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Genetic variability in Douglas-fir based on molecular genetic markers and morphological traits Ponoy, Bundit


Genetic variability in Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) in British Columbia was assessed both by analyzing molecular genetic markers at the population level and by evaluation of quantitative traits in parent trees. Genetic variability in the natural populations of Douglas-fir in B.C. selected from three geographic regions (coastal, transitional, and interior) was assessed by analyzing restriction fragment length polymorphisms (RFLP) for chloroplast (cpDNA) and mitochondrial (mtDNA) DNA, and random amplified DNA fingerprinting (RADF) markers for the nuclear genome. Genetic diversity and the degree of population differentiation for cpDNA and mtDNA were estimated at 3-hierarchical levels. Among the three regions, highest diversity of cpDNA was observed in the transition populations, although it was not significantly different from the other two regions. In mtDNA, more polymorphism with no significant difference was observed in interior populations than coastal and transition populations. Haplotype frequencies were found to be better parameters for genetic diversity estimates than allelic frequencies with organellar DNA. Nuclear genomes of populations in two geographic regions, coastal and interior, were evaluated using RADF markers. Allelic frequencies were calculated at each locus and used to estimate genetic diversity and the degree of population differentiation. Higher levels of within population genetic diversity were obtained than have been reported in studies using allozyme markers. With all three genomes, higher genetic diversities within populations than among populations were observed in all three regions. Several combined evolutionary forces are likely to be responsible for the current genetic make-up of B.C. Douglas-fir populations. Quantitative traits were evaluated in 100 families of 17-year old coastal Douglas-fir progenies in progeny tests at three locations, including Caycuse, Courtenay, and Gold River. The progeny tests used a systematic single tree plot-design and included four Abstract family types -- full-sib, half-sib from clone bank (C), half-sib from original plus tree (P) and control. Full-sib and half-sib (C) families had higher survival percentages and faster growth rates than half-sib (P) and control families. However, lower wood densities were observed in full-sib and in half-sib (C) families. Individual tree narrow sense heritability estimates in growth traits (0.116-0.234) for half-sib (C) and half-sib (P) families were comparable whereas heritability estimates in full-sib families ranged from 0.068 to 0.102 for growth traits. Moderately high heritabilities in wood density were observed in full-sib (0.256) and in half-sib (C) (0.494) families and lower heritability estimates were observed in half-sib (P) (0.189). Genetic gains were estimated for height, diameter, and volume at different selection intensities. About 18-30% gain for volume was obtained when selection was made at 10% of the best parents in each family type. Age-age correlations when carried out for height growth, it was determined that field performance at years 5-6 could predict relative height growth at 17 years. However, when assessed over several age classes regression of Log [e subscript] of age ratio (LAR) estimates for predicting relative height growth suggested very low correlation (r²=0.148) and this may not be promising in future selection.

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