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Masters Degrees (Botany)

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    A contribution to knowledge of the genus Hypoxis L. (Hypoxidaceae) in Natal, South Africa.
    (1976) Wood, Susan Elizabeth.; Gordon-Gray, Kathleen Dixon.
    Abstract available in PDF.
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    Competitive interactions between savanna trees.
    (2011) Pillay, Tiffany Prileeni.; Ward, David Mercer.
    Savannas are socio-economically important ecosystems, which support high floral and faunal diversity. This biome covers large areas of Africa, Australia, South America, India and parts of North America, and is comprised of a mixture of grasses and woody plant biomass. Most empirical studies of savanna ecology have focused primarily on the interactions between trees and grasses, especially at the seedling stage where recruitment is regarded as a key driver of savanna dynamics. However, studies of interactions between woody savanna plants, such as competition and facilitation, are less common in the literature. Considering the increasingly negative effects of woody plant encroachment and global climate change, interactions between woody plants need to be closely monitored and evaluated. In this thesis, I investigated the effects of neighbourhood competition on four dominant tree species from humid savannas (receiving more than 1000 mm of mean annual rainfall, hereafter referred to as “humid species”) and four dominant tree species from mesic savannas (receiving around 650 mm of mean annual rainfall, hereafter referred to as “mesic species”). I employed a greenhouse-based study to examine the effects of neighbour density on the growth, survival and biomass of savanna tree seedling species. I quantified two aspects of competitive ability (competitive effect and response), and compiled competitive hierarchies for both groups. In addition, I correlated competitive ability with several plant traits. Using field surveys of natural stands of Acacia karroo from humid savanna sites across KwaZulu-Natal, South Africa, I examined the spatial patterns and competitive interactions between trees. A greenhouse experiment revealed that mesic species suffered high levels of mortality when exposed to increasing neighbour density, while humid species were relatively unaffected in terms of survival. However, mesic species were able to maintain constant relative growth rates (RGR) despite increasing neighbourhood competition while the RGR of humid species decreased as neighbour density increased. The total biomass of both humid and mesic species also declined as the neighbourhood competition increased. In terms of competitive effect and response, we found that these two aspects of competitive ability were not concordant (i.e. good effect competitors were not necessarily good response competitors). Lastly, we found that plant traits such as specific leaf area and above-ground features (e.g. shoot biomass and leaf number) were significantly related to the competitive response or effect of savanna tree seedlings. Spatial distribution patterns of a dominant humid savanna species, Acacia karroo, revealed that juvenile plants are aggregated, as expected due to facilitation, seed dispersal and vegetative reproduction. However, the regular spacing of larger individuals due to competition and density-dependant mortality were not detected. We found, using nearest neighbour analysis, that trees with closer neighbours had smaller canopy diameters. This suggests that while competitive interactions are present, they may be weak and insufficient to cause mortality, rather resulting in decreased plant performance. Overall, I found that, at the seedling stage, neighbourhood competition was particularly important for both humid and mesic savanna trees. Competitive interactions between mesic seedlings resulted in significantly higher mortality rates, greatly reducing the recruitment of these species. Humid species, although able to successfully recruit, experienced reduced growth rates under dense neighbourhood competition. In the field, patterns of competitive interactions were difficult to detect using spatial statistics alone. However, we did find evidence of weak competitive interactions among humid savanna trees. In summary, competitive interactions were important for all savanna species at the crucial seedling stage. However, field comparisons showed that competitive interactions were relatively weak in A. karroo and resulted in reduced performance rather than differential mortality.
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    Differing responses of embryonic axes of four recalcitrant-seeded species from temperate and tropical provenances to the procedures involved in cryopreservation.
    (2016) Mshengu, Thembela Mathews.; Pammenter, Norman William.; Berjak, Patricia.
    Abstract available in PDF file.
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    Effects of pruning and fertilizer on growth, phytochemistry and biological activity of Sutherlandia frutescens (L.) R.Br.
    (2017) Raselabe, Maanda Benjamin.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.; Abdelgadir, Hafiz Ahmed.; Ndhlala, Ashwell Rungano.
    Sutherlandia frutescens (L.) R.Br. (Fabaceae), commonly known as cancer bush, is a herb with a long history of traditional use by a variety of cultures. The plant mainly grows in the dry parts of southern Africa, mostly in the Western and Eastern Cape as well as the neighbouring countries like Lesotho, Botswana and Namibia. Cancer bush is traditionally used for the treatment of external wounds, internally for fevers, stomach problems, cancer, diabetes, influenza, HIV, depression, eye problems, TB, colds and asthma. The plant is famously known for the treatment of Type 2 diabetes, cancer and HIV. However, these claims remain inconclusive. Recent studies have shown S. frutescens to have antidiabetic, anti-HIV, anti-inflammatory, antibacterial, analgesic, anti-stress, anticonvulsant, antiproliferative and antithrombotic activities. Phytochemical investigations of S. frutescens leaves detected the presence of high levels of free amino acids and non-protein amino acids namely: canavanine, gamma aminobutyric acid (GABA) and pinitol. The presence of these compounds has been reported to be responsible for its reputed effectiveness in a wide range of illnesses. In view of its importance as a multipurpose medicinal crop, it is important to bring this plant under cultivation and determine agronomic requirements for its successful cultivation. Several factors can be investigated to enhance the growth and increase the level of active ingredients. The current study was aimed at evaluating the effect of pruning and fertilizer levels on the growth, phytochemistry and biological activity of Sutherlandia frutescens. Seeds were sown in seedling trays to produce seedlings. One-month-old seedlings were then transplanted on a prepared field. The study trial was carried out at the Agricultural Research Council-Vegetable and Ornamental Plants Research Station (ARC-VOP). The experiment was conducted in a randomized complete block design (RCBD) with three pruning levels, three fertilizer levels and four replicates. There were 9 treatments, namely; no pruning (P0), tip-pruning (P1) and heading back (P2) in combination with levels of fertilizers as follows: 200 kg/ha NPK (F1), 100 kg/ha NPK (F2) and 0 kg/ha NPK (F0). Plants without treatments were considered as controls. Growth parameters taken were plant height, stem diameter, chlorophyll and Leaf Area Index (LAI). Dried leaf samples were analysed for the presence of secondary metabolites and antidiabetic activities. There was no significant interaction effect between pruning and fertilizer levels amongst all parameters measured in this study. Pruning treatments had a significant effect on the LAI at week one and week two but did not affect the plant height, stem diameter and chlorophyll content. Different levels of fertilizers had a significant effect on the LAI, where 100 kg/ha NPK significantly increased LAI at week one and week two. In an investigation which was conducted from January to May 2015, plants showed yellowing, stunting, and high levels of infestation expressed as extensive galling on the roots which led to the nematode infestation study. Nematodes were extracted from the roots of a healthy living, a wilted and a dead plant, as well as from the rhizosphere soil. A small population of Scutellonema, Pratylenchus, Helicotylenchus and Tylenchorhynchus were identified. Examination of the root of an infected plant revealed the presence of root-knot nematodes (Meloidogyne javanica) in large numbers. Juveniles, eggs and females were isolated, and the species were identified on the basis of morphological characteristics. Symptoms usually associated with root-knot nematodes were observed on the roots of the wilted plant and the soil in which the plant was growing. Extracts from all nine treatments showed stronger activity against α-glucosidase than the positive control acarbose. The highest α-glucosidase inhibitory activity was demonstrated by the treatment with no pruning (P0) while the heading back (P2) treatment exhibited the lowest inhibitory activity. Fertilizer levels at 200 kg/ha (F1) NPK resulted in a significantly higher α-glucosidase inhibitory activity compared to other fertilizer treatments. The presence of secondary metabolites (including total phenolics and flavonoids) was determined qualitatively. The total phenolic content was determined using the Folin-Ciocalteu method and flavonoids were determined using the vanillin HCL assay. The study showed that pruning and fertilizer increased the production of secondary metabolites in S. frutescens as compared to the control. Fertilizer at 200 kg/ha NPK (F1) did seem to improve phenolics and flavonoids with pruning but phenolic levels were actually quite low when treatment was P0F1. Total phenolics and flavonoids were significantly increased by the heading back (P2) treatment and decreased in the treatment with no pruning (P0). The application of fertilizer at 200 kg/ha NPK (F1) improved the production of secondary metabolites, and reduced production of secondary metabolites was recorded in plants that received no fertilizer. There was no direct correlation between the level of phytochemicals and the antidiabetic activity recorded. This study examined the effects of different levels of pruning and fertilizers on the growth of S. frutescens. The results showed that there was no significant difference. At this stage, no positive recommendations can be made for cultivating S. frutescens. Plant extracts showed good antidiabetic activities in response to different pruning and fertilizer treatments. This was further seen as an increase in the production for secondary metabolites. However, further investigation of plant cultivation practices and further screening for bioactivities is required. S. frutescens may offer a new source of drugs for diabetes mellitus and other related diseases.
