Lamprecht S.C.,Agricultural Research Council Plant Protection Research Institute |
Tewoldemedhin Y.T.,Agricultural Research Council Plant Protection Research Institute |
Hardy M.,Private Bag X1 |
Calitz F.J.,Agricultural Research Council Biometry Unit |
Mazzola M.,Tree Fruit Research Laboratory
European Journal of Plant Pathology | Year: 2011
Rhizoctonia spp. anastomosis groups (AGs) associated with canola and lupin in the southern and western production areas of the Western Cape province of South Africa were recovered during the 2006 and 2007 growing seasons and identified using sequence analyses of the rDNA internal transcribed spacer regions. The effect of crop rotation systems and tillage practices on the recovery of Rhizoctonia spp. was evaluated at Tygerhoek (southern Cape, Riviersonderend) and Langgewens (western Cape, Moorreesburg) experimental farms. Isolations were conducted from canola planted after barley, medic/clover mixture and wheat, and lupin planted after barley and wheat, with sampling at the seedling, mid-season and seedpod growth stages. In the 2006 study, 93. 5% of the Rhizoctonia isolates recovered were binucleate and 6. 5% multinucleate; in 2007, 72. 8% were binucleate and 27. 2% were multinucleate. The most abundant AGs within the population recovered included A, Bo, I and K, among binucleate isolates and 2-1, 2-2 and 11 among multinucleate isolates. Crop rotation sequence, tillage and plant growth stage at sampling all affected the incidence of recovery of Rhizoctonia, but certain effects were site-specific. The binucleate group was more frequently isolated from lupin and the multinucleate group from canola. AG-2-1 was only isolated from canola and AG-11 only from lupin. This study showed that important Rhizoctonia AGs such as AG-2-1, 2-2 and 11 occur in both the southern and the western production areas of the Western Cape province and that crop rotation consistently influences the incidence and composition of the Rhizoctonia community recovered from the cropping system. © 2011 KNPV.
Gaertner M.,Stellenbosch University |
Nottebrock H.,University of Potsdam |
Fourie H.,Private Bag X1 |
Privett S.D.J.,Fynbos Ecoscapes |
Richardson D.M.,Stellenbosch University
Perspectives in Plant Ecology, Evolution and Systematics | Year: 2012
Restoration is gaining importance in the management of plant invasions. As the success of restoration projects is frequently determined by factors other than ecological ones, we explored the ecological and financial feasibility of active restoration on three different invaded sites in South Africas Cape Floristic Region. The aim of our study was to identify cost-effective ways of restoring functional native ecosystems following invasion by alien plants. Over three years we evaluated different restoration approaches using field trials and experimental manipulations (i.e. mechanical clearing, burning, different soil restoration techniques and sowing of native species) to reduce elevated soil nutrient levels and to re-establish native fynbos communities. Furthermore we investigated the possibility of introducing native fynbos species that can be used for sustainable harvesting to create an incentive for restoration on private land.Diversity and evenness of native plant species increased significantly after restoration at all three sites, whereas cover of alien plants decreased significantly, confirming that active restoration was successful. However, sowing of native fynbos species had no significant effect on native cover, species richness, diversity or evenness in the Acacia thicket and Kikuyu field, implying that the ecosystem was sufficiently resilient to allow autogenic recovery following clearing and burning of the invasive species. Soil restoration treatments resulted in an increase of available nitrogen in the Acacia thicket, but had no significant effects in the Eucalyptus plantation. However, despite elevated available soil nitrogen levels, native species germinated irrespective whether sown or unsown (i.e. regeneration from the soil seed bank).Without active introduction of native species, native grasses, forbs and other shrubs would have dominated, and proteoids and ericoids (the major fynbos growth forms) would have been under-represented.The financial analysis shows that income from flower harvesting following active restoration consistently outweighs income following passive restoration, but that the associated increase in income does not always justify the higher costs. We conclude that active restoration can be effective and financially feasible when compared to passive restoration, depending on the density of invasion. Active restoration of densely invaded sites may therefore only be justifiable if the target area is in a region of high conservation priority. © 2012 Perspectives in Plant Ecology, Evolution and Systematics.
Dillen J.,Private Bag X1
Journal of Computational Chemistry | Year: 2015
The topology of the Ehrenfest force density was studied with Slater-type orbitals (STO). At larger distances from the nuclei, STOs generate similar artefacts as noticed before with Gaussian-type orbitals. The topology of the Ehrenfest force density was found to be mainly homeomorphic with the topology of the electron density. For the first time, reliable integrations of several properties over force density atomic basins were performed successfully. Integration of the electron density of a number of hydrides, fluorides, and chlorides of first row elements over force density basins indicate substantial differences between the partial charges of the atoms as compared with those obtained from electron density basins. Calculations on saturated hydrocarbons confirm that the electronegativity of carbon atoms increases with increasing geometrical strain. Atomic interaction lines are observed to exist in the Ehrenfest force density between the hydrogen atoms of several so-called "congested" molecules, and also in some inclusion complexes of alkanes with helium. However, interaction lines are lacking in several other controversial cases. © 2015 Wiley Periodicals, Inc.
Amankwah A.,University of Ghana |
Aldrich C.,Private Bag X1 |
Aldrich C.,Khan Research Laboratories
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2015
This paper presents a new band selection method for the visualization of hyperspectral images. The method selects three relevant spectral bands to build the red-green-blue composite. The proposed method uses not only mutual information, but also spatial information to select the bands. Results from the proposed method are presented and compared to other state-of-the-art methods in terms of informative content, gradient magnitude and variance. The results show that the proposed method compares favourably with alternative approaches. © 2015 IEEE.
Schoeman S.J.,University of Pretoria |
Cloete S.W.P.,Private Bag X1 |
Cloete S.W.P.,Institute for Animal Production |
Olivier J.J.,Private Bag X1 |
Olivier J.J.,ARC Animal Production Institute
Livestock Science | Year: 2010
The small stock industry in South Africa is of crucial importance as 80% of the agricultural land is unsuitable for intensive agricultural production. The contribution of 19 resource sheep flocks and goat herds towards breeding objective formulation, genetic improvement and parameter estimation was summarized. Substantial genetic gains resulting from selection for a range of economically important traits were demonstrated, lending impetus to the development and extension of the National Small Stock Improvement Scheme (NSIS). Responses in monetary values in the respective participating small stock breeds ranged from R0.098 for the Dormer to R0.818 for the S.A. Mutton Merino per small stock unit per annum for animals born in the interval from 2000 to 2006. This response is well below what was attained in the resource flocks and in the best participating flocks and herds. Even with this less than optimal change on a national basis, the impact on the sectoral economy is substantial. When related to the cost associated with the NSIS, this improvement is highly cost-effective. The impact of research and development in the small stock industry is therefore substantial, and the small stock industry is foreseen to continue playing an integral role in the national economy. © 2010 Elsevier B.V. All rights reserved.