Genetic variation in growth, stem straightness, pilodyn and dynamic modulus of elasticity in secondgeneration progeny tests of Acacia mangium at three sites in Vietnam

New Forests (2015) 46:577–591 DOI 10.1007/s11056-015-9484-6 Genetic variation in growth, stem straightness, pilodyn and dynamic modulus of elasticity in second-generation progeny tests of Acacia mangium at three sites in Vietnam Phi Hong Hai1 • La Anh Duong1 • Nguyen Quoc Toan2 • Trieu Thi Thu Ha2 Received: 30 July 2014 / Accepted: 23 April 2015 / Published online: 28 April 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract 164 open-pollinated families of Acacia mangium from six different genetic groups were tested in three second-generation progeny tests planted at Tuyen Quang and Ba Vi in northern Vietnam and Bau Bang in the south All trees were measured to estimate individual heritabilities and genetic correlations for growth traits, stem straightness and pilodyn in the three trials, and dynamic modulus of elasticity (MoEd) of standing trees was only assessed in Tuyen Quang There were significant differences between families for growth traits, stem straightness, pilodyn penetration and predicted MoEd Heritabilities of growth traits, stem straightness, pilodyn and dynamic modulus of elasticity were low to moderate (h2 = 0.11–0.30) The coefficient of additive genetic variation for DBH, pilodyn and MoEd were moderate at age or years (CVa = 4.9–9.4 %) Genetic correlations between stem straightness, pilodyn and growth traits were favourable but weak, while those between growth traits and dynamic modulus of elasticity were weak and unfavourable The substantial coefficients of additive genetic variation and significant heritabilities for all traits indicate that it should be possible to use a selection strategy that combines improvements in growth, stem straightness, and wood quality for A mangium in Vietnam The site–site genetic correlations between the two northern trials and Bau Bang site were low for growth traits, indicating that G E effects are of practical importance for growth and different deployment populations will be required for different sites Keywords Acacia mangium Á Genetic variation Á Growth Á Pilodyn Á Wood stiffness & Phi Hong Hai phi.hong.hai@vafs.gov.vn Department of Planning and Sciences, Vietnamese Academy of Forest Sciences, Duc Thang, Bac Tu Liem, Ha Noi, Viet Nam Institute of Forest Tree Improvement and Biotechnology, Vietnamese Academy of Forest Sciences, Duc Thang, Bac Tu Liem, Ha Noi, Viet Nam 123 578 New Forests (2015) 46:577–591 Introduction Acacia mangium Willd was introduced into Vietnam in the 1980s The species has become important commercially (Nghia 2003; Turnbull et al 1997), especially in northern Vietnam, because it displays adaptability to a wide range of site conditions, produces straight stems, and grows faster than alternative short-rotation plantation species such as A auriculiformis and Eucalyptus urophylla It produces pulp logs and small sawlogs on rotations as short as years At present, A mangium occupies about 500,000 of the total area of forest plantation of over million This makes A mangium the most important acacia species in Vietnam However, the productivity of A mangium plantations in Vietnam is moderate compared to rest of South-East Asia (Harwood and Nambiar 2014), averaging 15 m3 ha-1 yr-1 (Nghia 2003), although it can be higher in the south (Kha 2003) The natural distribution of A mangium includes northern Queensland (QLD, Australia), Western Province, Papua New Guinea (PNG) and Indonesia (West Papua, adjacent to PNG and outlying populations in the Aru Islands and Ceram) Commonly used seed material in Vietnam plantations includes origins from provenances in both QLD and PNG (Kha 2003) Provenances from PNG consistently show better growth than those from QLD or local commercially-sold seed (Harwood and Williams 1992; Kha 2003; Nghia 2003) Within QLD, provenances from the Cairns region (16°–18°S) were slower-growing than those from Claudie R.