Masters Degrees (Botany)

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Above-ground allometry, biomass and nutrient content of acacia mearnsii across four ages and three sites in the Kwazulu-Natal Midlands.
(2005) Dovey, Steven B.; Pammenter, Norman William.
Acacia mearnsii (black wattle) is one of the few tree crops of which both timber and bark are utilised, with branches sometimes being collected for fuel wood. There is a great potential for nutrient loss from plantations with intense harvesting practices. Allometric relationships were developed to estimate above-ground biomass across four ages and three site qualities of A. meamsii stands. The three sites were based on high, medium and low site quality classes of productivity. Differences in biomass and the distribution of biomass between the stem, bark, live branches, dead branches and foliage components are described in relation to site and age. Relationships between biomass and light interception and plant area index are investigated and show some merit. Nutrient concentrations were used with the above-ground biomass data to estimate quantities of nutrients held in the various biomass components in each of the stands. Nutrient distributions in the above-ground biomass (AGB) were examined and compared to other studies. Foliar phosphorus (P) and potassium (K) concentrations were shown to be sub optimal, agreeing with results and recommendations of South African fertilisation stupies. Some concentration differences were observed between site and age classes for certain nutrients, although these differences may have been due to seasonal effects. Biomass and nutrient quantities were adjusted to yield a wood production of 100 t ha01 and compared with adjusted calculations for similar studies on other plantation crops. Total nutrients contained in the AGB of the adjusted calculations were 540.8 kg ha01 nitrogen (N), 20.4 kg ha-I P, 200.6 kg ha01 K, 241 kg ha-I calcium (Ca), 55.7 kg ha-I magnesium (Mg), with a half to two thirds of the nutrients held in the stem and bark alone. Nutrients losses vary with harvesting intensity as bark and branches may be harvested with the stem wood. Levels of nutrient removal with harvesting intensity are discussed with reference to estimated losses and gains from natural processes and management practices. An incomplete nutrient budget calculation indicated that P, K, Ca and Mg might potentially be removed in quantities greater than replaced by natural processes under stem and bark harvesting. The budget calculations lack processes such as leaching and N-fixation. It is highly probable that these processes, once quantified, may yield more negative budget results, especially for the base cations K, Ca and Mg.
Alkaloids of Catha Spp.
(2001) Field, Courtney Robin.; Smith, Michael Trevor.
The levels of the psychoactive alkaloids S-(-)-cathinone and its primary metabolite cathine, consisting of the diastereomers (+) -norpseudoephedrine and (-)- norephedrine were determined in Catha edulis (Vahl) Forssk. ex Endl., Catha transvaalensis Codd and Catha abbottii Van Wyk & Prins. Alkaloid levels were investigated in C. edulis plants collected from three different localities in South Africa, and one from a Nairobi khat market. The efficiency of three different methods for the extraction and isolation of cathinone and cathine were investigated, viz. an aqueous acid extraction, an organic solvent extraction and an aqueous acid extraction using the commercially available Extrelutᴿ procedure. The aqueous acid extraction resulted in the rapid loss of cathinone and yielded variable alkaloid levels in replicate studies. This was also observed when this method was coupled with the Extrelutᴿ procedure. In contrast, the organic solvent extraction did not result in a loss of cathinone and provided consistent results over a number of replicates; it also proved to be a simple and rapid method for extracting and isolating cathinone and cathine. A trifluoroacetic acid (TFA) derivatization procedure which has been suggested to produce characteristic diagnostic fragments for gas chromatography / mass spectrometry (GC/MS) identification, was investigated, but failed to produce consistent TFA derivatives of cathinone and cathine. However, underivatized cathinone and cathine were easily identified by GCMS due to their unambiguous mass spectra. All subsequent studies were undertaken using the organic solvent extraction and isolation method, coupled with GC analysis and GC/MS identification of underivatized cathinone and cathine. Leaves of C. edulis were found to contain cathinone and cathine at levels 100 times higher than those of C. transvaalensis. The alkaloids were undetectable in C. abbottii. Plants grown from cuttings of C. edulis collected from the Durban Botanical Gardens were found to contain cathinone and cathine at levels of 0.410 mg per gram fresh weight and 0.157 mg per gram fresh weight in leaves, respectively, while these levels in plants derived from different localities decreased in the order: Eastern Cape (0.319 mg/g f.w cathinone and 0.029 mg/g f.w cathine), Mpumalanga (0.139 mg/g f.w. cathinone and 0.171 mg/g f.w. cathine) and Nairobi (0.032 mg/g f.w. cathinone and 0.025 mg/g f. w. cathine). In an investigation of the cathinone levels in the different plant parts it was found that the highest levels were found in leaves of the shoot tip (0.243 mg/g f.w.) but decreased with the age of the leaf and developmental stage of the plant in the order: juvenile leaves (0.124 mg/g f.w.), mature leaves (0.035 mg/g f.w.), young stem (0.033 mg/g f.w.) and mature stem (0.004 mg/g f.w.). Concomitantly, cathine levels increased with the age of the leaf: leaves of the shoot tip (0.006 mg/g f.w.), juvenile leaves (0.011 mg/g f.w.), mature leaves (0.019 mg/g f.w.). The cathine level in the young stem material was found to be the highest in the entire plant (0.270 mg/g f.w.) but decreased markedly in the mature stem (0.052 mg/g f.w.). Both cathinone and cathine levels in the mature root were greater than levels in the mature stern, being 0.012 mg cathinone per gram fresh weight, and 0.063 mg cathine per gram fresh weight. Neither cathinone nor cathine were detectable in young root material.
Aluminium-induced gene expression in sugarcane roots.
(2002) Graham, Natalie Jane.; Watt, Derek Alexander.
