Microsatellite analysis of seed production systems in Acacia mangium

Acacia species, especially A. mangium, have performed well in plantations, with a wide range of uses either local or industrial. Therefore, A. mangium has been selected as a major plantation species in Southeast Asia. Tree improvement programs for A. mangium have been started in several countries. The development of interspecific hybridization techniques has been an important new-development for Acacia species because of the outstanding performance of selected clones of the A. mangium xA. auriculiformis hybrid in plantation forestry. In addition, in recent years, tetraplc:>i~ clones of A. mangium have been introduced to Vietnam. It was hoped that tetraploid A. mangium could be used to develop triploid individuals which might have the advantage of sterility or low fertility; and in the case of triploid A. mangium x A. auriculiformis retain the superior growth performance and/or wood properties _ of the hybrid. This thesis reports two studies that used micro satellite markers to support tree improvement for A. mangium. The first study used seven microsatellite markers to test the success of different _ methods of producing control-pollinated seed of A. mangium, with and without emasculation. Only 3% of selfing and approximately 9% contamination with nontarget outcross pollen were detected in un-emasculated methods, while the level of contamination found in emasculated methods was 19%. No difference in the levels of selfing and contamination were found between methods when a sugar solution was added to the female flowers prior to pollination. It is suggested that emasculation may not be necessary to produce controlled pollinated seed for A. mangium. The second study also used seve~ microsatellite markers to compare outcrbssing rates between diploid and tetraploid A. mangium in a clonal seed orchard that was established in Vietnam with.alternate rows oftetraploidA. mangium, diploid A. mangium and diploid A. auriculiformis. There was a large and 'significant difference in outcrossing rate between diploid clones which had almost complete outcrossing _ (97%, s.e. 5.3%) and tetraploidA. mangium clones that displayed a very low degree of outcrossing (1.9%, s.e. 1.1 %). One of the main purposes of establishment of this mixed seed orchard was to produce triploid seeds. However, no triploid progeny were found among 96 diploid and 161 tetraploid seedlings, while three tetraploid progeny were confirmed to be outcrosses between different teraploid clones. Several explanations for the absence of triploids are considered. While it is probable that there may be a barrier to pollination between diploid and tetraploid clones in this seed orchard, phenological data showed that the flowering times of adjacent diploid and tetraploid individuals overlapped, so the barrier to production of triploids does not appear to be the result of differences in flowering time.