High throughput breeding for wood quality improvement. (2019)
Type of ContentElectronic Thesis or Dissertation
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
AuthorsDavies, Nicholas T.show all
Eucalypt species are fast-growing and can produce high quality timber for appearance and structural products including Laminated Veneer Lumber (LVL). Their use for solid wood products is hindered by the fact that they can contain large growth-strains, which impose substantial processing costs. Growth-strains are associated with log splitting, warp, collapse and brittle-heart. The body of work presented here focused on the possibility of very-early selection at two years of age, of Eucalyptus bosistoana trees for growth-strain and other wood properties, including an in-depth assessment of the accuracy of the methodology used.
Chapter 1 gives an introduction on growth-stresses in trees and how this knowledge developed over the last century. Chapter 2 describes a pilot study assessing wood properties at a young age. Growth-strain was assessed by measuring stem openings after splitting along the pith, which resulted in a left-censored dataset. A Bayesian approach to the analysis was used to increase the accuracy of genetic parameter prediction from the left- censored data. Chapter 3 tested the hypothesis that the reason for the left-censored data was tension wood formed early in growth resulting in a reversed stress profile. The testing showed this was not the case, at least under the given experimental conditions. Chapter 4 describes a very-early selection trial (age 2) of 81 Eucalyptus bosistoana families with seven measured traits (growth-strain, under-bark diameter, density, stiffness, volumetric shrinkage, height and acoustic velocity), which yielded heritability estimates of 0.23, 0.57, 0.70, 0.77, 0.39, 0.71, and 0.80 respectively. Following this the precision of the splitting test was investigated. Chapter 5 describes an experimental approach which found that the splitting test could predict surface growth-strains with a precision of ±1003 micro- strain (Chapter 5). The accuracy of the splitting test was further investigated in Chapter 6 using a classical mechanics model. The effect of differing surface strain fields on the results of both the splitting test and point measurements such as strain-gauges, indicated that the theoretically obtainable maximum accuracy of the splitting test is approximately ±281 micro-strains. This is similar to four evenly spaced strain-gauges. Finally, Chapter 7 reviews very-early selection and provides guidelines for future breeding projects where reduced cycle times are desired.