Genetic Analysis of Diallel Tests of Loblolly Pine (Pinus taeda L.)

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Title: Genetic Analysis of Diallel Tests of Loblolly Pine (Pinus taeda L.)
Author: Xiang, Bin
Advisors: Bailian Li, Chair
Eugene Eisen, Member
Gary Hodge, Member
Roger Berger, Member
Abstract: A new approach was developed for analyzing diallel tests with SAS PROC MIXED and PROC IML. The new method can estimate variance components, obtain BLUE (best linear unbiased estimators) of fixed effects and BLUP (best linear unbiased predictors) of random genetic effects simultaneously. A new formula based on BLUP was further developed to predict individual tree breeding values. This new analytical method was validated using computer simulation and was compared with other existing programs. To analyze disconnected diallel mating designs with more than one diallel, simulated data generated with known parameters were analyzed using BLUP to compare three alternative models, which include diallel as fixed effect (Model 1), random effect (Model 2) or no diallel effect (Model 3). Both Model 1 and Model 3 produced unbiased GCA (general combining ability) variance estimates, while Model 2 resulted in downward biased GCA variance estimate. The accuracy of BLUP prediction for three models was very close, with Model 3 slightly better than the other two. Statistical approaches were also evaluated for combining multiple disconnected diallel test series in a given region. The best GCA sample variance prediction in the class of linear combination of local variance estimates was derived. Simulation study showed that a checklot adjustment was very critical to improve the prediction of genetic values obtained using BLUP analysis. Additional adjustment with improved GCA sample variance prediction could improve the correlation slightly beyond checklot adjustment.Analysis of annual measurement through age 8 from a total of 275 parents, 690 full-sib families from 23 diallel tests of loblolly pine in Northern, Coastal and Piedmont test regions showed: 1) dominance variance was small (20-40% of total genetic variance) relative to additive variance; 2) heritability increased over time, and the magnitude of heritabilities for diameter at breast height (DBH) and volume was comparable with the corresponding heritabilities for height; 3) DBH and volume had higher genetic correlation with 8-year volume than height. Genetic gain prediction in year-8 volume for selection on height and volume indicated that: 1) selection on volume yielded more gain than selection on height; 2) Coastal population had the greatest correlated response, followed by Piedmont and Northern population; 3) family plus within family selection based on total genetic component can capture the most genetic gain; 4) for all selection methods, additional gain (10-40%) can be achieved by capturing non-additive genetic component.Selection efficiency study of height and volume for three test regions indicated that earlier selection appeared to be more efficient than direct selection on year-8 volume in most selection methods. Family selection can be performed at age 2 or 3 for height and at age 4 for DBH and volume. Combined selection (family plus within family) was highly efficient at age 3 or 4.
Date: 2001-01-09
Degree: PhD
Discipline: Forestry

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