Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references.

Thesis (doctoral)--Tartu University, 1999. / Curriculum vitae. Includes bibliographical references.

Submitted in fulfilment of the requirements for the degree of Master of Applied Sciences in Biotechnology, Durban University of Technology, Durban, South Africa, 2015. / In contrast to orthodox seeds, recalcitrant seeds are short-lived, shed at relatively high water contents (WCs), and are desiccation sensitive. Presently, the only option for long-term conservation of genetic resources of such plant species is by cryostorage in liquid nitrogen (LN; -196°C) or in the vapour phase over LN (at -150⁰C to -160⁰C). A number of cryopreservation protocols applied for recalcitrant zygotic embryos or embryonic axes of tropical/sub-tropical species have reported survival as either root or shoot development or callus formation, with no shoot or root production after cryopreservation. This is a consequence of the challenges encountered when optimising the WC for successful cryopreservation across species. Other shortcomings may also be the formation of ice or the sensitivity to desiccation resulting in lethal damage or poor re-growth. However, for successful cryopreservation, a normal plantlet with a shoot and a root needs to be obtained post-cryo. Specimens required for successful cryopreservation must be small; therefore embryonic axes excised from seeds have been often used as the explants of choice. However, in some cases, excised embryonic axes of mature recalcitrant seeds are too large to be cryopreserved, or, even if small, may be adversely affected by excision, dehydration and/or immersion in LN, thus failing to produce plantlets after cryopreservation. As a result, in such cases, there is a need to develop explants alternative to zygotic axes such as buds derived from in vitro shoots, shoot meristems, or shoot apices and somatic embryos. These alternative explants must have a high capacity for plantlet formation before and after cryopreservation. The present study aimed to successfully cryopreserve shoot apices of Trichilia emetica and T. dregeana, tropical recalcitrant-seeded tree species, and monitor the responses or effects of some of the procedural steps involved in cryopreservation on the survival and shoot production from these shoot apices. The main foci of the investigation were to produce vigorous plantlets after cryopreservation and ultimately develop a protocol for the successful cryopreservation of germplasm of these species. Furthermore, this study reports on a number of factors that may affect survival after cryopreservation, viz. WC of the explants, PVS2 treatment, production of reactive oxygen species (ROS) and levels of endogenous total aqueous antioxidants (TAA) during the various steps of cryopreservation. The effects of the various steps of cryopreservation on the ultra-structure of the shoot apices were also observed. Cathodic protection (by using highly reducing cathodic water; CW) of the explants was attempted to improve vigour and shoot production from the surviving shoot apices after cryopreservation as cathodic water has been reported to ameliorate the excessive burst of ROS, which often accompanies the stresses imposed by the procedural steps of cryopreservation. Experiments were also performed to optimise the medium for vigorous shoot formation from the shoot apices. Shoot apices of T. emetica in this study had an initial WC of ca. 2.2 g g -1 dry weight (DW) upon excision. Although the WC of the shoot apices decreased slightly after cryoprotection with PVS2, it did not result in sufficient dehydration before cooling. Upon retrieval from LN, 68% of the shoot apices survived and 40% of those produced shoots. Treatment of shoot apices with CW did not improve the survival or shoot production from the apices following cryo-retrieval. This could be a direct consequence of increase in WC of the shoot apices following CW treatment. Water content is not the only factor affecting successful cryopreservation; the production of ROS and the level of antioxidants may also have an impact on regrowth after cryogen exposure. Rapid changes in temperature when the samples are cryo-stored and then rewarmed result in an increase in ROS production, which could have affected the shoot production. More importantly the antioxidant activity showed a rapid decrease during recovery, especially in the CW treated shoot apices, which might have also led to the poor survival and shoot production from the shoot apices. Ultrastructural observations showed the injurious effects of PVS2 treatment typified by derangement of plastids, development of numerous small vesicles along the cell membrane and abnormalities in the structure of the nuclear envelope in the shoot apical cells both before and after cryogen exposure. Following cryo-retrieval, the meristem cells were