Immature, green female cones of Pinus patula Scheide et Deppe. were collected on a weekly basis during the South African summer months from December 1991 to February 1992 and from December 1992 to March 1993. Embryogenic tissue was initiated from excised megagametophyte explants containing immature zygotic embryos. Embryogenic induction was achieved using both MSG (BECWAR, NAGMANI & WANN 1990) and DCR (GUPTA & DURZAN 1985) media. The highest induction frequency was obtained on DCR1 (Douglas-fir Cotyledon Revised) medium supplemented with 0.5 mg 1 ¯¹ BA and 3.0 mg 1 ¯¹ 2,4-D, using L-glutamine as the major nitrogen source. Embryogenic tissue was translucent-to- white and mucilaginous in nature, composed of elongated, suspensor-like cells. The tissue was extruded from the micropylar end of the female gametophyte. In comparison, nonembryogenic tissue was produced from the gametophytic tissue itself and consisted of small, compact, spherical cells, crystalline in nature. Anatomical studies of developing patula seed demonstrated that the production of embryogenic tissue from the immature explants co-incided with the period, approximately two weeks after fertilization and with the occurrence of cleavage polyembryony in the developing zygotic embryos. Embryogenic tissue was maintained in culture by a recapitulation of the cleavage process. Transfer of the embryogenic tissue to DCR2 medium containing 1.3 mg 1 ¯¹ ABA resulted in tissue maturation and in the subsequent development of somatic embryos. Presence of ABA in the culture medium stimulated the development of cotyledonary initials in the apical region of the embryos. Elongated embryos, possessing small cotyledons, were rooted (50 to 60 %) on MSG6 medium containing no plant growth regulators. Somatic plantlets were successfully hardened-off under greenhouse conditions. Liquid culture methods were found to be a useful means of rapidly increasing the volume of embryogenic suspensor masses. Maturation , in terms of somatic embryo development and the production of cotyledonary initials, though , was not obtained in suspension. Reestablishment onto agar-solidified medium (DCR2) was required before maturation could occur. ABA is also responsible for stimulating reserve deposition and mobilization. In this regard, lipid accumulation in the developing somatic embryos was quantified and found to be significantly lower than in developing zygotic embryos. Similarly, non-matured embryogenic tissue contained less lipid deposits than matured (ABA-treated) tissue, indicating the requirement for ABA during maturation. Quantification of the lipids deposits is useful in determining the potential for somatic embryos to acclimatize to ex vitro conditions since their further growth and development is based on their ability to accumulate storage reserves. Somatic embryogenesis was found to be a useful method of propagation, producing plantlets with seedling-like qualities. This development has important consequences for the production of clonal plantlets in the Forestry Industry. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

A comprehensive revision of the genus Justicia L and, the closely related genera Siphonoglossa Oersted and Aulojusticia Lindau in southern Africa was undertaken as part of the Flora of Southern Africa project. Taxonomic characters re-examined include traditional morphological features and novel characters such as SEM studies of pollen~ seed and indumentum morphology, as well as chromatographic work on floral , pigments. Traditional morphological features examined included habit, the size and shape of leaves, the corolla, anthers and capsules. Inflorescence features were thoroughly re-examined. Pollen morphology was found to be diverse with three types of grain present in the genus. The number of colpi was either two or three and there were major differences in the appearance of the sexine. Pollen and inflorescence type were found to correlate. On the basis of this a natural infrageneric