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.