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    Author(s): E. C. Franklin
    Date: 1979
    Source: Silvae Genetica
    Publication Series: Scientific Journal (JRNL)
    Station: Southern Research Station
    PDF: Download Publication  (651.0 KB)

    Description

    Rate of genetic improvement over time of any long-lived organism can be increased to some degree by early testing and selection if genetic correlations in juvenile-mature traits are strong and positive. Through the use of path coefficients, the required relationships were illustrated. Most genetic analyses of juvenile-mature relationships in growth traits such as height and volume have been based on estimates of phenotypic rather than genotypic correlations. Predictions about genetic gains based on phenotypic correlations are accurate only insofar as associated environmental correlations are negligible. Only in the recent past has analysis of long-term data on families of forest trees provided for recognition of the impact of stand development on the expression of genetic variance. From published data on Douglasfir and ponderosa pine, a hypothetical model interpreting the expression of genetic and environmental variances in height growth was proposed. The model permits the comparison of the magnitude of genetic versus environmental variances at various stages of stand development. Under the model, stand development was divided into juvenilegenotypic, mature-genotypic, and codominance-suppression phases. Data on loblolly and slash pines were fitted to the model; all four sets of data showed good agreement on phase changes relative to expression of additive genetic variance. The most important recommendation based on the model is that selection for gain in height and volume with conifers grown at conventional spacings should be deferred at least until half rotation age.

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    Citation

    Franklin, E. C. 1979. Model relating levels of genetic variance to stand development of four North American conifers. Silvae Genetica. 28(5-6): 207-212.

    Keywords

    Juvenile-mature correlation, progeny testing, genetic gain, environmental correlation, genetic selection, juvenile testing

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