Due to the increasing prevalence and severity of Al phytoxicity in certain regions of the South African sugar industry, a research programme has been initiated at SASEX to elucidate the molecular mechanisms by which sugarcane detects and responds to the metal. As part of this larger investigation, the current study aimed to assess the response of a reportedly Al tolerant cultivar, Saccharum spp. hybrid cv. N12, to phytotoxic levels of Al. Hydroponically-grown plants of this commercial genotype were used in Al inhibition studies, the results of which indicated that exposure of plants to 250µM Al for 24 hours resulted in maximum reduction of root elongation. Under these conditions, root growth was inhibited by approximately 36%, compared with only 4% for the 50µM Al treatment. Subsequently, this exposure regime was used to gather the terminal 5 to 10mm of root tips, the site of the primary Al lesion, of challenged and control, unchallenged plants for molecular analysis. Total RNA was extracted from the Al challenged and control root tips, from which mRNA was subsequently isolated, reverse transcribed and converted to double-stranded cDNA. The two populations of cDNA were reciprocally subtracted from each other and used to construct subtractive cDNA libraries in Lambda ZAP®II phages. Randomly selected clones, 576 representatives from each of the libraries, were screened using membrane-based array technology. Results indicated that only 33% (190) of the Al-treatment specific library cDNAs were found to be more highly expressed under conditions of Al stress than under control conditions. Of these potentially Al response-related cDNAs, 25 were sequenced and submitted to sequence databases for the assignment of putative identities. No genic sequences known to be directly associated with the Al stress response were identified, however, several were found to be related to pathogenesis or general stress pathways. Although further Northern hybridisation work is required to validate these results, they suggest that the induction of general stress response pathways may be involved in the aluminium stress response of this sugarcane cultivar. Such Al stress-related sequences could have applications in marker-assisted breeding programmes and as candidate genes for the genetic engineering of tolerant genotypes.
Analysis of historical flowering data, investigations into aspects of pollen biology and selected biotechniques to complement sugarcane breeding in South Africa.
(2016) Mhlongo, Nonsikelelo Yvonne.; Snyman, Sandra Jane.
Abstract available in PDF file.
Another culture of Solanum genotypes.
(1995) Liebenberg, Denise.; Van Staden, Johannes.
Being the third most cultivated crop in South Africa, potatoes are of great economic importance. As potatoes originated from cooler areas in the world, they do not easily adapt to South African conditions. The main objective of potato breeding is, therefore, to extend the crop's limited genetic base. Progress in crop improvement is slow due to dominance, segregation and other factors caused by the tetraploid character of cultivated potatoes. A new breeding program for rapid progress has been initiated at the Vegetable and Ornamental Plant Institute, Roodeplaat, South Africa, which comprises the combination of conventional and unconventional breeding techniques. The program is based on the reduction of the ploidy level from the tetraploid to the dihaploid level to facilitate crossings with diploid wild species. Anther culture is the preferred technique for the rapid reduction of the ploidy level and has been successfully applied on different members of the Solanaceae. Cultivated potato, Solanum tuberosum is, however, an important exception. In this study various potato genotypes (tetraploid cultivars, dihaploid breeding lines and a diploid wild species) were used in experiments concerning microtechniques, alternative culture methods and medium manipulation. The main objectives were to evaluate and compare the androgenetic ability of the various genotypes used and to try and identify the factors limiting their in vitro response. Regarding microtechnique, the study focussed on the investigation of the frequency of androgenesis - as a function of plant age - and the determination of defined flower bud lenqths representative of the correct microspore developmental stage for optimal androgenetic response. Combined with an extensive histological study on the microspore development within anthers, from the time of flower selection, after a cold-pretreatment and at various time-intervals during the culture period of 42 days, the following conclusions were reached: In vitro androgenetic response proved optimal when flowers of responsive genotypes were selected during the first seven to 21 days of the flowering period. Both microspore derived embryoid- and callus development were visible within responsive anthers after a culture period of only seven days. The flower bud length required for anthers to be in the optimal stage of microspore development, e.g. the uninucleate stage, varied between the different genotypes but could readily be determined with the DAPI (4,6-diamidino-2- phenylindole) technique. It was also concluded that anthers of the tetraploid cultivar Atzimba should be selected later, between the late-uninucleate and the early-binucleate developmental stages. This suggested a limited selection period for Atzimba anthers, as starch depositioning - which prevent embryogenesis - occurs within anthers during the binucleate stage. Histologically, Atzimba showed limited embryoid development with no embryoid release, while the diploid wild species, S. canasense, proved androgenetically unresponsive. Alternative culture methods were applied to study the effect of different culture phases (liquid, double layered and agar solidified) and anther orientations (lateral, dorsal and ventral) on the androgenetic response of the potato genotypes used. Liquid cultures, based on the so-called shed-pollen technique, enhanced the androgenetic response of the tetraploid cultivar Atzimba. Optimal embryogenesis was obtained for responsive breeding line 87.2002/3 with the utilization of agar solidified media, with maximal response when anthers were cultured in the lateral orientation. No response was observed from S. canasense. The effect of medium manipulation on the androgenetic response of the three genotypes was investigated. The utilization of various combinations of different concentrations of indole-3-acetic acid (1M) and benzyladenine (BA), the alteration of the initial time of incubation of anthers on the initiation media and the use of media without growth regulators compared to that containing gibberellic acid (GA[3]), were investigated. BA had to be present in the initiation media and had a major, though not exclusive, effect on embryogenesis compared to 1M. The optimal BA concentration varied between the two trials. IAA also had an increasing effect on anther response, both in the absence of BA and, especially, in addition with relatively high BA concentrations. In this experiment, only breeding line 87.2002/3 responded. The initial culture of anthers, during the first seven to 21 days of the culture period, on media containing growth regulators proved essential for microspore derived embryoid production in the tetraploid cultivar Atzimba. As these growth regulators are metabolized in the culture media, the regular transfer at shorter, two-weekly intervals to media containing metabolically active substances, proved important. GA[3] had no enhancing-effect on embryogenesis in any of the three tetraploid cultivars. The results obtained in this study suggest that the first 21 days is the critical stage in the anther culture period in terms of the optimal time for flower selection, embryoid induction and the increase in embryogenetic response due to growth regulator influence. It is important to pre-determine the developmental stage when most microspores were in the uninucleate stage of development and to correlate this stage with a specific flower bud length. This would assure maximum response of those genotypes amenable to anther culture. It also implies a more practical and economical starting pOint to anther culture experiments. Following the determination of microspore developmental stage and pollen fertility, flowers should be selected from the donor plants only during the first three weeks of the flowering period. The composition of the nutrient media used for potato anther cultures were sufficient with respect to growth regulators. The growth regulators SA, IAA and the amines glutamine and asparagine had to be present in the initiation media, especially during the first three weeks of the culture period. As microspore development within anyone anther was found to be asynchronous, the regular transfer of anthers to fresh media is recommended to assure proper development of all microspores. The use of a slightly higher IAA concentration could be considered, but care should be taken as too-high concentrations would induce callus production. Microspore derived embryoid production is preferred, as the ploidy level of callus derived plantlets normally varies and somaclonal variation can occur. Liquid media should be considered for anther culture of tetraploid genotypes, while embryoid production can be increased by culturing the anthers of responsive genotypes on agar solidified media on the lateral orientation. Finally, the diploid wild species S. canasense seemed androgenetically unresponsive, or the media and culture conditions used did not satisfy the specific requirements of this genotype. Androgenetic amenability should first be transferred by means of interspecific crossings with a responsive dihaploid genotype, such as the breeding line 87.2002/3.
