A total of 1640 increment cores from 343 radiata pine ( Pinus radiata D. Don) families were sampled at two second-generation progeny trials, aged 6 and 7 years, for a detailed genetic study of juvenile wood quality traits. Density, microfibril angle (MFA), and modulus of elasticity (MOE) were determined from pith to bark using SilviScan® technology. Heritability was greatest for area-weighted density at the two sites (0.63 and 0.77, respectively), and the lowest for growth traits (<0.23). Genotype by environment interaction was low for all three wood quality traits. A positive genetic correlation between density and MOE (0.43), and a highly negative, and therefore, favourable genetic correlation between MFA and MOE (–0.92) were observed, implying that improvement of multiple juvenile wood properties is possible. The genetic correlations between whole-core wood quality traits and individual-ring measurements suggest that improvement for juvenile wood properties across the entire profile of the corewood including the innermost rings can be achieved. However, density, MFA, and MOE had unfavourable genetic correlations with diameter growth suggesting that selection for increased density and MOE, and reduced MFA in the absence of selection for growth will result in a genetic loss for growth rate.

The Forest Biology Research Cooperative recently established a series of loblolly pine clonal trials known as CCLONES (Comparing Clonal Lines on Experimental Sites). There are three primary levels of genetic structure in this study (parental, full-sib family, clone) that strengthen the power of CCLONES for examining genetic mechanisms and interactions with cultural treatments and locations. A fourth level of genetic structure can be added by considering the provenance of the parents. This report includes some preliminary results from the genetic analyses of 2 nd year growth traits that were recently measured at the CCLONES loblolly pine trials. The specific objectives of this report are 1) to determine heritability estimates for various growth traits for loblolly pine clones and seedlings, 2) to compare the genetic correlations between parents and families when grown as cuttings versus seedlings, and 3) to determine the genotype x environment interaction by looking at the genetic correlations for parents, families, and clones for paired trials. MATERIALS AND METHODSThe parental population consisted of twenty first-generation and ten second-generation selections from a larger population that is part of the Loblolly Pine Lower Gulf Elite Population. In addition two slow-growing parents were included. These selections represent the Atlantic Coastal Plain (ACP), Florida (FL), and Lower Gulf (LG) provenances of loblolly pine. These thirty-two elite loblolly pine parents were mated in a partial diallel design and created 70 full-sib families from which a total of 2,000 vegetatively propagated clones were generated. Rooted cuttings from approximately 1,000 of these clones from 61 full-sib families and seedlings from the same full-sib families were established at seven field sites across the southeastern United States utilizing a resolvable incomplete block design (Tests A-G).Each growth variable (2 nd year height, height increment, and crown width) was analyzed for cuttings and seedlings simultaneously with a bivariate analysis in ASREML. Narrow-sense heritability ( 2 h ) was estimated using the corresponding variance components. Type B genetic correlations for general combining ability ( between cuttings and seedlings were estimated in order to compare parental and family performance between propagule types. In order to quantify the extent of genotype x environment interaction, type B genetic correlations across pairs of trials were estimated for the clonal data.

Tree growth and vegetative propagation are complex but important traits under selection in many tree improvement programmes. To understand the genetic control of these traits, we conducted a quantitative trait locus (QTL) study in three full-sib families of Eucalyptus nitens growing at two different sites. One family growing at Ridgley, Tasmania had 300 progeny and two clonally replicated families growing at Mt. Gambier, South Australia had 327 and 210 progeny. Tree growth was measured over several years at both sites and percentages of roots produced by either stem cuttings or tissue culture were assessed in the two Mt. Gambier families. Linkage analysis of growth traits revealed several QTLs for later year traits but few for early year traits, reflecting temporal differences in the heritabilities of these traits. Two growth QTL positions, one on LG8 and another on LG11 were common between the Ridgley and Mt. Gambier families. Four QTLs were observed for each of the two vegetative propagation methods. Two QTLs for vegetative propagation on LG7 and LG11 were validated in the second family at Mt. Gambier. These results suggest that growth and vegetative propagation traits are controlled by several small effect loci. The QTLs identified in this study are useful starting points for identifying candidate genes using the Eucalyptus grandis genome sequence.

Quantifying foliar stable carbon isotope discrimination (Δ) is a powerful approach for understanding genetic variation in gas exchange traits in large populations. The genetic architecture of Δ and third-year height is described for more than 1,000 clones of Pinus taeda tested on two contrasting sites. b h 2 for Δ was 0.14 (±0.03), 0.20 (±0.07), and 0.09 (±0.04) at Florida, Georgia, and across sites, respectively. b H 2 for stable carbon isotope discrimination ranged from 0.25 (±0.03) at the Florida site to 0.33 (±0.03) at the Georgia site, while the across-site estimate of b H 2 was 0.19 (±0.02). For third-year height, b h 2 ranged from 0.13 (±0.05) at the Georgia site to 0.20 (±0.06) at the Florida site with an across-site estimate of 0.09 (±0.05). Broad-sense heritability estimates for third-year height were 0.23 (±0.03), 0.28 (±0.03), and 0.13 (±0.02) at the Florida site, Georgia site, and across sites, respectively. Type B total genetic correlation for Δ was 0.70±0.06, indicating that clonal rankings were relatively stable across sites, while for third-year height, rankings of clones were more unstable across the two trials b r B TG ¼ 0:55 AE 0:08 ð Þ . Thirdyear height and Δ were negatively correlated at the parental b r ADD ¼ À0:42 AE 0:33 ð Þ , full-sib family b r FS ¼ À0:54AE ð 0:25Þ, and clonal b r TG ¼ À0:30 AE 0:11 ð Þ levels, suggesting that genetic variation for Δ in P. taeda may be a result of differences in photosynthetic capacity. We conclude that Δ may be a useful selection trait to improve water-use efficiency and for guiding deployment decisions in P. taeda.

