Effect of seed weight and light on in vitro germination of Afzelia africana Sm. ex pers

Abstract

The micropropagation potential of Afzelia africana; a threatened multipurpose tree plant was investigated in this study with the aim to determine the effect of seed weight on its in vitro germination as well as the impact of light and dark photoperiod on the seed germination. Murashige and Skoog (MS) 1962 media was used for this study. Five categories of seed weight were used 3.3 – 3.7 g (Wt1), 2.8 – 3.2 g (Wt2), 2.3 – 2.7 g (Wt3), 1.8 – 2.2g (Wt4) and 1.3 – 1.7g (Wt5). The seeds were cultured on MS media after disinfection with H₂SO₄ for 30 minutes followed by soaking in distilled water for 120 minutes. Cultured seeds were then kept in the incubator at a temperature of 25 ± 2^oC and 16/8-hour photoperiod and under complete dark condition. Observable physiological responses of seed coat break (SB), root emergence (RE), cotyledon opening (Cop), shoot emergence (SE), and plant height (PH) of cultured seedlings were recorded after 4 weeks. Morphological data including the ratio of epicotyl to hypocotyl was also documented. Using one-way analysis of variance (ANOVA), seed weight had no significant effect on SB, RE and SE, however, it had significant effect on CoP as a seeds with the highest weight Wt1 had their cotyledons opening earlier (14.50±0.50^a ) compared to seeds with the lowest weight Wt5 (16.50±0.50^b ). Also, LN of Wt1 was significantly higher than LN in other seed weights, while with PH, Wt1 (14.86±0.24^a ) was significantly higher than Wt4 (12.86±0.43^b ) and Wt5 (10.16±0.19^c) at P<0.05. The seed weight of Afzelia africana has effect on its in vitro germination parameters, thus to produce vigorous seedlings of significant leaf numbers and plant height, seeds with weight range of 3.3 – 3.7 g should be cultured and to produce higher height seedlings, the seeds should be grown first under total darkness and transferred to light photoperiod of 16/8 hours.