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Genetic variation in western red cedar (Thuja plicata Donn) seedlings

University of British Columbia

To determine whether the apparent lack of genetic variation in western red cedar (Thujaplicata Donn), as previously inferred by isozyme and terpene studies, would hold true for quantitative seedling traits, a provenance study was initiated to investigate patterns of variation in seedling growth and survival characteristics, cold temperature acclimation, and response to inbreeding. Seedlings from ten coastal and ten interior provenances, half with family structure (five families / provenance), were grown for three years at one coastal (Vancouver) and one interior (Salmon Arm) location. Twenty-three potted clones were both self-pollinated and polycrossed at Cowichan Lake; resulting progeny were monitored for growth and frost hardiness. Genetic variation could be detected from the first year, and increased annually. The narrow-sense individual heritability, assuming some inbreeding, of final heights of trees growing in Vancouver was 0.38. Height, root collar diameter, acclimation, and deacclimation exhibited mainly within-population variation, while variation in dry weight measurements, foliar nutrient content, survival at Salmon Arm, and maximum cold hardiness was evident mainly between populations. Coastal / interior differences were noted in first-year heights, branch number, height, survival, and crown dieback at Salmon Arm following a severe winter in which trees suffered major desiccation damage, and in acclimation and deacclimation. In general, adaptive traits appeared to show more between-population differences, while traits under less selective pressure showed mainly within-population variation. Provenances displaying the greatest variation at the family level were those from Vancouver Island. Between-population variability appeared to be highest in the B.C. interior, and lowest in northern B.C. populations. Elevation influenced all traits displaying provenance variation. Location effects occurred, and some genotype by environmental interactions were noted. Plasticity was evident in timing of growth initiation and cessation, timing of acclimation and deacclimation, and in depth of maximum hardiness reached per year. Early traits showed little evidence of inbreeding depression, but there seemed to be a trend towards gradual expression of inbreeding depression over time, at least in traits under selective pressure. This research showed that western red cedar is much more complex than previously believed, and substantial genetic variation exists in several traits of this species.

Thesis/Dissertation

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2009-06-04

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http://hdl.handle.net/2429/8774

Forestry

University of British Columbia

UBCV

DSpace