Abstract

Studies on the ecology, morphology and molecular phylogeny were undertaken with a view to understand the colonisation patterns and evolution of the Diospyros species in Mauritius. On another front, phytochemical screening and antibacterial properties of plant extracts from the Diospyros species were carried out to investigate the pharmacological properties of these species. The distribution of the Diospyros species and populations were examined with respect to their presence in the different altitudinal ranges, humidity zones, soil and forest types. Analysis of the results obtained showed that except for D. egrettarum which is restricted to the east coast of Mauritius, the other Diospyros species have a relatively broad distribution. However, the abundance of these species indicated that some of them have a marked preference for humid to super humid habitats while others seem to favour sub humid to dry regions. Phenological observations revealed that Diospyros species, which share neighbouring habitats, tend to have staggered flowering periods that act as reproductive barriers among these species. Although the Mascarene Diospyros species are all dioecious, female flowers still retain a number of staminodes suggesting that they have the potential of developing functional stamens while the male flowers have only male reproductive organs. Examination of the flowers of the local Diospyros species indicated the occurrence of leaky dioecy in one species namely, D. egrettarum. Furthermore, these leaky dioecious plants produced fruits with viable seeds. A male-biased sex ratio was noted in the species D. egrettarum, D. leucomelas, D. melanida, D. revaughanii and D. tessellaria. Given that in all Diospyros species, the germination of Diospyros seeds is relatively low and the sex ratio in Diospyros populations is male-biased, germination of the seeds which first landed in Mauritius would have led to more adult male than female plants. Therefore, leaky dioecy could have come to the rescue of a solitary male Diospyros plant whose survival would have depended on its ability to bear fruits with viable seeds. In an attempt to find molecular markers to distinguish between female and male Diospyros plants, the genomic DNA of male and female D. egrettarum plants was assessed by Random amplified polymorphic DNA (RAPD), using fifty random decamer primers. The RAPD profiles generated were highly monomorphic. Out of the three polymorphic bands for the female samples tested only the one generated by the primer OPC02 consistently appeared in all the female samples and was hence considered as a potential sex-associated RAPD band for Degrettarum Phylogenetic trees based on 35 morphological characters and the Internal Transcribed Spacer (ITS) regions of the ribosomal DNA were reconstructed for the Mascarene Diospyros species. The morphology and molecular trees had limited agreement on the relative positions of the major clades. It would seem that parallel or convergent evolution of some morphological traits obscured the actual phylogenetic relationships of some species and their relative positions could not be determined in the morphology based strict consensus tree. On the other hand, the molecular data generated well resolved phylogenetic trees that have provided additional information on the colonisation patterns of the Diospyros species in Mauritius. The general trend outlined by the phylogenetic analysis showed that closely related species shared neighbouring habitats. Morphological and molecular data sets also suggest that Mauritius could have acted as a centre for the dispersal of Diospyros species in the Mascarenes as both D. borbonica (Reunion) and D. diversifolia (Rodrigues) are nested within the Mauritian Diospyros species. The Mauritian endemic Diospyros species were screened for their phytochemical contents, polyphenolic contents and their antibacterial properties. Preliminary phytochemical screening showed the presence of reducing sugars, tannins, cardiac glycosides and terpenoids in all the eleven species. Steroids, saponins and anthraquinones were present in all species except for D.pterocalyx and D.egrettarum. However, alkaloids were present in D.neraudii and D.revaughanii only. D.eggretarum contained the smallest amount of polyphenolics compounds whereas D.melanida had the highest amount of polyphenols. Bacterial strains B.cereus, B.spizizenii, S.aureus, S.epidermidis, P.mirabilis, K.pneumoniae, A.baumanii, E.coli and P.aeruginosa were sensitive to the Diospyros extracts while S.aureus, P.aeruginosa and A.baumanii were resistant to positive controls but were sensitive to the plant extracts. These properties can be attributed to the high presence of polyphenols, flavonoids, tannins, saponins, anthraquinones and especially terpenoids.