Time filter

Source Type

Myburgh P.A.,Agricultural Research Council Infruitec Nietvoorbij
South African Journal of Plant and Soil | Year: 2015

Estimating soil evaporation (Es) is an important part of modelling vineyard evapotranspiration for irrigation purposes. Furthermore, quantification of possible soil texture and trellis effects is essential. Daily Es from six topsoils packed into lysimeters was measured under grapevines on slanting and vertical trellises, respectively. Following irrigation, cumulative soil evaporation (ΣEs) from the bare, untilled soils over 14-day drying cycles was plotted against cumulative reference evapotranspiration (ΣETo) to determine Es transition from the constant rate stage (Stage 1) to the falling-rate stage (Stage 2). During Stages 1 and 2, rate of Es is determined by atmospheric conditions and soil properties, respectively. Slopes of ΣEs vs square root of ΣETo plots in Stage 2 provided the input constant (β value) for each soil. In Stage 1, ΣEs was almost equal to ΣETo but the ratio varied as grapevine canopies developed. The β values varied between 2.15 ± 0.09 mm0.5 and 4.68 ± 0.14 mm0.5. The β values were best related to clay content (R2 was 0.7861 and 0.5108 for horizontal and vertical canopies, respectively). The vertical trellis seemed to have a windbreak effect that tended to reduce Es compared to the slanting trellis. Therefore, clay content and trellis orientation effects on β need to be considered. © 2015 © Southern African Plant & Soil Sciences Committee. Source

Mutawila C.,Stellenbosch University | Halleen F.,Agricultural Research Council Infruitec Nietvoorbij | Mostert L.,Stellenbosch University
BioControl | Year: 2015

In the protection of grapevine pruning wounds from trunk pathogen infection, fungicides provide mainly short term protection while biocontrol agents provide mainly long term protection. The integration of fungicide and biological wound protection could provide better wound protection, but is limited by the susceptibility of the biocontrol agents to the fungicides. Stable benzimidazole resistant mutants were generated by gamma irradiation (250 Gy) from three wild-type Trichoderma Pers. isolates (UST1, UST2 and T77) shown to provide wound protection. The wild-type Trichoderma isolates were found to be naturally resistant to thiophanate methyl while mycelial growth was completely inhibited by 2.5 μg ml−1 of benomyl and carbendazim. There was no reduction in biological fitness and in vitro antagonist activity for mutants generated from UST1 and UST2 while the mutant from T77 had reduced fitness and antagonistic activity compared to its wild type. The wild type and the mutant of UST1 were further tested in the field and significantly (P < 0.001) reduced pruning wound infection by Phaeomoniellachlamydospora (W. Gams, Crous, M.J. Wingf. & Mugnai) Crous & W. Gams, when applied alone and in combination with thiophanate methyl and carbendazim, respectively. The combination of the mutant UST1 with carbendazim gave the highest reduction of infection compared to the rest of the treatments when P. chlamydospora was inoculated 24 h after pruning. The Trichoderma transformants generated in this study can be applied in combination with benzimidazole fungicides for a more effective and sustainable wound protection. © 2014, International Organization for Biological Control (IOBC). Source

Tounekti T.,Gabes University | Joubert E.,Agricultural Research Council Infruitec Nietvoorbij | Joubert E.,Stellenbosch University | Hernandez I.,University of Barcelona | Munne-Bosch S.,University of Barcelona
Critical Reviews in Plant Sciences | Year: 2013

Tea, prepared from the leaves of Camellia species, has one of the highest contents of flavonoids among common food and beverage products. Tea consumption has moved beyond its pleasant flavor and cultural significance since a number of health promoting properties have been ascribed to this widespread beverage (e.g., anticancer, antiobesity and hypotensive effects). The major bioactive compounds in tea are catechins (flavan-3-ols), a group of flavonoids that include, among others, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), and (-)-epigallocatechin-3-gallate (EGCG). These compounds are also the precursors of theaflavins and thearubigins, oxidation products responsible for the taste and colour of certain tea types such as black tea. The composition of the tea leaf, and thus tea quality, is influenced by many pre-harvest factors such as the genetic make-up of the plant, region of production, horticultural and harvesting practices, and environmental conditions. Once harvested, processing, brewing, and storage conditions influence the phenolic composition and quality of tea infusions as well. In the present review we aim at outlining our current knowledge about means to increase the catechin content of teas, a cornerstone for improving the health-promoting properties of this beverage. © 2013 Copyright Taylor and Francis Group, LLC. Source