—Iron Range in far north QLD (FNQ) (11°–13°S) A breeding program for A mangium in Vietnam commenced in 1996 In the first generation, 150 families from 10 provenances of A mangium were tested in two progeny tests in northern and southern Vietnam, which were selectively thinned to convert them to seedling seed orchards At age years, significant site by family interactions for growth between the northern and southern sites were reported (Dao 2012) 150 superior individual trees in the southern trial were selected using an index that combined growth rate and stem straightness, clonally propagated and established in a clonal seed orchard in southern Vietnam A study in the first generation progeny test in northern Vietnam showed that narrow-sense heritabilities for growth traits ranged from 0.12 to 0.33 at 11 years (Dao 2012), while heritabilities were higher (0.21–0.40) for wood basic density, cellulose content, shrinkage, collapse, stiffness and strength Age-age genetic correlations were strong for growth traits measured at 3, 5, and 11 years To continue the breeding program, second-generation progeny tests were established using individual seedlots collected from superior trees in the northern progeny test and the clonal seed orchard Acacia mangium is known to have exceptionally low allelic diversity compared to other forest trees, as assessed by isozyme analysis (Butcher et al 1998) If there were correspondingly low levels of quantitative genetic variation in production traits, little genetic gain could be made from breeding, beyond the gains of initial provenance selection Therefore, the aim of this paper was to determine the prospects for ongoing genetic improvement of A mangium in Vietnam for solid wood production The specific questions addressed are: (1) How strong is the genetic variation and degree of genetic control for growth traits, stem straightness, pilodyn and dynamic stiffness of A mangium from the second generation progeny tests at Tuyen Quang, Ba Vi and Bau Bang?; (2) How strong are the genotype by environment interactions for growth?; (3) How large are the predicted gains from the breeding of A mangium? 123 New Forests (2015) 46:577–591 579 Materials and methods Material A total of 164 families were used to establish the second-generation progeny tests in the current study Families were from different genetic groups, including four groups originating from PNG and FNQ, which were collected from the first-generation progeny tests or clonal seed orchards, as well as two infusion groups from seed orchards in the Philippines and Australia Some of families come from sib (sister) trees descended from the same mother (original seed tree in QLD or PNG) in the first-generation trials and the clonal seed orchard Numbers of families in each genetic group, families common to pairs of sites and families across the three trials are shown in Table Location and trial description The second-generation progeny tests were established at Ba Vi in Hanoi Province and Son Duong, Tuyen Quang Province, both in northern Vietnam and Bau Bang in Binh Duong province in southern Vietnam Site conditions, experimental designs, site preparation and fertilizer applications are described in Table The trials were planted during the rainy seasons of 2008 or 2009, in September at Ba Vi and Tuyen Quang, and August in Bau Bang Planting materials were 4-month-old seedlings, raised in polythene bags in a soilbased potting mixture The tests at Ba Vi and Tuyen Quang used 10 replicates and 3-tree plots, but the test at Bau Bang only used replicates and 2-tree plots All tests used rowcolumn designs generated by the computer program CycDesigN (Williams et al 2002), providing 2-dimensional incomplete blocking (rows and columns) within replicates Table Number of A mangium families in six genetic groups, families common to pairs of sites and families in each progeny test Genetic group Total number of families in group Number of families in each site Ba Vi Tuyen Quang Bau Bang CSO-PNG 84 60 44 CSO-FN 11 SSO-PNG 40 23 14 31 SSO-FN IN-SSO-FN 5 100 IN-SSO-PNG 15 15 164 112 70 Number of families common to Bau Bang 50 35 Number of families common to Tuyen Quang 54 Total families tested Number of families tested in all three sites 52 28 CSO, Families collected from Vietnam clonal seed orchard; SSO, families collected from Vietnam 1st opened-pollinated seed orchard; IN-SSO, Families collected from international seed orchard; PNG, FNQ, family group originating from PNG and FNQ 123 580 New Forests (2015) 46:577–591 Table Description of A mangium progeny tests Latitude Ba Vi–Ha Noi Tuyen Quang Bau Bang–Binh Duong 21°070 N 21°490 N 11°320 N 0 Longitude 105°26 E 105°13 E 105°560 E Altitude 60 m 100 m 50 m Soil type Ferralitic clay loam with heavy lateritization Ferralitic clay loam Sandy alluvium Annual rainfall (mm) 1680 1641 1917 Annual average temperature (°C) 23.2 22.9 26.2 Site preparation Slash burned and ripped Slash burned and holes dug Slash burned and ploughed Planting time September 2008 September 2009 August 2009 Fertilizer (per tree) kg cattle manure ? 