Propagation techniques for a spineless Acacia wrightii and a weeping Ulmus parvifolia

Abstract

Three spineless phenotypes of Acacia wrightii G. Bentham ex A. Gray were identified with aesthetic landscape potential. Experiments in seed, cutting, grafting, and tissue culture propagation were undertaken to perpetuate this desired spineless phenotype. Germination percentages for mechanically scarified seeds ranged from 33% to 94%, however yield of spineless seedlings was low (0 to 34%). Sulfuric acid scarification for 10, 20, 30, or 60 minutes hastened and unified germination compared to non-treated seeds by seven to eight days. Vegetative propagation was successful for softwood cuttings. Rooting measures increased with auxin concentration from 0 to 15000 mg· L⁻¹, with maximum rooting percentage, root number, and root length per softwood cutting of 70%, 9.2 roots, and 12.4 cm, respectively, at 15000 mg· L⁻¹ auxin eight weeks after treatment. Rooting was not successful for semi-hardwood and hardwood cuttings. Whip-and-tongue and T-bud grafting were not successful with the treatments used, likely due to accumulation of phenolic compounds and inexperience in these techniques. Tissue culture of shoots from in vitro germinated seedlings indicated that shoot proliferation was greater in Murishige and Skoog (MS) medium with 15 to 20 [u]M zeatin in the first experiment. Shoot proliferation was greater on Woody Plant Medium with 20 [u]M benzyladenine in the second experiment. A weeping phenotype of Ulmus parvifolia Jacq. was identified with aesthetic landscape value. Cuttings at different growth stages using varied concentrations of a rooting hormone were compared to determine the most efficient method to perpetuate this desired phenotype. Softwood cuttings had a higher rooting percentage (84%), more roots regenerated per cutting (18) and longer total root lengths (50 cm) than either semi-hardwood or hardwood cuttings using 10000 mgʺL⁻¹ auxin. Semi-hardwood cuttings had greater height (153.4 cm) and trunk diameter (12.5 mm) at end of production in 6.3 L containers than softwood and hardwood cuttings, however, the survival rates were lower for semi-hardwood cuttings (29%) than for softwood cuttings (86%). Although successful rooting techniques were identified for the Ulmus clone, the weeping phenotype was not stable.