Genotypic parameters of wood density and fiber traits in triploid hybrid clones of Populus tomentosa at five clonal trials

? Context

A clear understanding of the genetic control of wood properties is a prerequisite for breeding for higher wood quality in Populus tomentosa Carr. hybrid clones.

? Aims

The experiments aimed at unraveling genetic and environmental effects on wood properties among triploid hybrid clones of P. tomentosa.

? Methods

We used 5-year-old clonal trials established in Northern China to assess the heritability of wood density and fiber traits. Two hundred seventy trees from nine clones were sampled in five sites.

? Results

Site had a very significant effect on all recorded traits. Despite this large site effect, a tight genetic control was detected and clonal repeatability varied between 0.53 and 0.95. Significant genotype?×?environment interactions were detected for most of the traits. Moderate to tight correlation were evidenced among traits but they were not consistent with that in several cases that were site-dependent.

? Conclusions

Our results revealed a tight genetic control over several wood properties and therefore breeding programs might be able to improve wood density, fiber length, and coarseness in these hybrids.     

Within-stem variation in wood properties of triploid hybrids of Populus tomentosa at three clonal trials

To obtain a better understanding of variability in wood properties along the stem in triploid hybrids of Populus tomentosa L., basic wood density (BWD) and fiber traits were measured at four sample heights for each tree sampled from three clonal trials. The BWD showed a similar trend at each site in that density was initially decreased then increased with increasing height position. For fiber traits, the fiber length (FL) decreased linearly with the height of the trunk, whereas fiber width and coarseness changed relatively slightly with increasing height position. In addition, the vertical wood properties distribution patterns were different from clones so that some clones showed more markedly change in height positions than others. The joint analysis indicated significant height position effect for BWD and fiber traits, in accordance with site and clonal effect. Significant site × height interaction was found on wood properties, whereas the significant clone × height interaction was only obtained at fiber width. Moreover, variation in the relationships between FL and BWD or other fiber traits showed no consistent pattern with increasing height position.     

柳树杂种木材基本密度的遗传变异

利用柳属和钻天柳属种间、属间杂交１５个杂种３９个杂交组合１５１个无性系材料，对木材基本密度的遗传变异情况进行了研究。结果表明，杂种间和无性系间，在木材基本密度上存在极显著（α＝０．０１）差异，其中属间杂种（旱柳×钻天柳）×旱柳平均木材基本密度达到０．４８８，显著（α＝０．０５）超过各杂种平均值；柳树杂种及无性系木材基本密度是受强遗传控制的，被研究群体的广义遗传力达到０．９２￣０．９８，遗传变异系数     

Genetic variation of wood tracheid traits and their relationships with growth and wood density in clones of Pinus tabuliformis