Anti-inflammatory and anti-bacterial activity of South African Erythrina species.
(2000) Pillay, Candice Claudia Natasha.; Van Staden, Johannes.; Jäger, Anna Katharina.
An investigation was undertaken to determine whether Erythrina species indigenous to South Africa contained the same type of compounds as Erythrina species not found in South Africa and to determine whether they displayed any anti-inflammatory and antibacterial activity. Phytochemical analysis was conducted using thin layer chromatography. A great similarity was found in the leaf profiles of the species being studied. The leaf and bark extracts of E. caffra and E. lysistemon appear to have similar profiles when viewed under normal light and ultraviolet light, (254 and 366 nm). These two species have similar banding patterns when stained with fast blue reagent for flavonoids and potassium hydroxide reagent for coumarins. The five species that were tested appear to contain alkaloids, flavonoids, coumarins and triterpenes just like the species not found in South Africa from this genus. Dried bark and leaves from E. caffra, E. humeana, E. latissima, E. lysistemon and E. zeyheri were screened for anti-inflammatory and anti-bacterial activity. Ethanol, ethyl acetate and water extracts were screened for both anti-inflammatory and anti-bacterial activity. The cyclooxygenase bioassay was used to test for anti-inflammatory activity. The ethanol and ethyl acetate extracts generally displayed activity while the water extracts displayed no activity for both the bark and the leaves. The bark generally displayed more cyclooxygenase inhibitory activity than the leaves. The bark of E. caffra and E. lysistemon displayed the highest cyclooxygenase inhibitory activity. The disc diffussion bioassay was used to screen for anti-bacterial activity. Anti-bacterial activity was only detected in the water extracts of the leaves. The water extracts of the bark showed very little or no activity. The bark yielded more anti-bacterial activity than the leaves. Anti-bacterial activity was mainly displayed against Gram positive bacteria. The bark of E. caffra and E. lysistemon displayed the highest anti-bacterial activity. On the basis of the screening results it was decided to use bioasssay guided fractionation in an attempt to isolate putative anti-inflammatory and anti-bacterial compounds. A hexane extract from the bark of E. lysistemon was prepared and purified using a range of chromatographic methods. Vacuum liquid chromatography, separation using a chromatotron, thin layer chromatography and high performance liquid chromatography were used to isolate anti-inflammatory compound(s). The isolation proved to be unsuccessful as the pure compound had no cyclooxygenase inhibitory activity. It was subsequently determined that the compounds were lost during the HPLC procedure. An ethanolic extract of the bark of E. Iysistemon was purified in an attempt to isolate an anti-bacterial compound(s). Vacuum liquid chromatography and separation using the chromatotron was used to purify the crude extract. The more sensitive microtitre bioassay was used to test for anti-bacterial activity against S. aureus. The isoflavone, Wighteone was isolated.
The application of microsatellites to sugarcane parentage determination and varietal identification.
(2002) Hack, Simon Matthew.; Huckett, Barbara Isobel.; Butterfield, Michael.
The use of microsatellite markers has matured and become commonplace for plant genome analyses and is now poised for widespread practical application in sugarcane. Sequence Tagged Microsatellite Site (STMS) amplification is the most prevalent microsatellite-based approach and involves the amplification of a microsatellite by designing primers that flank and hence define the microsatellite site, revealing variation in the length of repeat motifs between individuals. Twenty-six microsatellite primer pairs received from the International Sugarcane Microsatellite Consortium (ISMC) were evaluated and the STMS protocol was optimised to ensure robust and reproducible results. The objectives of this study were to use STMS for sugarcane parentage analysis and fingerprinting. Previously, Restriction Fragment Length Polymorphism (RFLP) marker data had suggested that the parentage of a genetic mapping population, sugarcane cross AA40 (N18 x CP57/614), was incorrect. Based on the assertion that the incorrect parentage was as a result of either mislabelling at planting or at seed collection, microsatellite parentage analysis was carried out on eight potential parent pairs (13 cultivars). A total of 75 markers were scored with non-parental bands (12 on average) being observed for all of the potential parent pairs and none could be identified as the true AA40 parents. It has been suggested in other plant species that PCR artefacts could give rise to non-parental bands and to investigate this the marker data of single parent DNA reactions and pooled parent pair DNA reactions or 'synthetic offspring' were compared. The results suggested that either a certain percentage of non-parental bands, perhaps 10% (maximum value observed), should be tolerated in microsatellite parentage analysis or a marker should only be considered to be discriminating for parentage if it is absent in both the parents and the pooled parent pair amplifications. Fingerprinting of 20 cultivars using 14 microsatellite primer pairs was conducted to evaluate the potential of the STMS approach for sugarcane varietal identification. It was found that only two microsatellite primer pairs were required to discriminate between all 20 cultivars with a theoretical number of non-differentiated pairs of cultivars (XK) of only 0.03. This estimator was used to determine the approximate number of microsatellites necessary for large-scale sugarcane fingerprinting.
