Improving propagation methods of Gnetum africanum and G. buchholzianum from cuttings for rapid multiplication, domestication and conservation

Deforestation and increased demand of G. africanum and G. buchholzianum leaves have considerably resulted in a decline of the wild population of these valuable agroforestry products only found in Africa. A study was conducted to improve adventitious rooting using cuttings of each species soaked for 12h in solution of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) or 1-naphthaleneacetic acid (NAA) at 0, 50, 100, 150 or 200mg/L before planting in non-mist propagators. Cuttings of G. buchholzianum showed better rooting performances than those of G. africanum. Apart from cuttings of G. africanum treated with IAA at 200mg/L, the three auxins significantly increased the percentage of rooting compared to the control. The best rooting percentage in G. africanum (77.33%) and G. buchholzianum (95.33%) was noticed in cuttings treated with NAA (100mg/L) and IBA (100mg/L), respectively. Pretreatment of African Gnetum cuttings with auxins at almost all the tested concentrations significantly increased root length, root number and root dry weight compared to the control. The pretreatment duration of cuttings also significantly affected rooting efficiency in both species with maximum rooting percentage observed on cuttings pretreated for 12h. However, above the 12-h duration, majority of the measured rooting traits were reduced in treated cuttings. Rooted cuttings grew successfully after being transferred to pots filled with soil substrate. This study demonstrates the utility of auxin treatment of cuttings for the mass production of African Gnetum plantlets, which will facilitate the domestication and prevent the overexploitation of wild stocks.