classification was proposed. The seeds showed a number of testa patterns: smooth, papillate, reticulate or with long scales. These types in many cases also correlated with the proposed infra-generic classification. The indumentum of leaves, stems and bracts was examined for each taxon, and in many cases proved valuable for identification of the taxon. The floral pigments were analysed using by 2D paper chromatography but, except in one species, did not prove useful in species or sectional delimitation. As a result of these studies, Justicia in southern Africa was divided into eight sections containing 22 species with six subspecies. One species and two subspecies were new and there is one new record for the region. These new taxa and a number of nomenclatural changes were published by Immelman (1986). The genus Aulojusticia was reassessed and is here regarded as a synonym of Siphonoglossa. Siphonoglossa, therefore, is considered' here to include three species and one subspecies in the southern African region. The species and subspecific taxa recognised in this revision are: Justicia 1. J. glabra Koenig ex Roxb. - N. Botswana, N. Transvaal and Zululand; also in tropical Africa. 2. J. campylostemon (Nees) T. Anders. - from N.E. Transvaal to E. Cape. 3. J. bolussi, C.B. Cl. restricted to the E. Cape and the Transkei. 4. J. betonica L. - from N. Namibia and N.E. Botswana, through the Transvaal to the E. Cape; also in tropical Africa and India. 5. J. montis-salinarum A. Meeuse - restricted to the Soutpansberg (N. Transvaal). 6. J. flava (Vahl) Vahl - from E. Botswana through the Transvaal and Natal to the Transkei, also widespread in Africa. 7. J. kirkiana T. Anders. - a common species in Africa, occurring in the region covered only from two localities in N. Botswana. 8. J. petiolaris (Nees) T. Anders. - (a) subsp. petiolaris from E. Transvaal to the Transkei (b) subsp. bowiei (C.B. Cl.) Immelman stat. nov. restricted to the E. Cape (c) subsp. incerta (C.B. Cl.) Immelman stat. nov. from the Transvaal and Zululand. 9. J. protracta (Nees) T. Anders. - (a) subsp. protracta from the Transvaal to the S. Cape (b) subsp. rhodesiana (S. Moore) Immelman stat. nov. from Namibia, W. Botswana and the N. and E. Transvaal. 10. J. parvibracteata Immelman sp. nov. - from the N. Cape, with one record from the N. Transvaal. 11. J. dinteri S. Moore Transvaal. N. Namibia, N.E. Botswana and W_o 12. J. odora (Forssk.) Vahl - N. Namibia, N. and E. Botswana, the Transvaal and Natal, also in tropical Africa. 13. J. capensis Thunb. N. Natal and also, disjunctly, the Transkei and E. and S. Cape. 14. J. cuneata Vahl - (a) subsp. cuneata which is restricted to the E. Cape (b) subsp. latifolia (Nees) Immelman from Namaqualand, W. Karoo and E. Cape (c) subsp. hoerleinlana (P.G. Mey.) Immelman stat. nov. from S. Namibia 15. J. Orchioides L. f. - (a) subsp. orchioides restricted to the E. Cape (b) subsp. glabrata Immelman subsp. nov. from the S. and E. Cape, E. Karoo, O.F.S., and S.W. Transvaal. 16. J.thymlfoila (Nees) C.B. C1. - restricted to the N. Cape. 17. J. guerkeana Schinz - mainly in S. Namibia. 18. J. platysepala (S. Moore) P.G. Mey. - mainly in N. Namibia. 19. J. minima A. Meeuse - endemic to the Waterberg (Transvaal). 20. J. a nagalloides (Nees) T. Anders. - Transvaal to Natal. 21. J. crassiradix Burkill & Clarke (new record for southern Africa) - one record from the E. Caprivi. 22. J. anselliana (Nees) T. Anders. - N. Namibia, N. and E. Botswana and the Transvaal. Siphonoglossa 1. S. leptantha (Nees) Immelman - (a) subsp. leptantha - from Natal to the E. Cape (b) subsp. late-ovata - (C.B.Cl.) Immelman comb. nov. ined. from the E. to the S. Cape. 2. S. nkandlaensis Immelman sp.nov. ined. - Central Natal. 3. S. linifolia (Lindau) C.B. Cl. (= Aulojusticia linifolia Lindau) - endemic to the Barberton area (Transvaal). A formal taxonomic revision including keys to genera, sections and species has been included. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1987.