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.
Aspects of seed propagation of commonly utilised medicinal trees of KwaZulu-Natal.
(1996) Netshiluvhi, Thiambi Reuben.; Pammenter, Norman William.; Cooke, John Anthony.
Due to over-exploitation of commonly-used medicinal plants, mainly from KwaZuluNatal, because of ever-increasing human population growth, many of the useful medicinal plants are becoming depleted in their natural habitats. Some species like Warburgia salutaris, which is currently declared very rare in the KwaZulu-Natal province, appear to be on the verge of extinction. In order to counteract this overexploitation, this study sought to provide information that could help resource users to grow these threatened species through ex situ conservation methods. A short list of heavily utilised medicinal tree specles was selected from the approximately 700 tree species indigenous to KwaZulu/Natal. The criteria considered for short listing were; life form, species scarcity, past population status and part used. A total of 23 species were short listed, but a subset of 12 species was selected based on the availability of fruits and seeds. The aim of short-listing was to work on a manageable number of commonly utilised medicinal tree species. The seed physiology and growth of these species were studied. With the exception of Erythrophleum lasianthum and Curtisia dentata, all of them had a moisture content of 2': 20 % (on a dry mass basis), which is indicative of a recalcitrant behaviour. However, it could not be concluded that these seeds were truly recalcitrant because desiccation sensitivity was not directly assessed. Using the triphenyl tetrazolium chloride (TTC) viability test, most of the seeds of the 12 species seemed to be of good quality. Results of the TTC test for seed viability were similar to results obtained v using direct germination for most species. Results of flotation test for seed viability were different from the results obtained using direct germination for most spcies. The pre-treatment which achieved the highest germination percentage in almost all the seed types was cracking the outer coverings. Cracking pre-treatment appeared to be efficient in enhancing the removal of some substances which might inhibit germination of seeds. Hot water and acid pre-treatments frequently reduced germination. Growth of young seedlings was assessed in terms of stem diameter, height, and leaf area under sun and shade. Seedling growth in terms of stem diameter and height of most species did not show any significant difference. One of the few species which showed statistically significant differences in stem diameter growth was Ekebergia capensis. It was found that 3 out of lO of the species showed statistically significant differences in height growth. Two of the statistically significant differences in height occured on seedlings in the sun while one had statistically significant difference in the 40% shadecloth while 7 did not. Significant differences in leaf area occured on 7 out of lO species. Of these, 4 species had higher growth in the shade than in the sun while 3 had higher growth in the sun than in the shade. Generally, it appears that young developing seedlings establish themselves well under shade environment; this could be because most of the species used in this study are forest species.
Aspects of the influence of temperature on the desiccation responses of seeds of Zizania palustris (Wild rice)
(1996) Ntuli, Tobias M.; Berjak, Patricia.; Pammenter, Norman William.
Seeds of wild rice (Zizania palustris var. interior) have been reported to show highest survival when dehydrated at 25 QC. It has also been reported that axis cells sustained least damage at this drying temperature. In the present study, a linear relationship between drying rate and dehydration temperature was established. Whereas highest positive tetrazolium staining and lowest leakage were recorded for seeds that were dehydrated at 25 QC, maximum germination was recorded for seeds dried at 20 QC. A proportion of seeds showed the presence of glasses, irrespective of the dehydration temperatures used. Parameters of the glass to liquid transition, however, correlated with neither water content nor sugar profiles. The ratio of raffinose to sucrose was similar among all the treatments. A hydroperoxide test revealed a linear relationship between peroxide levels and temperature of drying although the levels of fatty acids were not correlated with hydroperoxide levels. Butanal levels and total aldehydes evolved, on the other hand, showed a high negative correlation with peroxide levels. Electron microscopy showed that the variability and relative abundance of peripheral membrane complexes (PMCs) was the highest for cells of embryonic axes dehydrated at 25 QC and the lowest for embryonic axes of seeds dried at 10 QC. Furthermore, intramembrane particles (IMPs) were evenly distributed in cells of axes dried at 25 or 37 QC. In contrast, membranes of cells of axes dehydrated at 10 QC showed large IMP-free areas. The relative abundance of IMPs was the highest for cells of embryonic axes dried at 25 QC, and the lowest for cells of axes dehydrated at 10 QC. From these observations, it is suggested that membrane phase transition, with the concomitant elimination of proteins, accompanies dehydration of Z. paluslris seeds at 10 QC, whereas at 37 QC peroxidation may predominate.
Aspects of the invasion of southern tall grassveld by Aristida junciformis subsp. junciformis Trin. et Rupr.
(1998) Van Zyl, Douglas Dirk.; Granger, James Edmund.; Zacharias, Peter John Kenneth.
