Age trends in the genetic parameters of wood density and the relationship with growth rates in hybrid larch (Larix gmelinii var. japonica × L. kaempferi) F1

Age trends in variance components and heritability of overall wood density, earlywood and latewood density, and latewood proportion were investigated in 29-year-old trees of 19 full-sib families of hybrid larch (Larix gmelinii var. japonica × Larix kaempferi) F₁. The age–age correlation and optimum selection age for these traits were also estimated and genetic and phenotypic correlations between wood density and radial growth rate were calculated for each growth ring. Intraring wood density data were obtained using X-ray densitometry. The coefficient of additive genetic variance was stable over all ages, whereas the coefficient of environmental variances gradually decreased with increasing age, resulting in increases in heritability estimates with age for overall density. The latewood proportion had the highest heritability estimates at all ages, ranging from 0.44 to 0.66. Overall density and its various components at 28 years of age showed strong genetic correlations with their respective traits at all younger ages. Optimum selection ages for the wood density traits ranged from 8 to 14 years, at which point maximum gain efficiencies per year were obtained. There were negative correlations between wood density and radial growth rate at early ages, although these relationships tended to be weaker with increasing age. These results suggest that selection at a young age is effective for wood density, but particular care must be taken in selecting trees with an improved radial growth rate because rapid growth will result in a low-density wood product, especially in the early growth period.     

Genetic variation in wood stiffness and strength properties of hybrid larch (Larix gmelinii var. japonica × L. kaempferi)

Genetic parameters for wood stiffness and strength properties were estimated in a 29-year-old hybrid larch stand (Larix gmelinii var. japonica × Larix kaempferi). The study included 19 full-sib larch families from Hokkaido, northern Japan. Implications of these genetic parameters in wood quality improvement are subsequently discussed. Traits included in the analyses were the dynamic modulus of elasticity of green logs (E _log), the modulus of elasticity (MOE), the modulus of rupture (MOR), compression strength parallel to the grain (CS) in small clear specimens, wood density (DEN), and diameter at breast height (DBH). DEN had the lowest coefficients of variation and MOE the highest. The narrow-sense heritability estimates of E _log, MOE, MOR, and CS were 0.61, 0.44, 0.60, and 0.43, respectively, and those of DEN and all mechanical properties increased from an inner to outer position within the stem. E _log and DEN had high positive phenotypic (0.52–0.83) and genetic (0.70–0.92) correlations with MOE, MOR, and CS. The mechanical properties of the inner position of the stem had rather high phenotypic and genetic correlations with those of the outer position and overall mean. The predicted gains in wood stiffness (E _log and MOE) were higher than those of the strength properties (MOR and CS). The predicted correlated responses in MOE, MOR, and CS when selecting for E _log and DEN were 72.6%–97.8% of a gain achievable from direct selection of these traits. DBH showed an insignificant correlation with all mechanical properties, although selection of this trait had a slightly negative effect on the mechanical properties.     

Optimum age for selection based on a time trend of genetic parameters related to diameter growth in seedling seed orchards of Eucalyptus pellita in Indonesia

The time trend of genetic parameters related to diameter growth was investigated using data at ages from 1 to 6 years to determine the optimum age for selection in four seedling seed orchards of Eucalyptus pellita in South Kalimantan and Riau (Sumatra), Indonesia. The seed orchards at each location were from three geographically distinct provenances from Papua New Guinea. The pooled sum of squares and sum of cross products derived from an analysis of variance of growth of the three provenance populations were used to estimate genetic parameters at each location. Because the genetic parameters at rotation age, 8 years in this study, were not available, they were estimated using functions derived from their time trends. Phenotypic variances and genetic variances calculated at each age were converted to the corresponding square roots, and then analyzed by the linear regression using means as independent variables. The trend of juvenile–mature correlation was fitted by a modified Richards function with the ratio of the older diameter mean to the juvenile diameter as an independent variable. Early selection always resulted in more genetic gain per year than selection at rotation age, and the optimum age for selection, where genetic gain per year was maximized, was found to be 4 and 5 years in the two locations.     

马尾松半同胞家系多年度测定与早期选择

利用15年生的马尾松种子园自由授粉子代测定林多年份生长性状的观测数据,分析多年份家系间变异、家系表型、遗传相关、遗传力的变化趋势。结果表明,马尾松半同胞家系之间生长存在极显著差异,并主要由遗传所控制。马尾松家系选择从8年生开始是可行的,胸径生长是早期选择较好指标,并讨论了早期选择应用问题。     

短轮伐期日本落叶松家系生长性状遗传参数的变化

以湖北省建始县长岭岗林场 15年生日本落叶松自由授粉家系子代测定林为研究对象 ,研究纸浆材轮伐期内不同年龄阶段生长性状的家系间遗传变异、早 -晚相关关系及主要遗传参数随时间变化的趋势 ,确定早期选择年龄及早期选择因子。结果表明 :各年龄胸径、树高不仅在家系水平上存在着极显著的变异 ,家系内个体间也存在着丰富的变异 ,具有很大的遗传改良潜力 ,家系和家系内个体选择是日本落叶松改良的主体 ;性状的方差分量、遗传力、变异系数在树木生长过程中一直处于动态变化中 ,并表现出一定的规律性 ;胸径、树高的早 -晚相关十分紧密 ,且这种相关关系主要受遗传因素制约 ;对胸径和树高进行家系早期选择的最适年龄为 6年生 ,进行家系内个体选择年龄为 8年生 ,胸径作为早期选择指标较树高更能准确地表达成熟时的信息。     

