Thesis (MSc (Wine Biotechnology))--University of Stellenbosch, 2006. / Plants have evolved photosynthetic systems to efficiently harvest sunlight energy for the production of carbohydrates, but these systems also are extremely susceptible to an excess of light. To combat the potential damaging effects of light, plants have developed various mechanisms to control and cope with light stress. These mechanisms include the movement of either leaves, cells (negative phototaxis) or chloroplasts to adjust the light-capturing potential, the adjustment of the light-harvesting antenna size through gene expression or protein degradation, the removal of excess excitation energy either through an alternative electron transport pathway or as heat. However, the latter mechanism based on thermal dissipation, remains the most effective to rid the plant of damaging excess light energy. This process involves several carotenoid pathway pigments, specifically the de-epoxidised xanthophyll cycle pigments. The process and extent of thermal dissipation in plants can be measured and quantified as non-photochemical quenching (NPQ) of chlorophyll fluorescence by using well-established methodologies. Several Arabidopsis and Chlamydomonas mutants affected in the xanthophyll cycle have been isolated. These mutants have provided evidence for the correlation between the de-epoxidised xanthophyll cycle pigments and NPQ as well as better understanding of the operation of the xanthophyll cycle and the related carotenoid biosynthetic enzymes. This key photoprotective role of the xanthophyll cycle is therefore a promising target for genetic engineering to enhance environmental stress tolerance in plants. Several genes from the carotenoid biosynthetic pathway of grapevine (Vitis vinifera L.) were isolated previously in our laboratory. The main aim of this study was to over-express two xanthophyll cycle genes from grapevine in Arabidopsis and to analyse the transgenic population with regards to pigment content and levels as well as certain photosynthetic parameters. The transgenic lines were compared with wild type Arabidopsis (untransformed) plants and two xanthophyll cycle mutants under non-limiting conditions as well as a stress condition, specifically a high light treatment to induce possible photodamage and photoinhibition. Transgenic Arabidopsis lines over-expressing the two V. vinifera xanthophyll cycle genes, β-carotene hydroxylase (VvBCH) and zeaxanthin epoxidase (VvZEP), were established following Agrobacterium transformation. In addition to the untransformed wild type, two NPQ mutants, npq1 (lacking violaxanthin de-epoxidase) and npq2 (lacking zeaxanthin epoxidase), were used as controls throughout this study. The transgenic lines were propagated to a homozygous T3-generation, where stable integration and expression of the transgenes were confirmed in only 16% and 12% for VvBCH and VvZEP lines, respectively. No phenotypical differences could be observed for the transgenic lines compared to the wild type, but the npq2 mutant showed a stunted and ‘wilty’ phenotype, as was previously described. To evaluate the pigment composition of the transgenic lines a reliable and reproducible method was needed to analyse carotenoids from leafy material. To this end a new high-performance liquid chromatography (HPLC) method was developed for the quantitative profiling of eight major carotenoids and chlorophyll a and b. Emphasis was placed on baseline separation of the xanthophyll pigments, lutein and zeaxanthin as well as the cis- and trans-forms of violaxanthin and neoxanthin. The method effectively distinguished Arabidopsis wild type plantlets from the two NPQ mutant lines (npq1 and 2) and could possibly find application for green leafy tissue samples in general. The carotenoid content of the NPQ mutants were in accordance with previous reports. The lack of zeaxanthin epoxidase activity in the npq2 mutant resulted in the accumulation of zeaxanthin under both low and high light conditions. This high level zeaxanthin was found to cause an initial rapid induction of NPQ at low to moderate light intensities, but this difference disappeared at high light, where zeaxanthin formation induced considerable NPQ in the wild type. Similarly, the npq1 mutant was unable to de-epoxidise violaxanthin to zeaxanthin under high light conditions, which resulted in severe inhibition of NPQ induction. Furthermore, these mutant plantlets were shown to be more susceptible to photoinhibition compared to that of the wild type. The over-expression of VvBCH resulted in a marked increase in the xanthophyll cycle pool pigments (violaxanthin, antheraxanthin and zeaxanthin) and reduced β-carotene levels under both low and high light conditions compared to that the wild type, indicating elevated β-carotene hydroxylase activity possibly due to over-expression of the VvBCH gene. Similar to the induction of NPQ in the npq2 mutant, the increased levels of zeaxanthin in the VvBCH lines did not offer any additional photoprotection. This would suggest that the heightened zeaxanthin levels observed for the VvBCH lines do not necessarily enhance photoprotection, however may protect the thylakoid membrane against lipid peroxidation as has been shown previously. The VvZEP lines however, showed reduce levels of zeaxanthin in high light conditions to that of the wild type, probably due to the competing epoxidation and de-epoxidation reactions of the xanthophyll cycle. This reduction in zeaxanthin synthesis in the VvZEP lines resulted in significant reduced NPQ induction compared that of the wild type, a phenomenon also observed for the npq1 mutant. Similar to the npq1 mutant, these lines displayed significantly increased photoinhibition, which may be due to photodamage of the reaction centers if one considers the lowered photosystem II photochemistry efficiency and reaction center openness of these lines compared to the wild type. This may suggest that even small reductions in zeaxanthin amounts can result in an increase in photoinhibition, under high light conditions. This study and its results provide fundamental information regarding two grapevine-derived carotenoid pathway genes and their possible physiological roles. Moreover, studies like these provide information that is essential when possible biotechnological approaches are planned with this central plant metabolic pathway in mind. The results highlighted the complex regulation of this pathway, necessitating attention to flux control, simultaneous manipulation of several pathway genes, and the measurement of other compounds derived from this pathway when evaluating the possible applications of the carotenoid pathway of plants.