Aristida junciformis subsp. junciformis Trin. et Rupr. is an indigenous, densely tufted, evergreen perennial grass associated with the degeneration of grasslands over large areas of South Africa. More than two hundred thousand square kilometres of veld, c. 17% of the total land area of South Africa, contains A. junciformis. The aim of this study was to improve our understanding of the mechanisms by which this species invades and dominates grassland, specifically in this study, Southern Tall Grassveld. Aristida junciformis also has a low nutritional value resulting in a very low grazing value. The unpalatability of the plant is due to the high tensile strength of the leaves, whose hard, fibrous laminas are very difficult for a grazing animal to crop once their length attains 30 cm or more. This species lack of response to conventional grazing practices has often resulted in a grassland in which the carrying capacity has diminished to such an extent as to be virtually useless for grazing in a relatively short time. The extent of encroachment of veld by A. junciformis appears dependant on the frequency of disturbance and rest afforded to the veld. Annual burning and mowing maintained the species composition of A. junciformis at levels <10% whilst protection from fire, burning or grazing allows this species to dominate the herbaceous layer at levels approaching 90%. Aristida junciformis does not become moribund and is unlikely to die if left undefoliated. As the abundance of A. junciformis increases, veld deterioration gradually accelerates through increased selective grazing on remaining palatable species. Competition from adult A. junciformis plants increases the mortality of seedlings and constrains growth of surviving seedlings. Tiller production of Aristida junciformis seedlings declined from an average of 5.2 tillers per seedling in a no competition situation to 2.2 tillers per seedling when subjected to full competition. Tiller production of T. triandra seedlings decreased from 9.6 tillers per seedling free from competition to 3.3 tillers per seedling subject to full competition for resources. Once these seedlings have become adult plants they are avoided by grazing animals and grazing pressure on the remaining palatable species consequently increases. This allows the A. junciformis plants to increase their size and density in the sward. Once this density is sufficiently high, grass seedlings of either A. junciformis or more desirable grass species such as T. triandra are unable to establish, eventually resulting in a monospecific stand of A. junciformis if left undisturbed. Large amounts of caryopses are produced by A. junciformis - up to a 19 000 caryopses from a large mature plant (c. 38 000 caryopses/m²). Of these c. 40% is likely to be infertile but the remaining c. 60% viable caryopses are dispersed in a typically leptokurtic distribution, the number of caryopses dispersed rapidly declining within a 10 metre radius. A large proportion of the caryopses was trapped in surrounding foliage but in open swards caryopses had greater opportunity to be blown further distances than in a closed sward. The density of A. junciformis caryopses on the soil surface was positively correlated with the density of flowering adult plants in the area and varied from 400 caryopses/m² (density of parent plants c. 0.6 plants/m²) in less effected areas to 11000 caryopses/m² (density of adult plants c. 6 plants/m²) in severely encroached areas. The primary function of the three awns appears to be orientating the caryopsis correctly for in its descent from the parent plant to expedite germination. Caryopses orientated vertically with the awns uppermost exhibited the highest and most rapid germination (67%) compared to caryopses lying horizontally (35%) whilst only 1% of inverted caryopses germinated. Caryopses trapped in litter and effectively held off the soil surface failed to germinate. Removal of the glumes from A junciformis seed greatly enhanced the rate and overall germination of the seed except for inverted seed of which <1% germinated. The highest numbers of A. junciformis seedlings (32 seedlings/m²) were found in those areas with the highest density of caryopses on the soil surface. Despite the large amounts of caryopses produced, dispersed and landing in apparently suitable micro-sites for germination, comparatively few A. junciformis seedlings (n=992) were found and overall germination ranged between 1 % and 4% of the initial caryopses density on the soil surface. Seedling survival through winter was low with only 13% surviving to the following spring. The basal areas of A. junciformis increased overall by 66% whilst that of other grass species increased overall by only 3% in the time monitored. These results suggest that the primary method of encroachment of A. junciformis in the grass sward appears to be through vegetative expansion and not seedling recruitment. Frequent defoliation of the sward and avoidance of overgrazing to enhance the competitive abilities of palatable species and provide as high a fuel load as possible appear to be the most economically and logistically feasible ways to remove or at least inhibit A. junciformis veld encroachment at present.
Aspects of the role of cytokinins in adventitious root formation.
(1996) Taylor, Joslyn Leanda Susan.; Van Staden, Johannes.
The initiation and development of adventitious roots in cuttings are highly complex processes, influenced by both endogenous and exogenous factors. These vary from the environmental factors prior to the striking of the cutting, to the anatomical and physiological factors, within the stem. Encompassed are the nutrient status, physiological age and degree of differentiation of the tissues, and the balance of endogenous rooting inhibitors and/or promoters (including hormones). The role of cytokinins in root initiation and development has been perceived as that of an inhibitor. This investigation considered several aspects of the role played by cytokinins in the process of root development. A qualitative/quantitative analysis of the cytokinin-like activity in stem cuttings of several plants, including both easy- and difficult-to-root species was conducted on a comparative basis. There was no clear correlation between the type / level of cytokinins detected in the cuttings and the relative ease of root formation. Both qualitative and quantitative changes in the compounds exhibiting activity in the soybean callus bioassay were observed over the period of root formation in Impatiens stem cuttings. The effects on root formation in cuttings of exogenously applied auxins and cytokinins were investigated. Auxins generally promoted root number and elongation at relatively high concentrations (10[-4] M), but showed less effect on lateral root initiation and development. At high concentrations, cytokinins strongly inhibited root development, but did promote lateral root growth. In suspension culture, the effect of these hormones differed slightly, with IAA and IBA having no significant effect on root development, but NAA strongly stimulating lateral root initiation. Zeatin (10¯¹¹ M) significantly increased root length and the number of lateral roots produced. The effect of treatment of the stem cuttings with potassium permanganate and centrifugation was examined. While both these treatments have been perceived to increase root production in cuttings, no significant improvement in rooting ability following centrifugation (relative to the control) was observed. Impatiens cuttings centrifuged in the presence of distilled water showed a significantly reduced rooting ability relative to those centrifuged in the dry state. Treatment with an 8-hour pulse in 0.05 % potassium permanganate significantly increased the average root length. These treatments had an effect on the cytokinin levels and distribution in the stem cuttings. Slightly higher levels of cytokinins were associated with the increase in root number and length in both experiments.
Aspects of the structure and functioning of the vegetation of the Hlatikulu Vlei.
(1996) Guthrie, Iain Andrew.; Granger, James Edmund.
