School of Agriculture, Food and Ecosystem Sciences - Theses

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End date: 2021 × Subject: Pinus radiata × Author: Nyakuengama, John Gwinyai. ×

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    Quantitative genetics of wood quality traits in Pinus radiata D. Don
    Nyakuengama, John Gwinyai. (University of Melbourne, 1997)
    In order to understand the variability of traits important in pulping and sawn timber (heartwood formation, moisture status, density and fibre cross-sectional dimensions, fibre coarseness and fibre specific surface), wood from 4 radiata pine (Pines radiata D. Don) plustrees, including parent 80055, and their progeny comprising of a small 4 x 4, 23 year-old, unthinned, diallel progeny test was studied. 80055 progeny is renowned for consuming low energy and producing bright newsprint during thermomechanical pulping. However, the newsprint is of low tear strength. No reciprocal or maternal effects were found in all the traits, probably because of the small number of reciprocal pairs in the diallel experiment. Otherwise, results imply that future wood quality experiments could be simplified by excluding reciprocal crosses. The study found that the o-anisidine and sodium nitrite method was useful to differentiate heartwood formation from sapwood in studies involving a large number of samples. A low narrow sense heritability (NSH) was found for heartwood and its formation was accompanied with a decrease in moisture content. This accounted for a strong inverse correlation found between heartwood formation and moisture content. 80055 progeny had the most heartwood and this explained why its corewood was the driest in the diallel experiment. Technologically, drier heartwood is undesirable in refining because its pulp fibres have a lower wettability, are more brittle and produce newsprint of inferior strength and lower brightness than wetter sapwood. Wood microstructure was studied using a recently commissioned Silviscan 1 system which incorporates an X-ray densitometer and video-microscope. Protocols were set up in this pioneer study for future CSIRO-Forestry and Forest Products progeny tests (and silvicultural studies). Area-weighted fibre size (ie., fibre perimeter, fibre radial and tangential diameters) and density had the highest NSH among traits but these had large standard errors due to a narrow genetic base. The NSH of fibre coarseness was intermediate while those of area-weighted fibre wall thickness and ring width were the lowest. Additive genetic variance was high in all arbitrary classes of fibre diameters, unlike in density and fibre coarseness where it was high in all but an intermediate class representing the transition zone between earlywood and latewood. 80055 progeny had the least dense wood and the highest fibre coarseness in the diallel experiment on account of possessing the largest amount of fibres with large diameters (tangential and radial) or earlywood (as defined as wood with a density less than 400 kg m-3). Technologically, this wood microstructure could translate to low strength in sawn timber. Density and fibre traits had different genetic structures, which accounted for difference in age-age correlations and selection efficiencies at a juvenile age in relation to those at a mature age in these traits. Results indicate that fibre coarseness increased with fibre size only, in 80055 progeny. Fibre coarseness increased directly with increases in fibre wall thickness only in progeny of other parents. Technologically, this implies that fibres of 80055 progeny have thinner fibre walls at a comparable fibre coarseness than non-80055 progeny. This finding could explain why make 80055 fibres make somewhat weak refiner pulp. NSH estimates of density and fibre traits calculated in whole-cores and individual growth rings from parent-offspring regressions were generally more conservative than those from sib analysis of the diallel progeny test but the magnitude of estimates was comparable. Despite large standard errors associated with NSH estimates which were caused by the narrow genetic base of the study material, estimates tended to differ between traits and with physiological and chronological age of parents and offspring. A holistic study based on principal component analysis concluded that fibre diameter and fibre coarseness, but not density, were directly related to tree height and diameter (growth traits). Heartwood formation was directly related to the growth traits, implying that selection of one trait would influence the other.