Germination characteristics and early seedling growth performances of vachellia erioloba, pterocarpus angolensis and dalbergia melanoxylon

Dissertation

The exploitation of Miombo trees, including Vachellia erioloba, Pterocarpus angolensis and Dalbergia melanoxylon depends on the naturally growing populations because their domestication in artificial plantations has little success. The rate at which D. melanoxylon and P. angolensis are harvested is of great concern considering that the trees regenerate poorly in the forest because of poor survival of seedlings. There is also a delay in seed production for D. melanoxylon and the seed is susceptible to diseases. The assessment of germination characteristics and early seedling growth of V. erioloba, P. angolensis and D. melanoxylon was conducted to provide scientific recommendations on the outcomes of the effects of pre-treatments on germination and seedling growth. Two experiments were conducted on seed germination with a complete randomized design (CRD) with four replications in the laboratory and on the seedling growth from germinated seeds in the nursery. The germination experiment involved five pre-germination treatments; (i) hot water treatment at temperature of 100oC for 30 minutes; (ii) chemical scarification method using concentrated Sulphuric acid (H 2 SO 4 ) 98% exposure for 20 minutes; (iii) 6% Hydrogen peroxide (H 2 O 2 ) exposure for 20 minutes; (iv) mechanical scarification; and (v) control. After the germination experiment, seedlings were taken to the growth room then arranged in a CRD design. Shoot length, root collar diameter, and number of leaves were measured after every five days until they reached five months old. Root diameter, root length, dry weight and green weight were taken at the end of the experiment. Results from the study identified optimum seed germination mean percentages of the three species to five pre-treatments where by mechanical scarification showed a higher percentage of 78% in V. erioloba while hot water had a lowest percentage of 23%. For P. angolensis, mechanical scarification had the highest percentage of 68%, while the lowest percentage was 33% in the Hydrogen peroxide treatment. D. melanoxylon, had a higher germinationiii of 58% with hot water treatment while seeds could not germinate (0%) with Sulphuric acid treatment. Moreover, results showed a significant differences in the shoot length, number of leaves and root- collar diameter in all pre-sowing treatments for the three tree species (P<0.05). The recommended pretreatment for P. angolensis and V. erioloba is mechanical scarification while hot water is recommended for D. melanoxylon.

The Ministry of Environment, Natural Resources Conservation and Tourism of the Republic of Botswana