Genetic Variation and Parameter Estimation of Juvenile Wood Properties in a Diallel Loblolly Pine (Pinus taeda L.) Population.

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Title: Genetic Variation and Parameter Estimation of Juvenile Wood Properties in a Diallel Loblolly Pine (Pinus taeda L.) Population.
Author: Sykes, Robert Wayne
Advisors: Bailian Li, Committee Chair
Gary Hodge, Committee Member
Barry Goldfarb, Committee Member
John Kadla, Committee Member
Abstract: Genetic tree improvement has made substantial gains in productivity, stem straightness, and rust resistance for loblolly pine (Pinus taeda L.) in the southern U.S. Improved growth has reduced rotation ages to 20 to 25 years for intensively managed plantations, resulting in a higher percentage of juvenile wood from plantations. Juvenile wood, with low density, shorter tracheid length and higher lignin content, has been shown to reduce yields and increase pulping costs. However, wood properties of juvenile wood can be improved if there is sufficient genetic variation within the breeding population. This study examined the genetic variation and genotype by environment interaction for several important wood properties in loblolly pine, and investigated the rapid assessment of these wood traits by Near Infrared spectroscopy. Increment cores were collected from fourteen 11-year-old full-sib families from one progeny test. Earlywood and latewood of ring 3 (juvenile wood) and ring 8 (transition wood) for each increment core was analyzed for α-cellulose content (ACY), average fiber length (FLW), coarseness (COA) and lignin content (LIG). Transition wood had significantly higher ACY, FLW and COA and lower LIG than juvenile wood. Latewood of both rings had higher ACY, FLW and COA than earlywood. Loblolly pine families differed significantly for ACY, FLW and COA, but not for LIG. In general, additive genetic effects explained greater percentages of family variation than dominance genetic effects in these traits. For all traits, genetic variation increased from juvenile to transition wood. While weak individual heritabilities were found for ACY, FLW and COA for juvenile wood, individual and family heritability estimates for transition wood were moderate. Genetic variation and genotype by environment (GxE) interaction were examined for these juvenile wood properties by combining the data from an additional test site. Families differed significantly for all the chemical and morphological wood properties on both sites. Genetic variation due to general combining ability and specific combining ability was greater in transition wood than juvenile wood. Noticeable family rank changes were observed between two sites for these traits, which were largely due to a significant site by specific combining ability interaction. The family heritability estimates from the combined analysis showed that ACY, FLW, and COA in transition wood were under moderate degrees of genetic control. Favorable genetic correlations with stem straightness were found for ACY and FLW. Near infrared (NIR) spectroscopy was examined for the rapid estimation of ACY, FLW, and COA. Transmittance measurements of NIR spectra from thin wood wafers cut from increment cores were used to develop calibration models for ACY, FLW, LIG, and COA measured in the laboratory. Calibrations based on one site were generally reliable with coefficients of determination (R²) ranging from 0.55 to 0.86 for FLW and ACY, respectively. Predicting ring 8 spectra using ring 3 calibration equations may be possible for ACY and COA with R2 values around 0.60. Predicting the wood properties from one site to the other may be possible for ACY and COA but not for FLW. Significant genetic variation among and within families and moderate heritabilities from this study suggest that it may be possible to improve wood properties of juvenile wood through tree improvement programs in loblolly pine. Positive genetic correlations of wood density with ACY, FLW and COA indicate that genetic improvement of wood density may improve these important wood and traits. While NIR spectroscopy showed feasibility as a rapid method to predict wood properties for many trees, sampling techniques need to be refined before using NIR to assess wood properties for breeding programs.
Date: 2004-05-17
Degree: MS
Discipline: Forestry

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