Thesis (MScAgric (Viticulture and Oenology)--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: ‘Crimson Seedless’ is currently one of the most important and popular table grape cultivars produced in South Africa, and as such it is of great economic value for table grape producers. Major concerns with ‘Crimson Seedless’ is that it is prone to inadequate colouring, and with increased yields the berry size decreases. An additional difficulty is that methods used to increase berry size, further impede berry colouring. A plant growth regulator (PGR) commonly used in table grape production, to enhance colour formation, is ethephon (2-chloro-ethyl-phosphonic acid, 2-CEPA). In recent years significant research has been done on the effect of sunlight on anthocyanin production in grapes, although this has primarily been on wine grape cultivars. Currently, there is limited knowledge on the effect of sunlight on table grapes, and how this might influence their anthocyanin composition and content. The effect of ethephon on colour of grapes and other fruit have been extensively researched and well documented. However, the effect of ethephon on the anthocyanin composition of ‘Crimson Seedless’ is not well known. The current study aimed to explore the effect of sunlight (by matter of exclusion) and management practices, namely defoliation and ethephon application, on the anthocyanin profile and content of ‘Crimson Seedless’. Four different treatments were applied to two ‘Crimson Seedless’ vineyards, the first site located in Paarl, and the second in De Doorns. The treatments were: 1. Naturally exposed bunches, 2. Exposed bunches treated with ethephon, 3. Bunches kept in shade boxes, 4. Shaded bunches treated with ethephon. At the De Doorns site an additional defoliation treatment was superimposed over the above treatments. An HPLC technique was modified for the separation and detailed profiling of ‘Crimson Seedless’ anthocyanins and was used to analyse the effect of the reported treatments on the anthocyanin profile of berry skins. The predominant anthocyanin in ‘Crimson Seedless’ is peonidin-3-glucoside (Pn-gluc), and this was found to be significantly increased only by ethephon application, and was not altered by sunlight or leaf removal. The responses of the other anthocyanin types varied according to the respective treatments applied. However, a general observation was that ethephon application more consistently increased the concentration of anthocyanins in berry skins than did sunlight. Leaf removal had the least significant effect on anthocyanin concentration. / AFRIKAANSE OPSOMMIMG: ‘Crimson Seedless’ is tans een van die belangrikste en gewildste tafeldruif cultivars wat in Suid-Afrika verbou word en daarom is dit van groot ekonomiese waarde vir tafeldruifprodusente. ‘Crimson Seedless’ is egter daarvoor bekend dat dit te swak kleur (volgens uitvoer spesifikasies) en tweedens is die cultivar geneig om kleiner korrels te ontwikkel wanneer die oeslading vermeerder word. ‘n Addisionele probleem is dat die praktyke wat in die industrie gebruik word om korrels te vergroot ‘n verdere negatiewe impak op ‘Crimson Seedless’ se kleur ontwikkeling kan veroorsaak. Die plant-groei-reguleerder wat algemeen in tafeldruif verbouing gebruik word, ten einde beter gekleurde druiwe te produseer, is ethephon (2-chloro-ethyl-phosphonic acid, 2-CEPA). In die laaste paar jaar was daar baie navorsing gedoen oor die effek wat sonlig het op die antosianien produksie van druiwe, maar navorsing was gefokus op wyndruif cultivars. Huidiglik is daar beperkte tegniese kennis oor die effek wat sonlig op tafeldruiwe het, en hoe dit moontlik die antosianien samestelling en inhoud kan beïnvloed. Daar is ook reeds verskeie studies gedoen en data gepubliseer oor die invloed wat ethephon op die kleur het van druiwe en ander vrugte, maar die invloed wat ethephon op die antosianien samestelling van ‘Crimson Seedless’ het, is nie wel bekend nie. Die doel van hierdie studie was om die effek van sonlig (deur uitsluiting) en bestuurspraktyke (blaarverwydering en ethephon toediening) te bestudeer en hoe dit die antosianien samestelling van ‘Crimson Seedless’ beïnvloed. Vier verskillende behandelings is toegedien in twee ‘Crimson Seedless’ wingerde, die eerste proefperseel in die Paarl en