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    On the vacuolar system in maize roots.
    (1979) Lamb, Jennifer Margaret.; Berjak, Patricia.
    Root-cap cells of Zea mays L proliferate by division in the cap meristem, and subsequently differentiate and mature as they move towards the periphery of the cap, where ' they undergo autolysis and are sloughed. Vacuolar ontogeny has been shown to be complex, several different mechanisms operating not only within the root cap tissue, but within the single cells. Vacuolar initials (provacuoles) are formed in the meristem by the pinching off of single- or doublemembrane bound vesiculations of the E.R. In some instances large vacuoles appear to be formed in the mature region of the cap through the sequestering of large organelle-free regions of cytoplasm by vesicles and small cisternae, thought to be of E.R. origin. Further development of provacuoles comprises their expansion and extensive fusion, this process culminating in the formation, in a mature cell, of just one large vacuole. The vacuoles of the mature region are autophagically active, engulfing all types of cytoplasmic organelle which are subsequently lysed; these vacuoles show a positive cytochemical reaction for acid-phosphatase, further indicating that they are lysosomal in nature. The dictyosomes of the late mature cells are hypersecretory and autoradiographic and cytochemical evidence indicates that the vesicles contain an accumulation of polysaccharide. These vesicles appear to follow two secretory pathways; firstly fusion with the plasmalemma, with secretion of their content into the extra-protoplasmic space where it accumulates, finally penetrating the cell wall and middle-lamella and forming viscous polysaccharide slime on the exterior of the cap. Secondly, these vesicles appear to be engulfed by and broken down within the vacuoles. At this stage the vacuole expands considerably, and it has been postulated (Berjak and Villiers, pers. corom.) that hydrolysis of the dictyosomally-derived polysaccharide within the vacuole to monosaccharide units results in osmotic. changes leading to an influx of water into the vacuole, and its consequent expansion. Autoradiographic, cytochemical and chromatographic evidence is not inconsistent with an accumulation of monosaccharide units being at least partially responsible for the osmotic uptake of water into the swelling vacuole. Finally, the vacuolar membrane becomes discontinuous, allowing hydrolytic enzymes p~esumably contained within the vacuole to come into contact with the cytoplasm, which consequently undergoes autolysis. At this stage the cell is sloughed from the cap.
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    Optimising mini-plug transplanting of Eucalyptus dunnii seedlings.
    (2013) Newmarch, Tracy Yvonne.; Finnie, Jeffrey Franklin.; Van Staden, Johannes.
    Mini-plug transplanting has only recently been described as a useful propagation method for use in forestry nurseries. Mini-plug seedlings are seedlings that have been pre-cultivated in containers with volumes less than 33-ml. These seedlings are re-planted into containers of a larger volume at a later stage in the growing season. The many advantages of mini-plug transplanting include decreased seedling production costs, improved space use efficacy and the flexibility of producing larger seedlings for harsh field conditions. However, the effect of mini-plug transplanting on seedling quality and root architecture is unknown and may influence seedling survival after planting in the field. This research aimed to optimise a mini-plug transplanting protocol for use in a commercial forestry nursery to limit the development of root deformities and enhance seedling quality in Eucalyptus dunnii seedlings. The effects of mini-plug container type and mini-plug cultivation time prior to transplanting on seedling quality were evaluated. Seedlings were grown in two mini-plug containers, MP288 and MP544, for one, two, three and four months before transplanting the mini-plug seedlings into the final container. In this experiment it was confirmed that the mini-plug container design had an effect on mini-plug seedling quality. Seedlings grown in MP288 containers had lower sturdiness and shoot-to-root ratios compared to MP544-reared seedlings. This was attributed to the lower planting density and higher cavity volume of the MP288 trays. However, MP288 trays increased the frequency of root deformities in the E. dunnii mini-plug seedlings as these trays were constructed out of plastic which encouraged root coiling. The MP544 trays produced seedlings with actively growing, fibrous roots which were attributed to the root pruning properties of the copper oxychloride that the polystyrene mini-plug containers were initially treated with. It is therefore recommended that the MP544 tray should be used for the cultivation of mini-plug seedlings. The age of the mini-plug seedlings also affected transplanting success. Based on the results it was concluded that the optimal age to transplant mini-plug seedlings was between two and three months after sowing. Transplanting one-month-old seedlings tended to increase the frequency of J-roots after transplanting and four-month-old seedlings delayed seedling growth. Once the optimal seedling age and mini-plug tray type to be used for container-to-container transplanting was confirmed, the effects of the propagation method (directly-sown and transplanting) on seedling quality were compared using various containers. Transplanted seedling quality was inferior compared to directly-sown seedlings. This was caused by delayed growth directly after transplanting. The substrate composition that the mini-plug seedlings had been grown in had not been optimised for mini-plug cultivation and may have reduced mini-plug seedling quality which resulted in delayed seedling growth after transplanting. In addition, transplanting increased the incidence of root deformities and using polystyrene containers as the final container for transplanting did not reduce root deformation. The presence of J-roots was believed to be caused by the transplanting process itself. The negative effects of container design observed in the mini-plug containers were also observed in the final container after transplanting. Low plug volumes decreased seedling growth and increased seedling competition due to the higher planting densities. Following the results of the second study, the optimal substrate composition to be used for mini-plug seedling cultivation and in the final container after transplanting was investigated. This investigation confirmed that the substrate composition affected seedling development and growth. In the mini-plug trays, the physical properties of the substrate were shown to be important factors affecting both root development and seedling growth. Substrates with low air-filled porosity values reduced root growth and the negative effects of low air-filled porosity were enhanced when seedlings were cultivated in mini-plug containers. The results also indicated that different substrate compositions were required for the different seedling propagation methods tested and for the different physiological stages in seedling growth. It was recommended that E. dunnii mini-plug seedlings are cultivated using an 80:20 (v/v) mixture of 6-mm pine bark and perlite. For the final container, the recommended substrate was a 90:10 (v/v) mixture of 6-mm pine bark and perlite. The effects of vermicompost leachate, seaweed extract and smoke-water on seedling growth after transplanting were evaluated as many beneficial effects of these supplements have been reported. The use of vermicompost leachate, seaweed extract and smoke-water were not effective in improving E. dunnii seedling growth after transplanting in this study. However, these supplements may have needed to be applied to the seedlings more regularly and at higher concentrations. Further research is required to optimise the concentration and frequency of application to ensure improved seedling growth after transplanting. Although, during the course of this study some improvements to the container to-container transplanting procedure were made, the seedling quality of directly-sown seedlings was still superior. By transplanting mini-plug seedlings a delay in seedling growth was observed and the incidence of J-rooting was increased. Neither, tray type, cultivation time nor substrate composition was able to limit the incidence of J-roots in transplanted seedlings or prevent the delayed seedling growth. For a mini-plug transplanting method to be successful in a commercial forestry nursery, further research is required to overcome the limitations of this method.
