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Key message: Larger differences of maximum load among families were found in mature wood compared to juve - nile wood, suggesting the possibility of improving mature wood with higher resistance to rupture and maintaining characteristics of material in Larix kaempferi (Lamb.) Carr. by selecting specific mating parents. Context: Because the wood from L. kaempferi trees is used for construction lumber, wood properties and bending properties should be focused on as targeted traits of tree breeding programs. Aims: We clarified the radial variation of inheritance for wood properties and bending properties and classified the features of bending properties among families in L. kaempferi. Methods: Annual ring width, latewood percentage, air-dry density, microfibril angle, modulus of elasticity, modulus of rupture, and bending work at five radial positions were investigated for 15 full-sib families of 36-year-old L. kaemp - feri grown in two progeny test sites in Japan. Results: Higher heritability at almost all radial positions was found in air-dry density. Phenotypic and genetic cor- relations between air-dry density and bending properties showed relatively higher values at almost all radial posi- tions. Load-deflection curves in 15 families could be divided into three groups in juvenile and mature wood. Variation among groups for load-deflection curves in mature wood was relatively larger than that in juvenile wood. Conclusion: Air-dry density can be used as a criterion to select trees with superior bending properties. Mature wood in L. kaempferi could be effectively improved by selecting individuals. Keywords: Heritability, Air-dry density, Microfibril angle, Bending properties, Load-deflection curve of the most major softwood plantation species in Japan 1 Introduction (Takata et al. 2005). Plantations of L. kaempferi are mainly Larix kaempferi (Lamb.) Carr. (karamatsu in Japanese distributed in Hokkaido and northern Japan, includ- and Japanese larch in English) is a deciduous conifer spe- ing the Tohoku and Chubu regions (Forestry Agency cies that is naturally distributed in cold and high eleva- 2019). The trees of L. kaempferi and hybrids between L. tion areas in the central region of Honshu, Japan. It is one kaempferi and other Larix species have been planted in Japan (Iizuka et al. 2000; Fujimoto et al. 2006a, b; Fukatsu Handling editor: Jean-Michel Leban et al. 2015), North America (Cáceres et al. 2018), China (Dong et al. 2019), and Europe (Pâques et al. 2010). This *Correspondence: firstname.lastname@example.org species is one of the target species for tree breeding pro- School of Agriculture, Utsunomiya University, Utsunomiya 321-8505, Japan grams managed by the Forestry Agency in Japan; it is also Full list of author information is available at the end of the article © The Author(s) 2022. 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Annals of Forest Science (2023) 80:1 Page 2 of 15 used for breeding materials in many countries (Kurinobu trees with higher mechanical properties of wood can be 2005). The tree breeding programs of L. kaempferi in achieved by the selection of wood with higher wood den- Japan were started in the 1950s, selecting plus trees with sity and lower MFA. superior growth rates and straightness as criteria in arti- For tree breeding of wood quality in L. kaempferi, an ficial and natural forests (Kurinobu 2005). Recently, the accumulation of information about the inheritance of selection of second-generation plus trees crossbred by static bending properties is necessary. To clarify the using selected first-generation plus trees has been started inheritance and relationship with wood properties in to improve growth rate and wood quality as target traits, static bending properties, it is useful to understand the with plans to establish seed orchards in each prefecture variation in the shapes of load-deflection curves among in Japan (Fukatsu et al. 2015). families. In the present study, wood properties and bend- Since the structural lumber in L. kaempferi is often sub- ing properties were measured for 15 full-sib families of jected to bending load, bending properties—including 36-year-old L. kaempferi trees grown at two progeny test the modulus of elasticity (MOE) and the modulus of rup- sites located in Gunma and Nagano prefectures, Japan. ture (MOR)—are important criteria for assessing wood We aimed to clarify the inheritances of wood properties quality. It has been reported that mechanical properties and radial variations, as well as the relationships between are highly heritable traits in softwood species (Fujimoto wood properties and bending properties. Furthermore, et al. 2006a; Lenz et al. 2010; Chen et al. 2014; Taka- we tried to classify families by differences in the types of hashi et al. 2021). For example, Fujimoto et al. (2006a) load-deflection curves in the static bending test. reported that the heritability values of MOE and MOR in hybrid larch (L. gmelinii × L. kaempferi) were 0.44 and 2 Materials and methods 0.66, respectively. In addition to MOE and MOR, bend- 2.1 Progeny test sites ing work (W)—which is the amount of energy absorbed Materials were collected from two L. kaempferi progeny until the wood is broken—is also important in bending test sites (Gunma and Nagano prefectures, located in properties because it can be used to evaluate tough- Central Japan), and two progeny test sites were defined ness. Static bending properties are calculated from load- as the Gunma and Nagano sites in the present study. deflection curves obtained from a static bending test. The Gunma site is located 40 km north of the Nagano u Th s, the shape of the load-deflection curve is important site (Figure 5 in Appendix). An outline