Effects of substrates, different pretreatment protocols and dehydration on the induction of seeds germination of Xylopia aethiopica (Dunal) A. Rich.

Abstract

Despite its socio-economic importance, the cultivation of Xylopia aethiopica is not popular owing to the difficulty in seed germination. As a step in its domestication process, investigations were undertaken on germination requirements and desiccation tolerance of seeds. Three substrates (forest top soil, river sand and a mixture of forest top soil and river sand) and 18 pre-germination treatments including a control (untreated seeds), a mechanical scarification, six heat treatments which were done by soaking seeds in hot water (100 °C) for different lengths of time, and ten acid scarifications which were done by soaking seeds in either sulfuric acid or hydrochloric acid for different lengths of time were tested for their effect on seed germination. Results showed that mean percentage germination was higher on the mixture of forest top soil and river sand (29.4 ± 2.6%) than on other substrates tested. While untreated seeds and those soaked in hot water irrespective of the duration of treatment failed to germinate, seed dormancy was successfully broken by either mechanical or chemical scarification. Soaking seeds in either concentrated HCl or concentrated H₂SO₂ for 5 min were the most effective treatments in breaking dormancy, with 80 ± 6.3% and 70 ± 6.3% mean germination recorded respectively. The desiccation tolerance test showed that X. aethiopica seeds are desiccation-tolerant and their storage behaviour is orthodox. This study shows that for propagating X. aethiopica from seeds, it is recommended that fresh or dried seeds be soaked in either concentrated HCl or concentrated H₂SO₄ for 5 min, and that seeding be done in substrate composed of a mixture of forest top soil and river sand in a 1:1 (v/v) ratio.

Keywords: Spice tree, domestication, seed dormancy, scarification, desiccation tolerance.