0.2 kg NPK kg cattle manure ? 0.2 kg NPK 0.5 kg micro-organic fertilizer ? 0.2 kg NPK Replicates 10 10 Rows/replicate 16 10 10 Columns per replicate 7 10 Trees per plot 3 Spacing 4m92m 4m92m 4m92m Design Assessments Total tree height (HT), diameter at breast height (DBH) and stem straightness (STR) of all trees were recorded annually to years at Ba Vi and years at the other two trials The stem straightness was scored using a scale with classes: for a very crooked stem with [2 serious bends (serious bends occur when the main stem is bent to the right or left with more than 20° along its axis); for crooked stem with serious bends; for slightly crooked stem with serious bend and/or [2 small bends (small bends occur when the main stem is bent to the right or left with \10° along its axis); for almost straight stem with 1–2 small bends and for a perfectly straight stem Stem volume over bark of each tree was calculated for the last measure of each trial using the following formula: VOL ¼ p  HT  DBH =4  0:45=10 where VOL is stem volume (dm3/tree), DBH (cm), HT (m) and 0.45 is the form factor The form factor of 0.45 was the same as that from a study of A mangium in Sumatra, Indonesia (Hardiyanto and Nambiar 2014) 123 New Forests (2015) 46:577–591 581 Pilodyn penetration was measured for all trees in the tests by using a J Forest Pilodyn, by removing a small section of the bark at 1.3 m above the ground and taking two readings for each tree, one from the east side and one from the north Acoustic measurements at the Tuyen Quang trial were made using a FAKOPP microsecond timer (Ross 1999) This instrument measures transmission of sound waves between a transmitting and a receiving probe Probes were positioned at 0.1 m and 2.0 m above the ground Stress waves are generated by tapping the transmitting probe with a hammer Sound transit time is converted to sound flight velocity through the outer stem wood using the distance between the two probes This velocity is used to predict dynamic modulus of elasticity (MoEd in GPa) according to: MoEd ¼ Green density  velocity2 where green density is assumed to be a constant at 1060 kg m-3 for A mangium (Moya and Mun˜oz 2010) Statistical analysis Single-site analysis Some of individuals with obviously hybrids morphology in the tets were excluded from data sets before single-site analysis Stem straightness was not normally distributed It was assumed that this trait was controlled genetically by an underlying polyfactorially-determined liability scale (Falconer and Mackay 1996), and that the given scores were caused by imposed thresholds Prior to analysis class scores were therefore transformed into asymptotic ‘normal scores’ (Gianola and Norton 1981) in order to adjust for non-adequate or variable spacing of classes and to improve the efficiency of subsequent analyses (Ericsson and Danell, 1995) The statistical analysis was based on individual tree observations according to the linear mixed model (1): y ¼ XB m þ XP p þ ZW w þ ZN n þ ZT t þ ZF f þ e with y ¼ ðy01 ; y02 ; ; y0n Þ0 , m ¼ ðm01 ; m02 ; ; m0n Þ0 , w02 ; ; w0n Þ0 , n ¼ ðn01 ; n02 ; ; n0n Þ0 , f ¼ ðf 01 ; f 02 ; ; f 0n Þ0 , ð1Þ p ¼ ðp01 ; p02 ; ; p0n Þ0 , e ¼ ðe01 ; e02 ; ; e0n Þ0 , X w ¼ ðw01 ; ¼ RÈ XBi , X ¼ RÈ XPi , ZW ¼ RÈ ZWi , ZN ¼ RÈ ZNi , ZT ¼ RÈ ZTi and ZF ¼ RÈ ZFi , RÈ denotes the direct sum, and i the number of traits from to n, y is the vector of individual observations for the different traits, m is the vector of fixed effect of replicate, p is the vector of fixed effect of genetic group, w is the vector of random row within replicate effect, n is the vector of random column within replicate effect, t is the