QTL influencing growth and wood properties in Eucalyptus globulus

Regions of the genome affecting physical and chemical wood properties (QTL), as well as growth, were identified using a clonally replicated, outbred F2 family (112 genotypes, each with 2 ramets) of Eucalyptus globulus, planted in a field trial in north-west Tasmania. Traits studied were growth (assessed by stem diameter), wood density, cellulose content, pulp yield and lignin content. These traits are important in breeding for pulpwood, and will be important in breeding for carbon sequestration and biofuel production. Between one and four QTL were located for each trait, with each QTL explaining between 9% and 24% of the variation between genotype means. Several QTL for chemical wood properties were co-located, consistent with their high phenotypic correlations, and may reflect pleiotropic effects of the same genes. In contrast, QTL for density and lignin content with overlapping confidence intervals were considered to be due to independent genes, since the QTL effects were inherited from different parents. The inclusion of fully informative microsatellites on the linkage map allowed the determination of homology at the linkage group level between QTL and candidate genes in different pedigrees of E. globulus and different eucalypt species. None of the candidate genes mapped in comparable studies co-located with our major QTL for wood chemical properties, arguing that there are important candidate genes yet to be discovered

Genetic parameters for growth, wood density and pulp yield in Eucalyptus globulus

Genetic variation and co-variation among the key pulpwood selection traits for Eucalyptus globulus were estimated for a range of sites in Portugal, with the aim of improving genetic parameters used to predict breeding values and correlated response to selection. The trials comprised clonally replicated full-sib families (eight trials) and unrelated clones (17 trials), and exhibited varying levels of pedigree connectivity. The traits studied were stem diameter at breast height, Pilodyn penetration (an indirect measure of wood basic density) and near infrared reflectance predicted pulp yield. Univariate and multivariate linear mixed models were fitted within and across sites, and estimates of additive genetic, total genetic, environmental and phenotypic variances and covariances were obtained. All traits studied exhibited significant levels of additive genetic variation. The average estimated within-site narrowsense heritability was 0.19±0.03 for diameter and 0.29± 0.03 for Pilodyn penetration, and the pooled estimate for predicted pulp yield was 0.42±0.14. When they could be tested, dominance and epistatic effects were generally not statistically significant, although broad-sense heritability estimates were slightly higher than narrow-sense heritability estimates. Averaged across trials, positive additive (0.64±0.08), total genetic (0.58±0.04), environmental (0.38±0.03) and phenotypic (0.43±0.02) correlation estimates were consistently obtained between diameter and Pilodyn penetration. This data argues for at least some form of pleiotropic relationship between these two traits and that selection for fast growth will adversely affect wood density in this population. Estimates of the across-site genetic correlations for diameter and Pilodyn penetration were high, indicating that the genotype by environment interaction is low across the range of sites tested. This result supports the use of single aggregated selection criteria for growth and wood density across planting environments in Portugal, as opposed to having to select for performance in different environment

Across-rotation factors affecting genetic improvement of Eucalyptus globulus in Australia

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Across-rotation factors affecting genetic improvement of Eucalyptus globulus in Australia

In forest tree improvement, ensuring that a breeding objective (BO) is well defined yet broad enough to cope with changes over time, is problematic. Two of the major changes to occur in the Eucalyptus globulus pulpwood plantation industry that may impact on tree improvement that were investigated in this study are coppice management of 2nd rotation crops and international demands for improved sustainability (e.g. the trade in environmental services such as carbon sequestration). Coppice can provide a cheap alternative to replanting in the 2nd rotation. Regeneration following felling of a 9 year old progeny trial revealed significant genetic diversity in coppicing traits both within and between subraces. After 14 months, 67% of trees coppiced but subrace means varied from 43 to 73%. Heritabilities for coppice success (0.07) and subsequent growth (0.16-0.17) were low but statistically significant. The ability of a tree to coppice was genetically correlated with tree size prior to felling (r\_g\ = 0.61), and with nursery-grown seedling traits such as the number of nodes with lignotubers (r\_g\ = 0.66) and seedling stem diameter at the cotyledonary node (r\_g\ = 0.91). These seedling traits were poorly correlated with later age growth and with each other. The results suggest coppicing is influenced by three independent factors - lignotuber development, enlargement of the seedling stem at the cotyledonary node and vigorous growth. A discounted cash-flow model was developed to compare the profitability of coppice and seedling crops in 2nd rotation E. globulus pulpwood plantations. A gain of 20% in dry matter production over the original seedling crop from 2nd rotation seedlings (through genetic improvement and provenance selection) would result in equivalent net present value (NPV) for 2nct rotation seedling and coppice crops. Incremental NPV was strongly affected by the level of genetic gain available (the genetic quality of 1 st rotation stock relative to the available genetically improved stock), and the productivity of coppice relative to the first rotation crop. The integration of environmental services (in the form of carbon seuquestration) into production system models to define economic BOs for the genetic improvement of pulpwood plantations was investigated. Carbon dioxide equivalent accumulation in biomass in the Australian E. globulus plantation estate between 2004 and 2012 was estimated at ~ 146 t CO\_2\e ha\^{-1}\, of which 62 t C0\_2\e ha\^{-1}\ were tradable in 2012 and a further 30 t C0\_2\e ha\^{-1}\ were tradable in 2016. Where revenues for carbon sequestration were dependant upon biomass in a plantation, it was possible to determine whether economic BOs were sensitive to the revenue from carbon sequestration. The correlated response of BOs with and without carbon revenues (˜ívÆ\{cG}\\_{H1}\) was 0.93. Where economic BOs were based on maximizing NPV by increasing biomass production, the consideration of carbon provided no significant gain in NPV

Molecular evidence shows that the tropical boxes (Eucalyptus subgenus minutifructus) are over-ranked

Molecular evidence shows that the tropical boxes (Eucalyptus subgenus Minutifructus) are overranked. Trans. R. Soc. S. Aust. 127(1), 27-32, 31 May, 2003. Australia’s tropical boxes, Eucalyptus deglupta, E. brachyandra, E. howittiana and E. raveretiana have been classified as subgenus Minutifructus, a taxon described on the basis of a single morphological character, a terminal inflorescence. Molecular data indicate that these species emerge from within subgenus Symphyomyrtus. There is also some evidence to suggest that they may not form a monophyletic group. Consequently, we recommend that subgenus Minutifructus should not be maintained as a separate subgenus, and that the four species should be included in subgenus Symphyomyrtus