Propagation for commercial production of sweet acacia (Vachellia farnesiana): a native plant with ornamental potential

Abstract

Sweet acacia (Vachellia farnesiana (L.) Wight & Arn. [Fabaceae]) is an evergreen or drought-deciduous tree with attractive foliage and fragrant yellow flowers. This Florida native has high drought tolerance and is underutilized in landscapes because of its limited availability and the limited knowledge of commercial production techniques. We conducted a series of 4 propagation studies for practical application by nurseries looking to grow sweet acacia. In Experiment 1, seeds were scarified with either sandpaper or boiling water treatments prior to soaking overnight. After 23 d, 62.7% and 76.0% emergence were achieved for the sandpaper and boiling water treatments, respectively, whereas the non-scarified control treatment resulted in only 1.3% emergence. For both the sandpaper and boiling water treatments, half of the seeds germinated by day 10.5 (T50). Two-thirds of the resultant seedlings were polycotyledonous, having 3 and 4 cotyledons and 6.8 times more branching when compared to those with 2 cotyledons. In Experiment 2, we scarified seeds with boiling water overnight and then sorted them by their appearance (imbibed versus non-imbibed). Initially, the visually imbibed seeds had the highest emergence followed by the visually non-imbibed seeds, and then the control seeds. Yet after 23 d, emergence was similar among imbibed (96.7%) and non-imbibed (87.8%) seeds and greater than the control (11.1%). We conducted Experiments 3 and 4 to determine if cutting propagation is a feasible alternative to seed propagation. In Experiment 3, the effects of liquid rooting hormone (auxin) concentrations on rooting were explored using semi-hardwood cuttings quick dipped with liquid Dip’N Grow (indole-3-butyric acid [IBA] + 1-naphthaleneacetic acid [NAA]) at concentrations of 4000:2000, 2000:1000, 1000:500, 500:250, and 0:0 mg/l (ppm) IBA:NAA. Regardless of treatment, few cuttings rooted and (or) survived the length of the experiment. In Experiment 4, the effects of talc rooting hormone concentrations on root formation were explored using younger stock plant cuttings and humidity domes placed within the mist house. When stuck with talc Hormex at 0, 8000, and 16,000 mg/l (ppm) IBA, 53% to 73% cutting survival was achieved with similar rooting percentage between treatments; however, cuttings treated with 16,000 mg/l (ppm) IBA had longer roots. Results confirm that asexual propagation of sweet acacia is possible by stem cuttings; however, the process is slow and not successful at rates necessary for commercial production. Instead, efficient sexual propagation can be reliably performed using a pre-sowing scarification treatment to alleviate physical seed dormancy.