vector of random effect of plot for assessments at age and age 4, f is the vector of random family within genetic group effects, and e is the vector of random residuals XB ; XP ; ZW ; ZN ; ZT and ZF are incidence matrix relating m, p, w, n, t and f to y The data analyses were implemented using ASReml software (Gilmour et al 2006) Assuming a multivariate normal distribution (MND), the expected mean and covariance were: 123 582 New Forests (2015) 46:577–591 WI 0 w 6n7 N  I 7 TI V6 t7¼6 4f5 0 0 0 e 0 FA 0 7 7 RI ð2Þ where is a null matrix, I is an identity matrix of order equal to the total number of rows, columns, plots, genetic, È Éand residuals, respectively, È É and Èis theÉ direct (Kronecker) È É product operation W ¼ rwi wj , N ¼ frni ni g, T ¼ rti tj , F ¼ rfi fi , and R ¼ rei ej are the row, column, plot, family and residual variance–covariance matrices between trait i and j, denoting variance when i = j A is the additive genetic relationship matrix To ensure that the variance–covariance matrix was positive definite, restrictions were in some cases applied to the parameters The significance of seed source effects was assessed using F-tests Genetic parameters Age-age and trait–trait genetic correlations and heritabilities were simultaneously estimated based on multivariate REML analysis using model (2) Family variance (r2f ), phenotypic variance (r2P ), plot variance (r2t ) and environmental variance (r2e ) for different traits and ages were estimated using ASReml The estimated variance components were used to calculate the narrow-sense heritabilities for the characters under consideration Open-pollinated families in the progeny test came from open-pollinated parent trees in seed orchards or wild stands There is some relatedness among the families within firstgeneration seed orchards Therefore, some degree of inbreeding (about 10 %) was expected, as a result of relatedness among families, particularly in the seed orchards the coefficient of relationship within families was assumed to be 0.33, making heritability values more conservative than if a value of 0.25 was assumed (Gilmour et al 2006) The additive genetic variance (r2a ), total phenotypic variance (r2P ) and individual-tree heritability (h^2 ) estimates were calculated as follows (Squillace 1974): r2a ¼ 3r2f r2P ¼ r2f þ r2t þ r2e and h^2 ¼ r2f r2a þ r2t þ r2e Coefficient of additive variation (CVa), additive genetic correlation (^ ) and phenotypic correlation (^ rP ) between traits or between ages were estimated as: 100 X a r^a ¼ ra1 ra2 rP1 P2 r^P ¼ rP1 rP2 CVa ¼ where X is the phenotypic mean, ra1 a2 and rP1 P2 are the genotypic and phenotypic covariance between two traits, respectively ra1 , ra2 and rP1 , rP2 are the genotypic and phenotypic standard deviations of trait and trait 2, respectively Standard errors of the estimates of heritabilities, genotypic and phenotypic correlations were calculated using a 123 New Forests (2015) 46:577–591 583 standard Taylor series approximation implemented in the ASReml program (Falconer and Mackay 1996) Predicted gain from genetic selection was calculated according to Mullin et al (1992) as GY ¼ in;N h^2Y rPY where Gy is the predicted selection gain, and in,N is the intensity of selection (10 %) based on selection of n genotypes from N tested Values for in,N were derived from Becker (1992) Across-site analysis Genetic correlations between sites were estimated based on multivariate REML analysis, by treating measurements from different sites as different traits based on model (2) In the across-site analysis R ¼ RÈ Rn where Rn is the individuals in trial n All off-diagonal elements were assumed to be zero for combinations of traits measured in different trials The aim of this analysis was to test the significance of genotype by environment (G E) interactions Log likelihood ratio tests were used to test if the correlations were significantly different from one, and also to test if the correlations between different pairs of trials differed significantly Results Differences between genetic groups for the growth traits (HT, DBH and VOL) were significant only in the Ba Vi test In contrast, significant differences among genetic groups were found for the quality traits of STR and pilodyn at all