John Mackay

Affiliation : U.Laval

Spécialité : Génétique

Courriel : jmackay@rsvs.ulaval.ca

Implication :

Projets dont John Mackay est Responsable :

Publications :

  • Quibin Yu, Tony Zhang, John Mackay, Jean Bousquet, Pierre Périnet. 2008. Variation in Mechanical Properties of Selected Young Poplar Hybrid Crosses. Forest Science. 54(3):255-259. Cet article est réalisé dans le cadre du Volet 1 TP 1

    (Résumé)

    To better understand the variability in mechanical properties caused by genetic differences in hybrid poplars, modulus of elasticity and modulus of rupture in static bending were examined at two 10-year-old clonal trials located at Windsor and St-Ours, southern Quebec, Canada. The materials consisted of three hybrids, Populus deltoides × Populus nigra, Populus trichocarpa × P. deltoides, Populus maximowiczii × Populus balsamifera, and native P. deltoides. Significant differences were observed in mechanical properties among hybrids and P. deltoides. The effects of growth on the mechanical properties were inconsistent and varied considerably by site and by hybrid. Results indicated no uniform trends relating growth rate to either higher or lower modulus of elasticity/modulus of rupture. It appears that selection for strength properties may not uniformly lead to decreased growth production, especially for P. trichocarpa × P. deltoides and P. maximowiczii × P. balsamifera.

  • Alfas Pliura, Tony Zhang, John Mackay, Jean Bousquet. 2007. Genotipic variation in wood density and growth traits s of poplar hybrids at four clonal trials. Forest Ecology and Management. 238(1-3):92-106 doi:10.1016/j.foreco.2006.09.082. Cet article est réalisé dans le cadre du Volet 1 TP 1

    (Résumé)

    Wood density is considered as one of the most important wood properties which affects the properties and value of both fibrous and solid wood products. The present study was intended for evaluating the possibilities of improving wood quality and growth of poplar hybrids. Wood density components of individual growth rings (minimum and maximum wood density, average ring density) and growth traits (tree height, dbh, stem volume) were measured in four 10- and 12-year-old clonal trials of four poplar hybrids, Populus deltoides × P. nigra, P. trichocarpa × P. deltoides, P. maximowiczii × P. balsamifera, and P. balsamifera × P. nigra, as well as P. deltoides. Wood density components of individual growth rings were obtained from microdensitometeric profiles measured with a direct reading X-ray densitometer. Site had a moderately significant effect on wood density and a highly significant effect on tree growth. The hybrid effect was highly significant (P < 0.001) for most traits. Minimum, maximum and weighted wood densities were found to be under strong genetic control, with clonal repeatabilities varying between 0.45 and 0.81. The coefficient of genotypic variation (CVG) for wood density at individual sites ranged from 4.0 to 6.8%, whereas CVG for dry fiber weight (mass) reached 32.8% with repeatabilities of up to 0.67. A small but significant (P = 0.028) hybrid × environment interaction was found for dry fiber weight. The highest ecological sensitivity was found for P. deltoides × P. nigra, with ecovalence reaching 32.3%. Clonal × environment interaction was significant for weighted, average, and minimum wood density. Significant negative genotypic correlations between stem volume and wood density ranged from −0.39 to −0.74. One possible strategy in tree breeding would be to maximize wood fiber production through selection for dry fiber weight.

    Copyright © 2009 Elsevier B.V.

  • Alfas Pliura, Tony Zhang, Jean Bousquet, John Mackay. 2006. Age trends in genotypic variation of wood density and its intra-ring components in young poplar hybrid crosses. Annals of Forest Science. 63(7):673-685 doi:10.1051/forest:2006048. Cet article est réalisé dans le cadre du Volet 1 TP 1

    (Résumé)

    Age related dynamics of genotypic, phenotypic, and environmental variation, clonal repeatability, and genotypic correlations for wood density and its intra-ring components were analyzed in four poplar hybrid crosses, Populus deltoides $ imes $ P. nigra, P. trichocarpa $ imes $ P. deltoides, P. maximowiczii $ imes $ P. balsamifera, and P. balsamifera $ imes $ P. nigra, as well as P. deltoides. Using X-ray densitometry, measurements were taken on increment cores sampled in four clonal trials at 10 and 12 years of age from ramets of 19 clones. Wood density of all hybrid crosses was highest at the pith and decreased with increasing cambial age. The significance of the hybrid cross effect increased with age for mean wood density, dry fiber weight, and ring width. The coefficient of genotypic variation of cumulated mean wood density was rather stable over the 10-year period at all three sites, and ranged from 4.8-6.8%. Clonal repeatability increased with age from 0.46 to 0.79, mainly because of decreasing random variation. Corresponding genotypic parameters for individual rings varied greatly with age and across sites. Significance of the site effect on wood density tended to decrease with age. Significant negative genotypic correlations between ring width and wood density were found at only two of the four sites and they weakened with age. Age-age genotypic correlations between wood densities at ages 10 and younger were strong and significant from age 6 and over. This trend suggests that selection before this age would be unreliable.