extensively deteriorated – indicating non-survival, however, some shoot apices had areas of surviving cells which might have led to 40% shoot production after cryopreservation. Based on the studies on optimising medium composition for shoot formation from the apices, woody plant medium (WPM) with 1 mg L-1 BAP + 0.1 mg L-1 IBA was found to be the best medium which gave a higher shoot production of 67 – 70% before cryopreservation compared with only 18 – 20% shoot formation on media used previously. Therefore, this medium was used as the recovery medium. Encapsulation-dehydration of the shoot apices and the use of PVS3 instead of PVS2 for cryoprotection were also employed in an attempt to improve the survival and shoot production after post-cryo, but both methods did not result in any shoot production although 92% and 90% of the shoot apices survived cryogen immersion, respectively. While the shoot apices of T. emetica resulted in 40% shoot production following retrieval from LN and recovery on WPM with 1 mg L-1 BAP + 0.1 mg L-1 IBA, attempts to further improve the shoot production were not successful. The results of this study suggest that the shoot apices used were possibly not sufficiently developed, and with the commensurately high WC, proved to be unsuitable explants for germplasm conservation of T. emetica. The injurious effects of PVS2 treatment both before and after cryogen exposure as observed from the ultra-structural studies provide a clue to the repeated failure to cryopreserve embryonic axes of many tropical recalcitrant-seeded species after treatment with PVS2. Maintaining mother material in culture for longer durations before explant excision in order to allow better development of the axillary buds and render the cytosol more concentrated, and optimising the exposure duration to loading solution and concentration of sucrose in the loading solution might however, provide sufficient dehydration tolerance to PVS2 leading to successful vitrification up on cooling.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. 5 September 2016, Johannesburg, South Africa. / There is an urgent need to study the effects of elephants on biodiversity given the ability of megaherbivores to transform vegetation composition, structure and function by killing selected plants. Within a biodiversity framework of different aspects of diversity across different scales, we need to understand elephant effects across time and space, acknowledging disequilibrium dynamics of savannas. However, most savanna studies are conducted either over a short time frame, over a limited spatial extent, or without species compositional data. The Linyanti riparian woodland in northern Botswana represents a valuable opportunity to study the effects of elephants as it is subject to extremely high elephant concentrations in the dry season as elephants congregate on the perennial river. Moreover, because of trampling effects by large herbivores and high soil moisture, fire is largely excluded, allowing the study of intense elephant impacts in relative isolation. This PhD thesis aims to assess long-term (16-18 years) compositional and structural change at a large spatial scale (50 km of riverfront) of the Linyanti riparian woodland, built upon two earlier studies in 1992/2 and 2001. Specifically, it aims to establish the effects of elephants on 1) the spatial heterogeneity of disturbance across the woodland; 2) compositional changes of the canopy tree layer caused by elephant impacts; 3) the potential of the woodland to regenerate from seedlings; 4) structural changes due to woodland decline and shrub increase. It finally aims to synthesise these findings for biodiversity and the implications for conservation and management. Spatial heterogeneity was assessed by delineating patches of intense disturbance using the clustering algorithm DBSCAN. I manually marked dead trees within a 2000 ha overlapping riparian area from the 1992, 2001, and 2010 aerial photographs and determined these trees were significantly clustered in the landscape to form patches of disturbance. Disturbance patches were highly dynamic over the period where small patches appeared, grew and coalesced over time, whilst a few patches fragmented or disappeared. The overall dynamic was of smaller patches coalescing resulting in the total patch area increasing from 6% in 1992 to 23% in 2010. Mortality increased mostly in the inter-patch areas but the overall dead tree appearance rate of 0.28 trees.ha.yr-1 was not much higher than a background tree death rate calculated for exclosures in other areas. The slow mortality rate coupled with progressive decline suggests there was little recruitment into the canopy to replace the trees that were lost. Even though large areas remained that were not classified as disturbance patches, there was evidence of increased fragmentation where inter-patch areas became increasingly small and isolated. This increase in greater areas of disturbance represents a state shift to decreased heterogeneity although landscape patchiness still remained in 2010. Projections were that mortality rate and patch formation would decrease. To assess compositional changes, I reconstructed the pre-1992 canopy tree woodland by combining both living and dead trees in 1992, and compared this to the 1992 and 2008 woodland composition. The woodland showed progressive declines from an Acacia spp.