Comparison of structural damage caused by Russian wheat aphid (Diuraphis noxia Mordvilko) and Bird cherry-oat aphid (Rhopalosiphum padi L.) in a susceptible barley cultivar, Hordeum vulgare L. cv Clipper
- Authors: Saheed, Sefiu Adekilekun , Botha, Christiaan Edward Johannes , Liu, Lin , Jonsson, Lisbeth
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6540 , http://hdl.handle.net/10962/d1005981
- Description: The Russian wheat aphid (RWA, (Diuraphis noxia Mordvilko) and the Bird cherry-oat aphid (BCA, (Rhopalosiphum padi L.) cause severe damage to grain crops, including barley. An investigation of the effects of these aphids on a susceptible cultivar revealed that BCA-infested barley plants remained healthy-looking for two weeks after feeding commenced. In contrast, signs of stress and damage, including chlorosis and leaf necrosis were evident in RWA infested plants. Our study suggests that damage to the vascular tissue due to sustained feeding by BCA, was not as extensive as that caused by RWA. In addition, there is a marked difference in the salivary secretion pattern within xylem elements punctured by aphids tapping the xylem for water. RWA deposit electron-dense, amorphous to smooth saliva, which completely encases the inner walls of affected elements, and saliva encases pit membranes between xylem elements, and between xylem vessels and xylem parenchyma. Xylem tapped by BCA, contained more granular saliva, which apparently does not occlude vessel wall apertures or the pit membranes to the same extent as was observed with RWA. Damage to phloem tissue, including phloem parenchyma elements, sieve tube-companion cell (CC-ST) complexes as well as thick-walled sieve tubes, was extensive. Plasmodesmata between phloem parenchyma elements as well as pore-plasmodesmata between the CC-ST were occluded by callose. We conclude that severe, perhaps permanent damage to conducting elements in RWA infested leaves may be responsible for the detrimental chlorosis and necrosis symptoms. These symptoms are absent in BCA-infested plants.
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- Date Issued: 2007
Patterns and processes underlying evolutionary significant units in the Platypleura stridula L. species complex (Hemiptera: Cicadidae) in the Cape Floristic Region, South Africa
- Authors: Price, Benjamin W , Barker, Nigel P , Villet, Martin H
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6964 , http://hdl.handle.net/10962/d1012027
- Description: Cicadas have been shown to be useful organisms for examining the effects of distribution, plant association and geographical barriers on gene flow between populations. The cicadas of the Platypleura stridula species complex are restricted to the biologically diverse Cape Floristic Region (CFR) of South Africa. They are thus an excellent study group for elucidating the mechanisms by which hemipteran diversity is generated and maintained in the CFR. Phylogeographical analysis of this species complex using mitochondrial DNA Cytochrome Oxidase I (COI) and ribosomal 16S sequence data, coupled with preliminary morphological and acoustic data, resolves six clades, each of which has specific host-plant associations and distinct geographical ranges. The phylogeographical structure implies simultaneous or near-simultaneous radiation events, coupled with shifts in host-plant associations. When calibrated using published COI and 16S substitution rates typical for related insects, these lineages date back to the late Pliocene - early Pleistocene, coincident with vegetation change, altered drainage patterns and accelerated erosion in response to neotectonic crustal uplift and cyclic Pleistocene climate change, and glaciation-associated changes in climate and sea level.
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- Date Issued: 2007
Re-examining ‘professionalism’ in pharmacy: a South African perspective
- Authors: Williams, K F
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6084 , http://hdl.handle.net/10962/d1008481 , http://dx.doi.org/10.1016/j.socscimed.2006.11.001
- Description: Although defining itself as a patient-centred profession, private sector (community and private hospital) pharmacy often appears to be that of a product-for-profit centred occupation. This perception has been at the core of the medical profession's attempts to reduce the professional autonomy of pharmacy, and has appeared at the forefront of the South African Department of Health's positioning of private sector pharmacy. Using as a starting point the debate surrounding attempts by the South African Minister of Health to regulate the price of medicines, I propose that the present negative positioning of private sector pharmacy in South Africa could be ameliorated by pharmacy practice that evidences a redefined understanding of professionalism.