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    Phytochemical and pharmacological investigations of invasive Chromolaena odorata (L.) R.M. King & H. Rob. (Asteraceae).
    (2015) Omokhua, Aitebiremen Gift.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.
    Chromolaena odorata (L.) R.M. King & H. Rob. (Asteraceae) is an invasive weedy scrambling perennial shrub native to the Americas that has proven to be a significant threat to both natural and semi-natural ecosystems as well as to livelihoods in the tropics and sub-tropics (including sub-Saharan Africa). Two biotypes of C. odorata are invasive in sub-Saharan Africa. The Asian/West African biotype (AWAB) is the more widespread form on the continent (being present in West, Central and East Africa), while the southern African biotype (SAB) is restricted to south-eastern Africa. Although the negative impact of the plant has received considerable attention in Africa, its medicinal and pharmacological significance is only beginning to be explored. The AWAB plant is exploited as a source of medicine in West and Central Africa for the treatment of malaria, wounds, diarrhoea, skin infections, toothache, dysentery, stomach ache, sore throat, convulsions, piles, coughs and colds, possibly because of the presence of flavonoids, essential oils, phenolics, tannins and saponins. The plant is reported to have antibacterial, anti-inflammatory, antioxidant, anthelminthic, antifungal, cytotoxic, anti-convulsant, anti-protozoal, antispasmodic, anti-pyretic and analgesic properties. Though the above usefulness has been reported with reference to the AWAB plant, the SAB plant has not been investigated. Hence this thesis attempts to comparatively document the phytochemistry and ethnopharmacological importance of both C. odorata biotypes. The antibacterial and antifungal activities of the leaf extract of the AWAB (mature non-flowering plants, AMNF) and the SAB (mature non-flowering plants, SMNF) were evaluated. Both biotypes exhibited good activity against E. faecalis (AWAB, 0.78; SAB, 0.78), but only the AWAB exhibited good activity against K. pneumoniae (AWAB, 0.78; SAB, 1.56) and S. aureus (AWAB, 0.39, 3.12), showing that the AWAB extracts were more effective than those of the SAB. For the antifungal activity against C. albicans only the SAB exhibited good fungicidal (SAB, 0.78; AWAB, 1.56) and fungistatic (SAB, 0.78; AWAB, 1.56) activity. The results of a further investigation of the antimicrobial activities of the different growth stages of the SAB plant showed that all growth stages exhibited some level of activity against the tested bacterial and fungal strains, although young and mature non-flowering plants displayed the better activities. Phytochemical analysis revealed the presence of saponins, phenolics, flavonoids and condensed tannins in varying amounts in the leaf extracts of the AWAB and SAB plants but alkaloids were only present in the AWAB plant. Quantitative determination showed that the AWAB contained higher amounts of phenolics and flavonoids than the SAB, but condensed tannins were higher in the SAB than the AWAB. In comparing the levels of phytochemicals between the three growth stages of the SAB, mature non-flowering plants contained the highest amount of phenolics, flavonoids and tannins compared to the young and flowering plants. This showed that the antimicrobial activity displayed by the extracts of the various growth stages of the SAB could not be correlated with the levels of various phytochemicals present. The tetrazolium-based colorimetric (MTT) assay for cytotoxicity and Ames test for mutagenicity were used to evaluate the safety of the plant extracts prepared from the three growth stages of the SAB. The results from the cytotoxicity assay showed that the young plant extract which showed the best antimicrobial activity was more cytotoxic than the mature flowering and mature non-flowering plants. The Ames test using Salmonella typhimurium tester strains TA98 and TA102 without S9 metabolic activation revealed that all plant extracts of the three growth stages of the SAB were non-mutagenic towards the S. typhimurium strains tested. The screening of the plant extracts for pharmacological activity and phytochemical composition provided valuable preliminary information in that both the AWAB and SAB may be good sources of antimicrobial agents. This study further demonstrated that the leaf extract of the young and mature non-flowering plants of the SAB plants may be exploited for medicinal purposes. While the medicinal potential of the AWAB sub-type has been demonstrated in this thesis and by other workers, this is the first study that simultaneously examined the phytochemistry and pharmacological potential of the SAB plant. The results suggest that the SAB plant can be exploited in southern Africa as a source of traditional medicine. This serves the dual purpose of exploring a use for this burgeoning weed problem as well as finding a possible alternative to highly exploited plant species with the same medicinal potential.
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    The morphology and chemical composition of the trichomes of Withania somnifera (Solanaceae)
    (2014) Munien, Prelina.; Naidoo, Yougasphree.; Naidoo, Gonasageran.
    For centuries, plants have been used in the cosmetic, culinary and medicinal industries. Recently however, the use of plants in the medicinal industry has increased due to the widespread awareness of the harmful effects of synthetic drugs on humans. Withania somnifera (Dunal.) is an evergreen perennial shrub found in the drier parts of Africa, particularly South Africa and Asia. Since the phytochemical compounds within the extracts of W. somnifera act upon both the nervous and reproductive systems, it is used to treat a wide variety of ailments such as arthritis, stress, ulcers, and tremors. This species has therefore been cultivated to extract the phytochemicals produced. The aim of this study was to characterise the micromorphology of the foliar trichomes of W. somnifera as well as to elucidate the location and composition of the secretory products. Stereomicroscopy and scanning electron microscopy (SEM) were used to characterise the foliar trichomes. A series of histochemical and phytochemical tests were performed to determine the location and composition of the compounds that are responsible for the healing properties of the extracts of W. somnifera. Trichome density and length was also determined in three developmental stages of the leaves. Histochemically stained leaf sections and SEM showed the presence of four morphologically distinct trichome types: glandular capitate, non-glandular dendritic, non-glandular bicellular and non-glandular multicellular. Uniseriate, glandular capitate trichomes consisted of a six-celled secretory head, single-celled stalk and a single basal cell. Secretions from the glandular heads of capitate trichomes were visible on the leaf surface during ESEM and histochemical staining. Non-glandular dendritic trichomes, which appeared to emanate from single basal cells, consisted of 2-4 celled stalks and varying branch numbers. These dendritic trichomes exhibited cuticular warts which are involved in the “Lotus-Effect”. Uniseriate, non-glandular bicellular and multicellular (3-6 cells) trichomes also appeared to emanate from single basal cells. Glandular capitate and non-glandular dendritic trichomes were aggregated on the mid-vein of young and mature leaves, possibly to protect underlying vasculature. Histochemical staining and phytochemical testing revealed the presence of two major phytochemical compounds of medicinal importance, i.e. alkaloids and phenolic compounds. These compounds are used to treat a wide variety of ailments, such as dysentery, TB, paralysis, asthma and inflammation, and also act as chemical deterrents in plants. The results of this study explain possible roles of glandular capitate, non-glandular dendritic, non-glandular bicellular and non-glandular multicellular trichomes based on their morphology and foliar distribution. Future studies should aim at determining the biosynthetic pathways, as well as the modes of secretion of alkaloids and phenolic compounds.