Hlatikulu Vlei, situated in the foothills of the Natal Drakensberg, is one of the priority wetlands in KwaZulu-Natal, occupying an area of 733 Hectares. The importance of Hlatikulu Vlei lies in its functions to store water, regulate stream flow and attenuate floods, as well as to provide suitable habitat for wildlife and grazing for livestock. Hlatikulu Vlei is a threatened system and has suffered the effects of human mismanagement. Forty-nine percent of the vlei has been classified as disturbed or destroyed, mainly due to the construction of two large dams and past drainage of vlei to facilitate pasture planting. The effects of grazing and fire on the plant communities has been considerably less. Vegetation communities at Hlatikulu Vlei have similarities with those at Ntabamhlope Vlei. The main plant communities present at Hlatikulu Vlei are: vlei grassland, sege-meadows, bulrushes and reedswamp. Species compositions of the mixed sedge and grass sedge-meadow community have a notably higher species diversity than similar communities sampled at Ntabamhlope Vlei and the mires at Highmoor. Soil type and moisture content are shown to be the most significant environmental factors determining the distribution of plant communities and species within the vlei. A wetland re-establishment and rehabilitation programme in the Hlatikulu Crane and Wetland Sanctuary has been effective in allowing many wetland plants to become reestablished. The sanctuary communities bear greater similarity to the sedge and rush sedge-meadow community, than the mixed sedge and grass sedge-meadow communities that were originally present. This is also reflected in the seed bank. All three Southern African crane species (Blue, Wattled and Crowned Crane) and fourteen species of waterfowl have been recorded in the Hlatikulu Crane and Wetland Sanctuary since the wetland rehabilitation programme. The waterfowl play a role in the dispersal of seeds into the sanctuary, particularly those of Schoenoplectus decipiens and Eleocharis dregeana and are in part responsible for the return of certain wetland plants to the sanctuary. The flooding of soils, the fluctuating water level and the soil type related to hummocks and to channels are shown to be responsible for the location of Cyperus denudatus, Arundinella nepalensis and Aristida junciformis in differing positions in the channels and on the hummocks and are also responsible for the maintenance and functioning of the hummocks and channels. Seed banks on the hummocks are similar to seed banks in the channels, however the extant vegetation on the hummocks is distinctly different to that in the channels. Certain species represented in the channel seed bank are being excluded from surviving to maturity.
Bark in traditional healthcare in KwaZulu-Natal, South Africa : usage, authentication and sustainability.
(2002) Grace, Olwen Megan.; Jäger, Anna Katharina.; Prendergast, Hew D. V.; Van Staden, Johannes.
Healthcare in South Africa is polarised between western and traditional African systems of therapy. The latter is consulted by the majority of the population and therefore plays an integral role in the delivery of healthcare to South Africans. Traditional medicines are primarily plant products with long storage lives, among which the dominance of bark is typical of southern African traditional healthcare systems. Expansion of the traditional healthcare sector during the twentieth century, in response to rising consumer demands, stimulated a lucrative trade in medicinal plants that is centred in KwaZulu-Natal. Since herbal medicines are sourced almost exclusively from indigenous vegetation, harvesting pressures exerted on the indigenous flora to meet demands for traditional medicines have rendered such resources non-sustainable. Although trees comprise a small fraction of South African medicinal plant species, bark from them constitutes a substantial proportion of the plant products used medicinally. Trees are among the most threatened medicinal plants in South African due to their limited abundance, the ecological sensitivity of the vegetation in which they occur, and destructive methods of commercial bark harvesting that frequently take place within protected areas. In KwaZulu-Natal, bark is harvested primarily from forests that occupy an extent of only 0.1 % in the province. Conservation of economically valuable tree species is particularly problematic since data necessary for the establishment of sustainable usage systems are absent or inaccessible. Alternatives to in situ conservation for renewable bark resources include propagation, multi-use timber systems and reintroduction of locally extinct species. To facilitate appropriate management of bark resources, there is a need for specialist publications and consolidated data with which sustainable usage levels may be determined. The importance of bark in South African traditional healthcare is poorly reflected by the ethno botanical literature. In this study, 180 bark species used in traditional healthcare in KwaZulu-Natal were inventoried from thorough literature surveys, but this number is anticipated to be a conservative reflection of actual statistics. Where trade data were recorded in the literature, they indicated intensive exploitation of bark resources in KwaZulu-Natal and throughout South Africa, but conservation and management data were lacking for 72 % of the species inventoried. A number of problems were encountered in the literature, of which vague information and the documentation of local vernacular nomenclature were the most troublesome. Despite the importance of traditional medicine, the country's political history led to the prevailing situation, where the traditional healthcare sector is largely unregulated. Coupled with increasingly limited availability of medicinal plants, the quality and appropriate use of traditional medicines is negatively affected by growing numbers of inadequately trained practitioners, herbalist retailers and plant gatherers. Possibilities of misidentification or purposeful adulteration of medicinal bark products therefore lead to concerns for patient safety, since dried bark is difficult or impossible to identify. Whilst bark characters are useful for field identifications, many useful diagnostic characters are lost through desiccation, and anatomy and morphology of bark are variable. Additionally, medicinal bark products used in KwaZulu-Natal, and their identification, are largely undocumented. This study focussed on eight bark species used medicinally in the province, elected by an esteemed traditional medical practitioner as having problematic identity. Monograph-type characterisation profiles were drawn up for reference specimens collected from various localities, and their medicinal bark products traded under vernacular names recorded in the literature. In the absence of standardised traditional medicines, there is a need for reliable and affordable methods for their authentication. Phytochemical bark characters identified by Thin Layer Chromatography (TLC) have proved useful in chemotaxonomic studies, and the technique is widely used for herbal drug authentication. TLC was tested here for authentication of medicinal bark products from the aforementioned study species. Three reference samples of each species were collected, and TLC-generated fingerprints compared. At the intraspecific level, TLC was useful in confirming the relationship of ethanol and hexane bark extracts, but was less meaningful in distinguishing between fingerprints of different species. Three medicinal bark products of each study species were purchased and fingerprints compared to a reference. The technique proved useful in confirming the identity of several medicinal bark products. Authentication of medicinal bark products may be useful in toxicology cases and in the accurate documentation of their trade. This research identified a complexity of issues surrounding the use of bark in traditional healthcare in KwaZulu-Natal, and indeed South Africa. A multi-faceted approach is required to secure their sustainability. Critical, however, to factors such as effective conservation and regulation of the traditional healthcare sector, is recognition of the importance, and documentation, of traditional bark medicines. The integrity of traditional healthcare, and the future of the South African flora, hinge upon the sustainable use of medicinal products such as bark.