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- Date Issued: 2007
Restructuring implicational meaning through memory-based imagery: some historical notes
- Authors: Edwards, David J A
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6239 , http://hdl.handle.net/10962/d1007851
- Description: This paper provides a historical perspective on the recent increase in the clinical application of imagery techniques to restructure systems of implicational meaning that drive emotional distress or self-defeating behaviors. Janet's early application of such techniques was largely ignored except by a few hypnotherapists. Current applications in cognitive therapy were adapted and extended in the early 1980s from Perls’ Gestalt therapy methods. Some precursors to Perls are examined, as well as the work of some of those who developed and formulated the integration of his techniques into Beck's cognitive therapy. It is argued that this process amounted to a significant paradigm shift.
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- Date Issued: 2007
Topographic controls on the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) district, Eastern Cape, South Africa
- Authors: Kakembo, V , Rowntree, Kate M , Palmer, Anthony R
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6689 , http://hdl.handle.net/10962/d1006708
- Description: The role of topographic factors in the invasion of hillslopes by Pteronia incana, an unpalatable shrub, was investigated. The study combined field observations with image analysis based on high-resolution infrared imagery. A Digital Elevation Model (DEM) of 20 m spatial resolution was used to derive terrain parameters. The Topographic Wetness Index (WI), a component of the TOPMODEL, was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots on hillslopes. The combined influence of slope gradient and aspect, and land use was noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. The WI confirmed the bearing local topographic variations have on P. incana spatial distribution such that, P. incana was associated with the low WI values of convexities. The coupling between local topography and soil surface crusting underpins soil moisture variability. This in turn determines the competition between the patchy P. incana and grass species and the eventual replacement of the latter by the former. Restoration efforts of the invaded lands should focus on trapping of sediment and litter, and moisture retention on the inter-patch bare areas.
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- Date Issued: 2007
Translation processes in the design of an education for sustainable development innovations course for universities in Africa
- Authors: Lotz-Sisitka, Heila , Lupele, Justin , Ogbuigwe, Akpezi
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127213 , vital:35978 , https://10.1080/02607470701259440
- Description: This paper traces the translation processes associated with the mobilization of resources and human agency in the development of a United Nations Environment Programme (UNEP) Education for Sustainable Development (ESD) Innovations Course for universities in Africa. University teachers are often neglected in teacher education initiatives. There are few formal professional development opportunities available for university teachers given the traditionally established hierarchy in the higher education sector as university teachers are normally the ones offering professional development to others. The paper explores how a participatory, deliberative translation process has served to provide professional development and professional exchange opportunities for university teachers which are non‐traditional and responsive to diversity, history, context and risk. The emergence of the modern African university is essentially a post‐independence (post‐1960s) phenomenon, with a few earlier African universities being colonially structured, controlled and inspired. Through a short historical overview, we introduce the African university landscape and some of its contemporary contextual and educational challenges. We then describe the process of deliberation that took place amongst university teachers from 23 African countries to initiate and establish the ESD Innovations Course. The paper concludes by arguing for open and participatory approaches in ESD teacher education course design, if we are to support university teachers (including teacher educators) to engage in mainstreaming environment and sustainability questions in higher education. The paper draws on the translation model provided by Latour in his actor network theory to describe and explain the deliberative translation process in the UNEP ESD Innovations Course. In doing this, it illuminates the possibilities of such a deliberative translation process for university teacher education. It also points to limitations encountered in applying this framework to this analysis, opening new vantage points for research of this nature in teacher education.
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- Date Issued: 2007
WET-Roadmap:
- Authors: Dada, Rehana , Kotze, Donovan C , Ellery, William F N , Uys, Mary , Breen, Charles , Dini, John , Mitchell, Steve
- Date: 2007
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/176596 , vital:40093 , ISBN 978-1-77005-632-9 , http://www.wrc.org.za/wp-content/uploads/mdocs/TT 321-07.pdf
- Description: The WET-Management Series is a set of integrated tools that can be used to guide well-informed and effective wetland management and rehabilitation. Wetland loss in South Africa has been significant and the need for wetland rehabilitation as part of good wetland stewardship and management is compelling. National policy and legislation provide clear direction and support for rehabilitation, but the very complex links between people and wetlands mean that actions aimed at sustainably rehabilitating and conserving wetlands will depend on the dedication and commitment of all stakeholders, especially landowners and wetland users.
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- Date Issued: 2007