Genetic parameters for lignin, extractives and decay in Eucalyptus globulus

ABSTRACT Eucalyptus globulus is grown in temperate regions of the world for pulp production. The chemical and physical properties of its wood make it highly suited to this purpose. This study analysed genetic variation in lignin content, extractives content and decay, for nine localities of E. globulus. Heritability estimates were also obtained, and the relationships between these traits and physical wood traits and growth were examined. Significant genetic variation was found between localities for lignin content (Klason lignin and acid-soluble lignin contents) and decay. The only trait for which significant variation between families within locality was detected was acid-soluble lignin content, which resulted in this trait also having the highest narrow-sense heritability ($0.51 \pm 0.26$). However, family means heritabilities were high for lignin content, extractives content and decay (0.42–0.64). The chemical wood traits were strongly correlated with each other both phenotypically and genetically, with important correlations found with density and microfibril angle. Correlations suggested that during selection for the breeding objective traits, it is likely that favourable states in the chemical wood traits, decay resistance and fibre properties are concurrently being selected, whereas growth may be selected for independently. This initial study provides a stepping stone for future studies where particular localities of the breeding population may be characterised further. Paramètres génétiques pour la lignine, les extractibles et la pourriture chez Eucalyptus globulus. Eucalyptus globulus est cultivé dans de nombreuses régions tempérées pour la production de pâte à papier. Les propriétés physiques et chimiques de ce bois en font un matériau très apprécié pour cette utilisation. Cette étude analyse les variations génétiques de la teneur en lignine, en composés extractibles et de la sensibilité à la décomposition du bois de neuf provenances de Eucalyptus globulus. L'héritabilité de ces propriétés ainsi que leurs relations avec les caractéristiques physiques du bois et la croissance ont été examinées. Des différences inter-provenances significatives ont été détectées pour les teneurs en lignine (lignines dosées par la méthode de Klason, ou lignines soluble en solution acide) et la vitesse de décomposition. Le seul caractère qui a présenté une variation significative entre familles dans les provenances a été la teneur en lignines solubles en solution acide. De ce fait, une forte héritabilité (au sens strict) a été détectée pour ce caractère ($0,51 \pm 0,26$). Cependant, les héritabilités moyennes dans les familles étaient élevées pour la teneur en lignine, les teneurs en composés extractibles et la vitesse de décomposition (0,42–0,64). Les caractéristiques chimiques du bois étaient fortement inter-corrélées au niveau phénotypique et génétique, avec des corrélations importantes également avec la densité et l'angle des microfibrilles. Les corrélations suggèrent que durant la sélection de caractères objectifs d'amélioration, des traits favorables associant caractéristiques chimiques du bois, résistance à la décomposition et propriétés des fibres puissent être sélectionnés simultanément, alors que la croissance doit faire l'objet d'une sélection indépendante. Cette étude constitue une base pour de futurs travaux permettant une caractérisation plus fine de provenances particulières dans cette population de sélection.

