Aspects of seed propagation of commonly utilised medicinal trees of KwaZulu-Natal.

Abstract

Due to over-exploitation of commonly-used medicinal plants, mainly from KwaZuluNatal, because of ever-increasing human population growth, many of the useful medicinal plants are becoming depleted in their natural habitats. Some species like Warburgia salutaris, which is currently declared very rare in the KwaZulu-Natal province, appear to be on the verge of extinction. In order to counteract this overexploitation, this study sought to provide information that could help resource users to grow these threatened species through ex situ conservation methods. A short list of heavily utilised medicinal tree specles was selected from the approximately 700 tree species indigenous to KwaZulu/Natal. The criteria considered for short listing were; life form, species scarcity, past population status and part used. A total of 23 species were short listed, but a subset of 12 species was selected based on the availability of fruits and seeds. The aim of short-listing was to work on a manageable number of commonly utilised medicinal tree species. The seed physiology and growth of these species were studied. With the exception of Erythrophleum lasianthum and Curtisia dentata, all of them had a moisture content of 2': 20 % (on a dry mass basis), which is indicative of a recalcitrant behaviour. However, it could not be concluded that these seeds were truly recalcitrant because desiccation sensitivity was not directly assessed. Using the triphenyl tetrazolium chloride (TTC) viability test, most of the seeds of the 12 species seemed to be of good quality. Results of the TTC test for seed viability were similar to results obtained v using direct germination for most species. Results of flotation test for seed viability were different from the results obtained using direct germination for most spcies. The pre-treatment which achieved the highest germination percentage in almost all the seed types was cracking the outer coverings. Cracking pre-treatment appeared to be efficient in enhancing the removal of some substances which might inhibit germination of seeds. Hot water and acid pre-treatments frequently reduced germination. Growth of young seedlings was assessed in terms of stem diameter, height, and leaf area under sun and shade. Seedling growth in terms of stem diameter and height of most species did not show any significant difference. One of the few species which showed statistically significant differences in stem diameter growth was Ekebergia capensis. It was found that 3 out of lO of the species showed statistically significant differences in height growth. Two of the statistically significant differences in height occured on seedlings in the sun while one had statistically significant difference in the 40% shadecloth while 7 did not. Significant differences in leaf area occured on 7 out of lO species. Of these, 4 species had higher growth in the shade than in the sun while 3 had higher growth in the sun than in the shade. Generally, it appears that young developing seedlings establish themselves well under shade environment; this could be because most of the species used in this study are forest species.