    La dynamique inter-annuelle de la variabilité génotypique, phénotypique et environnementale, de la répétabilité clonale et des corrélations génotypiques entre paramètres de densité du bois ont été analysées pour quatre hybrides de peuplier : Populus deltoides $ imes $ P. nigra, P. trichocarpa $ imes $ P. deltoides, P. maximowiczii $ imes $ P. balsamifera, and P. balsamifera $ imes $ P. nigra, ainsi que pour P. deltoides. Les mesures ont été effectuées par microdensitométrie à rayon X sur des carottes échantillonnées à partir des ramets de 19 clones issus de quatre tests clonaux (âge: 10 et 12 ans). Les résultats montrent que la densité du bois de tous les hybrides est la plus élevée près de la moëlle puis qu'elle diminue avec l'âge cambial. L'effet statistique du type d'hybrides augmente avec l'âge pour la densité moyenne, le poids sec des fibres et la largeur de cernes. Les coefficients de variation génotypique pour la densité moyenne du bois sont stables au cours des 10 ans sur 3 sites et s'élèvent à 4.8-6.8 %. La répétabilité clonale augmente avec l'âge de 0.46 à 0.79. Les paramètres génotypiques pour les caractéristiques individuelles des cernes varient fortement avec l'âge et les sites. Le degré de signification de l'effet site tend à décroître avec l'âge pour la densité du bois. Des liaisons négatives significatives entre largeur de cernes et densité du bois sont observées sur seulement 2 des 4 sites et leur intensité s'affaiblit avec l'âge. Les liaisons génotypiques entre densité du bois à 10 ans et à des âges plus jeunes sont fortes et significatives à partir de 6 ans et au-delà. Une sélection avant cette âge semble donc peu fiable.

    © INRA, EDP Sciences 2006

  • Alfas Pliura, Quibin Yu, Tony Zhang, John Mackay, Pierre Périnet, Jean Bousquet. 2005. Variation in wood density and shrinkage and their relationship to growth of selected young poplar hybrid crosses. Forest Science. 51(5):472-482. Cet article est réalisé dans le cadre du Volet 1 TP 1

    (Résumé)

    Wood density, various shrinkages and several growth traits were measured in two 10-year-old clonal trials at sites of contrasting growth potential. The material studied consisted of 12 clones of three poplar hybrid crosses, Populus deltoides × P. nigra, P. trichocarpa × P. deltoides, and P. maximowiczii × P. balsamifera, as well as P. deltoides. Wood density and longitudinal and radial wood shrinkages were significantly lower at the St-Ours than at the Windsor site, by 6.7, 46.7, and 14.9%, respectively, while growth rate was increased. The differences among hybrid crosses were significant for all growth traits and wood properties except for radial and tangential shrinkages of juvenile wood. P. deltoides had the highest wood density of 363.2 kg/m3, whereas P. maximowiczii × P. balsamifera wood had the lowest density of 299.8 kg/m3. The differences among hybrid crosses were significant for growth traits, primarily due to the fast growth of P. trichocarpa × P. deltoides and slow growth of P. deltoides. Among the wood properties measured, only tangential wood shrinkage exhibited clear radial intertree changes with cambial age. The tangential wood shrinkage increased from pith to mid-diameter and then started to decrease outward, with each hybrid showing a different pattern of variation. Phenotypic clonal mean correlations among growth traits and wood density were weakly negative. Correlations among growth traits and radial wood shrinkage ranged from weakly to strongly negative. Longitudinal shrinkage displayed strong negative correlations with radial and tangential shrinkages. Negative correlations found between wood density and longitudinal shrinkage and positive correlations between density and both radial and tangential shrinkages suggest that selection for high wood density may lead to increased transverse wood shrinkage but decreased longitudinal shrinkage.