In maximizing South Africa's floral diversity, plant propagators have begun exploiting the rich array of indigenous plants, especially those with horticultural potential. Plants previously unavailable to the professional and amateur gardeners alike, are legally becoming common-place in nurseries. However, in promoting the trade of indigenous plants to nursery-owners, rapid, easy and cost effective methods of propagating these plants need to be established. Combretum bracteosum is one such indigenous plant, the aesthetic appeal thereof exhibits great potential for ornamentation, especially when flowering. In facilitating the introduction of Combretum bracteosum into nurseries, small gardens or even pots, investigations carried out aimed to determine and analyse quick and easy methods of propagating this plant. Of the various propagation techniques considered, only one, micropropagation, required specialized skill and training prior to carrying out the relevant procedures and protocols. The two other techniques used, which are accessible to most plant propagators, were seed germination and propagation from cuttings. Propagation by seed germination yielded less than optimal results from a commercial perspective. Although the hard pericarp surrounding the embryo did not impose any dormancy inducing mechanisms, such as the restriction of water uptake or the leaching of an inhibitory compounds, it did act as a mechanical barrier to the emerging radicle and roots. Recommendations for optimal Combretum bracteosum seed germination would be to remove the protective pericarp completely, incubate imbibed embryos in complete darkness at 25°C. After radicle emergence the germinating embryos could be moved into an alternating light: dark cycle. A more viable and simpler alternative to seed germination, was propagation by stem cuttings. Treating the cuttings with 10% and 50% or 75% of the commercially available Kelpak concentrate (using the Soak Method and Quick-dip Methods respectively), provided the most promising results, with the rapid development of roots and subsequent vegetative growth. Synthetic hormones such as IBA and NAA were also applied to the cuttings both alone or in combination however, although callus growth was profuse, root development was slow and unsubstantial, if any at all. Therefore, in recommending a protocol for the successful rooting of Combretum bracteosum cuttings taken during spring, summer or early autumn, the application of Kelpak at either 10% (Soak Method) or 50% (Quick-dip Method) of the full strength solution, is advised. Subsequent to hormone treatment, the cuttings still required attention with regard to nutrient supplementation as well as atmospheric moisture and temperature regulation. Success in generating Combretum bracteosum plantlets was obtained by germinating the seed in vitro as well as stimulating axillary shoot elongation from nodal explants. Placing the sterilized Combretum bracteosum embryo onto a nutrient rich basal medium (containing no hormones) was sufficient to stimulate 100% germination. The frequent poor availability of the seed may hamper the use of in vitro seed germination for commercial propagation purposes. The use of nodal explants from in vitro germinated stock plants, is a rapid and reliable means of generating a large seedling stock. Nodal explants excised from the newly developed shoot were subsequently placed onto 0.5 mg.ℓ ¯¹ BA which encouraged axillary bud elongation. After elongation, the lateral shoots were removed and placed onto a rooting medium (1.0 mg.ℓ ¯¹ IBA). The more mature nodal explants, collected from parent plants growing in vivo, required either a BA: NAA hormone combination or Kelpak to stimulate axillary shoot elongation, with the latter being most successful. Root initiation followed the protocol described above. Once rooted plantlets were hardened off they displayed a strong and vigorous growth, which is desirable from a commercial perspective. Upon maturity, the habit of many indigenous trees and shrubs could become too big for confined spaces such as the urban garden. Therefore, determining a means of modifying the plants' habit in order to maintain its suitability as a smaller garden plant was important. Treating the Combretum bracteosum plants with a 50 mg.ℓ ¯¹ paclobutrazol soil drench proved most successful, with the desired effects being visible within a few weeks of initial application. No negative morphological or developmental effects were noted on plants treated with the dwarfing agent, conversely however, the treated Combretum bracteosum plants were compact and bushy, with considerable visual appeal and aesthetic attractiveness. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2001.

