| Summary: | The study involved 13-year old provenance trials of Acacia mangium which are established at five sites, i.e. Sabal, Jakar, Oya, Labang and Sawai in the state of Sarawak, Malaysia. Five provenances are planted in those trials. Three provenances are from Australia (Rex Range, Broken Pole and Cassowary) and two are from Indonesia (Piru Ceram and Sidei). The main objectives of this study are to study the variation, the contribution effect of provenances, environments and genotype by environment interactions and their stability in growth and wood properties in provenances of Acacia mangium planted in Malaysia. It also aims to establish a radial trend of specific gravity and microfibril angle from pith to bark of those materials.
Substantial variations exist in all of the characteristics namely height, diameter, survival rate, specific gravity, microfibril angle, modulus of elasticity and modulus of rupture. Provenances have substantial effects only on diameter, specific gravity, microfibril angle, modulus of elasticity and modulus of rupture and very small effects on height and survival rate. Environmental factors play the major role affecting the growth characteristics i.e. height diameter and survival rate. However, the effects are not significant in all of the wood properties in Acacia mangium.
Genotype by environment interaction contributed significantly towards all but height involving in change of rank of all provenances across the sites. Although environment is not an important factor in influencing wood properties, a study to identify the environmental factors affecting the characteristics and causing the interactions would be vital to reduce the effect. All provenances performs inconsistently across all the five sites. This is well reflected in the stability analysis. Most of the provenances display an average stability based on growth characteristics while none of them display an average stability based on the wood properties.
Differences in linear regressions accounted for a small proportion of the total variation in interaction suggesting a non-linear relationship for most characters. Furthermore, the presence of GXElinear is very small and could not account for the total variation in interaction. Relatively large and significant mean square deviation from regression accounted for a major part of interaction effects, which further support the suggestion of non-linear
interaction.
Radial variation in specific gravity increases significantly from pith to bark. It ranges from 0.20 at pith to 0.80 at bark with a mean coefficient of variation of 0.56. In contrast, microfibril angle decreases significantly from pith to bark. The largest decrease occurs within the 50% of the stem from pith followed by a gradual decrease in the last 50% towards bark.
Radial variation is the most important factor affecting variation in specific gravity and microfibril angle (MFA) Of. Acacia mangium, contribute for 52% and 65% of the total variation respectively. Regression analysis shows very strong dependence of MFA on radial variation. Trees are the second largest contributor, accounting for 16% and 25% respectively. This variation provides a basis for an improvement in specific gravity and MFA of Acacia mangium.
Based on the results of this study, three options are available for breeding program of Acacia mangium in Malaysia. The first option requires the establishment of a number of breeding programs for each planting region. The second requires the establishment of only one breeding program. The first option produces good breeds which are good in specific environment. The second option produces good breeds with average stability and good in a range of environments. The third option is to make use of breeds with below average stability with good performance in poor environments. The third option is very suitable in Malaysian forest plantation by capitalising on the land with relatively poor soils allocated to the forest plantation sector.
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