of these sites is for understanding the elastic and plastic properties of shown in Table 6 in Appendix. The two sites were estab - wood, for example, a higher proportional limit showing lished by planting the seedlings of 56 full-sib families resistance to deformation by load and the higher maxi- produced with a full diallel mating design of eight com- mum load and the longer deflection in the plastic region mon plus-tree clones without selfing, using a randomized showing resistance to failure. We previously reported block design with five replicates. Each family was planted that the type of load-deflection curve obtained in the in a quadratic plot with 20 trees at each replicate block. static bending test of juvenile wood genetically varied Gunma and Nagano sites were planted in 1977 at spac- among 18 families of 20-year-old Cryptomeria japonica, ings of 2.2 × 2.2 m and 2.0 × 2.0 m, respectively. No thin- and the load-deflection curves affected by mating parents ning treatment was conducted before sampling for the could be divided into four types (Takahashi et al. 2021). present study. However, information on the inheritance of mechanical properties, such as static bending properties, is still lim-2.2 Materials ited for full-sib families of L. kaempferi, despite being one From the diallel crossing of eight plus-tree clones of of the important first steps to be studied for the improve - five replicate blocks, the complete diallel crossing of six ment of wood quality. plus-tree clones of three replicate blocks was selected for Superior trees with higher mechanical properties of the present study. Fifteen full-sib families were pooled wood would be indirectly selected by wood density and with reciprocal families due to the limited number of microfibril angle (MFA) for the effective selection of remaining trees. A total of 269 and 260 trees were used trees (Alteyrac et al. 2006; Lenz et al. 2010; Pâques et al. as samples at the Gunma and Nagano sites, respectively 2010; Chen et al. 2014; Takahashi et al. 2021). Pâques (Table 1). The stem diameter at 1.2 m above the ground et al. (2010) found higher genetic correlations between and tree height were measured for each tree at the age wood density and MOE for 16- and 19-year-old hybrid of 30. Mean values and standard deviations of stem larch (Larix × eurolepis Henry). In 12 trees of 80-year- diameter at 1.2 m above the ground in the Gunma and old Picea mariana, MFA was negatively correlated Nagano sites were 15.4 cm and 15.5 cm, respectively; with MOE (r = −0.78) or MOR (r = −0.53) (Alteyrac similarly, those of tree height were 14.0 m and 14.1 m, et al. 2006). These results suggest that the selection of respectively (Table 2). For all sample trees in Gunma and T akahashi et al. Annals of Forest Science (2023) 80:1 Page 3 of 15 Table 1 Combination of mating parents, family ID, and number of trees in each site Seed parent Pollen parent PL1 PL2 PL3 PL4 PL5 PL6 PL1 9/9 (1) 9/8 (2) 9/9 (3) 9/6 (4) 9/9 (5) PL2 9/9 (1) 9/9 (6) 9/9 (7) 9/9 (8) 9/9 (9) PL3 9/9 (2) 9/9 (6) 9/9 (10) 9/9 (11) 9/9 (12) PL4 9/8 (3) 9/9 (7) 9/9 (10) 9/8 (13) 9/9 (14) PL5 9/9 (4) 9/9 (8) 9/9 (11) 9/9 (13) 9/6 (15) PL6 9/9 (5) 8/9 (9) 9/9 (12) 9/9 (14) 9/8 (15) Left number and right number indicate the number of trees of the Gunma and Nagano sites, respectively. Values in parentheses represent the family ID in the present study. PL1, PL2, PL3, PL4, PL5, and PL6 were mating parent codes in the present study earlywood. Latewood percentage (LWP) was calculated as Table 2 Mean values of wood properties in 15 families planted in each site the proportion of latewood width to ARW in each annual ring. Trait Gunma site Nagano site The MFA of the S layer in latewood tracheids was deter- Mean CV (%) Mean CV (%) mined using the iodine method (Senft and Bendtsen 1985). At each site, 90 trees in a replicate block were subjected D (cm) 15.4 4.5 15.5 5.8 to measuring the MFA. Small blocks were prepared at the TH (m) 14.0 4.3 14.1 5.0 5th, 10th, 15th, 20th, and 25th annual rings from one radial ARW (mm) 2.3 8.7 2.6 3.8 direction of the pith to the bark in an obtained strip. At LWP (%) 28.3 4.2 26.7 4.9 −3 each radial position, the MFA of the S layer was measured AD (g cm ) 0.506 9.5 0.448 6.5 2 for 30 latewood tracheids on digital photomicrographs MFA (°) 10.6 8.5 10.6 6.6 using ImageJ. The mean values were then calculated at each MOE (GPa) 8.98 9.1 8.75 9.5 radial position. MOR (MPa) 84.3 10.4 83.9 8.9 W (N m) 5.58 14.1 5.27 12.0 2.4 Static bending properties n = 15 Radial boards from the pith to the bark sides were planned Mean in AD, MOE, MOR, and bending work was calculated using area-weighed at 15 mm in thickness, and then, the boards were cut at mean of each individual CV Coefficient of variation, D Stem diameter at 1.2 m above the ground, TH Tree 15 mm intervals from the pith to obtain the small-clear height, ARW Annual ring width, LWP Latewood percentage, AD Air-dry density, specimens (ca. 15 [R] × 15 [T] × 240 [L] mm). A total of MFA Microfibril angle, MOE Modulus of elasticity, MOR Modulus of rupture, W 2414 specimens were obtained (1956 and 458 specimens Bending work were from juvenile wood and mature wood, respectively). The average number of specimens per individual was 4.55 Nagano sites, 40-cm-long logs were obtained from 1.0 to specimens. When small-clear specimens were prepared, 1.4 m above the ground in October and November 2013, we carefully prepared the specimens without severe curva- respectively. The trees were 36 years old. Pith-to-bark ture of annual rings. The static bending test was conducted radial boards of 30 mm thickness were prepared from the using a universal testing machine (MSC-5/200-2, Tokyo logs. After air-drying the boards, one radial direction of Testing Machine, Tokyo, Japan). The span and load speed each radial board (from the pith to the bark) was used for were 210 mm and 4 mm/min, respectively. The MOE and the following experiments (Takahashi et al. 2022b). MOR were calculated from the load-deflection curve after a bending test using Eqs. 1 and 2, respectively (Figure 6 in Appendix; Takahashi et al. 2021). 