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    Micromorphology and phytochemistry of the foliar secretory structures of Stachys natalensis Hochst. and development of an in vitro propagation protocol.
    (2014) Kalicharan, Benita.; Naidoo, Yougasphree.; Nakhooda, Muhammad.
    Many members of the genus Stachys have been used as ornamental plants, or as edible foods and, in a number of cultures, as traditional medicine. One such species, Stachys natalensis Hochst., is a perennial, straggling shrub with aromatic leaves that are covered with hairs. Despite its widespread use for a number of reasons, little information has been available on this plant thus far, its foliar secretory apparatus, or the nature and potential therapeutic value of these secretions. Hence, the aims and objectives of the present study were to elucidate key micromorphological features of the leaf secretory structures of S. natalensis, using both light and electron microscopy and to determine the location and chemical composition of the exudates using various histochemical and phytochemical techniques. An additional aim was to establish an in vitro micropropagation protocol for the sustained and high-yielding production of this elusive and often difficult to cultivate species. Furthermore, the foliar micromorphological fidelity between field and in vitro propagated material was compared. Electron micrographs indicated the presence of glandular and non-glandular trichomes on both abaxial and adaxial foliar surfaces of field grown plants. Greater trichome density was observed on the abaxial surface with trichome distribution decreasing as the leaf developed (p<0.05). Uniseriate, unbranched and striated non-glandular trichomes, present on the foliar surfaces of S. natalensis are known to play a role in physical plant defence mechanisms against herbivory. The presence of an elevated cellular pedestal and striated micro-ornamentation on the stalk served as characteristic features of the non-glandular trichomes. Peltate and capitate glandular trichomes were also identified on the foliar surfaces across all developmental stages. Peltate glands consisted of a short stalk and a multicellular head containing two to eight secretory cells. Two types of capitate trichomes were observed. Type I capitate trichomes consisted of a striated stalk, cutinized neck cell and bulbous head which may be uni- or bi-cellular;Type II capitate trichomes were comprised of a wide base, long and tapering, septate stalk, neck cell and a multicellular secretory head cell. The process of secretion differed between the peltate and capitate glandular trichomes. The peltate and Type II capitate trichomes included a porose cuticle which facilitated the release of secretion to the exterior. Cuticular rupture at weak points of the equatorial plane of the secretory head was observed in Type I capitate trichomes. Qualitative histochemical staining of leaf sections and preliminary phytochemical tests revealed the presence of alkaloids, lipid components, terpenoids and complex polysaccharides concentrated in the glandular trichome head cells and leaf crude extracts, respectively. The perceived therapeutic benefits of this plant are likely to lie within this suite of secondary metabolites. Stachys natalensis plant extracts also contained considerable levels of total phenolic compounds (3.43 ± 0.01 mg GAE/g dry material) and flavonoids (3.04 ± 0.01 mg QE/g dry material). The methanolic extracts demonstrated significant free radical scavenging ability (49.49 ± 3.87 ug/ml) which indicates the potential for its use as a natural antioxidant. In vitro propagation protocol using axillary bud explants was developed for this species. A multi-step decontamination treatment involving explant immersion in 1% and 3% NaClO, followed by 0.1% HgCl₂ was the most efficient method for explant decontamination, resulting in overall explant survival of 48%. All media preparations resulted in > 70% bud break within three weeks with cultures initiated on Medium C ( MS supplemented with 0.5 mg/l BAP and 0.5 mg/l IBA) showing the highest percentage of bud break. Growth medium B (0.5 mg/l kinetin and 0.5 mg/l IAA) showed the greatest total shoot multiplication, number of shoots/explant (9.1 ± 3.6) and height/explant (50.2 ± 5.0 mm) compared to other PGR combinations after 12 weeks. The addition of exogenous auxin (2 mg/l IAA) to MS medium allowed for 64% of plantlets to produce adventitious roots in five weeks, after which rooted plants were acclimatized. Acclimatized plantlets (92 ± 4.2 %) did not show any gross morphological abnormalities compared to field-grown plants, apart from the presence of visibly longer non-glandular trichomes. The peltate and both subtypes of capitate glandular trichomes of acclimatized plants were morphologically similar to their field-grown counterparts. Trichome density on acclimatized plants was greater on the abaxial surface of emergent leaves and this density decreased with leaf maturity, as was observed with field-grown plants. This study appears to be the first investigation of the micromorphology of the foliar structures of S. natalensis. Future studies on morphological aspects of secretory structures should include cytochemical investigations to determine the exact mechanism and origin of glandular secretions. Further analyses regarding the composition of the glandular essential oils and its potential pharmacological efficacy are required. With an effective in vitro propagation protocol being presently established, further optimisation with respect to the type and concentration of exogenous PGRs, explant type or even various routes of organogenesis can be investigated. This may provide a means of enhancing plantlet production, maintaining superior-selected genotypes, and thus potentially maximising the yield of putative pharmacologically-important secondary metabolites.
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    Aspects of avian thermal physiology and frugivory of indigenous and invasive fruits in South Africa.
    (2014) Thabethe, Vuyisile.; Downs, Colleen Thelma.