The alkaloid content of three Crinum species namely C. bulbispermum, C. macowanii and C. moorei was investigated. The ethanolic extracts of C. bulbispermum yielded seven compounds. The new alkaloids 8α-ethoxyprecriwelline, N-desmethyl-8α-ethoxypretazettine and N-desmethyl-8β-ethoxypretazettine were isolated for the first time from a natural source. In addition, the known alkaloids bulbispermine, crinamine, 6-hydroxycrinamine and 3-O-acetylhamayne were isolated in this study. The ethanolic extracts of C. moorei were found to contain Iycorine, 1-O-acetyllycorine, crinine, 3-O-acetyllycrinine, epibuphanisine, powelline, crinamidine, undulatine, epivittatine, 1-epideacetylbowdensine, cherylline and the new alkaloids mooreine and 3-[4'-(2'-aminoethyl)phenoxy]bulbispermine. The alkaloids crinine, lycorine, bulbispermine, cherylline and hamayne were obtained from the ethanolic extracts of C. macowanii. In addition, the amine tyramine was identified during the isolation process. Dilute HCl solution extraction followed by GC analysis was used to investigate organ-to-organ and seasonal variation of alkaloids in each Crinum species, as well as the interspecific variation in these alkaloids over two consecutive years. Twelve alkaloids were identified, including crinine, epibuphanisine, powelline, crinamine, crinamidine, 6-hydroxycrinamine, 1-epideacetylbowdensine, 3-O-acetylhamayne, undulatine, Iycorine, 1-O-acetyllycorine and cherylline. Alkaloids were detected in all organs of C. moorei and C. macowanii. However, alkaloids were not detected in the leaves of C. bulbispermum. Organ-to-organ and seasonal variations in the total yield and total ring types of these alkaloids were noticed. Organ-to-organ and seasonal statistical variations were also detected for some of the individual alkaloids detected in each of these species. The results also showed that C. moorei had the highest levels of all individual alkaloids except crinamine when compared to C. bulbispermum and C. macowanii. Quantitatively, the detected alkaloids chemotaxonomically separated C. moorei from C. bulbispermum and C. macowanii. The results also indicated that C. macowanii is more closely related to C. bulbispermum. Qualitatively, Iycorine, 1-O-acetyllycorine, cherylline, crinamidine, 1-epideacetylbowdensine, crinine, crinamine and 3-O-acetylhamayne were detected in both C. moorei and C. macowanii, indicating the close relationship of these species. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

No abstract available. / Thesis (M.Sc.)-University of Durban-Westville, 1988.

Sugarcane is challenged by a number of phytopathogenic bacteria and viruses that are best managed by the development of resistant varieties. Genetic engineering is a promising strategy in such breeding efforts, as it allows novel mechanisms of resistance not available in any parent germplasm to be introduced into the crop. DNA sequences encoding cystatin from papaya (Carica papaya), and pleurocidin from the winter flounder (Pleuronectes americanus) were envisaged as transgenes in this work due to their theoretical potential to increase sugarcane resistance to viruses and pathogenic or opportunistic bacteria, respectively. Cystatin is a cysteine proteinase inhibitor. Cysteine proteinases are used by potyviruses to cleave the polyprotein gene product, an essential step in the viral life cycle. Constitutive expression of cystatin may therefore lend the host plant resistance to a range of potyviruses, including the economically important pathogen sugarcane mosaic virus (SCMV). Pleurocidin is an amphipathic, α-helical, cationic peptide, with broadspectrum anti-bacterial activity at physiological pH. By binding to the cell membranes of both Gram positive and Gram negative bacteria, pleurocidin disrupts the membrane potential, causing it to become more permeable, especially to cations, leading to death of the bacterial cell. Initial microbiological bioassays showed that pleurocidin has inhibitory and bactericidal effects on the organisms which cause leaf scald (Xanthomonas albilineans), gumming disease (Xanthomonas campestris pv. vasculorum) and post-harvest sucrose conversion in sugarcane, as well as inhibitory effects against Leifsonia xyli ssp. xyli, which causes ratoon stunting disease (RSD). For transformation vector construction, the cystatin and pleurocidin coding sequences were altered so that their start codons were in the most favourable consensus context for expression in monocotyledonous plants. In the case of pleurocidin, an extracellular peroxidase signal sequence was attached. The prepared sequences were spliced into the vector pUBI510 in which the gene of interest is driven by the CaMV 35S promoter linked in tandem to a derivative of the maize ubiquitin promoter. The constructs generated were named pUBI510-cys3 and pUBI510-pleur08 respectively. The plasmid structures were confirmed using restriction endonuclease analysis and DNA sequencing. Since the transformation of sugarcane is known to be inefficient, two routes of morphogenesis for the production of somatic embryos were