Acacia mangium and A. auriculiformis flowered between February and May, producing mature pods between October and April. The flowers of both species were similar in structure and showed weak protogyny and variable levels of andromonoecy. Male flowers either lacked pistils completely or had small sterile pistils. Controlled hand pollination resulted in pollen tubes in the pistil and penetration of the ovules following self and cross intraspecific and interspecific pollination. The cross A. auriculiformis × A. mangium was more successful than the reciprocal, but fertile seed was produced following interspecific pollination in both directions and all seedlings were shown to be hybrid by isozyme analysis of parents and seedlings. There were relatively few insect visitors to the flowering branches, but the same suite of insects was observed foraging for pollen on both species. Native bees belonging to the Halictidae carried most polyads on their hairy bodies and may act as pollinating agents. There appeared to be no major fertility barriers to interspecific hybridisation between Acacia mangium and A. auriculiformis, and hybrids could occur spontaneously via synchronous flowering and common insect visitors.

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Mass production of seed by controlled crossing of selected individuals is an increasingly important method of capturing genetic gain from tree breeding. In Eucalyptus the conventional controlled pollination (CP) method requires at least three separate visits to a flower, and seed is correspondingly costly. This paper reports development of a cost-efficient pollination technique referred to as one-stop pollination (OSP) for application in seed orchards of Eucalyptus globulus Labill. in Chile. Emasculation of the flower at anthesis is followed by slicing the stigma and top of the style to provide a site for pollen adherence. Pollen is applied immediately, followed by isolation of the style from contaminating pollen by covering with a section of tubing. It is then not necessary to revisit until capsule harvest. Seed yield per capsule after OSP treatment was equivalent to that achieved by treating flowers with supplementary pollination at the time of natural stigma receptivity. Only 5% of those flowers pollinated at anthesis without style wounding set a capsule, compared with 69% with OSP. Seed yield for OSP averaged 26 seeds per capsule compared with 12 for open-pollinated samples from the same trees. The effect of orchard location on OSP harvest percentage and seed yield was demonstrated. With application of OSP in the environment of the Chilean orchard, we estimate a sevenfold reduction in seed production cost in comparison to conventional pollination techniques.

Floral phenology and morphology of colchicine-induced auto-tetraploid trees of Acacia mangium Willd. (AM-4x) growing in Vietnam were compared with adjacent diploid A. mangium (AM-2x) and A. auriculiformis A.Cunn. ex Benth (AA-2x). Flowering lasted for several months with a slightly later peak flowering period for A. auriculiformis (December–January), than for A. mangium (November–December). Flower spikes of AM-4x were shorter and had fewer flowers per spike than those of AM-2x, but were longer and had more flowers than AA-2x. Percentages of male to hermaphrodite flowers were less than 23% for all three species/ploidy combinations. Flowers of AM-4x had slightly shorter styles than did AM-2x, but AM-4x stigma and polyad diameters were greater. For all polyad-stigma combinations among species/ploidy levels, at least one polyad could be accommodated. AM-4x had fewer (13) ovules per ovary, compared with AM-2x and AA-2x (14–16). AM-4x set fewer (less than 3) seeds per pod than did AM-2x and AA-2x (7–8 and 5–6, respectively). Foraging behaviour of the main insect pollinators (honeybees) and examination of polyads collected from them suggested interspecific and interploidy pollination would occur. There appeared to be no phenophase or flower structure barriers to interploidy pollination.

The paper reviews a decade of progress with breeding new polyploid varieties of Acacia mangium and other tropical acacias in Vietnam, and outlines plans for future strategies to complement conventional diploid breeding. Polyploid breeding is a means of introducing diversity into breeding populations, of making step-change improvements in wood fibre and other properties, and reducing reproductive output of these potentially weedy taxa. To date we have demonstrated that A. mangium tetraploids have larger and thicker wood fibres and we have strong preliminary evidence that the reproductive output of triploids is indeed reduced. Other potential benefits such as wind and stress tolerance and disease resistance are under field evaluation. Trials demonstrate that colchicine-induced tetraploids, whether derived from pure A. mangium seeds or from commercial hybrid clones, are substantially slower growing than diploids. While not the sole determinant of crop value, volume production is hugely important to growers, so long-term success of the program is critically dependent upon demonstration that this problem can be resolved in advanced generations. Future emphasis will be on production of triploid and tetraploids from the interspecific hybrid A. mangium  A. auriculiformis. The better rooting ability contributed by A. auriculiformis maximises prospects for operational cloning of select trees. Highly heterozygous hybrids also offer the better prospect for exploiting heterosis. A strategy for developing a diverse breeding population of neo-tetraploid F 1 hybrids is presented.