Graduate Thesis Or Dissertation
 

Genetic variation in shoot-growth patterns of Douglas-fir populations from southwest Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vm40xw81r

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  • This study had three objectives: (1) to teat the hypothesis that multiple flushing of the terminal shoot (intermittent growth pattern) in Douglas-fir seedlings (Pseudotsuca menziesii var. menziesii) has an adaptive significance, especially in inland populations from the drier regions in southwest Oregon; (2) to evaluate the genetic and adaptive consequences of selecting for height increment in early testing programs; (3) to evaluate the utility of indirectly selecting for height increment by directly selecting for length and number of stem units. To accomplish objectives 1 and 2, seedling families were grown from two inland and two coastal sources (160 open-pollinated families in total) for two growing seasons in two test environments. In one environment ("dry") an intermittent moisture regime was created by withholding water during the growing season until seedlings reached -12 bars of moisture stress. Seedlings were then rewatered on a weekly schedule. In the other environment ("wet"), seedlings were watered weekly to maintain water stress of seedlings at lees than -3 bars. For objective 3. seedling families from one inland and one coastal source of Douglas-fir (80 open-pollinated families) were grown in plastic tubes for two growing seasons. Results supported the hypothesis that intermittent shoot growth is of adaptive significance in Douglas-fir in the first growing season. Shoot growth patterns varied genetically both between populations and among families within populations. As expected. families from drier inland environments, where periodic summer droughts are commons responded to the intermittent moisture regime with a higher frequency of multiple flushing. Families from coastal environments, where the moisture regime is more consisitently favorable during the growing seasons were less sensitive to the dry treatment and had a much higher frequency of seedlings which continued to grow despite the imposed drought. In the second growing season. patterns of intermittent shoot growth in inland and coastal families were not as expected. Shoot growth patterns did vary genetically between inland and coastal populations. Inland populations however, did not respond to the dry treatment with a greater frequency of multiple flushing. Apparently, inland families have adapted to drier environment and shorter growing season by relying predominantly on predetermined growth for height increment and are not able to respond to favorable growing conditions by extended free growth. Coastal families however, have developed a less regulated pattern of growth and rely more heavily on free growth for attaining height increment. The magnitude of genetic and adaptive effects of selecting for height increment in early testing programs depended on the origin of population and the environment of planting site. In inland populations early selection for total height increment mainly selects for predetermined growth. This would not lead to maladaptation in the more severe planting sites of inland southwest Oregon. Selected genotypes however would not be able to take advantage of longer growing season at favorable planting sites. In coastal populations early selection for height increment mainly selects for free growth. This may lead to maladaptation on even the favorable planting sites because with increased free growth. the length of the growth period is also increased. Slecting for length and number of stem units does not appear to be an efficient way of selecting for height increment in Douglas-fir. For this procedure to be effective, heritabilities of stem-unit measurements must be higher than heritability of height increment itself. Also genetic correlations between stem-unit measurements and height increment or its components (predetermined and free growth) must be strong. In this study, heritabilities of stem-unit measurements were small and correlations were weak.
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