Floral phenology and morphology of colchicine-induced tetraploid Acacia mangium compared with diploid A. mangium and A. auriculiformis: implications for interploidy pollination

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.