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    ABSTRACT: We developed a quantitative and association genetic study with Eucalyptus urophylla using a progeny trial. Based on a sample of 831 trees distributed in 84 half-sib families whose wood was phenotyped by near-infrared spectroscopy, the results showed that traits related to lignin, cellulose, and wood extractives presented significant additive genetic variability with moderate to high narrow sense heritability (h 2 = 0.28 to 0.93). Genetic correlations varied with high standard error and showed low to moderate values. Using three cellulose synthase genes (EuCesA1, EuCesA2, and EuCesA3) and three candidate genes involved in the lignin pathway (EuC4H1, EuC4H2, and EuCAD2), an association study was performed for each of the gene action models (co-dominant, recessive, and dominant) using two methods. Firstly, single-marker association tests were done and 539 tests (49 single nucleotide polymorphisms (SNPs) × 11 traits) were analyzed. After Bonferroni correction with a significance level of P = 0.00102, only four SNPs presented significant association with syringyl and syringyl-to-guaiacyl ratio with an adjusted coefficient of determination varying between 2.6 and 4.4 %. Secondly, a model selection method, the backward approach, was implemented. Similar SNPs were detected by both the backward selection and the individual marker approaches. However, the latter detected new associations with other traits, genes, and SNPs and improved the quality of the model as shown by the BIC criteria and the higher adjusted determination coefficient (1.5 to 8.3 %). Our results reveal that cellulose genes can be associated with lignin traits (syringyl-to-guaiacyl ratio) and stress the possible pleiotropic effect of some genes.
    Tree Genetics & Genomes 06/2013; 9(4):927-942.. · 2.40 Impact Factor
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    ABSTRACT: Near infrared spectroscopy partial least squares (PLS) regression calibrations were developed for estimation of Klason lignin content in Leucaena leucocephala (Lam.) de Wit (commonly called Subabul in India) belonging to the family Fabaceae and sub-family Mimosoideae with solid radial-longitudinal strip and milled samples for trees having diameter ranging from 3.5 to 34.1 cm and age between 4 and 20 years. Samples were conditioned to 10–12 % moisture content. Two separate models were developed for milled samples having particle sizes of 250–400 μm (screened-1) and 420–1,000 μm (screened-2). Regression model using PLS regression with full cross validation were test validated on a separate set of samples. The three multisite calibrations gave RPD (ratio of performance to deviation) between 2.24 and 2.97 with lowest for solid radial strip samples (2.24) and highest for screened-1 powder (2.97). Screened-1 milled sample gave highest r p2 of prediction (0.92) with four factors compared to four that were used for solid strips and eight for screened-2 samples. Model with solid strips gave lowest r p2 of prediction (0.86). Results indicate that properly mixed milled samples having particle size 250–400 μm (screened-1) help in construction of PLS models with higher RPD and less number of factors compared to screened-2 samples (2.48) and solid strips (2.24). Particle size played an important role in construction of the model. Lower RPD with solid strips could be due to variation of chemical constituents from pith to bark. The standard error of calibration (SEC), standard error of cross validation (SECV) and standard error of prediction (SEP) were less than 1 % for Screened-1 samples. For screened-2 samples SEC and SECV were less than 1 % while SEP was 1 %. In case of radial solid strip SEP was slightly above 1 % (1.16) while SEC and SECV were less than 1 %. For constructing models of high accuracy with radial solid strips separate models may be constructed for juvenile and mature wood.
    Journal of the Indian Academy of Wood Science. 9(2).
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    ABSTRACT: • Context The genetic and environmental control of microfibril angle (MFA) and its genetic correlations with other wood and growth traits are still not well established in Eucalyptus sp. • Aims To determine the narrow-sense heritability estimates (h 2) of MFA, wood density (D), Klason lignin (KL) content, syringyl to guaiacyl (S/G) ratio and growth traits, their variation from pith to cambium and their genetic correlations. • Methods Heritability and correlations were assessed in 340 control-pollinated progenies of 14-year-Eucalyptus urophylla S.T. Blake using near infrared spectroscopic models. • Results Moderate to high heritability were found for MFA (h 2 = 0.43), D (h 2 = 0.61), S/G (h 2 = 0.71) and LK (h 2 = 0.76). The genetic control of D and MFA and the genetic and residual correlation between chemical and growth traits varied with age. The genetic correlation C × D was always strongly negative (r < −0.80) while the correlation D × MFA remained constant and positive in the juvenile wood (r = 0.7), before disappearing in the mature wood. These results could be explained by gene pleiotropic effect, low microfibril angle compensating for low wood density and fast growth or by linkage disequilibrium induced by sampling. Variations in MFA and KL in the mature wood were also genetically controlled. • Conclusions These findings provide the opportunity for developing breeding strategies for pulpwood, fuelwood and sawntimber production in Eucalyptus sp.
    Annals of Forest Science 02/2013; 69(6). · 1.63 Impact Factor


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