Clonal Variation of Stem Taper in Loblolly Pine (Pinus taeda L.)

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Title: Clonal Variation of Stem Taper in Loblolly Pine (Pinus taeda L.)
Author: Wood, Elizabeth Rachel
Advisors: Dr. Fikret Isik, Committee Member
Dr. Bronson P. Bullock, Committee Chair
Dr. Steven E. McKeand, Committee Member
Abstract: ABSTRACT WOOD, ELIZABETH RACHEL. Clonal Variation of Stem Taper in Loblolly Pine (Pinus taeda L.). (Under the direction of Dr. Bronson P. Bullock.) As volume is the primary measure of value in loblolly pine (Pinus taeda L.) stands, knowledge about the stem taper of commonly deployed clones may help breeders better describe genetic gains made by clonal selection and can provide more accurate volume estimates. This study assessed the genetic variation of stem taper among clones propagated by somatic embryogenesis (SE) and compared growth traits of SE clones and seedlings from the same full-sibling families. SE clones from fifteen full-sibling families were measured in the eighth growing season across three test sites in coastal Georgia and South Carolina. Variance components and genetic parameters for taper and growth traits were estimated using restricted maximum likelihood (REML) techniques. Ten form quotients were used to analyze stem taper differences among clones and to assess taper impacts on total stem volume. Significant clonal and family variation was found among clones and families for form quotients, indicating that differences exist in stem taper among different genotypes. Total outside-bark stem volume was calculated from the taper data and compared to volumes estimated by two combined variable (D2H) models (the Amateis and Burkhart (1987) and Warner-Goebel (1963) equations) to determine if these existing models could be used for clonal volume estimation. Total measured stem volume was found to be accurately predicted by the Amateis and Burkhart (1987) model. Taper impacts on total volume were minimal after accounting for diameter at breast height and total height. Variation among clones accounted for 3.4% to 26% of the total phenotypic variance for taper and growth traits. Clone mean heritability estimates for form quotients and growth traits were moderate to very high (0.60 to 0.94), indicative of substantial genetic variability for these stem form characteristics. While considerable genetic variation exists for stem taper among clones, the impacts of taper differences in the lower portion of the stem (below 12.5 feet) on total volume were small after accounting for total height and diameter at breast height. As long as volume remains the primary measure of value in loblolly pine, additional measures of taper beyond height and diameter at breast height are not necessary to describe differences in total volume among these particular SE clones. As vegetative propagation methods such as somatic embryogenesis are increasingly employed in clonal forestry, it is important that clones deployed commercially are well-tested and exhibit growth characteristics similar or superior to that of seedlings. SE clones and seedlings from the same nine full-sibling families were measured in the eighth growing season across three test sites in coastal Georgia and South Carolina. Stem taper and growth traits of SE trees and zygotic seedlings were compared in order to examine differences between propagule types. The effect of propagule type was statistically significant for all growth traits and form quotients. On average, zygotic seedlings were taller, larger in diameter, had larger total volumes, and exhibited 2% to 4% less taper than SE trees overall. Within seven of the nine families, seedlings demonstrated greater means than SE trees for total height, diameter at breast height, total measured volume, and form quotient. Though seedlings outperformed clones overall and within most families based on means, selection of the top performing clone was effective in achieving gains for growth traits in some families. Superior SE varieties demonstrated higher clone means for total height and total volume compared to the full-sib family mean of their seedling counterparts. In other families, however, seedlings outperformed the best clone mean within the respective family.
Date: 2009-11-30
Degree: MS
Discipline: Forestry
URI: http://www.lib.ncsu.edu/resolver/1840.16/2561


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