Population genetics and taxonomy of important medicinal tree species of the genus Warburgia
| dc.contributor.author | Muchugi, Alice Njeri | |
| dc.date.accessioned | 2019-06-19T08:12:10Z | |
| dc.date.available | 2019-06-19T08:12:10Z | |
| dc.date.issued | 2007-07 | |
| dc.description | A thesis submitted in fulfillment of the requirement for the award of the degree of Doctor of Philosophy in Molecular Genetics in the department of Biochemistry and Biotechnology of Kenyatta University, Kenya. July 2007 | en_US |
| dc.description.abstract | The genus Warburgia (Canellaceae) has only four species (W. elongata Verdc., W. salutaris (Berto; f). Chiov, W. stuhlmannii Engl. and W ugandensis Sprague, which occur in east and central Africa. These species are of valuable medicinal importance to the local communities where they occur and have also gained interest from international herbal markets. The taxonomy of the species in this genus is conflicting with some authorities referring to the distinct species as con specific or synonyms. Genetic diversity present in wild populations of these species is under great threat due to unsustainable harvesting for medicines and indiscriminate felling trees and therefore there is an urgent need for conservation of these species. On farm planting is one of the best alternatives for ensuring the survival of the species and sustainable harvesting for their medicinal products. This research aimed to resolve the taxonomic confusion using molecular markers and to determine the genetic relationships within and among populations of the species in the genus Warburgia in order to guide strategies for their conservation and sustainable utilisation. Ecological survey showed reduced populations sizes of Warburgia species, which has being caused by land clearance for farming and settlement, timber, charcoal and fuelwood harvesting. The study showed a discontinuous tree distribution where young plants were not replacing mature trees coming to the end of their reproductive life. Significant differences were found in fruit and seed size between W ugandensis and W stuhlmannii. The chromosome number in W ugandensis and W stuhlmannii was found to be 2n=22 for both species, which implied that the species have conserved the basic chromosome number in the genus despite adapting to divergent ecological zones. The genetic relationships among Warburgia species were determined using the AFLP technique. Genomic DNA for the AFLP analysis was obtained through the CTAB method, which proved to be the best in efficiency and cost among the tested methods. Analysis of molecular variance (AMOV A) on data obtained revealed most genetic variation being among individuals within populations (63%, P< 0.0001), but variation among populations (37%, P< 0.0001) was highly significant as well. High genetic diversity was found within the studied populations. A phenetic tree and constrained ordination analysis illustrating the relationship among populations of Warburgia species showed a clear distinction among Warburgia species. A populations' subgroup of W ugandensis from Uganda and western Kenya clustered away from the rest of W ugandensis implying genetic distinctiveness while the coastal species (W salutaris and W stulhmannii) showed little genetic differentiation. The utility of AFLP and RAPD techniques to resolve intraspecies genetic variation in W. ugandensis populations was assessed and the two techniques showed high correlation (r=78, P< 0.001). However, AFLP technique had a higher marker index (24.96) than RAPD analysis (19.70). Assessment of type of mating system in W. ugandensis using the AFLP markers showed the species to be predominantly outcrossing (88.9%) with a low level of selfing (11.1 %). Implications of these findings to the taxonomy and genetic management of species in genus Warburgia are discussed. | en_US |
| dc.identifier.uri | http://ir-library.ku.ac.ke/handle/123456789/19492 | |
| dc.language.iso | en | en_US |
| dc.publisher | Kenyatta University | en_US |
| dc.title | Population genetics and taxonomy of important medicinal tree species of the genus Warburgia | en_US |
| dc.type | Thesis | en_US |
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