compared in the transformation procedure. These were (1) indirect embryo production via callus and (2) the direct and indirect production of embryos from transverse sections of leaf roll. Field grown sugarcane varieties N12 and NCo376 were the source of explant material. Plasmids pUBI510-cys3 and pUBI510-pleuro8 were respectively co-delivered by microprojectile bombardment with the antibiotic resistance selection plasmid pUBIKN containing the neomycin phosphotransferase gene (npt-II). Cultures were maintained in the dark on selection medium containing various concentrations of the antibiotic geneticin (G418) for several weeks before being allowed to regenerate in the light. Plantlets coming through selection were hardened off in the glasshouse when approximately 100mm high. Primer pairs for amplification of the cystatin insert were designed in various ways. The primer pair which ultimately proved most useful was designed to be complementary to the 5' and 3' ends of the papaya cystatin nucleotide sequence. Primer Premier analysis of a sorghum cystatin sequence provided additional possible primers. A further pair for potential future use was devised based on complementarity to conserved regions on maize cystatins 1 and 2, sorghum, rice, and papaya cystatins. The nucleotide sequence was constructed using the most common monocotyledon codon permutations for each amino acid. Pleurocidin primers were designed to be complementary to 5' and 3' regions of the nucleotide sequence encoding the pleurocidin pre-pro-protein. PCR and RT-PCR protocols for the detection of transgenes and transcript production in putative transgenic plants were developed using these primers. No plants survived selection via the callus route, although some were regenerated via direct embryogenesis. Putative transformed plants were analysed using PCR to test for the presence of integrated transgenes and Southern hybridization to determine transgene copy number. Both types of transgene were reproducibly detectable by PCR in DNA from some immature plants, but results were negative in DNA from those same plants when mature. Southern hybridization analysis detected the cystatin transgene in DNA from immature plants but no transgenes were detected in up to 20 µg DNA from mature plants. Single copy constructions of the transgenes in backgrounds of non-transformed DNA were detectable by both PCR and Southern hybridization analysis. Overall, PCR, RT-PCR and Southern hybridization results indicated that the plants regenerated fell into two categories: non-transformed plants that had survived selection (escapes) and chimaeric individuals with a component of both transformed and non-transformed cells, in which the transgene had probably become diluted during plant development under non-selective conditions. A method for extracting leaf exudates was tested, in conjunction with a cysteine proteinase assay to detect the presence of cystatin transgenes in the intracellular spaces of sugarcane leaves of confirmed transformants. Although it could not be applied within the scope of this project, this assay will prove useful in future work. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

Hybrid clones of Eucalyptus grandis and E. nitens (GN) have consistently been shown to be suitable for planting in cold, dry, marginal plantation sites, where they exhibit high yields and superior pulp properties. However, their clonal propagation is hindered by the very poor rooting success of cuttings. The present study aimed at assessing the effect of cutting type, time of year of setting cuttings and Seradix 2 application on rooting and development of cuttings of a commercially important Eucalyptus grandis x Eucalyptus nitens clone (GN107). Cuttings were prepared from clonal hedge coppice at the Mondi Business Paper, Trahar Technology Centre, Hilton. Three cutting types were used (cut at different distances from the node) for each terminal (situated below the apical bud) and non-terminal cuttings. The leaves were trimmed and, for half the cuttings, the base of the stem of cuttings were dipped in Seradix 2 rooting powder (3 g kg-1 4-(indole-3-yl)-butyric acid (IBA). They were then placed into rooting trays (128 inserts/ tray arranged as 8 rows x 16 columns). Seradix 2-treated and Seradix 2-untreated terminal and non-terminal cuttings, cut at, above and below the node (twelve treatments in total) were set in trays with one treatment per column of eight replicates, per tray. There were nineteen trays overall. The trays were filled with peat, perlite and vermiculite (3:3:1) and were maintained in a Mondi greenhouse, with air temperature at 25°C to 27°C (thermostatically activated fans), root zone temperature at 28°C (bed heaters) and 20 second misting at 10 minute intervals (automatic misters). The study was carried out in November 2005, April 2006 and June 2006. In the first experiment, both terminal and non-terminal cuttings were used; thereafter only non-terminal cuttings were used. The plantlet yield was very low, regardless of cutting type, Seradix 2 treatment and the time of