2.3 Wood properties Strip specimens 10 mm thick were obtained from the Ppl radial boards to measure the annual ring width (ARW) MOE (GPa) = (1) and latewood width. Cross-sectional images of strip speci- 4Ypbh mens were captured using a scanner. ARW and latewood width were measured in each annual ring from the pith 3Pml MOR (MPa) = to the bark sides using an image analysis software, ImageJ (2) 2bh (National Institutes of Health, Bethesda, Maryland, USA). Latewood was identified by the color difference from Takahashi et al. Annals of Forest Science (2023) 80:1 Page 4 of 15 where Pp is load at proportional limit, Yp is deflection at σ ), respectively. Because the number of samples in GCA proportional limit, Pm is maximum load, l is the span, b the MFA was limited, the B and BG terms could not ij ijlm is the width of the specimen, and h is the height of the be included in Eq. 3 for the MFA. The random factors specimen. W is calculated as an area enclosed with the and breeding values of each mating parent were obtained OBC in Figure 6 in Appendix. using an “animal model” of the best linear unbiased pre- Small blocks without any damage were cut from each diction (BLUP). small-clear specimen to measure moisture content and The narrow-sense heritability (h ) of each trait was esti- air-dry density (AD). The mean values and standard devi - mated using Eq. 4: ations of moisture content in all small-clear specimens were 9.4 ± 0.6% at testing. The MOE and MOR values GCA h = (4) 2 2 2 2 2 were adjusted to those at 12% moisture content by the + + + + GCA SCA pg bg e methods described by Japan Housing and Wood Tech- 2 2 2 2 2 nology Center (Japan Housing and Wood Technology where σ , σ , σ , σ , and σ are variance com- GCA SCA pg bg e Center 2011). ponents of GCA, SCA, the interaction of progeny × GCA, the interaction of block × GCA, and the residual, respectively. These estimations were carried out using 2.5 Data analysis ASReml-R software (Butler 2021). The values of all wood properties at each radial position The genetic correlation between trait x and trait y were calculated by averaging the values from 1st to 5th, (r ) was estimated using Eq. 5: g(x,y) from 6th to 10th, from 11th to 15th, from 16th to 20th, and from 21st to 36th annual rings from the pith (Fig- COV g x,y ( ) ure 7 in Appendix; Tanabe et al. 2014). In addition, the r = g x,y ( ) (5) 2 2 overall mean at all radial positions in bending properties g(x) g(y) and AD was calculated by the weighted average method using the area based on the annual ring number in the where COV is the covariance of trait x and trait y and g(x,y) 2 2 center of each specimen. In L. kaempferi, Shiokura (1982) σ and σ are the additive genetic variances of trait x g(x) g(y) reported that the boundary between juvenile and mature and trait y, respectively. In addition, the phenotypic cor- wood was located at the 11th–19th annual rings from the relation between trait x and trait y was estimated based pith. In the present study, the 1st–20th radial positions on phenotypic variances. and the 21st–36th radial positions were regarded as juve- Principal component analysis (PCA) and cluster analy- nile and mature wood, respectively. The variance com - sis were employed to categorize the 15 families. Princi- ponents of each trait were estimated using the restricted pal component scores were calculated by a correlation maximum likelihood (REML) method using ASReml-R matrix with the four following variables: estimated fam- (Butler 2021). The estimation of the breeding value and ily mean values in load and deflection at the proportional variance components is expressed in the following linear limit and maximum load and deflection. The estimated mixed model (Eq. 3): family mean for the four variables was calculated by the sum of the general mean value (μ), breeding values Y = + P + B + G + G + S + PG + BG + e ijklm i ij k l kl ikl ijkl ijklm in each parent (G and G ), and breeding values in each k l (3) family (S ) (Eq. 4) to remove the effects of differences in kl th where Y is the measurement value of the m individ- environmental factors. Using the 1st and 2nd principal ijklm th th th ual of family of the k and l parents in the j block of component scores from PCA as variables, cluster analy- th the i site, μ is the general mean value, P is a fixed effect sis using the Ward hierarchical clustering algorithm was th th of the i site, B is the fixed effect of the j block in the performed for the categorization of 15 families. The opti - ij th i site, G and G are random effects of genetic combin - mal number of clusters was determined using the Jain- k l th th ing ability (GCA) of k and l parents, respectively, S Dubes method (Jain and Dubes 1988). These statistical kl th th is a specific combining ability (SCA) between k and l analyses were performed using open-source statistical parents, PG is the random interaction effect for the software R 4.0.3 (R Development Core Team 2020). ikl th th th i site and the GCA of the k and l parents, BG is ijkl th th the random interaction effect for j block in the i site th th and the GCA of the k and l parents, and e is the 3 Results ijklm random residual. Random factors were assumed to be 3.1 Mean values and radial variations of wood properties distributed normally, with an expectation of zero. The and bending properties random effects G and G were predicted from the vari- The mean values of the wood properties and