Production of colchicine-induced autotetraploids as a basis for sterility breeding in Acacia mangium Willd

Australian acacias are widely planted as exotics and in some cases as invasive. Impact may be reduced if sterile triploid planting stock can be developed. This article reports the first step in such a breeding programme, the production of a population of tetraploid lines for inter-breeding with diploids. Three methods of polyploid induction with colchicine were compared. A conversion rate of 8.9 per cent was obtained by applying 1.5 per cent colchicine to the shoot apical meristem of seedlings. A 7 per cent conversion rate was obtained by germination of scarified seed on filter paper saturated with 0.02 per cent colchicine for 16 h and this method is recommended on logistical and safety grounds. Poor results were obtained when scarified seed were submerged in aqueous solutions of colchicine. Flow cytometry is the preferred method for ploidy determination, sampling after vegetative phase change on a minimum of two opposing phyllodes per plant. Visual classification was inaccurate due to the confounding effects of growth-retarding properties of colchicine. Size and distribution of stomata can also be used but is more time consuming than flow cytometry. At 26 months, tetraploid plants had heavier, thicker, wider and more cupped shaped phyllodes than diploids and the bark: stem diameter ratio was greater.