    Indigenous and invasive plants have long been recognised as an important food source for avian frugivores worldwide. It has been suggested that seed germination success can vary amongst avian and plant species and that ingestion by avian frugivores can enhance, reduce or have no effect on seed germination. Few studies have looked at the role of both invasive and indigenous avian species on the germination success of invasive and indigenous plants in South Africa. Therefore the first aim of this study was to determine the effects of invasive rose-ringed parakeets (Psittacula krameri) and indigenous Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos on seed germination of invasive alien plant species (Solanum mauritianum, Cinnamomum camphora, Psidium guajava, and Morus alba). The second aim was to determine the effect of invasive rose-ringed parakeets on seed viability and germination of indigenous Ficus species (i.e. F. lutea, F. burkei, F. sur and F. natalensis). Previous studies have shown that many avian frugivores prefer invasive alien fruits suggesting that they may be able to efficiently assimilate energy from these fruits. However few studies have focused on the consumption and digestive efficiency of invasive fleshly fruits by indigenous and invasive birds simultaneously in one study. Consequently this study also investigated the digestive efficiency of invasive and indigenous avian frugivores feeding on invasive fleshy fruits. Finally, this study assessed the seasonal effects on the thermoregulation of invasive rose-ringed parakeets. As invasive bird species are spreading in South Africa, understanding the physiological responses that equip them to tolerate a wide range of climatic conditions would be useful for modelling potential distributions and effectively managing them. Seed ingestion by Knysna and purple-crested turacos resulted in significantly higher germination success than those from whole fruits for all invasive alien plant species in this study. Germination success of manually pulp-removed seeds did not differ from that of turacos ingested seeds, suggesting that seed coat abrasion was not important for germination of these invasive alien plants. Seed passage through the digestive tract of rose-ringed parakeets resulted in significantly reduced germination success and viability of all ingested plant species, suggestion that seed ingestion by this species is disadvantageous to these plant species. These results suggest that Knysna and purple-crested turacos are legitimate seed dispersers of the four fleshy-fruited invasive plants, while rose-ringed parakeets are mainly seed predators. Results obtained from this study also suggest that rose-ringed parakeets are mainly seed predators of Ficus fruit, as none of the ingested seeds managed to germinate. In addition, all three avian species investigated managed to meet their energetic demands by feeding on invasive alien fruit only, suggesting that these plant species may sustain avian frugivores especially during periods of food scarcity. Furthermore, the results obtained also suggest that rose-ringed parakeets show seasonal thermoregulatory responses representing energy conservation, as expected. This suggests that rose-ringed parakeets are physiologically equipped to cope with a range of environmental conditions and this partly explains their global success as an invasive species.
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    Vegetation change in Northern KwaZulu-Natal since the Anglo-Zulu war of 1879.
    (2013) Russell, Jennifer Mary.; Ward, David Mercer.
    Historic photographs have been successfully used to compare landscape change over time. I used photographs taken of the grassland biome during and just after the Anglo-Zulu War (1879) in KwaZulu-Natal (South Africa), which are some of the earliest known available landscape photographs. The study area encompassed Fugitives’ Drift, Isandlwana and Rorke’s Drift and included communal and commercial rangelands, as well as conservation areas. These fixed-point photographs showed a dramatic increase in woody cover (< 82.5%) since the Anglo-Zulu War in all three land-use types. Floristic sampling showed that while vegetation structure did not differ significantly, plant species diversity and richness differed significantly for each land-use type. I also used a set of aerial photographs to give a much wider perspective of the landscape changes for the study area from 1944 to 2005. These images indicated that the increase in woody cover was progressive, with most of the woody plant recruitment occurring prior to 1964. Thereafter, the increase in woody plant cover was due to bush-clump thickening rather than recruitment into grasslands. This pattern did not occur, however, in the commercial rangeland, where recruitment into open grassland commenced in the 1980s. Although the theory of patch dynamics is cyclical in nature, this model may fit the patterns observed in the study area. Analysis of rainfall and temperature data showed that there has been a decrease in average annual rainfall since 1902 and an increase in minimum daily temperature since 1973. However, the decrease in mean annual rainfall is not consistent with woody plant encroachment. While the increase in mean annual daily temperature appears consistent with a shift to an environment typical of savannas, woody plant encroachment started before the increase in daily temperature. A survey of long-term residents in the study area with regard to livestock numbers, grazing patterns, fire and wood harvesting was also inconclusive. I, therefore, speculate that increasing levels of atmospheric CO2 is driving bush encroachment, with the other drivers such as rainfall, temperature, absence of intense fires, grazing patterns and land-use, playing a modifying role.
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    Evaluation of recirculating hydroponic systems for eucalyptus cutting production.
    (2002) Alpoim, Giordano da Costa.; Van Staden, Johannes.; Blakeway, Felicity Clare.
    In South Africa, Eucalyptus grandis and hybrids of this genus are planted over 196000 ha of Mondi Forests land. The temperate and cold tolerant species (E. grandis, and E. grandis X E. nitens) occupy 142000 ha and the subtropical species (E. grandis, E. grandis X E. camaldulensis and E. grandis X E. urophylla) occupy a further 54000 ha. In Southern Africa, until 1998, there had not been any significant research undertaken into the development and application of hydroponics to cutting production in nurseries. Since then, research in Mondi Forests has focused on the evaluation of recirculating hydroponic systems for cutting production of the genus Eucalyptus. South American forestry companies have achieved noteworthy success in improving the rooting of cuttings of selected clonal Eucalyptus harvested from hydroponic gardens. Verifiable increases of up to 300% in rooting have been achieved. (JANSE, 2001 pers. comm.1). Towards this aim, protocols for the production of Eucalyptus cuttings in hydroponic systems were established, and implemented in a commercial hydroponic production system. Seven nutrient solutions with different concentrations of macro- and micro-nutrients were tested on three different substrates, viz perlite, sand and 6.2 mm dolomitic gravel. A pure nutrient film system (NFT) was also tested. Nutrients (1.2 -1.5 mS/cm) applied cyclically over a seven day period, followed by two days of leaching with clean water, were found to be suitable for cutting production. Excessive nutrient supply resulted in soft foliage, susceptibility to powdery mildew (Oidium eucalypti) and Botrytis infection. Foliar analyses showed that macro-element levels in leaves were similar to those of soil-derived plants, whilst micro-element levels were generally higher in the 'hydro-ramets.' Most significant were the higher concentrations of boron and calcium. Sand and perlite had the best water holding capacities, requiring hydration every 96 hours, whilst gravel sustained plants for up to 48 hours without any visible stress. The modified NFT unit, however, was the most efficient system in terms of managing cutting production. Some post-establishment mortalities occurred across all treatments and were attributed to pathological attack by Pylhium sp. Light source and intensity were critical. Initial low light levels (615 Lux) did not result in optimum growth and plants showed signs of being stressed, thus contributing to an increase in powdery mildew infection. Plant growth improved with increasing light levels (> 3000 Lux). Following this research, operational systems were developed. From first harvests, rooting of cuttings from the hydroponically-grown parent material were higher than those from field hedges. Mean rooting from the best performing nutrient and substrate combination was 67%, compared to 45% obtained from the field hedge. In addition, the hydroponic system was found to offer other advantages: 1) hydroponic hedges are less costly to maintain than field hedges; 2) hydroponic systems offer greater control of nutrients than can be achieved in field hedges; 3) hydroponically-grown hedge plants can be better shielded from environmental variables which impact on the productivity of field hedge plants; 4) the threat on the environment in terms of water use and effluent disposal is alleviated to a large degree.
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    Isolation and characterisation of senescence-related genes in carnations.
    (1995) Howden, Jean Blair.; Van Staden, Johannes.; Cress, William A.
    Senescence has been the subject of many studies, with the ultimate goal of increasing longevity of cut flowers, and for insight into the process of ageing. Senescence in the carnation is a complex phenomonen involving many physiological and molecular events. The carnation serves as an excellent subject for studies in senescence because of the clearly visible evidence of "in-rolling" of petals indicating the onset of senescence. Senescence in the carnation results in a large number of physiological changes in the flower which in many cases involve the action of the growth regulating hormones, particularly ethylene. Physiological studies of senescence, though exhaustive, have not as yet been able to pinpoint the source of control of senescence in the carnation and the exact controlling mechanism. Senescence has in the past been shown to be partially regulated at the transcriptional level, thus warranting studies in the area of molecular biology. The aim of the present investigation was to isolate genes active during senescence . To achieve this, mRNA from presenescent and senescing carnation petals, receptacles and ovaries was extracted. The mRNA was used to synthesise cDNA which was cloned into ۸gt10 phage to produce presenescent and senescing cDNA libraries of carnation material. The production of the petal library was the only library that, after boosting levels of petal cDNA using PCR (polymerase chain reaction) technology; was generated successfully. A subtraction procedure was carried out between the presenescent and senescing libraries to isolate the sequences unique to the senescing library ie. the genes active only during senescence. One sequence of 1 kb in size was isolated. This gene could be used for future research into the influence of the growth regulators on its activity, and also to pinpoint organs other than the petals where this particular gene is active. It would be of interest to investigate the sequence of the gene, for a comparison with other gene isolates in order to elucidate the identity and function of the gene product.