their radial k l ance of GCA as follows: G ~N (0, σ ) and G ~N (0, variations at each site are shown in Table 2 and Fig. 1, k GCA l T akahashi et al. Annals of Forest Science (2023) 80:1 Page 5 of 15 respectively. The mean ARW in the two sites decreased from the pith (Fig. 2). The radial variation of the MFA from 1st–5th to 21st–36th radial positions, with a dras- showed a similar pattern between the two sites (Fig. 2). tic decrease at the 11th–15th radial position (Fig. 1). The The mean value of the MFA in all families was 10.6° in mean values of LWP, AD, MOE, MOR, and W increased the two sites (Table 2). drastically from 1st–5th to 11th–15th radial positions and then slightly increased or became almost stable toward the outer radial positions (Fig. 1). The AD and bending 3.2 Heritability properties in the Nagano site were shown to have higher The heritability of ARW ranged from 0.000 at the 6th– values compared with those in the Gunma site, especially 10th radial position to 0.008 at the 11th–15th radial in the range from the 6th–10th to the 16th–20th radial position (Table 3). The highest heritability in LWP (h 2 2 positions (Fig. 1). The site effects as fixed effects were = 0.360), AD (h = 0.459), and MOR (h = 0.503) was significant at 6th–10th position in ARW and LWP, 11th– obtained in the 21st–36th radial positions among the 20th position in AD, 11th–36th position in MOR, 16th– five radial positions. In the MFA, heritability decreased 20th position in W, and all positions in MOE. from the inner position to the outer position, with the The mean values of the MFA at the 5th annual ring highest heritability at the 1st–5th radial positions (h from the pith showed the highest values in each family, = 0.137). The heritability of MOE and W ranged from being 16 to 17° (Fig. 2). Then, the mean MFA value rap - 0.000 in the 11th–15th to 0.263 in the 6th–10th radial idly decreased to about 7° toward the 25th annual ring positions and from 0.023 in the 11th–15th to 0.199 in the 6th–10th radial positions, respectively. Fig. 1 Radial variations of wood properties. Note: ARW, annual ring width; LWP, latewood percentage; AD, air-dry density; MOE, modulus of elasticity; MOR, modulus of rupture; W, bending work; open circles and closed circles indicate mean values of family mean values in the Gunma and Nagano sites, respectively; bar, standard deviation. ** and * significant site effects as fixed effects at p < 0.01 and p < 0.05, respectively Takahashi et al. Annals of Forest Science (2023) 80:1 Page 6 of 15 at 1st–5th (r = 0.890) and 6th–10th (r = 0.320) radial g g positions. In all bending properties, phenotypic correla- tions with MFA were shown in the range of −0.2 to −0.4 at 16th–36th radial positions. Table 4 shows the genetic correlations between the mean at all positions and the mean at each radial posi- tion for all wood properties. In ARW and AD, correla- tions were higher than 0.6 at all radial positions, while high correlations in LWP and bending properties were obtained in mainly 11th–36th radial positions. 3.4 Classification of load‑deflection curves The plot of principal components for the 15 families’ scores and the loading of principal components in juve- nile wood are shown in Fig. 4 and Table 5, respectively. The contributions of 1st and 2nd principal components Fig. 2 Radial variation of MFA. Note: MFA, microfibril angle; open circles and closed circles indicate mean values of family mean values were 52.0% and 29.1%, respectively, and, similarly, in in the Gunma and Nagano sites, respectively; bar, standard deviation. mature wood 55.8% and 25.8%, respectively (Fig. 4). In No significant effects (p > 0.05) of sites as fixed effects were obtained both juvenile and mature wood, the 1st and 2nd princi- in all radial position pal components mainly contributed to loads at the pro- portional limit and maximum load and deflection at the proportional limit and maximum deflection, respec - Table 3 Narrow-sense heritability of all wood properties tively (Table 5). Cluster analysis using 1st and 2nd prin- cipal components obtained from PCA as variables was Trait 1st–5th 6th–10th 11th–15th 16th–20th 21st–36th conducted to classify the 15 families. Based on the Jain- ARW 0.045 0.000 0.088 0.056 0.067 (0.061) Debus method (Jain and Dubes 1988), the optimal num- (0.093) (0.000) (0.105) (0.091) ber of clusters was determined to be three groups in LWP 0.028 0.068 0.000 0.094 0.360 (0.240) both juvenile and mature wood. The 15 families in juve - (0.061) (0.091) (0.000) (0.117) nile wood were grouped into three groups: group I (1, 2, AD 0.330 0.383 0.175 0.381 0.459 (0.287) (0.240) (0.255) (0.211) (0.249) 3, 6, 7, 8, 9, and 10 in family ID), group II (12 in Family MFA 0.137 0.122 0.000 0.000 0.000 (0.087) ID), and group III (4, 5, 11, 13, 14, and 15 in Family ID) (0.364) (0.184) (0.262) (0.000) (Fig. 4). In mature wood, the 15 families were divided into MOE 0.044 0.260 0.000 0.085 0.110 (0.142) three groups by cluster analysis: group I (2, 4, 5, 11, 12, (0.054) (0.175) (0.087) (0.117) and 15 in Family ID), group II (1 in Family ID), and group MOR 0.030 0.199 0.011 0.146 0.422 (0.271) III3 (3, 6, 7, 8, 9, 10, 13, and 14 in Family ID) (Fig. 4). (0.064) (0.145) (0.072) (0.150) Typical load-deflection curves for the three groups in W 0.035 0.199 0.023 0.105 0.120 (0.124) (0.053) (0.145) (0.078) (0.111) juvenile wood and mature wood are shown in Fig. 4. In juvenile wood, typical load-deflection curves differed Values represent narrow-sense heritability. Values in parentheses represent standard error in maximum load and load at proportional limit among ARW A nnual ring width, LWP Latewood percentage, AD Air-dry density, MFA groups, but there was no difference in the amount of Microfibril angle, MOE Modulus of elasticity, MOR