Overcoming dormancy, and establishment of a micropropagation protocol to conserve Ziziphus spina-christi

Ziziphus spina-christi is a multipurpose wild tree that has been described as endangered in Nigeria and Saudi Arabia due to anthropogenic activities, seed dormancy, and ineffective vegetative propagation methods. The present study aimed to develop efficient seed germination and micropropagation protocols for conservation of Z. spina-christi. The effects of seed pre-treatments and environmental conditions on seed germination were investigated via conventional germination methods. Removal of the seed coat improved germination from 46.6 (control) to 86.6% after 28 days of sowing. Watering the soil every day resulted in significantly lower germination (53.3%) than watering on alternate days (100%) or every four days (86.6%). The optimal temperature for germination was between 21 and 35 °C (86.6%). In the micropropagation experiments, the highest number of shoots/explant (5) was achieved through node culture when the second node was treated with 2 mg L−1 zeatin. Rhizogenesis was only achieved when the basal cut ends of shoots were dipped in 200 mg L−1 indole-3-butyric acid for one hour, resulting in 80% rooting and 4 roots/shoot. Rooted shoots were acclimatised in a sterile potting mix: vermiculite (1:1) with 100% plantlet survival in the greenhouse. Plantlet regeneration via somatic embryogenesis was unsuccessful as embryo induction with 1 mg L−1 each of 2,4-dichlorophenoxyacetic acid, picloram, indole-3-acetic acid, and naphthalene acetic acid inhibited embryo development on maturation media, attributable to the persistence of exogenous auxins in the tissue. This study provides cost-effective methods for conserving Z. spina-christi through seed propagation and also offers the alternate conservation approach of clonal propagation via node culture. Efficient protocols for seed germination and in vitro propagation through node culture have been developed for Ziziphus spina-christi. The work opens new pathways for the propagation and conservation of Z. spina-christi.