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    In vitro techniques for the improvement of growth and secondary metabolite production in Eucomis autumnalis subspecies autumnalis.
    (2014) Masondo, Nqobile Andile.; Van Staden, Johannes.; Finnie, Jeffrey Franklin.
    The wide utilization and popularity of medicinal plants in African Traditional Medicine (ATM) has been recognized and attributed to the effectiveness, affordability and accessibility of these medicinal plants. However, the extensive exploitation of medicinal plants has exacerbated the strain on the wild populations. In vitro propagation/micropropagation is an effective method which allows for mass production or multiplication of pathogen-free plants that are morphologically and genetically identical to the parent plant. In addition, the technique is contributing to the understanding of metabolic pathways and regulating the production of plant secondary products. Eucomis autumnalis (Mill.) Chitt. subspecies autumnalis (Hyacinthaceae) is a valuable medicinal species in ATM and commonly traded in the urban street markets of South Africa. Currently, the conservation status of this species has not been evaluated. However, as with most bulbous plants, the wild population is continuously under threat due to over-harvesting and habitat loss via various anthropogenic factors. Thus, in vitro propagation is a viable means of ensuring conservation of the plant species. However, mass propagation of medicinal plants should be accompanied with increased secondary metabolite production to guarantee their therapeutic efficacy. Therefore, the current study was aimed at understanding the different factors that affect the growth and secondary metabolite production in micropropagated E. autumnalis subspecies autumnalis. The influence of the type of gelling agent (gelrite versus agar) and source of initial/primary explant source (LDL = leaf explant derived from primary leaf regenerants and LDB = leaf explant derived from primary bulb regenerants) were evaluated. Gelrite-solidified medium significantly improved shoot proliferation when compared to the use of agar as a solidifying medium. In contrast, quantified phytochemicals such as flavonoids and phenolics were more enhanced in agar-supplemented media. On the basis of the explant source, shoot proliferation and secondary metabolites in regenerants from LDB were similar to those from LDL in most cases. Overall, the type of gelling agents and primary explant source individually or/and interactively significantly influenced the growth parameters as well as the production of iridoid, condensed tannin, flavonoid and phenolic content. The influence of different types of plant growth regulators (PGRs) on growth, phytochemical and antioxidant properties were evaluated. The PGRs were BA (benzyladenine); mT (meta-topolin); mTTHP [meta-topolin tetrahydropyran-2-yl or 6-(3-hydroxybenzylamino)-9-tetrahydropyran-2-ylpurine]; MemT [meta-methoxytopolin or 6-(3-methoxybenzylamino)purine]; MemTTHP [meta-methoxy 9-tetrahydropyran-2-yl topolin or 2-[6-(3-Methoxybenzylamino)-9-(tetrahydropyran-2-yl)purine] and NAA (α-naphthalene acetic acid). Five cytokinins (CKs) at 2 μM in combination with varying (0, 2.5, 5, 10, 15 μM) concentrations of NAA were tested. After 10 weeks of in vitro growth, the regenerants were acclimatized in the greenhouse for four months. Growth, phytochemical content and antioxidant activity of in vitro regenerants and ex vitro-acclimatized plants were evaluated. The highest number of shoots (approximately 9 shoots/explant) were observed with 15 μM NAA alone or with BA treatment. Acclimatized plants derived from the 15 μM NAA treatment had the highest number of roots, largest leaf area and widest bulb diameter. While applied PGRs increased the iridoids and condensed tannins in the in vitro regenerants, total phenolics and flavonoids were higher in the PGR-free treatment. In contrast to the PGR-free regenerants, 5 μM NAA and 2 μM BA treatments produced the highest antioxidant activity in the DPPH (55%) and beta-carotene (87%) test systems, respectively. A remarkable carry-over effect of the PGRs was noticeable on the phytochemical levels and antioxidant activity of the 4-month-old plants. In addition to the development of an optimized micropropagation protocol, manipulating the type and concentration of applied PGRs may serve as an alternative approach to regulate phytochemical production in Eucomis autumnalis subspecies autumnalis. The influence of smoke-water (SW), karrikinolide (KAR1) and CK analogues (PI-55 = 6-(2-hydroxy-3-methylbenzylamino)purine and INCYDE= inhibitor of cytokinin dehydrogenase or 2-chloro-6-(3-methoxyphenyl)aminopurine) individually or in combination with some selected PGRs [BA (4 μM), NAA (5 μM) and both] for in vitro propagated E. autumnalis subspecies autumnalis was evaluated. While these compounds had no significant stimulatory effect on shoot proliferation, they influenced root length at varying concentrations and when interacted with applied PGRs. The longest roots were observed in SW (1:1500), PI-55 and INCYDE (0.01 μM) treatments. There was an increase in the concentration of quantified phytochemicals (especially condensed tannins, flavonoids and phenolics) with the use of these compounds alone or when combined with PGRs. In the presence of BA, an increase in the concentration of PI-55 significantly enhanced the condensed tannin, flavonoid and phenolic contents in the regenerants. Both phenolic and flavonoid content in E. autumnalis subspecies autumnalis were significantly enhanced with 0.01 μM INCYDE. Condensed tannins was about 8-fold higher in 10-7 M KAR1 with BA and NAA treatment when compared to the control. To some varying degree, the effect of the tested compounds on the antioxidant activity of the in vitro regenerants was also noticeable. In most cases, there was no direct relationship between the level of phytochemicals and antioxidant activity recorded. The current findings indicate the array of physiological processes influenced by SW and KAR1 during micropropagation. In addition, targeting or manipulation of phytohormone metabolic pathways using CK analogues demonstrated some noteworthy effects. Perhaps, it may offer other potential practical applications in plant biotechnology and agriculture. Thus, more studies such as quantification of endogenous hormones and identification of specific phytochemicals responsible for the bioactivity in this species will provide better insights on the mechanism of action for CK analogues as well as SW and KAR1.
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    Effects of some of the procedural steps of cyropreservation on cryo-recalcitrant zygotic embryos of three amaryllid species producing desiccation-sensitive seeds.
    (2013) Ngobese, Nomali Ziphorah.; Berjak, Patricia.; Pammenter, Norman William.