Modulus of rupture, W deflection. A similar result was shown in mature wood, Bending work with a larger difference among the groups than in juve - nile wood. 3.3 G enetic and phenotypic correlations between AD or MFA and bending properties 4 Discussion Genetic correlations with AD in all bending properties 4.1 Mean values and radial variations of wood properties were high at almost all radial positions (Fig. 3). In addi- and bending properties tion, phenotypic correlations with AD were shown above Mean values of ARW, LWP, AD, MOE, and MOR in the 0.5 in MOE and MOR at 6th–36th radial positions. On present study were almost similar to those of other pre- the other hand, the estimated standard errors in the vious studies on larch (Table 7 in Appendix, Miyajima genetic correlations between the MFA and bending prop- 1958, 1985; Kawaguchi et al. 1987; Koizumi et al. 1987; erties were larger for most radial positions (Fig. 3). As the Zhu 2002; Karlman et al. 2005; Koizumi et al. 2005; exceptions, genetic correlations of MFA were obtained Cáceres et al. 2018). These radial variations obtained in T akahashi et al. Annals of Forest Science (2023) 80:1 Page 7 of 15 Fig. 3 Genetic and phenotypic correlations between wood properties and bending properties. Note: The grey and white bars indicate genetic and phenotypic correlations, respectively. Error bar shows standard error. The correlations with over 1 in standard error were not shown due to difficulty in conducting appropriate evaluations Table 4 Age-age genetic correlations for age trend between area-weighted overall mean and mean at each radial position Trait Parameter Radial position from pith 1st–5th 6th–10th 11th–15th 16th–20th 21st–36th ARW r 0.997 0.696 0.790 0.705 0.915 s.e. 0.058 0.437 0.399 0.402 0.130 LWP r –0.618 0.909 0.356 0.954 0.946 s.e. 0.507 0.144 0.531 0.060 0.055 AD r 0.796 0.873 0.837 0.915 0.847 s.e. 0.542 0.506 0.820 0.481 0.464 MFA r 0.882 0.959 0.906 - - s.e. 0.529 0.397 0.517 - - MOE r 0.576 0.830 0.273 0.729 0.971 s.e. 0.747 0.176 0.300 0.492 0.165 MOR r 0.648 0.999 0.899 0.754 0.963 s.e. 0.545 0.145 0.495 0.385 0.146 W r −0.184 0.992 0.838 0.984 0.733 s.e. 0.699 0.144 0.435 0.225 0.647 Results were not shown because the standard error exceeded 1 and could not be evaluated r Genetic correlation, s.e. Standard error, ARW A nnual ring width, LWP Latewood percentage, AD Air-dry density, MFA Microfibril angle, MOE Modulus of elasticity, MOR Modulus of rupture, W Bending work Takahashi et al. Annals of Forest Science (2023) 80:1 Page 8 of 15 Fig. 4 A plot of principal component scores, cluster dendrogram, and typical load-deflection curves for juvenile and mature wood. Note: PC1 and PC2, first and second principal components, respectively. The plotted numbers are Family ID. The vertical axis shows the distance between families based on squared Euclidean distance using the Ward hierarchical clustering algorithm the present study were almost similar to those reported pith and then becomes constant (Panshin and de Zeeuw by previous studies (Kawaguchi et al. 1987; Leban and 1980). This tendency is also true for L. kaempferi (Taki - Haines 1999; Zhu 2002; Karlman et al. 2005; Koizumi moto et al. 2013). The mean values and radial variations et al. 2005). of MFA obtained in the present study were almost simi- In general, the MFA in softwood species rapidly lar to those of previous studies in L. kaempferi (Takimoto decreases from the pith to around the 20th ring from the et al. 2013). T akahashi et al. Annals of Forest Science (2023) 80:1 Page 9 of 15 Table 5 Loading of principal components of PCA for 15 families that reported for P. abies (Chen et al. 2014). Chen et al. (2014) also reported that the heritability of wood density Variable Juvenile wood Mature wood and MOE increased from the pith to the bark sides. The PC1 PC2 PC1 PC2 higher heritability of AD, MOE, and MOR at the outer positions obtained in the present study was in accord- Load at proportional limit 0.671 0.091 0.621 0.349 ance with those of previous studies (Fujimoto et al. Deflection at proportional limit −0.131 −0.745 0.351 −0.556 2006b; Lenz et al. 2010; Chen et al. 2014). Based on these Maximum load 0.687 0.005 0.638 0.284 results, it is considered that the genetic control of the Maximum deflection 0.246 −0.660 0.290 −0.699 MFA near the pith is larger than that at the outer radial PC1 and PC2 First and second principal components, respectively positions. In addition, AD and bending properties in the 6th–10th radial positions were also relatively strongly genetically affected among juvenile wood positions. Because latewood shows a higher density compared Because the highest heritability was obtained, it is con- to earlywood, a higher LWP results in a higher wood cluded that wood properties, such as LWP, AD, and MOR density in softwood (Fukatsu et al. 2015). In the present in mature wood, can be effectively improved by selecting study, AD and bending properties at the Nagano site were individuals. higher in almost all radial positions compared to those at the Gunma site (Fig. 1), although LWP did not vary 4.3 Relationships between wood properties and bending among sites at all radial positions. Zamudio et al. (2005) properties reported that the environmental effect on latewood den - Many researchers have investigated phenotypic correla- sity was pronounced for 31 open-pollinated families tions between wood properties (AD, MFA, and others) planted in the Pinus radiata site in southern Chili. A sim- and mechanical properties, such as bending properties in ilar result was reported in Larix decidua trees located at softwood species (Cown et al. 1999; Alteyrac et al. 2006; different elevations and climates (Rozenberg et al. 2020). Fujimoto et al. 2006a; Kumar et al. 2006; Iki et al. 