three tests, and MoEd at Tuyen Quang (Table 3) Trees descended from the PNG provenances grew slightly faster than trees from the FNQ provenances at Ba Vi The infusion families of international seed orchards grew slower than the selected families from seed orchards in Vietnam However, families originating from FNQ had higher density (lower pilodyn) and higher dynamic modulus of elasticity than those from PNG The best growth was recorded at Bau Bang, where mean annual increment of DBH and HT was 4.3 cm/year and 4.3 m/year respectively, followed by Tuyen Quang (2.6 cm; 2.5 m) and Ba Vi (2.0 cm; 1.8 m) Ranking of families (data not presented) indicated that the best performing families in the three sites were among those selected from the clonal seed orchard at Bau Bang Heritability estimates for year or growth traits, pilodyn and dynamic modulus of elasticity ranged from low to moderate at all sites (Table 4) The heritabilities of growth traits in the Ba Vi test at years were higher than those at years in the other two sites Heritabilities for stem straightness were low at all sites The calculated coefficient of additive variation (CVa) was moderate for all studied traits at the three sites, ranging from 4.9 % to 9.4 % for HT and DBH CVa for DBH was higher than for HT at all sites Similarly, CVa ranged from 6.1 to 7.3 % for STR, Pilodyn and MoEd (Table 4) Predicted gain from selection of the best 10 % of trees varied from 12.4 to 15.6 % for growth traits, 8.7–10.3 % for stem straightness and 10.8–11.8 % for pilodyn at three tests and 11.3 % for MoEd at Tuyen Quang test Within each site, positive genetic correlations were observed among all the combinations of traits that were assessed, except for correlation between DBH and MoEd in the Tuyen Quang test (Table 5) Stem straightness (STR) showed consistent positive genetic 123 584 New Forests (2015) 46:577–591 Table Genetic group means for studied traits at age 3–4 years in the 2nd progeny test Genetic group Survival (%) DBH (cm) HT (m) VOL (dm3/tree) STR (score) Pilodyn (mm) MoEd (GPa) At Ba Vi (4 year old) CSO-PNG 82.4 8.3 7.2 20.1 3.8 14.3 CSO-FNQ 90.0 8.1 7.1 19.1 3.5 13.0 SSO-PNG 85.0 8.1 7.2 18.2 3.6 13.8 SSO-FNQ 84.2 7.9 7.0 17.9 3.4 12.3 IN-SSO-PNG 83.2 8.0 7.1 16.2 3.5 15.1 IN-SSO-FNQ 81.7 7.3 6.9 15.5 3.8 13.4 F probability ** *** *** *** *** *** At Tuyen Quang (3 year old) CSO-PNG 72.8 8.9 7.6 23.6 3.8 14.0 15.7 CSO-FNQ 78.6 8.3 7.2 20.1 3.5 11.5 18.3 SSO-PNG 76.7 7.8 6.9 16.5 3.6 13.3 16.8 SSO-FNQ 75.0 7.2 6.6 13.7 3.3 10.7 18.8 F probability ns ns ns ns *** *** *** At Bau Bang (3 year old) CSO-PNG 75.0 13.2 13.2 99.1 3.4 14.4 CSO-FNQ 73.0 13.0 12.7 94.3 3.7 13.1 SSO-PNG 78.4 13.0 12.7 93.9 3.6 14.3 SSO-FNQ 74.2 13.2 12.5 87.8 3.3 12.9 F probability ns ns ns ns *** *** ns not significant * F-probability \ 0.05; *** F-probability \ 0.001 correlations with DBH The estimates obtained were from 0.25 to 0.37 at three sites The positive correlations between DBH and pilodyn, and the negative correlation between DBH and MoEd were non-significant The log likelihood ratio test showed that the genetic correlations for growth traits between Tuyen Quang and Bau Bang, and between Ba Vi and Bau Bang, were different from 1, but the correlations between Tuyen Quang and Ba Vi did not differ significantly from Family-by-site interactions between the two northern sites and Bau Bang were significant (p \ 0.001) for Pilodyn (Table 6) Genetic correlations for STR between pairs of sites were all positive and non-significant (p [ 0.05) Discussion Growth performance Comparisons of growth rate between sites showed that VOL at Ba Vi were lower at age of years, having \20 % of the growth at Tuyen Quang and 85 % of the growth at Bau Bang In a series of species and provenance trials, Kha (2003) and Nghia (2003) also reported that A mangium at Tuyen Quang and Bau Bang performed better than Ba Vi At Tuyen Quang, site conditions are more favourable for A mangium than at Ba Vi, with 123 New Forests (2015) 46:577–591 585 Table Mean values, narrow-sense heritability (h^2 ), additive coefficient of variation (CVa) and predicted gain (GY %) based on a selection intensity of 1.755 (10 % selected) for studied traits at different ages in each site h^2 CVa GY % 8.12 0.26 ± 0.05 8.9 