    Cryopreservation is the most promising method for the long-term conservation of germplasm of plants producing desiccation-sensitive seeds. While such seeds are generally termed recalcitrant in the context of conventional storage practices, the term ‘cryo-recalcitrant’ is used for germplasm which is not readily amenable to cryopreservation. Cryo procedures usually involve a sequential combination of steps which must be optimised to limit the stresses experienced by specimens, thus promoting their survival. The present contribution reports on the effects of some of the steps involved in cryopreservation on the survival of the embryos of the amaryllids, Ammocharis coranica, Brunsvigia grandiflora and Haemanthus albiflos, with the ultimate aim of developing a protocol(s) for the successful cryopreservation of the germplasm of these species. The main foci of the investigations were the effects of rapid (flash) drying, the use of the cryoprotectant additives, glycerol (5 & 10%) and DMSO (0.1 & 0.25%), and employment of different cooling rates on the zygotic embryos of the selected species, which are known to be recalcitrant as well as being cryo-recalcitrant. Furthermore, this study reports on attempts at improving the rapidity of dehydration during flash drying by applying a vacuum, and also of providing cathodic protection (via highly reducing cathodic water and/or direct exposure to a static {negatively-charged} cathodic field during flash drying) to the explants at various stages in the protocol. These techniques were employed in attempts to ameliorate the adverse effects of reactive oxygen species associated with stresses imposed by the procedures during the cryopreservation process. The embryos of Ammocharis coranica, Brunsvigia grandiflora and Haemanthus albiflos were initially at water contents (WCs, dry mass basis) of 3.28±0.52, 2.55±0.22, 4.48±0.92 g g-1, respectively, after harvest. These embryos proved to be tolerant to moderately rapid water loss in the short term, with >60% retaining germinability at water contents ≥0.5 g g-1. The results from this study confirmed that dehydration to water contents below 0.5 g g-1 (dry mass basis) compromised survival, and that this effect was exacerbated if the embryos were cryoprotected prior to drying. Interestingly, the rate of water loss in embryos of these species differed, with A. coranica and H. albiflos drying at a (comparably) much slower rate than those of B. grandiflora. Subsequent rapid cooling yielded promising results when compared with slow cooling, as 30% of glycerol cryoprotected, rapidly cooled A. coranica embryos that had been flash-dried to 0.36±0.10 g g-1 generated normal seedlings. It was clear, however, that the effects of these procedures were exacerbated when all the steps of the cryo procedure were applied sequentially. However, the work also showed that these adverse effects may be ameliorated if each step of the cryopreservation protocol is optimised on a species-specific basis, thus promoting the chances of survival after cryopreservation and facilitating subsequent seedling establishment. This was evident in the 30% germination obtained when embryos of A. coranica, which had been cryoprotected with glycerol prior to flash drying before exposure to rapid cooling, while those that had not been cryoprotected or were cryoprotected with DMSO before drying did not survive. The incorporation of cathodic protection during flash drying appeared promising as it promoted the survival of 10% of H. albiflos embryos dehydrated to WCs between 0.37 and 0.26 g g-1 (whereas no survival was achieved without the inclusion of this step), and 70% of A. coranica embryos that were dehydrated to 0.35±0.21. In addition, the reduction of the explant size, from a whole 6 mm embryo to a 3-4 mm excised axis, promoted survival by up to 30% for A. coranica and H. albiflos, even at higher WCs. However, survival in these cases was based on observations of abnormal development, i.e. the development of roots or shoots, or calli. No surviving embryos were obtained from B. grandiflora after cooling, regardless of the preconditioning treatment or rate of cooling, and this was accredited to the greater degree of sensitivity of these embryos to the cryo procedures than those of the other two species. The use of cathodic water to re-hydrate explants after dehydration and of applying a vacuum during flash drying did not result in any observable benefits, and require further investigation for optimisation. The very limited success towards establishing a cryopreservation protocol for the species investigated in this study reinforces the difficulties associated with the cryopreservation of recalcitrant germplasm, which informs the cryo-recalcitrance of some explants. However, the results obtained have helped to identify a number of intervention points that could be used to minimise the damage incurred during the various procedural steps involved in cryopreservation.
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    Survival and rooting of selected vegetatively propagated Eucalyptus clones in relation to supplied auxin.
    (2013) Rambaran, Natasha.; Watt, Maria Paula Mousaco Deoliveira.; Mokotedi, Mompe Edward Oscar.; Nakhooda, Muhammad.
    Eucalyptus spp. and hybrids dominate the global plantation forestry industry, and vegetative propagation through cuttings is the preferred method for their commercial use. However, the cuttings of some species and hybrids show recalcitrance to rooting. The first aim of this study was to improve percentage rooting of three clones of E. grandis x E. nitens (Clones 1, 2 and 3) identified by a commercial nursery as having variable rooting abilities. The second was to relate their rooting responses as cuttings to their rooting responses in vitro. Minicuttings (3.5 – 4 cm in length) (hereafter referred to as cuttings) were subjected to commercial nursery propagation practices. Initial results revealed that in the absence of exogenous plant growth regulators (PGRs), soft (juvenile, thin diameter) cuttings survived (87 – 95%) and rooted (29 – 32%) significantly better than hard (mature, thick diameter) ones (62 – 71% survival and 2 – 8% rooting). This validated the use of soft cuttings by the nursery and all subsequent studies were conducted with soft cuttings. The other nursery practice of applying the commercial rooting powder Seradix 2 (3 g kgˉ¹ indole-3-butyric acid [IBA]) adversely affected the survival and subsequent rooting of cuttings of Clones 1 and 2. Ensuing studies investigated: 1) the effect of mode of IBA application (powder vs. liquid); 2) concentrations of Seradix (0, 0.5, 1, 2 and 3 g kgˉ¹ IBA), applied at initial placement of cuttings and two weeks later; and 3) the influence of season on the survival and subsequent rooting of cuttings. Results showed that regardless of the mode of application, IBA significantly reduced percentage survival and rooting in cuttings of Clones 1 and 2. The delayed application of Seradix, two weeks after cuttings were initially set, resulted in a higher percentage survival and rooting than when cuttings were supplied with Seradix at initial placement. Nevertheless, the best survival for Clones 1, 2 and 3 (95%, 99% and 71%, respectively) and rooting (83%, 64% and 47%, respectively) occurred in the absence of Seradix. In addition, the survival and rooting of cuttings were seasonally variable, with particularly low rooting during winter (e.g. for Clone 1, 32%) when compared with summer (e.g. for Clone 1, 83%). Shoots from all the clones were multiplied in vitro, followed by elongation on either of two media (E1= kinetin, α-naphthalene acetic acid [NAA] and IBA; E2 = kinetin and indole-3-acetic acid [IAA]), and then rooting on 0, 0.1 or 1.0 mg 1ˉ¹ IBA. The latter were selected to typify the range of Seradix concentrations used for the cuttings (i.e. no IBA, low and high IBA concentrations). For all three clones, shoots elongated on E1 or E2 displayed high survival (> 80%) but failed to root without IBA in the rooting medium. For Clones 1, 2 and 3 the best in vitro survival (80%, 100% and 100%, respectively) and rooting (40%, 75% and 40%, respectively) occurred when shoots were elongated on E2 and rooted on 0.1 mg 1ˉ¹ IBA. However, 1.0 mg 1ˉ¹ IBA in the rooting medium severely inhibited survival (0 – 50%), irrespective of the clone or the elongation treatment used. Overall, cuttings demonstrated the best survival and rooting in the absence of exogenous IBA, which suggested that sufficient endogenous auxin was present within the shoots for successful root induction. The application of exogenous IBA may have disrupted the cuttings’ endogenous PGR balance resulting in an inhibition of survival and rooting. In vitro shoots required a low concentration of IBA (0.1 mg 1ˉ¹) in order to counteract the antagonistic effect of cytokinins that were supplied during the multiplication and elongation culture stages, and promote rhizogenesis. Essentially, both cuttings and in vitro shoots demonstrated adverse survival and rooting responses when subjected to excessively high IBA concentrations.