Bester R.,Stellenbosch University | Jooste A.E.C.,Plant Protection Research Institute | Maree H.J.,Stellenbosch University | Maree H.J.,Agricultural Research Council Infruitec Nietvoorbij | Burger J.T.,Stellenbosch University
Virology Journal | Year: 2012

Background: Grapevine leafroll-associated virus 3 (GLRaV-3) is the main contributing agent of leafroll disease worldwide. Four of the six GLRaV-3 variant groups known have been found in South Africa, but their individual contribution to leafroll disease is unknown. In order to study the pathogenesis of leafroll disease, a sensitive and accurate diagnostic assay is required that can detect different variant groups of GLRaV-3. Methods. In this study, a one-step real-time RT-PCR, followed by high-resolution melting (HRM) curve analysis for the simultaneous detection and identification of GLRaV-3 variants of groups I, II, III and VI, was developed. A melting point confidence interval for each variant group was calculated to include at least 90% of all melting points observed. A multiplex RT-PCR protocol was developed to these four variant groups in order to assess the efficacy of the real-time RT-PCR HRM assay. Results: A universal primer set for GLRaV-3 targeting the heat shock protein 70 homologue (Hsp70h) gene of GLRaV-3 was designed that is able to detect GLRaV-3 variant groups I, II, III and VI and differentiate between them with high-resolution melting curve analysis. The real-time RT-PCR HRM and the multiplex RT-PCR were optimized using 121 GLRaV-3 positive samples. Due to a considerable variation in melting profile observed within each GLRaV-3 group, a confidence interval of above 90% was calculated for each variant group, based on the range and distribution of melting points. The intervals of groups I and II could not be distinguished and a 95% joint confidence interval was calculated for simultaneous detection of group I and II variants. An additional primer pair targeting GLRaV-3 ORF1a was developed that can be used in a subsequent real-time RT-PCR HRM to differentiate between variants of groups I and II. Additionally, the multiplex RT-PCR successfully validated 94.64% of the infections detected with the real-time RT-PCR HRM. Conclusion: The real-time RT-PCR HRM provides a sensitive, automated and rapid tool to detect and differentiate different variant groups in order to study the epidemiology of leafroll disease. © 2012 Bester et al.; licensee BioMed Central Ltd. Source

Mulidzi A.R.,Agricultural Research Council Infruitec Nietvoorbij
Water Science and Technology | Year: 2010

The rationale for using constructed wetlands for treating wastewater is that wetlands are naturally among the most biological active ecosystem on earth. The aim of the study was to determine the impact of shorter retention time on the performance of constructed wetland in terms of Chemical Oxygen Demand (COD) and other elements removal. The application of wastewater with retention time of seven days as well as the evaluation of water quality after treatment at Goudini experimental wetland was carried out throughout the year. The results had shown an overall average COD removal of 60% throughout the year. Results also showed reasonable removal of other elements namely; potassium, pH, nitrogen, electrical conductivity, calcium, sodium, magnesium and boron from the wastewater by constructed wetlands. The results showed low COD removal during July until September after which it improved tremendously. The reason for low COD removal during first three months could be attributed to the fact that there was no gradual increase of wastewater application to the wetlands i.e. from 4,050 litres per day to 8,100 litres per day. The results had showed that constructed wetland as a secondary treatment system is effective in terms of COD and other elements removal from winery and distillery wastewater. COD removal throughout the year was 60% with seven days retention time. When compared with previous studies that showed 80% COD removal within 14 days retention time, therefore the 60% removal is very critical to wine industries as more wastewater will be applied to the system. © IWA Publishing 2010. Source

Discover hidden collaborations