11.6 7.12 0.22 ± 0.05 4.9 10.8 19.53 0.25 ± 0.05 3.48 0.15 ± 0.04 7.0 10.3 13.94 0.25 ± 0.05 7.1 12.3 7.85 0.27 ± 0.06 9.4 15.4 7.57 0.24 ± 0.06 6.1 12.8 18.12 0.29 ± 0.06 Trial Age Trait Unit Mean Ba Vi DBH cm HT m VOL dm3/tree STR Score Pilodyn mm DBH cm HT m VOL dm3/tree STR Score Pilodyn mm Tuyen Quang Bau Bang 3.26 0.10 ± 0.04 7.0 9.9 17.52 0.21 ± 0.05 6.1 10.8 7.82 MoEd GPa 0.15 ± 0.05 7.3 11.8 DBH cm 13.0 0.14 ± 0.09 9.3 13.3 HT m 12.9 0.30 ± 0.09 7.7 12.4 VOL dm3/tree 95.6 0.17 ± 0.08 STR Score Pilodyn mm 3.54 0.11 ± 0.09 6.4 8.7 13.68 0.22 ± 0.05 7.4 11.7 deep, fertile soil (Nghia 2003) Also, the soil and climate are more favourable at Bau Bang (the south of Vietnam) than at Ba Vi (the north), there being deep soil and light soil texture as well as no temperature limitation in the winter months (Nghia 2003) The soil at Ba Vi was a yellow ferralitic, clay loam with strong laterisation evident in the profile, acidic (pH 3.5–4.5), and infertile, with low levels of phosphorus and potassium (Kha 2003) The natural provenances were not tested in the present study Number of families in each genetic group is not similar, some groups have 14–60 families, but some groups only have 4–9 families (Table 1) However, the results at age three/four years as reported here clearly showed that trees derived from PNG provenances were noted not only for fast growth but also for high frequency of single-stemmed trees with a good clear bole, as shown by high scoring for stem straightness (Table 3) and low frequency of upright branches on the lower part of the stem (data not presented) Therefore, additional imports and selections focusing on these provenances are recommended to augment the genetic base of these provenances already established in the second-generation progeny tests in Vietnam Consistent differences in growth performance among natural provenances of A mangium have been demonstrated in many trials across a number of countries (Harwood and Williams 1992) Provenances from the south west of Western Province, PNG, and adjacent Western Papua display the fastest growth, followed by Claudie River from FNQ (13°S) and then provenances from further south in Queensland (16°–18°S), with outlying provenances from the Indonesian island of Ceram, and Piru in Western Papua, growing the slowest The significant genetic variation in pilodyn and dynamic modulus of elasticity demonstrated in our study was also reported in other studies in A mangium (Dao 2012; Thinh et al 2011) and A auriculiformis (Aggarwal et al 2002; Firmanti et al 2007; Kumar et al 1987; Mahat 1999) Mossman (QLD Cairns Region) was the best provenance of A 123 586 Table Genetic (^ ), phenotypic correlations (^ rP ) and standard errors of correlations within parenthesis between growth traits and quality traits (straightness, pilodyn and dynamic stiffness in the progeny tests at Ba Vi, Tuyen Quang and Bau Bang) New Forests (2015) 46:577–591 r^a Trait–trait r^P In Ba Vi test DBH versus VOL 0.99 ± 0.01 0.97 ± 0.001 HT versus VOL 0.97 ± 0.03 0.75 ± 0.009 DBH versus STR 0.25 ± 0.15 0.14 ± 0.02 DBH versus Pilodyn 0.31 ± 0.14 0.05 ± 0.02 In Tuyen Quang test DBH versus VOL 0.99 ± 0.006 0.96 ± 0.002 HT versus HT 0.86 ± 0.07 0.67 ± 0.02 DBH versus STR 0.37 ± 0.23 0.10 ± 0.03 DBH versus Pilodyn 0.23 ± 0.15 0.06 ± 0.03 -0.31 ± 0.24 -0.06 ± 0.04 DBH versus MoEd In Bau Bang test Table Genetic correlations between sites for height, diameter, volume, stem straightness and pilodyn DBH versus VOL 0.99 ± 0.02 0.96 ± 0.003 HT versus VOL 0.99 ± 0.05 0.79 ± 0.017 DBH versus STR 0.33 ± 0.03 0.02 ± 0.08 DBH versus Pilodyn 0.27 ± 0.17 0.03 ± 0.02 Trait HT Site Ba Vi Tuyen Quang 0.68 ± 0.17*** Tuyen Quang 0.75 ± 0.17*** Tuyen Quang 0.67 ± 0.18*** Tuyen Quang 0.25 ± 0.31ns Tuyen Quang Ba Vi 0.44 ± 0.41ns 0.48 ± 0.43ns Ba Vi Pilodyn 0.16 ± 0.37ns 0.08 ± 0.39ns Ba Vi STR 0.12 ± 0.32ns 0.11 ± 0.32ns Ba Vi VOL 0.01 ± 0.03ns 0.23 ± 0.39ns Ba Vi DBH Bau Bang 0.71 ± 0.02*** 0.65 ± 0.04*** 0.63 ± 0.05*** mangium for mechanical properties (Ani and Lim 1993; Hazani 1994; Shanavas and Kumar 2006) Heritabilities and additive coefficients of variation Individual heritabilities reported here for growth traits, pilodyn and MoEd in all three tests ranged from low to moderate (from 0.17 to 