year the cuttings were set. The highest plantlet production (12.5%) and rooting frequencies (13.8%) were achieved with non-terminal cuttings treated with Seradix 2. Although not statistically significant, Seradix 2 inhibited shoot production (31.4% for Seradix 2-untreated and 24.2% for treated cuttings). The position at which inserts were cut in relation to the node did not significantly affect the number of plantlets produced and non-terminal cuttings appeared hardier and performed better than terminal cuttings. The time of year of setting cuttings did not have any significant effect on plantlet yield, nonetheless, plantlet yield was highest in cuttings set in November (9.2%) and lowest in April (0.4%). In addition, cuttings set in November (spring), had superior shoot development in terms of the number of cuttings that produced shoots (regardless of root production), shoot length and the mass of shoots relative to root mass. The highest percentages of cuttings that produced roots (regardless of shoot growth) (10%) and the highest number of roots per cutting (2) were part of the June trial. Therefore, cuttings set in June (winter) had superior root development as compared with cuttings set in November (spring) or April (autumn). In all of the studies, three rooting patterns were observed in cuttings: roots produced only from the cut area only (type 1), only from the sides of the stem (type 2) and from both sites (type 3). Non-terminal cuttings treated with Seradix 2 showed a higher incidence of types 2 and 3 rooting patterns than the terminal cuttings. Seradix 2 application increased the prevalence of types 2 and 3 rooting patterns. Although not statistically different, cuttings dipped 2.5 cm into Seradix 2 produced more types 2 and 3 rooting patterns than cuttings dipped at the abaxial end only. Light microscopy of stem sections of cuttings indicated that roots appeared to originate from the xylem archs as well as from the cambium. The collected data indicate that it is necessary to continue research towards improving the efficiency of plantlet production of GN107 via cuttings. It appears that cuttings of this clone may be set throughout the year and that terminal cuttings should be avoided. In addition, the present practice at the Mondi Hilton nursery of treating cuttings with Seradix 2 needs to be reconsidered as although it increases rooting, it does not increase plantlet production due to its apparent inhibitory effect on shoot development. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2007.

It has been proposed that the protective systems (photorespiration, the anti-oxidant system and non-radiative energy dissipation) alleviate or reduce photoinhibitory damage under high light conditions. To investigate the role of these mechanisms in C4 photosynthetic species, nine day old Zea mays seedlings were photoinhibited (30 minutes of 2500 J,Lmol m-2 s-1 PPFD) in the presence of various concentrations of 02 or CO2; or by photoinhibiting leaves in N2 after they had been fed glycolate or phosphoglycerate via the transpiration stream. The extent of the photoinhibition and the subsequent recovery from the photoinhibitory treatments was monitored with both CO2 gas exchange and chlorophyll fluorometry. Photoinhibitory treatments resulted in both a decrease in the rate of CO2 fixation and an interruption of PSII electron transport. CO2 response curves were used to monitor the efficiency of the carboxylation processes and the level of carbon metabolism substrate cycling during recovery following photoinhibitory treatments. Both were decreased by the treatment and recovered once leaves were returned to normal conditions. Low concentrations of 02 (2%) markedly reduced the extent of the photoinhibition. This protection could not be accounted for by photorespiration, which would be inoperative at such a low 02 concentration. Leaves fed glycolate exhibited enhanced photoinhibtion. It is also unlikely that the anti-oxidant system (Mehler reaction and associated glutathione and ascorbate reactions) could utilize sufficient reductant at such low 02 concentrations to produce the observed protection. Leaves inhibited in the presence of 02 had decreased maximum fluorescence yields (Fm) and little altered initial fluorescence yields (F0)' resulting in decreased PSlI efficiency (Fv/Fm)' Photoinhibition resulted in a small increase in the slow relaxing component (60 minute) of non-radiative energy dissipation. This component became more predominant as the 02 concentration was increased. The rate constant for photochemistry was also decreased by the inhibitory treatment. Leaves supplied with CO2 at a concentration above 50 J,Lmol mol-1 exhibited little photoinihibition suggesting that the protection was not due to a quantitative utilization of energy. PGA, fed via the transpiration strea~ enhanced the photoinhibition, suggesting that more than just the Benson-Calvin cycle is required to protect C4 plants from photoinhibition. At CO2 concentrations below this, the Fv/FID ratio was decreased due to large increases in the F0 values. Fm was little altered. These changes are characteristic of a decrease in the rate constant for photochemistry. The rate constant for non-radiative energy dissipation was little altered by the photoinhibition. The protection observed in the presence of either CO2 or 02 was not due to a quantitative utilization of energy and the different responses of F0' Fm and the rate constants KD and Kp, suggest that different mechanisms were operative in the presence or absence of oxygen. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

