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Assessing genetic parameters of growth and wood property traits, and deployement strategies, for pulpwood production improvement in Eucalyptus dunnii

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  • Title:
    Assessing genetic parameters of growth and wood property traits, and deployement strategies, for pulpwood production improvement in Eucalyptus dunnii
  • Author: Bird, Michael
  • Subjects: 300709 Tree improvement (incl. selection and breeding) ; 310207 Statistical and quantitative genetics ; Euclayptus ; Genotype by environment interaction ; Growth ; Queensland Alliance for Agriculture and Food Innovation ; Wood properties
  • Description: Eucalyptus dunnii Maiden (Dunn's white gum) is utilised internationally in commercial plantation forestry for the production of kraft pulp due to its fast growth and favourable wood properties (wood density and kraft pulp yield (KPY)). Testing and deployment of this species commonly uses open-pollinated (OP) families from seed orchards. Open-pollinated families are varying mixtures of unrelated (outcross) and inbred (mainly due to selfing) mating, which, due to unknown variation between and within families compared to more regular outcross mating designs, may reduce the genetic response to selection. The selection of OP families from clonal seed orchards for deployment usually occurs via backward selection of superior seed orchard mothers from their progenies performance in field trials. This selection within the same breeding cycle can take advantage of favourable correlations between traits that can be assessed at early ages (selection traits), and the breeding objective. Although E. dunnii is a globally important commercial plantation species, the genetic parameters of selection traits for a kraft pulp breeding objective, namely growth traits, density, and KPY, are not well characterised. To inform current and future breeding and deployment decisions of this species, information is required on the genetic architecture of these selection traits. Estimates of repeatability from OP families, and heritability and dominance ratio from full-sib (FS) families are used to determine the amount of genetic variation in traits and the amount of gain that can be made from selection. Additionally, the influence of genotype by environment interactions (G×E) when the same genetic material is deployed across a range of environments, can pay a crucial role in all stages of tree breeding, from assessment and genetic evaluation, through to deployment. Therefore, estimates of G×E are required to infer the response of across tested areas. This thesis aims to improve understanding of these selection traits in OP families of E. dunnii to inform decision making in new and existing genetic improvement programs by evaluating growth and wood quality data from OP families in 17 trials across Australia, China, Spain, Argentina, and Uruguay, and FS families across two trials in Uruguay. The first research chapter aimed to evaluate the performance and genetic architecture of growth traits across all 17 OP trials. This chapter reported consistently low individual OP progeny repeatabilities of growth traits, high age-age correlations, and genetic correlations between trials were generally high both within and between countries, indicating G×E was relatively unimportant for growth traits. The second research chapter aimed to compare genetic parameter estimates of wood properties assessed by multiple methods across two OP trials in Uruguay and two in Australia. This chapter reported that estimated individual OP progeny repeatabilities of all assessed wood properties were higher than growth traits. Density assessed by pilodyn penetration, wood cores, and turning resistance from the Resistograph were highly correlated, with lower correlations between these methods and near-infrared spectroscopy (NIR) predicted density. Genetic correlations were high between trials within each country for all traits assessed, although there were slightly lower correlations for some traits between countries, suggesting G×E, but may be more important between countries than within. The third research chapter aimed to evaluate alternative testing and selection strategies for deployment, by comparing predicted gain from deployment of selections made from each scenario. This chapter reported predicted gain of pulp productivity was maximised when using the data from all trials and selection was based on pulp productivity. However, comparable gain could be made in all scenarios based on selection for volume alone, which may be desirable in small scale breeding programs. The fourth research chapter aimed to compare genetic parameters and breeding values for growth traits estimated from OP and FS families. Variance components were estimated from OP and FS families under a single analytical model, observing growth traits are under non-additive genetic control and there is a strong correlation of a parent's additive effect on the performance of OP and FS progeny. The results from this chapter suggest that OP families from seed orchards could be improved with selection of pollen parents using OP maternal values, and the estimated specific combining ability (SCA) effects from FS families, to further improve the outcross SCA effect. This thesis focused on increasing understanding of the fundamental traits associated with a kraft pulp objective for the improvement of OP E. dunnii families pulp productivity. The key findings from the research chapters suggest the deployment of OP E. dunnii families could be facilitated with a single breeding program across tested environments based on selection of pulp productivity due to the low G×E of selection traits; while further improvement of the genetic quality of OP families from seed orchards can be facilitated through selection of SCA genetic effects. Source: TROVE
  • Creation Date: 2023
  • Language: English
  • Source: Trove Australian Thesis (Full Text Open Access)
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