Effects of seed viability and pre-treatments on seed germination of two indigenous species-Strychnos cocculoides Baker and Guibourtia coleosperma (Benth.) Leonard in Namibia

摘要

Strychnos cocculoides Baker (Monkey orange) and Guibourtia coleosperma (Benth.) Leonard (False mopane) are two socio-economically important indigenous species for rural communities in the northern regions of Namibia. The exploitation of these indigenous species is causing rapid declines in the goods and services produced. In addition, nursery experiments to assist the germination of these indigenous woodland trees are limited. This study aimed at investigating the effects of six pre-treatments [control, cold water (15 degrees C), warm water (50 degrees C), hot water (90 degrees C), scarification and chemical with 32% HCl] on the seed germination of both species. Prior to the pre-treatments, sample seeds were tested for viability using the tetrazolium and rag doll tests. This was conducted to determine whether the seeds used in this study were viable and had a germination potential. For both species, over 80% seeds were viable with the tetrazolium test. Germination results indicated a significant difference between the six pre-treatments, which was more pronounced for S. cocculoides than for G. coleosperma. For S. cocculoides seeds, warm water (80%), cold water (70%) and control (untreated seeds) (63%) yielded greater percentages of germination than hot water (40%), scarification (3%) and HCI-chemical (0%) after 7 weeks of germination. For G. coleosperma seeds, warm water (83%), cold water (80%), control (80%) and hot water (70%) produced the highest percentage of germination, compared to chemical (67%) and scarification (67%) pre-treatments. The control, cold and warm water pre-treatments showed germination of S. cocculoides seeds within 3 weeks of sowing, while for other treatments, seeds only germinated 4 weeks after sowing. Guibourtiacoleosperma untreated and warm water-treated seeds germinated earlier (week 2) compared to the other pre-treatments, for which germination only occurred during week 3. Therefore, the study recommends warm water as an ideal pre-treatment to promote germination in S. cocculoides and G. coleosperma species. Potential future studies could investigate effect of different temperatures and photoperiods on the germination percentage of the two species.