Solanum mauritianum Scop. is rated the worst invader species in pine plantations throughout the Republic of South Africa. Control is costly and apparently ineffectual since the species is spreading in pine plantations at a rate of 16 % per annum. This is due to the high reproductive potential of the species. S. mauritianum produces fruits throughout the year. Fruit and seed yield is related to tree size. S. mauritianum produced approximately 7.2 million viable seeds per hectare during 20 months when growing under conditions unfavourable for growth. Seeds are efficiently dispersed by animals and birds. Although high seed or seedling mortality occurs, the initial prolific seed production and efficient dispersal ensures the rapid spread of this species in South Africa. Surviving seeds form the source for both further encroachment and reinfestation of areas in which S. mauritianum has been controlled. S. mauritianum seeds require the presence of both light and alternating temperatures for optimum germination. Transfer of seeds from unfavourable to optimum conditions or the application of gibberellic acid (GA [3]) can promote high germination percentages. However, the germination requirements of S. mauritianum are highly variable. Germination is influenced by site, season and year of seed shed. Seeds varied in terms of primary dormancy; conditional dormancy; the response to transfer from unfavourable to favourable conditions; the response to application of GA[3]; and the occurrence of secondary dormancy. Germination requirements of seeds were also influenced by site, duration and depth of burial. All these factors contribute to a sporadic seedling emergence over a prolonged period, which results in current control operations being both costly and ineffective. Alternative control methods were therefore considered. These included the application of herbicides or heat to kill seeds, application of various gro~th regulators to stimulate germination, and the chemical extraction of alkaloids from fruits and seeds for use in the pharmaceutical industry. Two alkaloids (solasodine and a new molecule) were extracted from green bugweed fruits growing under unfavourable conditions. Although levels of solasodine extracted were very low compared with those from commercially grown species of this genus, extraction of the second alkaloid raised the potential of the species for utilization purposes. Utilization of the reproductive propagules could reduce the continual dispersal of seeds and thereby contribute to long-term control of this species. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1990.

Solasodine, a steroidal alkaloid, is used by the pharmaceutical industry in certain parts of the world, as a raw material in the synthesis of steroid drugs. The compound is contained in many members of the genus Solanum, including S. mauritianum Scop., a common weed in South Africa. The levels of solasodine in three culture systems of S. mauritianum under various cultural conditions were examined. A high performance liquid chromatographic (HPLC) method was developed for the detection of solasodine. In order that low-cost, fixed wavelength ultra-violet detectors could be used, which would make the technique more widely applicable, a derivatization step, namely benzoylation, was included in the sample preparation. An extraction and purification protocol was then established, that complemented the HPLC technique and allowed successful detection of solasodine levels in a whole range of different sample types, including callus, suspension cultured cells, roots, stems and leaves. The three culture systems examined were callus, suspension and hairy root cultures. The callus system was used to establish which cultural parameters affected solasodine content in vitro to the greatest extent. A control culture was grown on a MURASHIGE and SKOOG (1962) medium (excluding glycine) supplemented with 3 % sucrose, 0.1 g I ¯¹ myo-inositol and lacking hormones. This culture contained an average of 9.2 μg g ¯¹ DW of solasodine. Many factors, including alteration of the carbon : nitrogen ratio and substitution of Gelrite for agar as the gelling agent, had no significant effect on the solasodine content of the callus or its growth. Greatly increased solasodine productivity of the callus was recorded when glucose was substituted for sucrose, the medium strength was reduced by half, or certain combinations of the hormones benzyladenine and naphthaleneacetic acid were added to the medium. The maximum levels of solasodine recorded in these cultures, on a per gram dry weight basis, equalled those of the vegetative parts of an intact S. mauritianum plant, but were approximately three times lower than those of the green berries. Suspension cultures could not be grown on the same medium as the callus cultures. Substitution of the vitamin complement of MURASHIGE and SKOOG (1962) with the so-called RT vitamin complement of KHANNA and STAB A (1968), resulted in successful growth and maintenance of S. mauritianum suspension cultures. The auxin, 2,4-dichlorophenoxyacetic acid (1 mg I ¯¹) was included in the medium. None of the suspension cultures