To improve wood quality for pulpwood industries, it is important to examine not only wood density but also its components, especially tracheid characteristics.We studied genetic variations in the following tracheid traits by earlywood(EW) and latewood(LW): tracheid length(TL),double wall thickness(WT), radial lumen diameter(R_D1), tangential lumen diameter(T_D1), radial central diameter(R_D2), and tangential central diameter(T_D2).We also studied the relationship with the following growth traits: diameter at breast height(DBH), height(H), crown breadth south-north axis(NSC), crown breadth east–west axis(EWC), ring width(RW), latewood percentage (LWP), and wood density(WD).All sample materials were collected from a 33-year old clonal seed orchard of Pinus tabuliformis Carr.Genetic variation among clones was moderate for all tracheid traits, 9.49–26.03%.Clones significantly affected WT, R_D1, R_D2, T_D1, T_D2, and the two ratios WT/R_D1 and TL/T_D2 in EW but had no effects in LW.Clones significantly affected TL in LW but had no effects in EW.H2/C was higher in LW(0.50) than in EW(0.20) for TL, while H2/Cwas higher in EW(0.27–0.46)for other tracheid traits and the two ratios(TL/T_D2 and WT/R_D1) than in EW(0.06–0.22).WD and TL were significantly positively correlated, but WT and TL were negatively correlated both at individual and clone levels;all tracheid diameters and the four ratio values(EW_WT/R_D1, LW_WT/R_D1, EW_TL/T_D2 and LW_TL/T_D2), were strongly positively correlated with DBH, H,NSC, WEC and RW, and strongly negatively correlated with WD both at individual and clone levels.The most important variables for predicting WD were LW_TL,EW_WT and R_D1 in both EW and LW(r~2= 0.22).Selecting the top 10% of the clones by DBH would improve DBH growth by 12.19%(wood density was reduced by 0.14%) and produced similar responses between EW and LW for all tracheid traits: a reduction of0.94 and 3.69% in tracheid length and increases in tracheid diameters(from 0.36 to 5.24%) and double wall thickness(0.07 and 0.87%).The two ratios WT/R_D1 and TL/T_D2 across tissues(EW and LW) declined 0.59 and 4.56%,respectively.The decreased tracheid length and the ratio between tracheid length and diameter is disadvantageous for pulp production.The unfavorable relationship of tracheid traits with wood density indicate that multiple trait selection using optimal economic weights and optimal breeding strategies are recommended for the current longterm breeding program for P.tabuliformis.     

Genetic variation and relationships to growth traits for microfibril angle,wood density and modulus of elasticity in a Picea abies clonal trial in southern Sweden

Abstract

Genetic variation in wood density, microfibril angle (MFA), wood stiffness (MOE), height, diameter and volume was investigated in a 26-year-old Norway spruce [(Picea abies (L.) Karst.] clonal trial in southern Sweden. Wood quality measurements were performed on 10 mm increment cores using SilviScan. For MFA, mean values of annual rings showed the highest value (30°) at ring 2 counting from the pith, followed by a steep decrease and a gradual stabilization around ring 12 at approximately 14°. MOE showed a monotonic increase from 5 GPa to 14 GPa when moving from pith to bark. High broad-sense heritability values were found for wood density (0.48), MFA (0.41) and MOE (0.50). All growth traits displayed heritability values of similar magnitudes as reported in earlier studies. The generally high age–age correlations between different sections of the wood cores suggested that early selection for wood quality traits would be successful. Owing to unfavorable genetic correlations between volume and MOE, the correlated response indicated that selection for volume only at age 10 would result in a 0.27% decrease in weighted MOE at age 26 for every 1% increase in volume.     

Genotypic effects on the variation of wood quality and growth traits in plantation forest made by cutting cultivars of Japanese cedar

We studied the effect of genotypes of planting stocks regarding the variation of the modulus of elasticity of tree trunks on standing trees (trunk-MOE), tree height (TH), and diameter at breast height (DBH) in a 19-year-old Japanese cedar plantation made with root cuttings. Trunk-MOE was assessed nondestructively using a tree-bending method. Genotypes of individual trees were detected using the random amplified polymorphic DNA (RAPD) technique. RAPD analysis revealed that the sampled plantation consisted of 14 genotypes. Genotypic effects on DBH and TH were unclear, and there was no significant difference among genotypes. This result indicated that an acquired variation should have more influence than an inherited variation on DBH and TH. For trunk-MOE, there were significant differences among the four largest genotypes at the 5% level. However the coefficient of variation in trunk-MOE of each genotype ranged from 7.5% to 26.8%. It seems reasonable to assume that the wide variation in trunk-MOE in a sampled plantation may depend on the environmental effect within a clone as well as on the genetic origin of clones. We therefore conclude that the use of multiple planting stocks from different cuttings for which the wood quality is unknown contributed strongly to the wide variation in trunk-MOE in the plantation of Japanese cedar.     

