Germination response of Zanthoxylum capense (small knobwood) seeds to different pre-treatment protocols

Abstract

Background: Zanthoxylum capense is an important medicinal species in South Africa. It is propagated by seeds which are dispersed by different animals but the seeds rarely germinate even under favourable germination conditions which could be the result of dormancy. In addition, the species is currently listed as threatened in the Red List of South African Plants; therefore, it is of importance to find ways of promoting its propagation. Materials and Methods: The germination of Z. capense seeds in response to different scarification and stratification pre-sowing treatments was studied. Seed stratification included chilling at 4˚C. Seed scarification was performed mechanically, using hot and cold water, and using hydrochloric acid and sulphuric acid. Results: The highest final germination percentage (FGP) (71.1%) was obtained from seeds soaked in hot water for 15 minutes and grown in dark conditions. The 30 days chilling treatment also gave a good response (57.8%) when grown under light or dark conditions. Other FGPs of note included seeds soaked with 500 ppm gibberellic acid (GA3) (60%, light; 44.4%, dark) and 1000 ppm GA3 (46.7%, light; 48.9%, dark) and soaking in H2SO4or 5 minutes (42.2%, dark). Overall, the seeds sown under dark conditions produced better FGPs than those sown in light. Conclusion: These results reveal that Z. capense seeds display combinational dormancy that imposed physically by the seed coat and that imposed physiologically by the embryo. These dormancy traits can be easily overcome by either chilling or soaking in hot water or GA3.