0.30) Stem straightness at all sites showed low heritability (0.10–0.15) Sib trees contributing progenies in Vietnam descended from the same mother (original seed tree in QLD or PNG) are more closely related than is assumed in normal heritability calculations (it is normally assumed that progenies are unrelated through recent maternal descent) and this would tend to reduce our estimated heritabilities However, growth trait heritabilities are similar to heritabilities reported from other openpollinated family trials of A mangium (Arnold and Cuevas 2003; Dao 2012; Nirsatmanto 123 New Forests (2015) 46:577–591 587 and Kurinobu 2002) and of other Acacia species (Arnold and Cuevas 2003; Dunlop et al 2005; Hai et al 2008b; Luangviriyasaeng and Pinyopusarerk 2002) The additive coefficient of variation (CVa) for growth traits, pilodyn and MoEd at all sites reported in this study were [5 % At age and years, these CVa of growth traits were generally highest at Tuyen Quang and Bau Bang This may have been caused by genetic variation being better expressed at an early age in more favourable environments with a higher growth rate (Cotterill and Dean 1990) Also, greater competition would have developed at both sites because of the much faster growth there, and this may have accentuated differences between the families Furthermore, the Bau Bang site was very uniform, and intensive mechanical weed control with a tractor-plough was maintained after establishment These factors would reduce the environmental variance and thereby increase individual heritabilities and CVa of growth traits Low to moderate heritabilities, significant differences among genetic groups and relatively high CVa suggest that considerable selection responses could be expected for growth and wood quality traits, following selection of the best individuals for establishing new clonal seed orchards to meet improved seed requirements for operational planting targets in Vietnam Typically, progeny trials can be selectively thinned to cull poorer trees within families having slow growth and/or poor stem form, and completely remove the poorest families, converting them into seedling seed orchards (SSOs) Another option is to establish large areas of unpedigreed seed production areas (SPAs) using a broad and improved genetic base, such as a mix of equal quantities of seed from 50 or more unrelated superior trees in second-generation SSOs These SPAs can either be dedicated solely to seed production, or managed for both wood and seed production In this second approach, early selective thinning is undertaken, to promote development of heavy crowns on the retained, phenotypically superior trees Once the retained trees reach harvestable size, clear-felling of the entire stand for a commercial wood harvest is timed to coincide with ripening of a heavy seed crop deriving from a heavy, general flowering, which is then collected from the felled trees This approach was successful when tried on a pilot scale in Sarawak, Malaysia in the early 2000s (Harwood, unpublished data) In principle, it should produce, at low cost and with limited scientific inputs, large quantities of improved seed, without compromising timber production However, unpedigreed SPAs represent a dead end from a breeding perspective, as all pedigree information is lost and no information on genetic parameters is obtained The other strategy is clonal family forestry, which is to collect seed from the very best families in the second-generation tests and multiply these seedlots via CFF (clonal family forestry (White et al 2007) which is suited to tree species such as A mangium where it is difficult to propagate tested individual clones because of maturation problems Correlations between traits DBH had a slightly negative correlation with MoEd in Tuyen Quang test and non-significant correlations with pilodyn in all three tests This is consistent with the underlying non-significant negative relationship between growth rate and basic density or modulus of elasticity in previous studies of A mangium (Dao 2012; Khasa et al 1995) In other hardwood species, such as Eucalyptus species, Q petrea, Q rubra, Petersianthus macrocarpa and C spruceanum, non-significant correlations between growth traits and basic