-Colophospermum mopane dominated tall tree woodland pre-1992 to a woodland in 2008 composed primarily of two resilient species (C. mopane, Combretum hereroense), and one avoided species (Philenoptera violacea). I compiled Size Class Distributions of individual canopy tree species and compared proportional high impact on living and dead trees between 1992 and 2008. High elephant impact was defined as more than 50% stem circumference ringbarked or with the main stem or majority of side stems broken. I found that elephant impact was the likely cause of the woodland decline, although wind and natural senescence were variably important for some species. The acacias had nearly disappeared from the woodland, declining in proportional abundance from 30% in the reconstructed pre-1992 woodland to just 4% in 2008. Over time there was a progressive shift in elephant impact from abundant preferred and vulnerable species like Acacia spp. and Terminalia spp. to species more resistant to debarking like Combretum imberbe and Berchemia discolor. The abundant species C. mopane proved highly resilient to intensive elephant impact. The seedling layer (plants below 0.5m) had high proportions of canopy tree species including the acacias, and all but the rarest species were recorded. This suggests regeneration of the woodland is possible but there was a demographic bottleneck of seedling mortality with few saplings recorded over the time period. To determine the structural changes which have taken place, I separated shrub species and canopy-forming tree species and assessed density changes in the sapling (<2.5m) and tree (>2.5m) layers. Tall (>2.5m) canopy tree density decreased by half between 1992 and 2008, representing an annual loss rate of 2.7% without replacement. Except for Colophospermum mopane, there was no compensatory regeneration in the form of saplings. Colophospermum mopane was highly resilient to elephant impacts, coppicing vigorously following impact to form local ‘browsing lawns’ which may benefit other browsers. The overall shrub density increased 2.5 times while one shrub species (Combretum mossambicense) increased five-fold in density and came to constitute 50% of the total woody plant density. This shrub species increased rapidly, at an exponential growth rate of 10.5% per year, representing pervasive shrub encroachment. Its invasion wave was incipient in 1992 and by 2008 many of these plants had grown beyond 2.5 m in height, forming a dense screen. Small plants of this species <1 m in height had become sparse by 2008, suggesting that the invasion had become curtailed by then. I proposed that the spread of this shrub was due to its unpalatability by elephants, although it is an important browse species for ruminants. A potential global driver of enriched atmospheric CO2 or regional aridification could not be ruled out. The state shift from woodland towards dense shrubland caused by differential elephant impacts has potential negative consequences for structural and functional diversity. I attempted to synthesize the findings for biodiversity and concluded that there was a state shift towards pervasive disturbance with a corresponding decline in spatial heterogeneity, although composition of the disturbance patches was not studied. There has however, not been a state transformation from woodland and stands of tall trees were still present in the woodland. Coupled with the potential regeneration of the woodland from seedlings, these findings highlight the importance of long-term studies of non-equilibrium savannas. The main threat to biodiversity of the woodland was not elephant-induced mortality of large trees, but rather the lack of recruitment and the pervasive shrub encroachment of a single species. It may be, however, that alternate states of canopy trees and unpalatable shrubs exists, enhancing long-term functional diversity, provided the system remains relatively open and elephants are free to move to other areas. Ultimately the only management strategy of relatively open areas with high elephant concentrations is to accept changes and support transfrontier conservation efforts. I further assess the limitations of this study, and make recommendations for future study, specifically highlighting the need for a longer-term palaeo-ecological study to evaluate compositional changes due to episodic recruitment events. / LG2017