杨树新无性系木材性质的变异研究

The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-95 and Nanlin-895, respectively,for providing information on variation patterns of wood density, fiber characteristics and holocellulose content within trees and among clones. The results showed that significant variations about wood density, cellulose content, fiber diameter and the ratio of fiber length to diameter existed among poplar clones examined. Variance analysis indicated that there were significant differences in wood basic density, fiber length, fiber diameter and cellulose content among the growth rings, which had an increasing tendency along the direction from pith to bark. The significant differences also existed in wood basic density, fiber length and fiber diameter at different tree height. The mean wood basic density had a general increase trend with increasing height of trees and the lowest was found at the base, while fiber length and fiber diameter had a general decline pattern with increasing height of trees and the biggest value was observed at the height of 5.6 m. Regression analysis indicated that the relationship between examined wood properties and growth ring number (cambial age), and the relationship between examined wood properties and tree height can be described by polynomial functions.     

Variation analysis of growth traits of four poplar clones under different water and fertilizer management

To determine appropriate quantities of water and fertilizer required for early growth of hybrid poplar cuttings,we recorded the growth traits of four clones grown under four factors(irrigation and nitrogen,phosphorus,and potassium fertilizers),each with four levels,using an orthogonal experimental design.A logistic model was used to estimate growth in height.The growth curves for tree height were sigmoid,and the model R^2 values were greater than 0.9,which indicated that the fit was highly significant.ANOVA results for tree height and basal diameter indicated that all sources of variance showed significant differences(p<0.001).The average tree height and basal diameter for all the four clones under the different treatments ranged from 155.39 to 235.04 cm,and from 13.71 to 17.42 mm,respectively.A highly positive correlation between the extreme k value and tree height was observed,suggesting that the k value was an accurate estimation of tree height.For model parameters,the earliest average time point for the onset of the rapid growth period of poplar clones was 131 d,and the highest average increment in tree height during the rapid growth period was 138.78 cm.The highest average tree height for all clones under each factor was 219,210.51,200,and 201 cm when treated with either 1200 mL of water applied every third day,3 g of nitrogen,0 g of phosphorus,or 0 g of potassium,respectively.The most suitable treatment for the early growth of hybrid poplar cuttings,as suggested by the developed logistic model,was 1200 mL of water applied every third day and three applications of 1 g nitrogen(in the form of CH4N2O).     

Genotypic variation in drought tolerance of poplar in relation to abscisic acid

We investigated effects of water stress and external abscisic acid (ABA) supply on shoot growth, stomatal conductance and water status in 1-year-old cuttings of a drought-sensitive poplar genotype Populus x euramericana cv. I-214 (Italica) and a drought-tolerant genotype P. 'popularis 35-44' (popularis). Populus popularis was more productive and maintained higher leaf water potentials throughout the drought treatment than cv. Italica. Supply of ABA to the xylem sap caused a greater decline in growth and more leaf abscission in shoots of cv. Italica than in shoots of P. popularis. Immediately after initiation of the drought treatment in P. popularis, the ABA concentration ([ABA]) of the xylem increased rapidly and stomatal conductance declined; however, stomatal conductance had returned to control values by the third day of the drought treatment, coincident with a gradual decline in xylem [ABA]. In contrast, xylem [ABA] of cv. Italica initially increased more slowly than that of P. popularis in response to the drought treatment, but the increase continued for 3 days at which time a tenfold increase in xylem [ABA] was observed that was followed by abscission of more than 40% of the leaves. We conclude that sensitivity of poplar roots to variation in soil water content varies by clone and that a rapid short-term accumulation of ABA in shoots in response to water stress may contribute to drought tolerance.     

Variability of wood properties in two wild cherry clonal trials

There has been an increase in wild cherry cultivation over recent decades, revealing a need for improvements in planting material to be used for the production of high quality timber. To date, trial tests have been carried out mainly on growth and tree architectural traits, while no investigations have focused on wood properties. The present study investigated the variability of the growth traits and the physical and mechanical properties of wild cherry wood, both within the tree, within and among clones and between sites. The aims of the study are to provide useful information on the genetics of wood traits in valuable hardwoods and to discuss how within-tree variation can affect early selection of genotypes. The results suggest that site was the most important source of variation in growth traits and in the proportion of heartwood, although differences among clones were highly significant. The number of sapwood rings was very homogeneous both between sites and among clones. Concerning the wood traits, most variation was detected within the tree, rather than within or among clones or between sites. Within tree variability seems to be mainly due to heartwood/sapwood presence. However, since there is a high correlation between heartwood and sapwood properties, a quite efficient selection made on the basis of sapwood should provide an efficient means of selecting heartwood traits.     

