Graduate Thesis Or Dissertation
 

The effects of inbreeding and supplemental mass pollination upon seed yields in a Douglas-fir seedling seed orchard

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  • Effects of four inbreeding levels (F = 0, 0.125, 0.25, 0.5) and two supplemental mass pollination (SMP) methods (agitation of naturally shedding pollen with "air blaster" and pollen application from large "pollen wand" atomizer) were evaluated on seed of trees from eleven full-sibling Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) families in a 16-year-old seed orchard. SMP responses were tested at three crown levels on trees of three periods of reproductive maturity. Cones covered during SMP treatments were used as controls. Inbreeding did not significantly affect flat and round seed percentages or seed weights, but percent round, normal appearing seeds that were empty (PE) had a positive, linear relation to F. Filled seed yields after inbreeding did not differ among full-sib families; but variation among trees within families, as well as interactions between tree yields and inbreeding levels, were highly significant. At F = 0.5, PE was greater for seed orchard trees (98.2) than has been reported for trees in natural stands (90.9); juvenility and off-site planting of orchard trees may contribute to this difference. Between F = 0 and 0.5, an increase in F of 0.1 was associated with an increase of 12% PE. Self-pollination appears to have its greatest impact on orchard seedset. Half- and full-sib matings also give reduced seed yields (relative to outcrossing), but the relatively high levels of inbred seed production should have their greatest impacts upon the productivities of the resulting seedlings. This contrast is discussed using inbreeding depression values from the literature. In contrast with other reports, air blast SMP did not increase seedset, but increased PE relative to the controls. Dense crowns of seedling seed orchard trees appear to intercept more self pollen than do the more open crowns of previously studied clonal orchards. Wand application of pollen, which was used only in conjunction with the air blast treatment, reduced PE to the level of the controls. The effect of crown levels (upper, middle, lower), as well as an interaction between crown levels and the phenology and SMP treatment applied to specific trees, were highly significant; causes of these results are speculated. Practical implications are twofold. Because inbred seed production is high at F = 0.25 and 0.125, seedling orchard designs must minimize the possibility of within-family mating. Secondly, crown form should be considered prior to use of some supplemental mass polliantion treatments. In general, the dense crowns of young seedling orchard trees do not appear suitable for air blast SMP.
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