Abstract available in PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

This dissertation presents the results of studies of the generic concept of Senecio and the subsequent testing of the hypothes is: that many of the species of Senecio in Natal are congeneric with Senecio L. sensu stricto. The sample of taxa studied consisted of 87 Natal senecios, 5 Cape heterochromous senecios and 10 non-southern African senecios, including the type of the genus, S. vulgaris L. Also included in the study were 5 species from taxonomically closely related genera in the tribe Senecioneae and two senecios of uncertain taxonomic position. The phenotype of these taxa was investigated with respect to a large number of morphological and micromorphological characters (126) and the data obtained were analysed neurally and numerically. Aspects of the pollen micromorphology, of all the taxa studied, were also investigated using the scanning electron microscope. A review of the chemical complement of all the taxa studied. particularly with respect to terpenes and pyrrolizidine alkaloids, was also undertaken. Six characters were selected as being taxonomically significant with respect to elucidating the generic concept of Senecio. A further 31 characters and the aforementioned 6, were selected as .being taxonomically significant with respect to elucidating the interrelationships of the Natal senecios and all the senecios studied. The generic concept of Senecio has been re-circumscribed and the generic status of each of the senecios studied has been tested according to this concept of Senecio sensu Vincent. In the light of my concept of Senecio, the following species are excluded from Senecio sensu Vincent: S. barbertonicus Klatt, S. cissampelinus (DC.) Schultz Bipontinus, S. fulgens (J.D. Hooker) Nicholson, S. helminthioides (Schultz Bipontinus) Hilliard, S. hockii De Wild. & Muschl., S. medley-woodii Hutchinson, S. radicans (L.L) Schultz Bipontinus, S. syringifolius O.Hoffm., S. tamoides DC., S. transvaalensis Bolus and S. viminalis Bremekamp. Senecio brevilorus Hilliard, S. seminiveus Wood & Evans and S. tanacetopsis Hilliard are considered to be peripheral to Senecio s. str. sensu Vincent, and are included in Senecio s. lat. sensu Vincent. The hypothesis regarding the generic status of the Natal senecios has been accepted, subsequent to the circumscription of Senecio s. str. sensu Vincent. Estimates of the phenetic affinity of all the members of Senecio sensu stricto sensu Vincent, included in this study, have been made. The majority of the Natal senecios, while clearly being members of Senecio s. str. sensu Vincent, are distinct from virtually all the Cape and non-southern African senecios studied. Many of the non-yellow (purple) Natal senecios form clearly allied groups which are distinct from the groups (clusters) composed of yellow senecios. The taxonomic position of several taxa is questioned, in the light of the cluster analyses. The evidence from the palynological studies neither contradicts nor supports the proposed infrageneric interrelationships, with respect to the Natal members of Senecios. str. sensu Vincent. The evidence also neither contradicts nor supports the proposed interrelationships between the Natal, the Cape and the non-southern African members of Senecios. str. sensu Vincent. The terpene and pyrrolizidine chemistry of many of many of the senecios studied is characterised by the presence of furanoeremophilanes. Eremophilanes also occur and are particularly associated with a number of non-yellow (purple) senecios. Pyrrolizidine alkaloids are not ubiquitous amongst the senecios studied, while some senecios appear to only synthesise pyrrolizidine alKaloids. The review of the errpene and pyrrolizidine chemistry of the senecios investigated, illustrates how our knowledge at or near the level of analytic characters is far from complete. However, we have definitely progressed from the synthetic level of character use. Nevertheless, the relationships between the members of Senecios. str. sensu Vincent, could not be evaluated in the light of the individual chemical complement of terpenes and pyrrolizidine alkaloids, because of a lack of information. An hypothesis of the chemical evolution within the Senecioneae is tested with in Senecios. str. sensu Vincent . Before any taxonomic changes are made to t he current composition of Senecio L., the concept of Senecio L. s. str. sensu Vincent, needs to be tested against a far wider sample of the genus. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.