Correction of moisture effects on near infrared calibration for the analysis of phenol content in eucalyptus wood extracts

Les méthodes basées sur la spectroscopie proche infrarouge pour estimer les propriétés du bois sont sensibles aux variations des paramètres physiques (température, granulométrie. . . ). Le bois étant un matériau hygroscopique sensible, l'influence de l'humidité sur l'absorbance et l'étalonnage proche infrarouge a été étudiée afin de mieux considérer les possibilités d'applications dans des conditions réelles.Un étalonnage de référence de la quantité de polyphénols présents dans les extraits a été établi à partir de spectres d'une collection de bois d'hybrides d'Eucalyptus urophylla × E. grandis à humidité constante fixée. D'autres spectres ont été obtenus sur des échantillons de même provenance mais à 8 teneurs en eau couvrant une large plage de variation. L'influence de l'humidité sur l'absorbance proche infrarouge puis sur l'estimation par le modèle de référence a été analysée. / Methods based on near infrared spectroscopy used to assess wood properties are susceptible to variations in physical parameters (temperature, grain size, etc). As wood is a hygroscopically sensitive material, we studied the effects of moisure on near infrared absorbance and calibration to accurately determine the application potential of this technique under routine. A collection of Eucalyptus urophylla x E. grandis hybrid wood pieces were analysed to obtain reference calibration of polyphenol contents in wood extracts via NIR spectra acquired under constant moisture conditions.Others specimens from the same source were assessed to obtain spectra for eight moisture contents spanning a broad variation range. The effects of moisture on absorption and on estimates based on a reference model were analysed. An increase in moisture content prompteda rise in near infrared absorption over the entire spectrum and the water O-H absorption bands. The polyphenol content estimates obtained by assessing specimens against the reference calibration at variable moisture contents revealed prediction bias. Five correction methods were then tested on enhance the robustness relative to moisture. In-depth calibration and external parameter orthogonalization were found to be the most efficient methods for offsetting this factor

Comprehensive genetic dissection of wood properties in a widely-grown tropical tree: Eucalyptus

Background: Eucalyptus is an important genus in industrial plantations throughout the world and is grown for use as timber, pulp, paper and charcoal. Several breeding programmes have been launched worldwide to concomitantly improve growth performance and wood properties (WPs). In this study, an interspecific cross between Eucalyptus urophylla and E. grandis was used to identify major genomic regions (Quantitative Trait Loci, QTL) controlling the variability of WPs. Results: Linkage maps were generated for both parent species. A total of 117 QTLs were detected for a series of wood and end-use related traits, including chemical, technological, physical, mechanical and anatomical properties. The QTLs were mainly clustered into five linkage groups. In terms of distribution of QTL effects, our result agrees with the typical L-shape reported in most QTL studies, i.e. most WP QTLs had limited effects and only a few (13) had major effects (phenotypic variance explained > 15%). The co-locations of QTLs for different WPs as well as QTLs and candidate genes are discussed in terms of phenotypic correlations between traits, and of the function of the candidate genes. The major wood property QTL harbours a gene encoding a Cinnamoyl CoA reductase (CCR), a structural enzyme of the monolignol-specific biosynthesis pathway. Conclusions: Given the number of traits analysed, this study provides a comprehensive understanding of the genetic architecture of wood properties in this Eucalyptus full-sib pedigree. At the dawn of Eucalyptus genome sequence, it will provide a framework to identify the nature of genes underlying these important quantitative traits. (Résumé d'auteur

Genetic study on the physical properties of Coffea arabica L. wood

International audienceThe physical characteristics of wood are not usually considered as selection criteria when breeding perennial species that are grown for their fruits or seeds. In the coffee tree, stem breakage during harvesting and lodging during the growth period are major defects in some cultivars. These defects are linked to certain physical and mechanical properties of the wood, such as density or rigidity, which can be characterized by a parameter used in the resistance of materials: the Modulus of Elasticity (MOE). Wood density and the longitudinal MOE were studied on the stems of coffee trees of the species Coffee arabica L., derived from a diallel mating design. The MOE was measured by an acoustic system based on an analysis of the vibrations produced by a blow to the end of a piece of wood of known geometry. The MOE obtained in that way, along with the density of coffee tree stem wood, displayed substantial heritability. A strong link between the average internode length and the yield cumulated over 4 years was detected. Wood density was also correlated to yield and wood elasticity. Classification of parents according to the wood characteristics of their progenies depended on their degree of introgression by the species C. canephora. These traits could therefore be used to measure introgression, possibly as predictors of traits of agronomic interest, and as target traits in the creation of tall C. arabica varieties

Structure, composition chimique et retraits de maturation du bois chez les clones d'Eucalyptus

Contrairement à beaucoup d'arbres feuillus, le bois de réaction des Eucalyptus n'est pas caractérisé par les fibres G. II peut cependant être caractérisé par ses déformations de maturation. La mesure des déformations résiduelles longitudinales de maturation (DRLM) par relaxation de contraintes en périphérie des troncs a permis un classement continu et quantitatif d'échantillons de bois de clones d'Eucalyptus hybrides du Congo. Ce type de mesure permet d'identifier mécaniquement le bois de tension. Les relations entre structure et propriétés mécaniques de ces bois ont été étudiées par une analyse ultrastructurale et chimique des échantillons, en particulier par l'examen de la composition monomérique des lignines par thioacidolyse. Les résultats présentés ici montrent qu'il existe : i) une forte variabilité des DRLM avec des valeurs élevées, même sur nos arbres peu penchés et peu excentrés, et malgré l'absence de fibres G ; ii) une corrélation négative entre le niveau de DRLM, le taux de lignines et l'angle des microfibrilles de cellulose ; iii) une corrélation positive entre le niveau de DRLM et le rapport des taux de monomères de lignines : unités syringyles / unités guaiacyles. La signification de ces corrélations est discutée (causalité mécanique directe ou corrélations plus complexes entre variables structurales).Wood structure, chemical composition and growth strains in Eucalyptus clones. Contrary to a lot of hardwoods, the tension wood of Eucalyptus species is not characterised by G-fibres. It can however be characterised by its growth strains. The measurement of residual growth strains at the stem surface, by relaxing stresses at the periphery of trunks, allowed a continuous and quantitative classification of wooden samples coming from clones of hybrids Eucalyptus. This kind of measurement allows a mechanical identification of tension wood. The connections between structure and mechanical properties of these different woods were studied by ultrastructural and chemical analysis of samples, especially by a quantitative investigation of the monomeric compound of lignins by thioacidolysis. The results presented in this study show: i) a large variation of the residual growth strains with high values, in spite of the weak eccentricity, the good verticality and the absence in G-fibre in our trees; ii) a negative correlation between the level of the residual growth strains, the lignin content and the microfibril angle of cellulose (S2 layer of fibre); and iii) a positive correlation between the level of the residual growth strains and the ratio of the syringyl units to the guaiacyl units in lignin monomeric units. The significance of these correlations is discussed (direct mechanical causality or more intricate correlations between structural variables)