2010; u Th s, differences in AD and bending properties between Chen et al. 2014; Cáceres et al. 2018). For example, Cown sites might occur due to differences in latewood density et al. (1999) reported that the influence of MFA on MOE caused by environmental differences between sites. (r = −0.76) in 28-year-old Pinus radiata was larger than that of wood density (r = 0.58) in juvenile wood, whereas 4.2 R adial variations in heritability wood density showed a greater stimulus in mature wood. In softwood species, wood properties differ between On the other hand, Iki et al. (2010) reported that in juvenile and mature wood (Shiokura 1982; Cown et al. 43-year-old Abies sachalinensis masters, significant cor - 1999; Ishiguri et al. 2009; Iki et al. 2010). Therefore, to relations between AD and MOE were found at almost all clarify differences in the inheritance of wood properties radial positions, while no significant correlations were between juvenile and mature wood, radial variations in found between MFA and MOE at almost all radial posi- heritability have been investigated by several researchers tions. The results of phenotypic correlations obtained in (Fujimoto et al. 2006a; Kumar et al. 2006; Lenz et al. 2010; the present study were similar to those in hybrid larch Chen et al. 2014). In the present study, the heritability of (Fujimoto et al. 2006a) and P. radiata (Cown et al. 1999). ARW showed low values throughout the stem (Table 3), With a few exceptions, correlations of MOE, MOR, and suggesting that radial growth rate might be affected by W with AD at most radial positions showed higher val- environmental factors such as climatic conditions, soil ues of around 0.5, suggesting that bending properties in type, and canopy closure rather than genetic factors. In L. kaempferi were strongly affected by AD. The influence half-sib families of 20-year-old Picea glauca, the herit- of MFA on bending properties is limited in outer radial ability of MFA was almost constant, between 0.25 and positions (16th–36th). 0.30, over the range of cambial age (Lenz et al. 2010). In Genetic correlations can expect the responses of a trait half-sib families of 21-year-old P. abies, the heritability of when selection is applied to another trait (Falconer and MFA increased from the 1st annual ring to the 6th annual Mackay 1996). In 30-year-old P. radiata, Kumar et al. ring and then decreased up to the bark side (Chen et al. (2006) reported that genetic correlations between wood 2014). Fujimoto et al. (2006a) reported that the herit- density and static MOE were moderate (r = 0.51) in the ability values of MOE and MOR at the bark side (h = core wood zone (the 3rd to 4th annual ring from the pith) 0.42 and 0.61, respectively) for full-sib families of hybrid but high (r = 0.78) in the outer wood (the 9th to 10th larch (L. gmelinii × L. kaempferi) were higher than those annual ring from the pith). Chen et al. (2014) reported at the pith side (h = 0.28 and 0.49, respectively). The that genetic correlations between MFA and MOE were radial trend in the heritability of MFA was similar to high negative values, and the correlations between wood Takahashi et al. Annals of Forest Science (2023) 80:1 Page 10 of 15 density and MOE were high positive values across all 4.5 Implementation of wood quality improvement in L. annual rings in 21-year-old Norway spruce (Picea abies). kaempferi by tree breeding In the present study, high genetic correlations were found In breeding programs for L. kaempferi in Japan, the in AD with MOE and MOR at almost all radial positions. selection of second-generation plus trees has been cur- Based on the results, AD can be considered a criterion rently conducted from the breeding population in prog- for improving the bending properties of L. kaempferi. eny test sites (Kurinobu 2005; Fukatsu et al. 2015). In the On the other hand, W at 1st–10th radial positions cor- results obtained in the present study, AD was geneti- related with MFA. A similar result was found for juvenile cally strongly affected at almost all radial positions wood in C. japonica (Ishiguri et al. 2009). Wood proper- compared with other wood properties. In addition, sig- ties as a criterion for selecting trees with superior bend- nificant genetic correlations were found between AD and ing properties should be highly heritable. Therefore, it is MOE or MOR, especially in the outer radial positions suggested that trees with superior bending properties can (Fig. 3). u Th s, it is concluded that in L. kaempferi, genetic be effectively selected by the selection of trees using AD improvement for wood density and bending proper- as the criterion in L. kaempferi. ties was effective for mature wood compared to juvenile Fujimoto et al. (2006a) reported that overall means of wood, and improvements in wood density resulted in AD, MOE, and MOR can be estimated by mean values of improvement of bending properties, which are impor- those in inner wood (pith to 8th annual ring from pith) tant traits for use as structural lumber in L. kaempferi. in hybrid larch (L. gmelinii × L. kaempferi). In ARW, AD, Leban and Haines (1999) reported that specific MOE (the and MFA, higher correlations were obtained in the inner ratio of MOE and wood density) can be used as a crite- radial positions (Table 4), suggesting that early selection rion to evaluate the strength performance of wood. In the of these properties is possible in L. kaempferi. Based on present study, specific MOE in Nagano site (19.53) was the higher correlations in LWP and bending properties higher value than that in Gunma site (17.74), indicating in outer radial positions (11th–36th) higher than inner that wood produced from Nagano site was characterized positions, early selection for these wood properties is by