Biochemical and biophysical indicators of chilling tolerance in some species of Eucalyptus.
(1993) Stewart, Gwethlyn Meriel.; Amory, Alan M.
Although Eucalyptus species are indigenous to Australia, they have been successfully cultivated in South Africa, where they are mainly used in the mining and paper industries. With the explosion in these industries it has been necessary to increase Eucalyptus plantations, often into areas which experience frost and chilling temperatures. To combat this, high yielding Eucalyptus species able to cope with these conditions would be desirable. The ability to rank species according to their chilling tolerance will enhance decisions as to the suitability of species for use in the field. To this aim, two biochemical and two biophysical parameters were chosen to investigate and characterise Eucalyptus nitens, E. smithii, E. macarthurii, E. grandis and E. grandis x nitens (GNI026). Ranking of these species in terms of chilling tolerance did not appear possible using the data from the biochemical parameters (proline concentration and glutathione reductase activity), but the biophysical parameters (fluorescence characteristics and onset of temperature of melt) gave results comparable to those obtained in field trials using these species. Fluorescence characteristics were particularly useful in assessing the chilling tolerance of the species in question. Fluorescence is the recommended technique for further studies as it is relatively inexpensive, rapid, does not require destructive sampling and can be used in both the laboratory and field.
Biochemical and ultrastructural changes associated with chilling injury in soybean seeds during imbibition.
(1996) Roskruge, Carol Lynette.; Smith, Michael Trevor.
Biochemical and ultrastructural changes associated with chilling injury (CI) in soybean seeds imbibed at 5°C and 25°C were investigated. Soybean seed germination appeared to be affected by chilling temperatures and initial seed moisture content. Seeds with higher moisture contents exhibited 85% germination, while low moisture content seeds had a 32% germination. Leakage rates were greater in chilled seeds, indicating that membrane integrity in the tissues was impaired at chilling. The low rates of potassium ion leakage between 6 and 24 hours of imbibition compared to the high peroxide levels observed during this period led to the suggestion that lipid peroxidation was a better marker of CI than leakage. Transient changes in lipid hydroperoxide levels were observed in chilled and non-chilled seeds and axes. However, in axes, the increase in lipid hydroperoxides after 12 hours of imbibition at chilling temperatures was associated with an 18% decline in linoleic acid levels of total lipid fraction. Similarly, a 10% decline was observed in the polar lipid fraction. These results suggest that the capacity of seeds to control lipid peroxidation may be an important component in CI and that a consequence of peroxidation is likely to be a loss of fatty acid unsaturation. Sugar levels were not affected by chilling and non-chilling temperatures and no relationship could be established with CI. Antioxidant defense enzymes (catalase and superoxide dismutase) were expressed at chilling and non-chilling temperatures and increases were observed after 24 hours of imbibition which showed an apparent correlation with increases to lipid hydroperoxide levels. Enzyme levels decreased after 48 hours of imbibition at a time which coincided with the decline observed in the peroxide levels. Overall, no marked differences were observed in chilled and non-chilled cells at the ultrastructural level, except that vacuolar reserve mobilization was markedly impeded.
Biological nitrogen fixation (acetylene reduction) associated with blue-green algal communities in the Mgeni estuary mangrove swamp.
(1987) Mann, Fiona Denise.; Lambert, G.; Steinke, Trevor Desmond.
Nitrogen fixation of blue-green algae associated with Avicennia marina (Forssk.) Vierh. pneumatophores and wet and dry surface sediments were investigated in the Mgeni Estuary mangrove swamp by means of the acetylene reduction technique. Optimum partial pressures of acetylene ranged from 0,15 to 0,2 atm. for the different habitats. A lag phase of 3 h was observed in all habitats, followed by a period of linear ethylene production of 42 h for the pneumatophores and 72 h for the wet and dry mat areas. An assay period of 24 h was employed in all habitats. Laboratory studies revealed percentage moisture and temperature to be the prime factors influencing ARA (acetylene reduction activity) in all habitats and rates were highest under submerged conditions and at 22˚C. Short-term variations in ARA and salinity in the wet and dry mat areas, measured at 6 day intervals, were also related to percentage moisture. High concentrations of inorganic nitrogen (between 1 and 5 mg 1-1) significantly depressed ARA in all habitats. Increases in ARA occurred with increase in light intensity up to 40 μE m -2 s-1, with negligible dark rates being recorded in the wet and dry mat areas. Significant dark rates of ARA and stimulation of ARA by sucrose in association with the pneumatophores indicated that bacteria may also be contributing to ARA in this habitat. No organic carbon stimulation was noted in the other sites. Salinity had little effect on ARA over the range generally experienced in each habitat. Field studies revealed a marked seasonal variation in ARA, with summer maxima of 78, 678 and 341 nmol C2H4 cm-2 24 h-1 associated with the pneumatophore, wet and dry mat areas respectively. This coincided with maximum nitrogen-fixing blue-green algal numbers, temperature, light intensity and day length. No seasonal variations in organic carbon, inorganic nitrogen, salinity, percentage moisture or bacterial numbers were apparent. Rates of bacterial ARA associated with decomposing litter of A. marina were highest under exposed conditions and reached a maximum of 25 935 nmol C2H4 g dry wt -1 24 h -1 after 3 weeks. Maximum rates of ARA under submerged conditions of 5394 nmol C2H4 g dry wt -1 24 h -1were reached after 4 weeks of decomposition. An increase in percentage nitrogen occurred during decomposition and was greatest under submerged conditions. Rates of decomposition were highest under exposed conditions. It was estimated that nitrogen fixation by blue-green algal communities supplies 23,8% of the annual nitrogen requirements of the mangrove swamp.