Changes through time in traits of poplar clones in selection trials

Growth, survival, stem characteristics, resistance to wind, and canker disease of 51 poplar clones were evaluated at age 9 and 10 years, and compared to measurements at age 3 in two trials on the Lower Valley of the Colorado River, Argentina. About 30% of the clones in both trials had large changes in growth rankings at age 9 and 10 compared to rankings at age 3. Canker incidence increased about 4-fold between age 3, and measurements at age 9 and 10. Stem form was in general satisfactory, and wind incidence was almost nil. In trial 1, clones 588–1, Conti 12, 582–41, and 582–5 occupied the upper positions in the growth rankings at age 3 and 10, and the clone 588–1 ranked first both in growth and canker incidence in 1998. Stem growth trajectories of clones with similar growth rates did not differ among clones with, and without canker disease. In trial 2, the range in growth among clones was narrower than in trial 1, and canker disease, although of minor incidence, was present in most clones at age 9. Some of the P. deltoides clones in the trials had similar growth, and less canker disease than the Euroamerican clones commonly grown in the region, but progressive canker incidence should be addressed with additional selection trials.     

Genotypic variation in wood properties and growth traits of <Emphasis Type="Italic">Eucalyptus</Emphasis> hybrid clones in southern China

Growth traits, wood properties and bark percentage were assessed for 19 hybrid eucalypt clones at three sites in southern China sampled at age 51 months. Analysis of variance showed that there were significant differences in growth traits and wood properties between clones and sites, and that the clone × site interactions were also significant except for basic density. Coefficients of variation ranged from 8.4 to 27.9% for growth traits, 2.7–11.1% for wood properties and 14.0–23.3% for bark percentage. Repeatability ranged from 0.73 to 0.96 for growth traits, 0.32–0.93 for wood properties and 0.77–0.88 for bark percentage. Strong genotypic correlations between the same traits in clones at pairs of sites indicated that the traits were rather stable across sites. The genotypic correlations between growth traits and basic density ranged from −0.67 to 0.43, and generally favorable negative genotypic correlations between growth traits and bark percentage were also found. The correlations between growth traits and Pilodyn pin penetration were positive, ranging from 0.28 to 0.65 and therefore unfavorable as lower wood density will be associated with higher values of Pilodyn pin penetration and improved growth rate. The correlations between traits assessed using non-destructive field methods and wood property assessment results indicated that Pilodyn and Fakopp microsecond timer tools can be confidently used to indirectly select for fiber width and basic density.     

Variation in wood density and ring width in Acacia melanoxylon at four sites in Portugal

The radial variation in wood density in Acacia melanoxylon R. Br. was studied using microdensitometry by sampling 20 trees with a 40-cm diameter class at four sites in Portugal. The measurements were taken from pith to bark at breast height. A. melanoxylon had an average ring density of 0.607 g cm^?3, ranging from 0.556 to 0.630 g cm^?3. The mean growth was 6.0 mm year^?1. Latewood corresponded, on average, to 34 % of the ring width. Between-tree variability at each site was the main source of variation in the density components, representing between 30 and 54 % of the total variation. Between-sites variability represented from 0 to 21 % of the total variation in density components. The environmental effects (site related) were more pronounced on latewood, while the genetic effect (tree related) was more evident in earlywood. Ring width, latewood percentage and heterogeneity index were independent from site, trees in site and age effects. The values of wood density and radial growth revealed that A. melanoxylon can be important as a commercial timber species in Portugal.     