higher strength properties per unit weight compared considered desirable after 11 ages. to wood from Gunma site. Further research is needed for the evaluation of the possible application of specific MOE as a selection criterion of the superior tree for structural 4.4 I nheritance of load‑deflection curves in 15 full‑sib wood production in tree breeding. families In juvenile wood of C. japonica, we previously investi- gated the types of load-deflection curves and found that 5 Conclusions they were divided into four types by the effect of the The inheritance of wood properties (i.e., ARW, LWP, combinations of mating parents (Takahashi et al. 2021). AD, and MFA) and bending properties was investigated Although the load-deflection curves in juvenile wood for 15 full-sib families in 36-year-old L. kaempferi. In were not grouped distinctly compared to those in C. almost all wood properties, the mean values and radial japonica, the slight differences in load-deflection curves variations determined in the present study were similar among groups in juvenile wood of L. kaempferi were to those reported in previous studies. From the results of found in load at the proportional limit and maximum phenotypic and genetic correlations, AD can be used as load (Fig. 4). On the other hand, it was reported that the a criterion by which to select trees with superior bend- load-deflection curves of mature wood in Chamaecy - ing properties. Furthermore, significant correlations paris obtusa largely varied among six families compared were found between the overall mean and mean values at to juvenile wood (Takahashi et al. 2022a). Similar results almost all radial positions for AD, MFA, MOE, MOR, and were obtained in the present study (Fig. 4), but there was W. MFA was genetically controlled near the pith. In con- less difference in the amount of deflection compared trast, the heritability of LWP, AD, and MOR was shown with mature wood in C. obtusa (Takahashi et al. 2022a). to have the highest values on the outer side. Although These results suggest that the variation of load-deflection the load-deflection curves of 15 families in L. kaempferi curves, especially the amount of deflection in L. kaemp - could be divided into three groups in both juvenile and feri, was smaller in juvenile and mature wood than in C. mature wood, similar load-deflection curves with slight japonica and C. obtusa. Thus, in L. kaempferi, it is con - differences in loading parameters were obtained in all cluded that improving mature wood with higher bending groups for both juvenile and mature wood. Larger differ - properties while maintaining the characteristics of the ences in maximum load among families were obtained materials (higher proportional limit and smaller plastic in mature wood compared to juvenile wood, suggesting region) is possible in L. kaempferi by selection in tree the possibility of improving mature wood with higher breeding programs. T akahashi et al. Annals of Forest Science (2023) 80:1 Page 11 of 15 Table 7 Mean values of wood properties in L. kaempferi reported resistance to rupture and maintaining the characteristics by several researchers of materials (a higher proportional limit and smaller plas- tic region) in L. kaempferi by selection. However, because Age Country ARW LWP AD (g MOE MOR References −3 (mm) (%) cm ) (GPa) (MPa) the sample trees used in the present study were small- diameter trees that were not enough size for producing 52 Hok- 3.6 - 0.40 7.64 69.5 Miyajima the actual size of structural lumber, further study using kaido, (1958) Japan full-size structural lumber is necessary for evaluating 53 Hok- 3.0 - - 7.94 69.8 Miyajima wood quality and that inheritance in this species. kaido, (1985) Japan 67 Hok- - - 0.53 8.42 83.4 Kawaguchi Appendix kaido, et al. (1987) Japan 24 Hok- 3.8– - 0.47 7.94 68.8 Koizumi kaido, 6.6 et al. (1987) Table 6 Outline of two progeny test sites Japan Details Gunma Nagano 70 Nagano, 1.67– 30.7– 0.50– - - Zhu (2002) Japan 4.13 46.1 0.58 Latitude 36°30′ N 36°21′ N 35 Remn- 3.94 0.45 - - Karlman Longitude 138°26′ E 138°31′ E ingstorp, et al. (2005) Sweden Above sea level (m) 1360–1380 1120 31 Hok- - - 0.54– 8.2– 93.3– Koizumi Annual temperature (°C) kaido, 0.55 9.5 97.2 et al. (2005) Mean 6.1 7.2 Japan Minimum −4.4 (Jan.) −3.2 (Jan.) 12 Quebec, - - 0.45– - Cáceres Maximum 16.7 (Jul.) 17.9 (Jul.) Canada 0.50 et al. (2018) Annual precipitation (mm) ARW Annual ring width, LWP Latewood percentage, AD Air-dry density, MOE Mean 102.8 79.8 Modulus of elasticity, MOR Modulus of rupture Minimum 28.4 (Jan.) 19.8 (Jan.) Maximum 184.1 (Sep.) 154.8 (Jul.) Test site establishment May 1977 April 1977 Initial planting density (seedlings/ha) 2000 2500 Number of replicated blocks 5 5 Number of families 56 56 Slope inclination (°) 5–7 0–5 Soil type Bl B D D(d) The annual temperature and precipitation were estimated using data of the nearest meteorological station, provided by the Japan Meteorological Agency. Mean annual temperature was calculated by averaging monthly mean temperature obtained from 2008 to 2012. Mean annual precipitation was calculated by averaging total monthly precipitation obtained from 2008 to 2012 Bl Moderately moist black forest soil, B Moderately moist brown forest soil D D(d) Takahashi et al. Annals of Forest Science (2023) 80:1 Page 12 of 15 Fig. 5 Locations of two progeny trial sites. Note: a.s.l., above sea level; open and closed circles indicate progeny test sites at Tsumagoi, Gunma Prefecture, and Miyota, Nagano Prefecture, respectively. Fig. 6 Calculation of static bending properties from load-deflection curve of static bending test ( Takahashi et al. 2021). Note: Pm , maximum load; Pp, load at proportional limit; Ym, maximum deflection; Yp , deflection at proportional limit. MOE and MOR