Bioprospecting the flora of southern Africa : optimising plant selections.
(2005) Douwes, Errol.; Edwards, Trevor John.; Crouch, Neil Robert.
Focused procedures which streamline and optimise plant prioritisation and selection in bioprospecting have the potential to save both time and resources. A variety of semiquantitative techniques were assessed for their ability to prioritise ethnomedicinal taxa in the Flora of Southern Africa (FSA) region. These techniques were subsequently expanded upon for application in plant selection for the Novel Drug Development Platform bioprospecting programme. Least squares regression analyses were used to test the hypothesis that ethnomedicinal plant use in southern Africa is strictly random, i.e. no order or family contains significantly more medicinal plants, than any other order or family. This hypothesis was falsified revealing several 'hot' plant orders. The distribution of southern African ethnomedicinal taxa was investigated, and revealed low ethnomedicinal plant usage in the Western Cape and Northern Cape. The historical settlement of Bantu tribes in the eastern regions of southern Africa was one explanation for this discrepancy. Growth forms of ethnomedicinal taxa in 'hot' orders (identified in the regression analysis) were analysed. The results indicated no clear preferences across orders, but rather a preference for particular growth forms in certain orders. With respect to distribution, endemism and Red Data List status of ethnomedicinal taxa, the Western Cape had the greatest proportion of endemics and Namibia had the highest proportion of Red Data Listed ethnomedicinal taxa. With respect to chemotaxonomy, the Asteraceae contained the highest proportion of terpenoids, the Rubiaceae the highest proportion of alkaloids and the Fabaceae the highest proportion of flavonoids. The predictive value of regression analyses was tested against an existing analysis of anti-malarials and the subsequent in vitro bioassays on Plasmodium falciparum. In particular, the ability of these analyses to identify plants with anti plasmodial IC50 values of [less than or equal to] 10 [micro]g/ml was assessed. Most species in 'hot' genera showed comparatively good antiplasmodial activities (IC50 [less than or equal to] 10 [micro]g/ml). Plant candidates were prioritised for screening anti-tuberculosis, anti-diabetes and immune-modulatory compounds, using a weighting system based on; their ethnomedicinal application, chemotaxonomic potential, frequency in ethnomedicinal trade, association with the relative disease, toxicity, Red Data status, indigenous or endemic status, and family selection in ethnomedicine (identified through regression analyses). Other taxa were short-listed due to their presence in biodiversity hotspots where few ethnomedicinal plant use records are documented, and still others were incorporated due to their taxonomic association with efficacious exotic allies. Statistical analyses of the weighting processes employed were not possible in the absence of screening results which are due only in December 2006. The legislation governing bioprospecting in South Africa is discussed and several recommendations are presented to minimise negative impacts on the industry.
Character variation and a cladistic analysis of the genus Lachenalia Jacq.f. ex Murray (Hyacinthaceae:Massonieae)
(2005) Duncan, Graham D.; Edwards, Trevor John.
Morphological variation and a cladistic analysis of the large, endemic Southern African genus Lachenalia Jacq.f. ex Murray (Hyacinthaceae: Massonieae) is presented. Its close taxonomic relationship with the small endemic sympatric genus Polyxena Kunth (which has been included in the morphological and cladistic study) is discussed. The inclusion of Polyxena within Lachenalia is supported. One hundred and twenty species (139 taxa), comprising 115 Lachenalia and five Polyxena species are recognised. A wide range of morphological characters were analysed, including macromorphology, micromorphology, anatomy and palynology. A discussion and comparison of karyological data is also presented. A brief historical background, species diversity maps, figures, tables, appendices and illustrations of anatomical, micromorphological and macromorphological characters, and cladistic data, are presented, as well as discussions of pollination biology and phytogeography. This work is based on species studied in their natural habitats as well as under cultivation, and from representative herbarium specimens examined from BOL, NBG, PRE and SAM.
A comparative study of the plant ecology of three estuaries : Mgeni, Mhlanga and Mdloti.
(1986) Raiman, Feisal.; Ward, C. J.
The vegetation of the Mgeni Estuary, Mhlanga Estuary and Mdloti Estuary was analysed according to the Braun-Blanquet phytosociological method using quadrats of 4m2 and 25m2 in area placed subjectively and the Point-Centred Quarter method with points chosen whilst traversing. A classification of plant communities is given. These are described floristically and related to habitat variables. Indicator species of the climatic climax of coast forest occur within the study area. The absence of coast forest is ascribed to low altitude, tidal inundation and the consequent effect of salinity, basal inundation resulting in a high water-table and the influence of man. The floodplain of the Mgeni Estuary is dominated by mangrove vegetation comprising mainly Bruguiera gymnorrhiza and Avicennia marina whereas vegetation established on Athlone Island is dominated by mesophytic thicket comprising mainly Schinus terebinthifolius, Lantana camara, Chromolaena odorata and Cardiospermum grandiflorum. The floodplain of the Mhlanga Estuary is dominated by Phragmites australis. The shores of the Mdloti Estuary are dominated by Barringtonia racemosa, Phragmites australis and Echinochloa pyramidalis. Major differences in vegetation patterns of the three systems are related primarily to the differences in the open nature of the river mouths. This is controlled mainly by river flow and longshore drift. Differences in vegetation patterns within an estuary are dependent on differences in tolerances to salinity, basal inundation and shade, together with variations in altitude and edaphic factors and competition between species. Generally soils of Mgeni Estuary had higher contents of small sized fractions, bulk densities, reserve acidities, organic matter, salts and exchangeable bases and lower pH than soils at Mhlanga Estuary and Mdloti Estuary. Differences exist between mangrove and non-mangrove soils at Mgeni Estuary and differences between the non- mangrove soils at the three study sites. Major differences in soil characteristics are as a result of differences in tidal inundation, geogenetic parameters and biotic factors. Information on topography, hydrology, geology, climatic factors, biotic factors and historical background of the area is given. A check-list of vascular plants is included. The work is illustrated by 44 figures.

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