Thesis (M.S.)--University of Pretoria, 2003. / Title from PDF t.p. (viewed Apr. 30, 2006). Includes bibliographical references.

Thesis (doctoral)--Wageningen Universiteit, 2005. / "Propositions" inserted. Includes bibliographical references (p. 107-122).

No description available.

Orientador: Mario Luiz Teixeira de Moraes / Coorientador: Celso Luiz Marino / Banca: Alexandre Magno Sebbenn / Banca: Leo Zimback / Banca: Bruno Cesar Rossini / Banca: Evandro Vagner Tambarussi / Resumo: Myracrodruon urundeuva (Anacardiaceae) é uma espécie arbórea de ampla distribuição geográfica. Por possuir madeira de reconhecido valor econômico, associada à alta taxa de fragmentação dos seus habitats, encontra-se ameaçada de extinção. Com o intuito de manter a variabilidade genética existente das populações fragmentadas e reduzir perdas na base genética da espécie, sementes de polinização aberta de M. urundeuva foram coletadas em diferentes regiões, no Brasil, para formação do banco de conservação ex situ da Faculdade de Engenharia de Ilha Solteira, em Selvíria-MS. Esse trabalho foi realizado com o objetivo de caracterizar o sistema de reprodução e estimar parâmetros genéticos populacionais em progênies de M. urundeuva, procedentes de diferentes biomas brasileiros, por meio de caracteres quantitativos de crescimento e marcadores moleculares do tipo microssatélites. Os caracteres altura, diâmetro a altura do peito (DAP), diâmetro médio de copa e sobrevivência (SOB) foram utilizados para avaliar cinco populações: Aquidauana-MS, Selvíria-MS, Itarumã-GO, Paulo de Faria-SP e Seridó-RN. Os valores altos a medianos observados para SOB (96,4% - 70,8%) indicam boa adaptação das populações de M. urundeuva e potencial para uso em reflorestamentos. As estimativas do coeficiente de variação genética oscilaram de 3% a 24,6%, em nível de indivíduo, e de 1,5% a 12,3%, entre progênies, com os maiores valores obtidos para o DAP da população de Seridó. As herdabilidades individuais variaram ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Myracrodruon urundeuva (Anacardiaceae) is a tree species with a wide geographic distribution. Because it has wood of recognized economic value, associated with the high rate of fragmentation of its habitats, it is threatened with extinction. In order to maintain the existing genetic variability of the fragmented populations and reduce losses in the genetic base of the species, M. urundeuva seeds were collected in different regions in Brazil for the formation of the ex situ conservation bank of the Faculty of Engineering of Ilha Solteira (FEIS/UNESP), in Selvíria-MS. This work was conducted with the aims to characterize the mating system and estimate population genetic parameters in M. urundeuva offsprings from different Brazilian biomes, using quantitative growth traits and molecular markers of the microsatellite type. The height, diameter at breast height (DBH), mean crown diameter and survival were used to evaluate five populations: Aquidauana-MS, Selvíria-MS, Itarumã-GO, Paulo de Faria -SP and Seridó-RN. The values high to median observed for survival (96.4% - 70.8%) indicate good adaptation of populations of M. urundeuva and potential for use in reforestation. Estimates of the coefficient of genetic variation ranged from 3% to 24.6%, at the individual level, and from 1.5% to 12.3%, among progenies, with the highest values obtained for the DBH of the Seridó population. The individual heritabilities ranged from moderate (0.41) to low (0.01) for the characters. Using the gen... (Complete abstract click electronic access below) / Doutor

Agrobiodiversity constitutes an essential resource for traditional rural populations. Home gardens are "hotspots" of agrobiodiversity and important loci of in situ conservation efforts. This study seeks to understand the factors affecting gardeners' choices and to assess the accessibility of planting material in rural communities of the Peruvian Amazon. Household surveys and garden inventories conducted in 15 villages of the Corrientes river (n = 300), and case studies in three of these villages (n = 89), allowed to describe the local and regional patterns of garden agrobiodiversity and the structure of planting material exchange networks. Analyses reveal a strong link between species diversity and both household cultural and socioeconomic characteristics, and village ethnicity and size. Planting material flows primarily through matrilineal bonds, from advice-givers to advice-seekers, from old to young and from rich to poor. Farmers with exceptional species diversity, propensity to give and/or expertise are identified and their role in the conservation of cultivated plants is assessed. Expertise is not found to be as closely related to high species diversity as expected, but knowledge and planting stock dissemination go hand-in-hand.

The relations between environmental resources and biodiversity are crucial in the proper management and conservation of grasslands. Three nature reserves were chosen around the Gauteng Province, namely Roodeplaat Nature Reserve (RNR) in Tshwane, Suikerbosrand Nature Reserve (SNR) in Heidelberg, and Abe Bailey Nature Reserve (ANR) in Carletonville. We selected three sites within RNR, SNR and ANR, and paired these with adjacent sites in private farming/grazing areas adjacent to the nature reserves. At each site, species composition, species richness and plant diversity were determined with the use of 50m x 20m Modified-Whittaker plots (MWP), making a total of eighteen plots (MWP) at the nine paired sites. Two paired sites had high Shannon-Wiener Index (H’) average values at the adjacent grazing area as compared to the nature reserve area at ANR. Roodeplaat Nature Reserve (RNR) and Suikerbosrand Nature Reserve (SNR) had two paired sites with high H’ average values in the nature reserve as compared to the adjacent grazing area. The vegetation structure was similar for the three study locations, consisting of graminoids, herbs and isolated patches of shrubs. The species composition showed similarities between ANR and SNR sites, while RNR showed different species composition. SNR soils had the highest organic carbon (OC), total Carbon (C), total Nitrogen (N), Calcium (Ca), Potassium (K), Magnesium (Mg) and Sodium (Na) as compared to both ANR and RNR. Species richness had a significantly positive relationship with Organic Carbon and Total Nitrogen. Species diversity difference was detected between the nature reserves and adjacent grazing areas and the difference are likely due to a number of factors including soil properties, land disturbance and land use and management. More research is necessary to further understand the aspects impacting species richness, species diversity and species composition in grasslands. / School of Agriculture and Life Sciences / M. Sc.