density, and shrinkage parameters have been reported (Chafe 1994; Nepveu 1984; Sotelo Montes et al 2007) 123 588 New Forests (2015) 46:577–591 At age and years, the trait–trait correlations between STR and growth traits were consistently positive with a range from 0.25 to 0.37, indicating that larger diameters are associated with straighter stems In an early evaluation of first-generation progeny tests in Vietnam, Dao (2012) found that HT and DBH were not generally correlated to stem straightness Positive correlations between growth and stem straightness were also reported from low to high in other tropical species, such as A auriculiformis, A crassicarpa, A nilotica, Eucalyptus grandis and E camaldulensis (Arnold and Cuevas 2003; Gapare 2003; Mahmood et al 2003; Ginwal and Mandal 2004; Hai et al 2008a, b) Genotype by environment interactions To manage GxE interactions, the best families could be selected for specific sites to maximize deployment gains (Libby and Rauter 1984) This would involve identifying different plantation regions, representing homogenous environmental zones within which selections are deployed and used in further breeding Significant genotype by environment (G E) interaction effects were found in growth traits between the two northern sites and Bau Bang; i.e the most promising families were not the same at both sites Figure 1a–c show plots of family Best Linear Unbiased Prediction (BLUP) values for DBH in pairs of sites The figures illustrate that many families contribute to the interaction, and the (b) 1.0 BLUP values of DBH at Ba Vi BLUP values of DBh at Ba Vi (a) 0.5 0.0 -0.5 -1.0 ra=0.75 -1.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 -1 ra=0.11 -2 -3 -1.5 BLUP values of DBH at Tuyen Quang -1.0 -0.5 0.0 0.5 1.0 BLUP values of DBH at Bau Bang BLUP values of DBH at Tuyen Quang (c) -1 -2 -3 -1.5 ra=0.12 -1.0 -0.5 0.0 0.5 1.0 BLUP values of DBH at Bau Bang Fig Clonal BLUP of 28 the same families for diameter at breast height at a Ba Vi and Tuyen Quang, b Ba Vi and Bau Bang, and c Tuyen Quang and Bau Bang 123 New Forests (2015) 46:577–591 589 tendency was the same for all traits Therefore, G E effects were clearly of practical importance for breeding program of A mangium, separate seed orchards should be established for northern and southern Vietnam In further research, progeny tests should be also set up in central Vietnam to determine G E differences between that region and the north and south of the country Significant G E interactions were also reported in A mangium in Zaire (Libby and Rauter 1984) and Vietnam (Dao 2012), in A auriculiformis in Vietnam (Hai et al 2008a) and A mearnsii in South Africa (Dunlop et al 2005) The low genotypic correlations between northern and southern Vietnam in this study could be explained by differences in both soil and climatic conditions The experimental sites in Tuyen Quang and Ba Vi are typical of most hill-sites in northern Vietnam with yellow ferralitic clay loam soils, while the soil at Bau Bang is sandy alluvium, and light in texture The soils are fertile at Tuyen Quang and Bau Bang, but infertile and heavily laterized at Ba Vi (Kha 2003) In addition, lower temperature as well as reduced light in winter months reduce growth of the trees at Tuyen Quang and Ba Vi Conclusions In second-generation progeny tests of A mangium in Vietnam, significant differences between families were found for growth traits, stem straightness, pilodyn penetration and predicted MoEd Heritabilities of the studied traits ranged from low to moderate in all sites The CVa for DBH, pilodyn and MoEd were high after age years Genetic correlations between quality traits (pilodyn and dynamic modulus of elasticity) and growth traits were weak and favourable or unfavourable with large standard errors The substantial coefficients of additive genetic variation and significant heritabilities for all traits indicate that it should be possible to use a selection strategy that combines improvements in growth, stem, and wood quality for A mangium in Vietnam The genetic correlations between Tuyen Quang and Bau Bang site were low for all studied traits, indicating that G E effects are of practical importance for 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