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

Genetic variation in growth, stem straightness, pilodynand dynamic modulus of elasticity in second-generation progeny tests of Acacia mangium at three sites in Vietnam Phi Hong Hai1•La A

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 3 or 4 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 un-favourable The substantial coefficients of additive genetic variation and significant her-itabilities 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 9 E effects are of practical importance for growth and different deployment populations will be required for different sites

Keywords Acacia mangium Genetic variation  Growth  Pilodyn  Wood stiffness

& Phi Hong Hai

phi.hong.hai@vafs.gov.vn

1

Department of Planning and Sciences, Vietnamese Academy of Forest Sciences,

Duc Thang, Bac Tu Liem, Ha Noi, Viet Nam

2

Institute of Forest Tree Improvement and Biotechnology, Vietnamese Academy of Forest Sciences, Duc Thang, Bac Tu Liem, Ha Noi, Viet Nam

DOI 10.1007/s11056-015-9484-6

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 spe-cies such as A auriculiformis and Eucalyptus urophylla It produces pulp logs and small sawlogs on rotations as short as 7 years At present, A mangium occupies about 500,000 ha of the total area of forest plantation of over 2 million ha 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 Nambiar2014), averaging 15 m3ha-1yr-1(Nghia2003), 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 (Kha2003) 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 3 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, 7 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 corre-spondingly 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?

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 6 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 Table1

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 Table2 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 soil-based 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 6 replicates and 2-tree plots All tests used row-column designs generated by the computer program CycDesigN (Williams et al.2002), providing 2-dimensional incomplete blocking (rows and columns) within replicates

Table 1 Number of A mangium families in six genetic groups, families common to pairs of sites and families in each progeny test

families in group

Number of families in each site

Number of families common

to Bau Bang

Number of families common

to Tuyen Quang

54 Number of families tested

in all three sites

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

Total tree height (HT), diameter at breast height (DBH) and stem straightness (STR) of all trees were recorded annually to 4 years at Ba Vi and 3 years at the other two trials The stem straightness was scored using a scale with 5 classes:

1 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);

2 for crooked stem with 2 serious bends;

3 for slightly crooked stem with 1 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);

4 for almost straight stem with 1–2 small bends and

5 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:

VOL¼ p  HT  DBH2=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 Nambiar2014)

Table 2 Description of A mangium progeny tests

Soil type Ferralitic clay loam with

heavy lateritization

Ferralitic clay loam Sandy alluvium Annual rainfall

(mm)

Annual average

temperature (°C)

Site preparation Slash burned and ripped Slash burned and

holes dug

Slash burned and ploughed

Fertilizer (per tree) 3 kg cattle

manure ? 0.2 kg NPK

3 kg cattle manure ? 0.2 kg NPK

0.5 kg micro-organic fertilizer ? 0.2 kg NPK Design

Columns per

replicate

Pilodyn penetration was measured for all trees in the tests by using a 6 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 con-verted 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 (MoEdin GPa) according to:

MoEd¼ Green density  velocity2

where green density is assumed to be a constant at 1060 kg m-3for A mangium (Moya and Mun˜oz2010)

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-deter-mined liability scale (Falconer and Mackay1996), and that the given scores were caused

by imposed thresholds Prior to analysis class scores were therefore transformed into asymptotic ‘normal scores’ (Gianola and Norton1981) 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):

y¼ XBmþ XPpþ ZWwþ ZNnþ ZTtþ ZFfþ e ð1Þ with y¼ ðy0

1; y02; ; y0nÞ0, m¼ ðm0

1; m02; ; m0nÞ0, p¼ ðp0

1; p02; ; p0nÞ0, w¼ ðw0

1;

w02; ; w0nÞ0, n¼ ðn0

1; n02; ; n0nÞ0, f¼ ðf01; f02; ; f0nÞ0, e¼ ðe0

1; e02; ; e0nÞ0, X¼ RXB i,

X¼ RXP i, ZW ¼ RZW i, ZN¼ RZN i, ZT ¼ RZT i and ZF¼ RZF i, R denotes the direct sum, and i the number of traits from 1 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 3 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 ZFare 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:

w n t f e

2 6 6 4

3 7 7

5¼

2 6 6 4

3 7 7

where 0 is a null matrix, I is an identity matrix of order equal to the total number of rows, columns, plots, genetic, and residuals, respectively, and is the direct (Kronecker) product operation W¼ rw i w j