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    An investigation into the potential of faecal sludge for plant production.
    (2012) Taylor, Craig Robert.; Pammenter, Norman William.; Rodda, Nicola Heike.
    Abstract available in PDF file.
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    Host specificity of the hemiparasitic mistletoe, Agelanthus natalitius.
    (2009) Okubamichael, Desale Yosief.; Ward, David Mercer.; Griffiths, Megan Elizabeth.
    Mistletoes are a group of hemiparasitic plants that grow on a wide variety of host trees and differ in their degree of host specificity, ranging from specialists to generalists. Mistletoes can also be locally host specific where host preference varies geographically, i.e. at a given location a mistletoe species may infect only part of its overall host set. The mistletoe Agelanthus natalitius parasitises at least 11 tree genera distributed throughout South Africa. However, there is geographic variation in infection patterns over the parasite’s range, suggesting that A. natalitius may be locally host specific. We quantified the degree of host specificity and tested the mechanisms that direct host specialisation in two distinct mistletoe populations at Highover and Mtontwane (about 110 km apart) in KwaZulu-Natal, South Africa. We investigated the distribution, abundance and community composition of woody species that host the mistletoe. We also assessed the effect of light on germination and early survival of the mistletoes in a greenhouse experiment. We conducted field reciprocal transplant experiments at both sites to investigate the compatibility of these mistletoes with their hosts Acacia karroo and A. caffra during early development. We then analysed the nutrient and water contents of the mistletoe-host pairs to investigate the role of nutrient and water status in directing host specificity in mistletoes. We further studied avian dispersal in the field and in captivity to investigate optimal dispersal distance and germination success, and evaluated their role in determining mistletoe host specificity. At both study sites, five host species were recorded as being parasitised by the mistletoe A. natalitius. A. karroo and A. caffra appear to be the two most common host species in the region; both grow abundantly at the study sites and were recorded with high infection by A. natalitius. However, A. karroo is the most abundant host species and the mistletoe showed a high degree of host specificity on A. karroo. Infection by mistletoes was positively correlated with tree size, and was highly aggregated, both individually and locally. Field observations and greenhouse shade experiments showed that light can influence mistletoe distribution. Germination of mistletoe seeds was independent of host species and site. However, hypocotyls (the structures that develop into haustoria) grew longer when placed on their source host species within their locality. Additionally, they showed preference for the most abundant host species, A. karroo. Water and nutrient status of the host species A. karroo and A. caffra had no significant effect. Thus, host nutrient and water content may not account for host specificity in this mistletoe species. Mistletoes accumulated more nutrients and maintained more negative than their host trees. We also investigated the mistletoes’ use of passive nutrient uptake (from host xylem) and active nutrient uptake (from host phloem) by using the N:Ca ratio as an index of nutrient access. Mistletoes growing on A. caffra had a ratio > 1, i.e. the mistletoe actively accessed nutrients from the phloem of host trees. However, mistletoes on A. karroo had a N:Ca ratio < 1, which implies that they passively accessed nutrients from the xylem. The difference in mechanism of nutrient acquisition on different host species may reflect the level of compatibility between mistletoe and host. Several bird species were frequently observed to feed on mistletoes, many of which were used in our captivity studies. Although birds did not consume mistletoe fruits in captivity as they do in the field, they were effective in removing the pulp cover of mistletoe fruits and exposing seeds in germinable condition. In captivity, the Red-winged Starling ingested whole fruits and regurgitated seeds, deliberately wiping their bills on twigs to remove the sticky seeds. As a result, germination success of mistletoes processed by Red-winged Starlings was higher than any other bird species tested in captivity. Overall, there appears to be host specificity in morphologically identical mistletoes. Understanding the mechanisms that result in host race evolution are potentially important to the process of speciation in hemiparasitic mistletoes. We need to take into account genotypic matching in conserving these different forms of mistletoes and their host Acacia genotypes. Further research into the mechanisms of host specificity and patterns of genotypic matching is warranted.
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    The role of fire in bush encroachment in Ithala Game Reserve.
    (2010) Gordijn, Paul Jan.; Ward, David Mercer.
    The increase of woody vegetation (also known as bush or shrub encroachment) in savannas has become of global concern to conservationists and rangeland managers alike. Bush encroachment has been associated with a decrease in rageland palatability. In addition, the increase in woody biomass has consequences for climate change, carbon sequestration, rangeland hydrology and nutrient cycling. As a result of these large changes in ecosystem functioning with bush encroachment, biodiversity may be threatened. Fire is considered to be one of the most important management tools used to control woody biomass in savannas. However, despite the use of fire in Ithala Game Reserve, areas have become encroached. This thesis assesses the role of fire in bush encroachment in Ithala Game Reserve. I start this thesis with a discussion of the bottom-up (water, nutrients, and light) and topdown (fire and herbivory) ecosystem components in the literature review. This sets the foundation for an understanding of the factors that affect savanna tree:grass ratios for the rest of this thesis. In addition the review discusses the potential effects of climate change on savanna tree:grass ratios. Recently, it has been proposed that increasing atmospheric carbon dioxide concentrations result in an increased competitive ability for C3 woody plants against C4 grasses. Many models have been produced to explain savanna dynamics. By assessing the role of fire in Ithala Game Reserve, its functioning is assessed in light of the current issues of bush encroachment. Textural analysis is a remote sensing technique that has been used to detect changes in woody vegetation using aerial photographs. Textural analysis was used to assess changes in woody vegetation cover and density from 1943 (earliest period for which aerial photographs were available for the study area) to 1969, 1990 and 2007 in Ithala Game Reserve (IGR). Field surveys were performed to assess the effects of the fire regime in IGR on woody vegetation structure and composition. Transects were performed in areas with different fire frequencies. The effects of fire frequency were compared between similar vegetation communities. Textural analysis showed that woody vegetation cover (+32.5%) and density (657.9 indiv. ha-1) increased from 1943 to 2007. Importantly, in some areas of IGR, the suppression of fire led to the rapid invasion of woody plants from 1990 to 2007. Field studies demonstrated the importance of fire in controlling woody vegetation in IGR. The densities of the encroachers, Dichrostachys cinerea and Acacia karroo were resistant to annual burns. However, the height of these deciduous microphyllous woody encroachers was reduced by more frequent fires. Following the suppression of fire, these trees grew taller and their negative impact on the herbaceous layer increased. Consequently, fuel loads (grassy biomass) declined and prevented the use of frequent and intense fires by management. The reduction in fire frequency allowed the invasion of woody evergreen macrophyllous species. Continued development of fire-resistant patches of evergreen macrophyllous vegetation will further reduce the effectiveness of fire in controlling bush encroachment. To control bush encroachment in IGR and the consequential loss of biodiversity, an intermediate fire frequency (one burn every 2 to 4 years) is required. Burns also need to be hot enough to increase the current rate of topkill. Management should act to optimize the accumulation of grassy biomass to fuel fires.