were determined by the following equations: 3 3 2 MOE (GPa), Ppl /4Ypbh ; MOR (MPa), 3Pml/2bh , where l is the span, b is the width of the specimen, and h is the height of the specimen. W is an area enclosed with OBC in this graph T akahashi et al. Annals of Forest Science (2023) 80:1 Page 13 of 15 Fig. 7 Preparation of small clear specimens and calculation method of mean values at five radial positions (1st–5th, 6th–10th, 11th–15th, 16th–20th, and 21st–36th annual ring from the pith) ( Tanabe et al. 2014). Note: a and c, cross-sectional images of radial board in sample trees A and B, respectively; b and d, cross-sectional images of small clear specimen in sample trees A and B, respectively. Due to sample tree size, specimen could not be obtained from all radial positions (in this Fig., specimens were not obtained from the 16th–20th annual ring positions in sample tree A and the 21st–36th annual −3 ring positions in sample tree B). Numbers in parentheses show examples of AD value (g cm ). For example, the mean value of a family in the 1st–5th −3 −3 positions (0.46 g cm ) was calculated by averaging the values obtained from the same positions of sample tree A (0.45 g cm ), sample tree B (0.47 g −3 cm ), and other sample trees Takahashi et al. Annals of Forest Science (2023) 80:1 Page 14 of 15 Acknowledgements Dong L, Xie Y, Sun X (2019) Full-diallel-based analysis of genetic parameters for The authors would like to express their thanks and appreciation to all the growth traits in Japanese larch (Larix kaempferi). New For. https:// doi. org/ members of the Laboratory of Forest Products and Wood Material Science, 10. 1007/ s11056- 019- 09729-6 Utsunomiya University, for their assistance in conducting the present study. Falconer DS, Mackay TFC (1996) Introduction to quantitative genetics, 4th edn. The authors would also like to thank Dr. Makoto Takahashi and Dr. Akira Longman Group, Essex, p 464 Tamura for suggestions on an earlier draft of this manuscript. Forestry Agency (2019) Annual report on forest and forestry in Japan (FY2018). https:// www. rinya. maff. go. jp/j/ kikaku/ hakus yo/ r1hak usyo/ attach/ pdf/ Code availabilityzenbun- 27. pdf. Accessed 30 June 2021 (in Japanese) The code used in the current study is available from the corresponding author Fujimoto T, Akutsu H, Nei M, Kita K, Kuromaru M, Oda K (2006a) Genetic on reasonable request. variation in wood stiffness and strength properties of hybrid larch (Larix gmelinii var. japonica × L. kaempferi). J For Res 11:343–349 Authors’ contributions Fujimoto T, Kita K, Uchimiya K, Kuromaru M, Akutsu H, Oda K (2006b) Age Y T and FI designed the research layout, and Y T and YH supported the trends in the genetic parameters of wood density and the relationship statistical analysis. Y T and FI collected and analyzed the data and drafted the with growth rates in hybrid larch (Larix gmelinii var. japonica × L. kaemp- manuscript. All authors discussed results and conclusions and contributed feri) F1. J For Res 11:157–163 to writing the final manuscript. The author(s) read and approved the final Fukatsu E, Hiraoka Y, Matsunaga K, Tsubomura M, Nakada R (2015) Genetic manuscript. relationship between wood properties and growth traits in Larix kaemp- feri obtained from a diallel mating test. J Wood Sci 61:10–18 Funding Iizuka K, Kohno K, Fujimoto T (2000) Variations of growth and wood quality in None declared young interspecies between Larix gmelinii var. japonica and L. leptolepis. J Jpn For Soc 82:295–300 (In Japanese with English summary) Availability of data and materials Iki T, Fukushi T, Tanbo S, Tamura A, Ishiguri F, Iizuka K (2010) Clonal variations of The datasets have been deposited in the Figshare repository: https:// doi. org/ static bending properties and microfibril angle of the S layer in latewood 10. 6084/ m9. figsh are. 21397 674. v1. tracheids in todomatsu (Abies sachalinensis) plus-trees. Mokuzai Gakkaishi 56:265–273 (In Japanese with English summary) Ishiguri F, Terazawa E, Sanpe H, Matsumoto K, Ishidoh M, Ohno H, Iizuka K, Declarations Yokota S, Yoshizawa N (2009) Radial variation and difference between juvenile wood and mature wood in bending property of sugi (Crypto- Ethics approval and consent to participate meria japonica D. Don) originated from seedlings. Wood Ind 64:20–25 (In The authors declare that the study was not conducted on endangered, vulner- Japanese with English summary) able, or threatened species. Jain AK, Dubes RC (1988) Algorithms for clustering data. Prentice-Hall, Engle- wood Cliffs Consent for publication Japan Housing and Wood Technology Center (2011) Kouzouyoumokuzai no Not applicable. kyoudoshiken manual (Manual of strength testing for structural lumber). Available at www. howtec. or. jp/ files/ libs/ 1828/ 20171 21215 07021 978. pdf . 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Bull Shinshu Univ For 38:61–99 (In Japanese with English summary) Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in pub- lished maps and institutional affiliations. Re Read ady y to to submit y submit your our re researc search h ? Choose BMC and benefit fr ? Choose BMC and benefit from om: : fast, convenient online submission thorough peer review by experienced researchers in your ﬁeld rapid publication on acceptance support for research data, including large and complex data types • gold Open Access which fosters wider collaboration and increased citations maximum visibility for your research: over 100M website views per year At BMC, research is always in progress. Learn more biomedcentral.com/submissions
Annals of Forest Science – Springer Journals
Published: Jan 2, 2023
Keywords: Heritability; Air-dry density; Microfibril angle; Bending properties; Load-deflection curve
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