Tetraploid induction of Acacia crassicarpa using colchicine and oryzalin

Australian Acacia, including Acacia crassicarpa, are important plantation species but prolific seed production may lead to weediness concerns. Sterility via production of triploid Acacia is potentially a solution to combat weediness. The aim of this study was to describe tetraploid induction using colchicine and oryzalin on seeds of A. crassicarpa as the first step towards development of triploids. Seeds were nicked and exposed to different concentrations of colchicine and oryzalin for 24 hours, germinated and grown under natural light at 26°C. Germination, subsequent growth and survival were assessed and efficiency of induced tetraploidy determined using flow cytometry when seedlings were 2 to 7 months old. The highest conversion rate achieved was 21% with 61% survival when seeds were exposed to 0.02% colchicine. The most effective oryzalin treatment was exposure to 0.005% oryzalin with 5% tetraploidy and 62% survival. There were no survivors in the highest concentration of colchicine tested (0.5%). Germination and survival were not severely impeded by the highest concentration of oryzalin (0.01%). Treatment in oryzalin also produced more mixoploids relative to the number of tetraploids than colchicine treatment. The 2C DNA amounts for A. crassicarpa of differing ploidy were estimated as 1.75 (diploid), 2.74 (triploid) and 3.47 pg (tetraploid).