Juvenile genetic parameter estimates for vigour,stem form,branching habit and survival in three radiata pine (<Emphasis Type=Italic>Pinus radiata</Emphasis> D.Don) progeny tests in Galicia,NW Spain

Individual and family heritabilities, as well as phenotypic and genetic correlations were estimated 2 and 3 years after plantation, in progeny tests carried out in plantations of open-pollinated Pinus radiata D.Don progeny located at three different sites in Galicia (NW Spain). The following factors were considered: survival, growth (free growth, height, diameter, volume, height/diameter ratio), form (number of branches, number of whorls, number of branches per whorl, number of branches per tree height meter, number of ramicorn branches, diameter of the thickest branch, internode length, branch angle, stem straightness, stem sinuosity, number of forks) and resistance (frost and insect resistance). Each plantation contained 50 female parents that had been selected as plus trees in genetically unimproved plantations in Galicia, as well as 6 female parents selected from the radiata pine breeding programme in the Basque Country (northern Spain) and two commercial lots of seed from Galicia, as controls. Individual heritabilities varied from low to high levels for each trait studied. Family heritabilities followed similar trends for individual heritabilities, but were of much greater magnitude. The results suggested that all traits except the number of branches per whorl and insect resistance could be expected to respond to selection based on individual performance. The less heritable traits could be improved by progeny testing. Height and diameter were strongly and positively correlated, and both traits were also correlated with the number of branches, the number of whorls and the branch diameter. The results are compared with previously published data and discussed in relation to the implications for breeding activities.     

Estimation of genetic variances in flood tolerance of poplar and selection of resistant F1 generations

Five Aigeiros section poplar clones were adopted as parents to produce five full-sib families through cross-breeding. Morphological, ecophysiological, and growth characteristics of the five parents and their 15 superior F1 generations were investigated during 45 days of flooding followed by a 10-day recovery period. Cuttings were subjected to two treatments: watered (control) and flooded to 10 cm above the soil surface. Results showed that flooded cuttings showed significant reduction in growth of height, root-collar diameter and leaf area, and root and total biomass yield. All 20 clones formed hypertrophied lenticels and adventitious roots by day 6–14 of flooding. In flooded cuttings, net photosynthesis, stomatal conductance, transpiration, and chlorophyll fluorescence were decreased significantly compared with the control. After flooding ended, all plants recovered rapidly. Generally, progenies showed higher growth of height, root-collar diameter, root biomass and leaf area than their parents both under flooding and control conditions, showing that heterosis existed in F1 generations, regardless of flooding. However heterosis was lower under flooding conditions than in the control. Under flooding, the highest heterosis of higher-parent in height and root-collar diameter were 68.63 and 20.83%, respectively. Variability of flood tolerance among progenies was clear in growth of height and root-collar diameter. Selection criteria for parents in cross-breeding were different between control and flooding. Relative effect values of the specific combining ability (SCA) and relative effect values of the general combining ability (GCA) of parents were more important than their flood tolerance. Progenies with a higher level of flood tolerance could be obtained, even from parents intolerant to flooding. In terms of breeding, height growth would be most important characteristic to measure in flooding conditions, and root-collar diameter growth was also very useful. Based on all measured values, the tested 20 clones were classified into three groups using hierarchical cluster analysis. Clones Lu, E4, E9, E29, A2, A8, A9, B1, B3, B4, and D8, were flood-tolerant. Clones Lf, Ha, Lm, D1, D7, F9, and F21 were moderately flood-tolerant. Clones Sm and F13 were flood-susceptible.     

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.     

The utility of the predictive decapitation test as a tool for early genetic selection for Hypsipyla tolerance in big-leaf mahogany (Swietenia macrophylla King)

The plantation silviculture of mahogany (Swietenia spp.) has been severely limited by the attack of the mahogany shoot borer (Hypsipyla spp.), which greatly reduces or nullifies the commercial timber value of attacked trees by causing forking low on the stem. Selection for resistance, including tolerance (the capacity to retain apical dominance after attack), is widely considered to have potential as one element in an integrated pest management system. It has been suggested that the response of young seedlings to a predictive decapitation test might be useful as a means of detecting genotypes with high tolerance. This paper describes a pilot provenance/progeny experiment aimed at exploring this hypothesis. The number of shoots produced in response to attacks in the first year of field growth by Costa Rican material was found to be significantly correlated with response to decapitation in the nursery, on both individual tree and family mean bases. It appears, therefore, that the decapitation test could have a role in early selection for tolerance of Hypsipyla in mahogany. However, the presence of within-provenance genetic variation in response to Hypsipyla attack was not established.