, N¼ rf n i n ig, T ¼ rt i t j

, F¼ rf i f i

, and R¼ re i e j

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 ap-plied 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 esti-mated based on multivariate REML analysis using model (2) Family variance (r2

f), phenotypic variance (r2

P), plot variance (r2

t) and environmental variance (r2

e) 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 first-generation seed orchards Therefore, some degree of inbreeding (about 10 %) was ex-pected, 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 (r2), total phenotypic variance (r2

P) and individual-tree herit-ability (^h2) estimates were calculated as follows (Squillace1974):

r2¼ 3r2 f

r2

P¼ r2

f þ r2

t þ r2

e and

2

r2

f þ r2

t þ r2 e

Coefficient of additive variation (CVa), additive genetic correlation (^ra) and phenotypic correlation (^rP) between traits or between ages were estimated as:

CVa¼100 ra

X

^

ra¼ ra1 a 2

ra1ra2

^

rP¼ rP1 P 2

rP 1rP 2

where X is the phenotypic mean, ra 1 a 2 and rP 1 P 2 are the genotypic and phenotypic co-variance between two traits, respectively ra 1, ra 2 and rP 1, rP 2 are the genotypic and phenotypic standard deviations of trait 1 and trait 2, respectively Standard errors of the estimates of heritabilities, genotypic and phenotypic correlations were calculated using a

standard Taylor series approximation implemented in the ASReml program (Falconer and Mackay1996)

Predicted gain from genetic selection was calculated according to Mullin et al (1992) as

GY ¼ in;N^2

YrPY where Gyis the predicted selection gain, and in,Nis 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 R¼ RRn 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 9 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 MoEdat Tuyen Quang (Table3) 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 respec-tively, 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 3 or 4 growth traits, pilodyn and dynamic modulus of elasticity ranged from low to moderate at all sites (Table4) The heritabilities of growth traits in the Ba Vi test at 4 years were higher than those at 3 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, CVaranged from 6.1 to 7.3 % for STR, Pilodyn and MoEd(Table4) 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 MoEdat Tuyen Quang test

Within each site, positive genetic correlations were observed among all the combina-tions of traits that were assessed, except for correlation between DBH and MoEd in the Tuyen Quang test (Table5) Stem straightness (STR) showed consistent positive genetic

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 MoEdwere 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 1 Family-by-site interactions between the two northern sites and Bau Bang were significant (p \ 0.001) for Pilodyn (Table6) 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

4 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

Table 3 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)

MoE d

(GPa)

At Ba Vi (4 year old)

At Tuyen Quang (3 year old)

At Bau Bang (3 year old)

ns not significant

* F-probability \ 0.05; *** F-probability \ 0.001

deep, fertile soil (Nghia2003) 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 (Nghia2003) 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 (Kha2003) 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 (Table1) 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 (Table3) 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 (Dao2012; Thinh et al.2011) and A auriculiformis (Aggarwal et al.2002; Firmanti et al.2007; Kumar

et al.1987; Mahat1999) Mossman (QLD Cairns Region) was the best provenance of A

Table 4 Mean values, narrow-sense heritability ( ^ h 2 ), additive coefficient of variation (CV a ) and predicted gain (G Y %) based on a selection intensity of 1.755 (10 % selected) for studied traits at different ages in each site

mangium for mechanical properties (Ani and Lim 1993; Hazani 1994; Shanavas and Kumar2006)

Heritabilities and additive coefficients of variation

Individual heritabilities reported here for growth traits, pilodyn and MoEdin 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 open-pollinated family trials of A mangium (Arnold and Cuevas2003; Dao2012; Nirsatmanto

Table 5 Genetic (^ r a ),

pheno-typic correlations (^ r P ) and

stan-dard 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)

In Ba Vi test

In Tuyen Quang test

In Bau Bang test

Table 6 Genetic correlations

between sites for height,

di-ameter, volume, stem

straight-ness and pilodyn

HT Tuyen Quang 0.68 ± 0.17*** 0.01 ± 0.03 ns

DBH Tuyen Quang 0.75 ± 0.17*** 0.12 ± 0.32ns

VOL Tuyen Quang 0.67 ± 0.18*** 0.16 ± 0.37 ns

STR Tuyen Quang 0.25 ± 0.31ns 0.44 ± 0.41ns

Pilodyn Tuyen Quang 0.71 ± 0.02*** 0.65 ± 0.04***