Individual tree growth differences in a clonal eucalypt blanking trial at four years

Achieving a well-stocked stand at time of planting is important to compartment productivity and yield in clonal eucalypt stands for pulpwood production. The window period in which individuals that replace those that died after initial planting (blanks) still contribute meaningfully to final yield is set by the competition dynamics between individuals within the stand. The longer the period between planting and blanking, the greater the advantage achieved by original plantings in dominating site resources (light, water and nutrients) and suppressing blanks. A blanking trial was established to determine growth differences of blanked and original individuals and productivity per unit area. Factorial combinations of blanking period after planting, mortality pattern and extent of mortality were tested. Analysis of measurements at four years showed that the period before blanking is the only factor that significantly accounts for the variation in plot volume between treatments, although the percent mortality and pattern of mortality by percent mortality together also have influence on plot volume. Late blanking results in a higher proportion of suppressed trees that contribute little to total volume. Asymmetric competition is more pronounced where late blanking is carried out and where mortality is spread, rather than clumped.     

Genetic variation in growth,stem straightness and branch thickness in clonal trials of Acacia auriculiformis at three contrasting sites in Vietnam

Acacia auriculiformis has become an important species in Vietnam because it displays adaptability to a wide range of site conditions and produces pulp wood and sawlogs on short rotations. The aim of this study was to estimate genetic parameters and consider implications for development of clonal forestry. Clonal repeatabilities, genotypic correlations, genotype by environment interactions (G × E), genetic selection gains and correlated responses were estimated for total height (HT), diameter at breast height (DBH), stem volume (VOL), straightness (STR), and branch thickness (BRA) measured in three clonal trials of Acacia auriculiformis A. Cunn. ex Benth. in northern, central and southern Vietnam. Assessments were made at age 1, 2 and 3 years on all three trials and also at age 4 years in one of the trials. The estimates of the genetic parameters were based on a total of 130 clones, of which 115 were selected from a progeny test, and 15 were selected from plantations of the Coen River (Queensland, Australia) provenance in Vietnam. Seventy of these clones were planted in all three trials. The clonal repeatabilities for all studied traits increased with age. The repeatabilities at the latest assessment (3 and 4 years old) of the trials ranged from 0.28 to 0.47 for HT, 0.21–0.56 for DBH, 0.21–0.54 for VOL, 0.21–0.32 for STR, and 0.21–0.28 for BRA. Genotypic coefficients of variation ranged from 8.3 to 13.1% for HT and DBH and from 24.6 to 32.6% for VOL. Age–age genotypic correlations were strong for growth traits but ranged more widely from 0.22 to 0.98 for STR and BRA. Straightness and BRA correlated positively with growth traits, with these correlations ranging from 0.13 to 0.76. Low genotypic correlations between the same traits measured in the different trials at age 3 years indicated that G × E was important for this species in Vietnam. Selection of 10% of the clones resulted in gain varying from 14.3 to 23.0% for HT and DBH. Our results indicate that using HT and DBH as selection traits together with STR and BRA would be beneficial in clonal selection of A. auriculiformis for deployment in Vietnam.     

Genetic variation of wood tracheid traits and their relationships with growth and wood density in clones of <Emphasis Type="Italic">Pinus tabuliformis</Emphasis>

