Estimates of genetic parameters for growth and wood properties in Eucalyptus pellita F. Muell. to support tree breeding in Vietnam

Eucalyptus pellita demonstrated good growth and wood quality traits in this study, with young plantation grown timber being suitable for both solid and pulp wood products. All traits examined were under moderate levels of genetic control with little genotype by environment interaction when grown on two contrasting sites in Vietnam. Eucalyptus pellita currently has a significant role in reforestation in the tropics. Research to support expanded of use of this species is needed: particularly, research to better understand the genetic control of key traits will facilitate the development of genetically improved planting stock. This study aimed to provide estimates of the heritability of diameter at breast height over bark, wood basic density, Kraft pulp yield, modulus of elasticity and microfibril angle, and the genetic correlations among these traits, and understand the importance of genotype by environment interactions in Vietnam. Data for diameter and wood properties were collected from two 10-year-old, open-pollinated progeny trials of E. pellita in Vietnam that evaluated 104 families from six native range and three orchard sources. Wood properties were estimated from wood samples using near-infrared (NIR) spectroscopy. Data were analysed using mixed linear models to estimate genetic parameters (heritability, proportion of variance between seed sources and genetic correlations). Variation among the nine sources was small compared to additive variance. Narrow-sense heritability and genetic correlation estimates indicated that simultaneous improvements in most traits could be achieved from selection among and within families as the genetic correlations among traits were either favourable or close to zero. Type B genetic correlations approached one for all traits suggesting that genotype by environment interactions were of little importance. These results support a breeding strategy utilizing a single breeding population advanced by selecting the best individuals across all seed sources. Both growth and wood properties have been evaluated. Multi-trait selection for growth and wood property traits will lead to more productive populations of E. pellita both with improved productivity and improved timber and pulp properties.

Genetic variation in growth and wood-quality traits of Corymbia citriodora subsp. variegata across three sites in south-east Queensland, Australia

Ten growth or wood-quality traits were assessed in three nearby Corymbia citriodora subsp. variegata (CCV) open-pollinated family-within-provenance trials (18 provenances represented by a total of 374 families) to provide information for the development of a breeding program targeting both pulp and solid-wood products. Growth traits (diameter at breast high over bark [DBH], height and conical volume) were assessed at 3 and 7 years of age. Wood-quality traits (density [DEN], Kraft pulp yield [KPY], modulus of elasticity [MoE] and microfibril angle [MfA]) were predicted using near-infrared spectroscopy on wood samples collected from these trials when aged between 10 and 12 years. The high average KPY, DEN and MoE, and low average MfA observed indicates CCV is very suitable for both pulp and timber products. All traits were under moderate to strong genetic control. In across- trials analyses, high (>0.4) heritability estimates were observed for height, DEN, MoE and MfA, while moderate heritability estimates (0.24 to 0.34) were observed for DBH, volume and KPY. Most traits showed very low levels of genotype × site interaction. Estimated age–age genetic correlations for growth traits were strong at both the family (0.97) and provenance (0.99) levels. Relationships among traits (additive genetic correlation estimates) were favourable, with strong and positive estimates between growth traits (0.84 to 0.98), moderate and positive values between growth and wood-quality traits (0.32 to 0.68), moderate and positive between KPY and MoE (0.64), and high and positive between DEN and MoE (0.82). However, negative (but favourable) correlations were detected between MfA and all other evaluated traits (−0.31 to −0.96). The genetic correlation between the same trait expressed on two different sites, at family level, ranged from 0.24 to 0.42 for growth traits, and from 0.29 to 0.53 for wood traits. Therefore simultaneous genetic improvement of growth and wood property traits in CCV for the target environment in south-east Queensland should be possible, given the moderate to high estimates of heritability and favourable correlations amongst all traits studied, unless genotype × site interactions are greater than was evident. © 2016 NISC (Pty) Ltd

Use of short-term breath measures to estimate daily methane production by cattle

Methods to measure enteric methane (CH4) emissions from individual ruminants in their production environment are required to validate emission inventories and verify mitigation claims. Estimates of daily methane production (DMP) based on consolidated short-term emission measurements are developing, but method verification is required. Two cattle experiments were undertaken to test the hypothesis that DMP estimated by averaging multiple short-term breath measures of methane emission rate did not differ from DMP measured in respiration chambers (RC). Short-term emission rates were obtained from a GreenFeed Emissions Monitoring (GEM) unit, which measured emission rate while cattle consumed a dispensed supplement. In experiment 1 (Expt. 1), four non-lactating cattle (LW=518 kg) were adapted for 18 days then measured for six consecutive periods. Each period consisted of 2 days of ad libitum intake and GEM emission measurement followed by 1 day in the RC. A prototype GEM unit releasing water as an attractant (GEM water) was also evaluated in Expt. 1. Experiment 2 (Expt. 2) was a larger study based on similar design with 10 cattle (LW=365 kg), adapted for 21 days and GEM measurement was extended to 3 days in each of the six periods. In Expt. 1, there was no difference in DMP estimated by the GEM unit relative to the RC (209.7 v. 215.1 g CH4/day) and no difference between these methods in methane yield (MY, 22.7 v. 23.7 g CH4/kg of dry matter intake, DMI). In Expt. 2, the correlation between GEM and RC measures of DMP and MY were assessed using 95% confidence intervals, with no difference in DMP or MY between methods and high correlations between GEM and RC measures for DMP (r=0.85; 215 v. 198 g CH4/day SEM=3.0) and for MY (r=0.60; 23.8 v. 22.1 g CH4/kg DMI SEM=0.42). When data from both experiments was combined neither DMP nor MY differed between GEM- and RC-based measures (P>0.05). GEM water-based estimates of DMP and MY were lower than RC and GEM (P<0.05). Cattle accessed the GEM water unit with similar frequency to the GEM unit (2.8 v. 3.5 times/day, respectively) but eructation frequency was reduced from 1.31 times/min (GEM) to once every 2.6 min (GEM water). These studies confirm the hypothesis that DMP estimated by averaging multiple short-term breath measures of methane emission rate using GEM does not differ from measures of DMP obtained from RCs. Further, combining many short-term measures of methane production rate during supplement consumption provides an estimate of DMP, which can be usefully applied in estimating MY.