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Quentin A.G.,University of Tasmania | Quentin A.G.,CSIRO | O'Grady A.P.,University of Tasmania | O'Grady A.P.,CSIRO | And 5 more authors.
Tree Physiology | Year: 2012

Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (Asat), stomatal conductance (gs), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher Asat and gs compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (Emax) and canopy conductance (G Cmax) and soil-to-leaf hydraulic conductance (KP) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale gs and A sat following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation. © 2012 The Author. Published by Oxford University Press. All rights reserved. Source

Freeman J.S.,University of Tasmania | Freeman J.S.,Co operative Research Center for Forestry | Freeman J.S.,University of The Sunshine Coast | Potts B.M.,University of Tasmania | And 10 more authors.
New Phytologist | Year: 2013

Eucalypts are one of the most planted tree genera worldwide, and there is increasing interest in marker-assisted selection for tree improvement. Implementation of marker-assisted selection requires a knowledge of the stability of quantitative trait loci (QTLs). This study aims to investigate the stability of QTLs for wood properties and growth across contrasting sites and multiple pedigrees of Eucalyptus globulus. Saturated linkage maps were constructed using 663 genotypes from four separate families, grown at three widely separated sites, and were employed to construct a consensus map. This map was used for QTL analysis of growth, wood density and wood chemical traits, including pulp yield. Ninety-eight QTLs were identified across families and sites: 87 for wood properties and 11 for growth. These QTLs mapped to 38 discrete regions, some of which co-located with candidate genes. Although 16% of QTLs were verified across different families, 24% of wood property QTLs and 38% of growth QTLs exhibited significant genotype-by-environment interaction. This study provides the most detailed assessment of the effect of environment and pedigree on QTL detection in the genus. Despite markedly different environments and pedigrees, many QTLs were stable, providing promising targets for the application of marker-assisted selection. See also the Commentary by Mason. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust. Source

Thavamanikumar S.,University of Melbourne | Thavamanikumar S.,Co operative Research Center for Forestry | Thavamanikumar S.,CSIRO | McManus L.J.,University of Melbourne | And 19 more authors.
Tree Genetics and Genomes | Year: 2014

The moderate to high levels of nucleotide diversity and low linkage disequilibrium found in many forest tree species make them ideal candidates for association mapping. Here, we report candidate gene-based association mapping results for complex wood quality and growth traits in Eucalyptus globulus Labill. ssp. globulus, the most widely grown eucalypt in temperate regions of the world. Ninety-eight single nucleotide polymorphisms (SNPs) from 20 wood quality candidate genes were assayed in a discovery population consisting of 385 trees sourced from a provenance-progeny trial. Twenty-five selected SNPs with significant associations (P < 0.05) in the discovery population were assayed for validation in 296 trees sourced from an independent second-generation breeding trial. To account for background genetic structure, mixed models were used in the association analyses. Two associations identified in the discovery population were independently supported in the validation testing. However, combining the discovery and validation results in a combined analysis, we discovered nine stable marker-trait associations for seven traits. These associations link underlying complex wood and growth phenotypes to earlier putative selection signatures opening new avenues to accelerate the dissection of these traits. © 2014, Springer-Verlag Berlin Heidelberg. Source

Thavamanikumar S.,University of Melbourne | Thavamanikumar S.,Co operative Research Center for Forestry | Southerton S.G.,CSIRO | Bossinger G.,University of Melbourne | And 2 more authors.
Tree Genetics and Genomes | Year: 2013

Due to their long reproductive cycles and the time to expression of mature traits, marker-assisted selection is particularly attractive for tree breeding. In this review, we discuss different approaches used for developing markers and propose a method for application of markers in low linkage disequilibrium (LD) populations. Identification of useful markers for application in tree breeding is mainly based on two approaches, quantitative trait locus (QTL) mapping and association genetic studies. While several studies have identified significant markers, effect of the individual markers is low making it difficult to utilize them in breeding programs. Recently, genomic selection (GS) was proposed for overcoming some of these difficulties. In GS, high density markers are used for predicting phenotypes from genotypes. Currently small effective populations with high LD are being tested for GS in tree breeding. For wider application, GS needs to be applied in low LD populations which are found in many tree breeding programs. Here we propose an approach in which the significant markers from association studies may be used for developing prediction models in low LD populations using the same methods as in GS. Preliminary analyses indicate that a modest numbers of markers may be sufficient for developing prediction models in low LD populations. GS based on large numbers of random markers or small numbers of associated markers is poised to make marker-assisted selection a reality in forest tree breeding. © 2013 Springer-Verlag Berlin Heidelberg. Source

Thavamanikumar S.,University of Melbourne | Thavamanikumar S.,Co operative Research Center for Forestry | McManus L.J.,University of Melbourne | McManus L.J.,Co operative Research Center for Forestry | And 5 more authors.
Australian Forestry | Year: 2011

Eucalyptus globulus (Labill.) is the most widely planted eucalypt for pulpwood in temperate regions of the world. Breeding to improve pulp properties of this species has been hampered by the long time between planting and pulp trait assessment and the high cost of estimating pulp traits. Identifying and employing allelic variants that associate with superior pulp yield and quality has the potential to assist breeding programs. Before this strategy can deliver benefits, detailed knowledge of population structure, nucleotide diversity, haplotype diversity and linkage disequilibrium (LD) must be collected. To address this, 20 wood quality candidate genes were sequenced in 8 to 28 Eucalyptus globulus individuals. Relative to other tree species where such studies have been conducted, single nucleotide polymorphism (SNP) frequencies were high. Decay of linkage disequilibrium was rapid at all loci tested, with linkage rarely extending beyond 500 base pairs. Regions within many candidate genes exhibited significant positive or negative selection signatures, indicative of purifying or balancing selection, respectively. Our findings have implications for association mapping in Eucalyptus species. The potential for E. globulus pedigree reconstruction and whole-genome association approaches in eucalypts in general are discussed. Source

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