A successful clonal forestry program for loblolly pine based on rooted cutting technology needs to consider selection for both rooting ability and subsequent field growth. Rooting ability and second-year height were assessed in more than 2,000 clones from 70 full-sib families of loblolly pine. The bivariate analysis of rooting ability from five rooting trials and field growth from six field trials allowed for estimation of the genetic covariance between rooting ability and second-year height for parental effects, full-sib family effects, and the total genetic value of clones within full-sib family. There was a positive genetic relationship between rooting ability and second-year height at all three genetic levels. The genetic correlation at the parental level between rooting ability and second-year height b r B GCA ð Þ was 0.32. At the full-sib family level, the genetic correlation between traits b r B FS ð Þ was 0.39. The correlation of total genetic values of clones for rooting ability and second-year height b r B TG ð Þ was 0.29. The genetic gain in rooting ability and second-year height was estimated for a number of deployment options based on various selection scenarios using the best linear unbiased prediction (BLUP) values from the bivariate analysis. The deployment strategies compared were (1) half-sib family deployment, (2) full-sib family deployment, and (3) clonal deployment. Moderate to high family and clonal mean heritabilities, moderate to high type B genetic correlations, and substantial among-family and among-clone genetic variation indicate the potential for increasing rooting efficiency and improving growth.

Different methods for predicting clonal values were explored for diameter growth (diameter at breast height (DBH)) in a radiata pine clonal forestry program: (1) clones were analyzed with a full model in which the total genetic variation was partitioned into additive, dominance, and epistasis (Clone Only-Full Model); (2) clones were analyzed together with seedling base population data (Clone Plus Seedling (CPS)), and (3) clones were analyzed with a reduced model in which the only genetic term was the total genetic variance (Clone Only-Reduced Model). DBH was assessed at age 5 for clones and between ages 4 to 13 at the seedling trials. Significant additive, dominance, and epistatic genetic effects were estimated for DBH using the CPS model. Nonadditive genetic effects for DBH were 87% as large as additive genetic effects. Narrow-sense ( b h 2 ) and broad-sense ( b H 2 ) heritability estimates for DBH using the CPS model were 0.14 ± 0.01 and 0.26 ± 0.01, respectively. Accuracy of predicted clonal values increased 4% by combining the clone and seedling data over using clonal data alone, resulting in greater confidence in the predicted genetic performance of clones. Our results indicate that exploiting nonadditive genetic effects in clonal varieties will generate greater gains than that typically obtainable from conventional family-based forestry of radiata pine. The predicted genetic gain for DBH from deployment of the top 5% of clones was 24.0%-an improvement of more than 100% over family forestry at the same selection intensity. We conclude that it is best practice to predict clonal values by incorporating seedling base population data in the clonal analysis.

The phenotypic response of genotypes across different environments can be quantified by estimating the genotype by environment interaction (GxE). In a practical sense, GxE means that the relative performance of genotypes does not remain constant under all test conditions. Genetic parameters and genotype by environment interactions for wood density, growth, branching characteristics and stem straightness were investigated in eight radiata pine progeny trials derived from a second generation breeding population in Australia. Five trials were on the mainland, while three trials were in Tasmania. Generally, ĥ2 for density > branch angle > stem straightness > tree diameter > branch size; and significant ĥ2 was observed for all traits and at all trials with only two exceptions. Genetic correlations were estimated among the five traits, and a large negative genetic correlation observed between wood density and tree diameter indicated that a selection strategy should be developed in dealing with this adverse genetic correlation in advanced generations of breeding for radiata pine. Interactions for density, branch angle, and stem straightness were small within the two regions. Overall, branch angle had the least GxE, followed by density and stem straightness. Growth traits (tree diameter and branch size) tended to be the most interactive with substantial GxE present. Genotype by regional interactions (Mainland versus Tasmania) revealed that density and branch angle had the least interactions (ȓB = 0.98 and ȓB = 0.95, respectively). Branch size and tree diameter had the highest interactions among the two regions (ȓB = 0.55 and ȓB = 0.63, respectively). Within Tasmania, only branch size and tree diameter had a sizable interaction within the three sites. In contrast, there was little interaction for tree diameter among the Mainland trials. Branch size in the Mainland trials had a similar size of interaction as in Tasmania. Further research is recommended in identifying the cause of GxE for tree diameter and branch size in radiata pine across the entire radiata pine estate in Australia.

Genetic variation for wood quality traits and diameter growth for radiata pine (Pinus radiata D. Don) at age 20/21 years was estimated from eight trials in Australia. The traits studied were wood density, acoustic time-offlight (an indirect measure of stiffness) and diameter at breast height (DBH). Wood density and DBH exhibited significant additive genetic variation whereas non-additive effects were not significantly different from zero. Time of flight was also not significantly different from zero for both additive and non-additive effects, respectively. Average single-site heritability estimates (±SE) for wood density and DBH were 0.38±0.10 and 0.16±0.08, respectively. Pooledsite heritability estimates for wood density and DBH were 0.38±0.10 and 0.08±0.10, respectively. For density, there was little evidence of genotype-by-environment interaction (GEI) across the eight trials at the additive level (type B additive genetic correlation; r BADD =0.73±0.08) and type B genetic correlation for full-sib families (r BFS =0.64±0.08). In contrast, the type B additive genetic correlation for DBH was lower, (r BADD =0.51±0.14), suggesting evidence of GEI. However, type B genetic correlation for full-sib families was moderate (0.63±0.11) for DBH, suggesting that there may be some stable full-sib families. On the basis of the results of this study, GEI should be considered in order to optimise deployment of improved germplasm in Australia.