To improve wood quality for pulpwood industries, it is important to examine not only wood density but also its components, especially tracheid characteristics. We studied genetic variations in the following tracheid traits by earlywood (EW) and latewood (LW): tracheid length (TL), double wall thickness (WT), radial lumen diameter (R_D1), tangential lumen diameter (T_D1), radial central diameter (R_D2), and tangential central diameter (T_D2). We also studied the relationship with the following growth traits: diameter at breast height (DBH), height (H), crown breadth south-north axis (NSC), crown breadth east–west axis (EWC), ring width (RW), latewood percentage (LWP), and wood density (WD). All sample materials were collected from a 33-year old clonal seed orchard of Pinus tabuliformis Carr. Genetic variation among clones was moderate for all tracheid traits, 9.49–26.03%. Clones significantly affected WT, R_D1, R_D2, T_D1, T_D2, and the two ratios WT/R_D1 and TL/T_D2 in EW but had no effects in LW. Clones significantly affected TL in LW but had no effects in EW. \( H\frac{2}{C} \) was higher in LW (0.50) than in EW (0.20) for TL, while \( H\frac{2}{C} \) was higher in EW (0.27–0.46) for other tracheid traits and the two ratios (TL/T_D2 and WT/R_D1) than in EW (0.06–0.22). WD and TL were significantly positively correlated, but WT and TL were negatively correlated both at individual and clone levels; all tracheid diameters and the four ratio values (EW_WT/R_D1, LW_WT/R_D1, EW_TL/T_D2 and LW_TL/T_D2), were strongly positively correlated with DBH, H, NSC, WEC and RW, and strongly negatively correlated with WD both at individual and clone levels. The most important variables for predicting WD were LW_TL, EW_WT and R_D1 in both EW and LW (r² = 0.22). Selecting the top 10% of the clones by DBH would improve DBH growth by 12.19% (wood density was reduced by 0.14%) and produced similar responses between EW and LW for all tracheid traits: a reduction of 0.94 and 3.69% in tracheid length and increases in tracheid diameters (from 0.36 to 5.24%) and double wall thickness (0.07 and 0.87%). The two ratios WT/R_D1 and TL/T_D2 across tissues (EW and LW) declined 0.59 and 4.56%, respectively. The decreased tracheid length and the ratio between tracheid length and diameter is disadvantageous for pulp production. The unfavorable relationship of tracheid traits with wood density indicate that multiple trait selection using optimal economic weights and optimal breeding strategies are recommended for the current long-term breeding program for P. tabuliformis.     

Volume growth and wood density of plus tree progenies of Pinus contorta in two Swedish field trials

Seventy‐four half‐sib families of lodgepole pine (Pinus contorta ssp. latifolia Engelm.) plus trees were measured for vigour, height growth, stem diameter, wood density and ring width in two Swedish field trials at age 9. Height growth, wood density and ring width differed between families within provenances with variance components of 3–8 %. Coefficients of variation were highest for height growth and lowest for ring width. Heritabilities were similar for height growth and wood density but lower for ring width. These genetic parameters seemed to be equal for all provenances. Indirect selection for high dry stem biomass was more effective using height growth than wood density, and a correlated response in wood density of 2.1 % of mean by selecting the 15 highest parent trees was indicated. Juvenile wood density looks uncertain as a selection criterion for mature wood density.     

山杨木材材性的研究

对北方六省六个地区天然林中的山杨木材解剖, 物理力学性质, 化学成分进行的研究。结果表明：六个种源的山杨木材解剖特征，化学成分无明显差异，物理力学性质存在不同程度的差异。此外，还对六组山杨的胶质纤维，侵填体，髓斑进行了研究。     

Genetic variation in wood density and correlations with tree growth in Prosopis africana from Burkina Faso and Niger

? Variation in wood basic density and its correlation with tree growth were investigated at 13 years in a provenance/progeny test of Prosopis africana in Niger. The test included progeny from 256 trees sampled from 24 provenances in the Sahelian ecozone of Burkina Faso and Niger.

? Variation in wood density was significant due to provenances and families within provenances. Individual tree heritability was higher for wood density than for growth traits. Provenance means for wood density increased from the more humid to the drier parts of the sample region. Phenotypic correlations indicated that larger trees tended to have denser wood.

? Clines suggest that natural populations of P. africana from the drier parts of the sample region have the genetic capacity to produce denser wood, compared with populations from the more humid parts of the region. Correlations and heritability estimates suggest that selection of faster-growing trees may produce a small gain in wood volume but little (if any) gain in density in the subsequent generation. Multi-location provenance/tests are needed to confirm this tentative conclusion.