1,721,033 research outputs found
An overview of the biology, epidemiology and control of uncinula necator (powdery mildew) on grapevine, with reference to South Africa
Get PDFCITATION: Halleen, F. & Holz, G. 2001. An overview of the biology, epidemiology and control of uncinula necator (powdery mildew) on grapevine, with reference to South Africa. South African Journal of Enology & Viticulture, 22(2):111-121, doi:10.21548/22-2-2205.The original publication is available at http://www.journals.ac.za/index.php/sajevGrape powdery mildew, caused by Uncinula necator, is the most widespread and destructive disease of grapevine. The disease can be found in most grape-growing areas of the world, including the tropics. In South Africa, grape powdery mildew was first reported in 1880, and since then has become the most important disease of grapevine. The disease can effect all phases of plant growth, and without necessarily causing obvious symptoms, may have a harmful effect on the vine and its products. The pathogen follows a specific pattern in each part of the world to create an epidemic. This pattern is determined by biological characteristics of the organism, climatic factors, cultivation practices and cultivar choices. Increased world-wide emphasis on the production of disease-free grapes with minimal fungicide input provides a sound reason for exploring more efficient disease management strategies through a better understanding of U. necator epidemiology and population genetics. Knowledge of these aspects is available for various parts of the world, but little is known about its relevance to South African vineyards. In this article a South African perspective of the pathogen and its control is outlined, based on recent local findings, and considered in the light of knowledge available in other parts of the world.http://www.journals.ac.za/index.php/sajev/article/view/2205Publisher's versio
Cleistothecia and flag shoots : sources of primary inoculum for grape powdery mildew in the Western Cape Province, South Africa
Get PDFCITATION: Halleen, F. & Holz, G. 2000. Cleistothecia and flag shoots : sources of primary inoculum for grape powdery mildew in the Western Cape Province, South Africa. South African Journal of Enology & Viticulture, 21(2):66-70, doi:10.21548/21-2-2212.The original publication is available at http://www.journals.ac.za/index.php/sajevLittle is known about the mode of survival and sources of primary inoculum of Uncinula necator, the causal pathogen of grapevine powdery mildew, in vineyards in the Western Cape province. A study was therefore undertaken to determine whether cleistothecia and flag shoots are formed on vines in local vineyards. Flag shoots were found shortly after budbreak in September 1997 in a Carignane vineyard near Somerset West. Cleistothecia were first observed during April to May 1996 on severely infected leaves from three vineyards in the main grapegrowing areas of Stellenbosch. This was the first report of cleistothecia and flag shoot formation in vineyards in the Western Cape province. Cleistothecia occurred in small numbers on leaves (1 - 10 per leaf) and all were immature. Cleistothecia were dispersed by late summer and autumn rains from leaves to bark of grapevines, where they overwinter. No conclusion could be made regarding the viability of cleistothecia. However, the characteristics of the first symptoms that developed on leaves, namely separate, individual lesions formed at random on first-formed leaves growing in close proximity to the bark, provided circumstantial evidence that cleistothecia are dispersed to the bark. Weather conditions suitable for release of ascospores from overwintered cleistothecia occurred frequently between budbreak and bloom in all the areas.http://www.journals.ac.za/index.php/sajev/article/view/2212Publisher's versio
Isolation, production andin vitroeffects of the major secondary metabolite produced byTrichodermaspecies used for the control of grapevine trunk diseases
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An integrated strategy for the proactive management of grapevine trunk disease pathogen infections in grapevine nurseries
Get PDFCITATION: Halleen, F. & Fourie, P. H. 2016. An integrated strategy for the proactive management of grapevine trunk disease pathogen infections in grapevine nurseries. South African Journal of Enology & Viticulture, 37(2):104-114, doi:10.21548/37-2-825.The original publication is available at http://www.journals.ac.za/index.php/sajevThe aim of this study was to compare 11 treatment regimes (TR) in grapevine nurseries in order to eradicate
trunk pathogens. Grapevine propagation material was subjected to treatments before cold storage, before
and after grafting, before planting and after uprooting. Isolations were made from roots, rootstocks and
graft unions of uprooted vines. None of the treatments consistently affected the number of certifiable vines
produced. TR 1 (benomyl), TR 3 (Sporekill) and TR 4 (Trichoflow) increased root mass. Phaeomoniella
chlamydospora was the most frequently isolated pathogen from all plant parts. In general, TR 2, 7, 9
and 11 caused the lowest occurrence of Phaeomoniella. TR 9 consistently reduced the incidence of
Phaeoacremonium. Pleurostomophora richardsiae occurred most frequently in graft unions, but treatments
were too inconsistent to draw meaningful conclusions. TR 7 (hot water treatment (HWT) of uprooted
grapevines) consistently reduced incidences of black foot disease (BFD) pathogens. The highest incidence
of Botryosphaeriaceae occurred in graft unions, but all treatments significantly reduced infections. The
colonisation of rootstocks and graft unions by Trichoderma was significantly better with TR 4 (Trichoflow).
The other Trichoderma treatments (TR 9, 10 and 11) differed from the control treatment only in the graft
unions. This is a first report of an integrated strategy covering all the phases of the propagation process,
from the moment the nursery receives the propagation material until the dormant vines are removed. TR
9 is recommended for use in nurseries, although HWT of dormant vines is recommended to eradicate BFD
pathogens. Benomyl can be replaced by carbendazim when benomyl is no longer available.http://www.journals.ac.za/index.php/sajev/article/view/825Publisher's versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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