL x environment interactions and developmental changes in QTL expression of a host of adaptive, growth, and wood quality traits for many years to come.
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