grown on this medium, or slight modifications thereof, contained any trace of solasodine. This system could therefore not be used for the synthesis of solasodine in vitro. Hairy root cultures were initiated by inoculation of an excised hypocotyl of an in vitro-grown seedling of S. mauritianum with a 48 hour culture of Agrobacterium rhizogenes LBA 9402. Transformation frequency was extremely low. The transformed roots could be excised and grown successfully on a phytohormone-free medium, either in the solid or liquid form. Solasodine was extracted from hairy roots grown in a full-strength liquid MURASHIGE and SKOOG (1962) medium (excluding glycine) supplemented with 3 % sucrose and 0.1 g I ¯¹ myo-inositol, a half-strength such medium and a full-strength medium with 3 % glucose substituting for 3 % sucrose. In the latter medium, growth was very poor, whereas in the other two media, growth was very rapid . Both solasodine content (126 μg g¯¹DW) and root growth were greatest in the full-strength medium supplemented with 3 % sucrose. This level of solasodine was greater than that found in any of the callus cultures or vegetative parts of the plant and approached that of the green berries of S. mauritianum. Overall, of the culture types of S. mauritianum tested, the hairy root culture system appears to be most favourable for the in vitro production of solasodine. / Thesis (Ph.D)-University of Natal, Pietermaritzburg, 1993.

Student Number : 9202137P - MSc Dissertation - School of Animal, Plant and Environmental Studies - Faculty of Science / The Reconstruction and Development Programme’s Mpumalanga Working for Water Programme (WWP) has cleared exotic and commercial weed species from the riverine environment since 1994. This study serves as an assessment of the impact and modification caused as a result of invasion and the subsequent clearing of the exotic vegetation on flora in the riverine zone of the Sabie River Catchment. The experimental design compares the before and after clearing effects and includes altitude and invasion intensity variables. The investigations included: in situ soil seed banks, environmental modification, vegetation structure, species diversity and effectiveness of clearing. Clearing and invasion by exotic species altered soil chemical, physical and ground cover parameters. The extent of these modifications was dependent on the extent of invasion and clearing done within the community. Clearing of exotic species however, acted as an additional disturbance to that caused by invasion. Environmental modifications that occurred with clearing and invasion within the study were positively related to percentage soil organic matter, and ground cover (soil, litter, vegetation). Invasion by exotic species alters the vegetation structure, the extent of which was directly related to the invasion intensity. The main source of vegetation structure modification is attributed to tall growing exotic species such as Eucalyptus grandis and Solanum mauritianum. Both of these species dominated the indigenous vegetation, E. grandis by expanding the upper canopy and S. mauritianum by dominating the mid canopy. Clearing of invasive vegetation resulted in an additional disturbance proportional to the extent of invasion intensity. Invasion did not result in any large changes to the vegetation at low intensity but clearing at this intensity increased the disturbance and altered the vegetation structure. Soil seed banks were limited in the number of species and dominated by two exotic species. The soil seed bank of woody species related positively to the community species richness. The total soil seed bank density did not relate to invasion intensity or clearing thereof but propagules of individual species within the soil seed banks did. The seeds of the exotic species, Acacia mearnsii and S. mauritianum, illustrated burial as prerequisite for persistence in the soil seed bank. A. mearnsii and S. mauritianum seeds were found to have half-life’s of up to 25 years and 13 months respectively. The species richness and diversity varied only marginally because of invasion and clearing. Species alpha diversity increased with clearing due to weedy and pioneer species establishment. Beta diversity effectively highlights the species turnover with clearing and invasion. Success in eradication of exotic species had mixed results. Clearing of high invasion sites was effective but in lower invasion categories a number of exotic individuals were missed. Clearing effectiveness was good for certain species such as E. grandis and Pinus patula, but poor for others such as S. mauritianum. Coppicing is a significant issue for E. grandis and S. mauritianum. The persistence of individuals (coppicing & missed individuals) coupled with very large persistent seed banks has repercussions for the clearing programme, as it may prevent effective eradication. Initially the WWP has been successful in removing exotic vegetation, however there is a failure to address the regenerative properties of some exotic species. Unless a rigid schedule of follow up clearing treatments occurs, an even larger invasion problem could exist.