die tweede proefperseel in De Doorns. Die behandelings was: 1. Natuurlik blootgestelde trosse, 2. blootgestelde trosse met ethephon, 3. Trosse met skadubokse omhul, 4. Skaduboks trosse met ethephon. By De Doorns is ‘n addisionele blaarverwydering proef bygebring. ‘n HPLC tegniek was aangepas om die antosianien samestelling en inhoud van ‘Crimson Seedless’ te bepaal, en om die effek van die behandelings te ondersoek. Die HPLC data het getoon dat peonodien-3-glukosied (Pn-gluc) die primêre antosianien in ‘Crimson Seedless’ is met die hoogste inhoud van al die antosianiene. Pn-gluc was betekenisvol beïnvloed deur ethephon toediening, terwyl die ander behandelings geen betekenisvolle effekte daarop gehad het nie. Die effekte wat die ander antosianiene gehad het, het gevarieer volgens die behandelings wat toegedien was. ‘n Algemene observasie was dat ethephon toediening die antosianien konsentrasie in ‘Crimson Seedless’ druiwe skille meer konsekwent vermeerder het as die sonlig blootstelling. Die blaarverwydering het die minste betekenisvolle effek op die antosianien inhoud van ‘Crimson Seedless’ gehad.

Thesis (MScAgric)--University of Stellenbosch, 1955. / No Abstract Available

Thesis (MSc)--Stellenbosch University, 1964. / ENGLISH ABSTRACT: The influence of manganese sulphate sprays on the yield and ripening of fruit of manganese-deficient Vitis vinifera L. (cv. Pinotage) plants was investigated. Ripening was determined in terms of changes in concentration of the indivi= dual and total sugars and organic acids. Increasing concentrations of manganese sulphate resulted in significant increases in the manganese content of the leaves. The higher levels of manganese were associated with an increase in yield. Ripening, however, was retarded, in that the percentage sugar of the fruit was decreased and titrable acid content increased. The principal sugars present in the fruit were sucrose, glucose, fructose and xylose. Malic and tartaric acids were the main organic acid constituents. Glucose and fructose increased sharply, and sucrose and xylose slightly during ripening of the fruit, whereas malic and tartaric acid de= creased. Glucose, fructose, tartaric and malic acid tended to increase with increasing manganese content. Sucrose and xylose were not appreciably affected. An application of 1% manganese sulphate can be recommend- · ed for manganese deficient vineyards, as it results in an increased yield, in addition to delaying ripening until a more favourable time for handling. Furthermore, the lowered sugar content of the fruit may be advantageous for the pro= duction of dry wines from Pinotage grapes . / AFRIKAANSE OPSOMMING: Die invloed van mangaansulfaatbespuiting op die opbrengs en vrugrypwording van Vitis vinifera L. cv. Pinotage, wat aan ernstige mangaantekorte gely het, is ondersoek. Rypwording is met betrekking tot veranderings in die konsentrasies van totale en indiwiduele suikers en sure bepaal. 2. Toenemende konsentrasies Mnso4 (van O.2% tot l.O%) het n betekenisvolle toename in die mangaangehalte van die blare (van 3 tot 80 d.p.m.) tot gevolg gehad. Die ver= hoogde mangaangehalte het gepaard gegaan met n toe= name in opbrengs, terwyl rypwording vertraag is, deurdat die suikerpersentasie en die titreerbare suurgehalte ver= meerder is in vergelyking met die kontroleplante. 3. Die vernaamste suikers in die vrugte was sukrose, glukose, fruktose en xilose. Glukose en fruktose het vinnig en sukrose en xilose geleidelik toegeneem met die verloop van rypwording. In die ryp vrugte was glukose en fruk= tose oorheersend. Glukose en fruktose was geneig om toe te neem met toenemende mangaangehalte, terwyl sukrose en xilose nie beinvloed is nie. 4. Appelsuur en Wynsteensuur was die oorwegende sure in die vrugte. Beide hierdie sure het gedurende rypwording verminder. Hulle konsentrasies het oor die algemeen toegeneem namate die mangaankonsentrasie verhoog is. 5. Dit is afgelei dat bespuiting met 1.0% MnS04 aanbeveel kan word vir wingerde met mangaantekorte, daar dit n toename in opbrengs, gepaard met 'n vertraging in rypwording tot gevolg gehad het. So 'n vertraging mag moontlik in parstyd voordelig wees. Die verlaagde suikerpersentasie van die vrugte is moontlik gunstig vir die bereiding van droe wyne, waarvoor Pinotage hoofsaaklik gebruik word.

Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Viruses are some of the most important pathogens of grapevines. There are no effective chemical treatments, and no grapevine- or other natural resistance genes have been discovered against grapevine infecting viruses. The primary method of grapevine virus control is prevention by biological indexing and molecular- and serological screening of rootstocks and scions before propagation. Due to the spread of grapevine viruses through insect vectors, and in the case of GRSPaV the absence of serological screening, these methods of virus control are not always effective. In the past several methods, from cross-protection to pathogen derived resistance (PDR), have been applied to induce plant virus resistance, but with inconsistent results. In recent years the application of post-transcriptional gene silencing (PTGS), a naturally occurring plant defense mechanism, to induce targeted virus resistance has achieved great success. The Waterhouse research group has designed plant transformation vectors that facilitate specific virus resistance through PTGS. The primary focus of this study was the production of virus specific transformation vectors for the introduction of grapevine virus resistance. The Waterhouse system has been successfully utilised for the construction of three transformation vectors with the pHannibal vector as backbone. Each vector contains homologous virus coat protein (CP) gene segments, cloned in a complementary conformation upstream and downstream of an intron sequence. The primary vector (pHann-SAScon) contains complementary CP gene segments of both GRSPaV and GLRaV-3 and was designed for the introduction of multiple-virus resistance. For the construction of the primary vector the GRSPaV CP gene was isolated from RSP infected grapevines. A clone of the GLRaV-3 CP gene was acquired. The second vector (pHann- LR3CPsas) contains complementary CP gene segments of GLRaV-3. The third vector (pHann-LR2CPsas) contains complementary CP gene segments of GLRaV-2. The cassette containing the complementary CP gene segments of both GRSPaV and GLRaV-3 was cloned into pART27 (pART27-HSAScon), and used to transform N tabacum cv. Petit Havana (SRI), through A. tumefaciens mediated transformation. Unfortunately potential transformants failed to regenerate on rooting media; hence no molecular tests were performed to confirm transformation. Once successful transformants are generated, infection with a recombinant virus vector (consisting of PYX, the GFP gene as screenable marker and the complementary CP gene segments of both GRSPaV and GLRaV-3) will be used to test for the efficacy of the vectors to induce resistance. A secondary aim was added to this project when a need was identified within the South African viticulture industry for GRSPaV specific antibodies to be used in serological screening. To facilitate future serological detection of GRSPaV, the CP gene was isolated and expressed with a bacterial expression system (pETI4b) within the E. coli BL2I(DE3)pLysS cell line. The expressed protein will be used to generate GRSPaV CP specific antibodies. / AFRIKAANSE OPSOMMING: Virusse is van die belangrikste patogene by wingerd. Daar bestaan geen effektiewe chemiese beheer nie, en geen wingerd- of ander natuurlike weerstandsgene teen wingerdvirusse is al ontdek nie. Die primêre metode van beheer t.o.v. wingerdvirusse is voorkoming deur biologiese indeksering, en molekulêre- en serologiese toetsing van onderstokke en entlote voor verspreiding. As gevolg van die verspreiding van wingerdvirusse deur insekvektore, en in die geval van GRSPa V die tekort aan serologiese toetsing, is dié metodes van virusbeheer nie altyd effektief nie. In die verlede is metodes soos kruis-beskerming en patogeen-afgeleide weerstand (PDR) gebruik om virusweerstand te induseer, maar met inkonsekwente resultate. In onlangse jare is post-transkripsionele geenonderdrukking (PTGS), 'n natuurlike plantbeskermingsmeganisme, met groot sukses toegepas om geteikende virusweerstand te induseer. Die Waterhouse-navorsingsgroep het planttransformasievektore ontwerp wat spesifieke virusweerstand induseer d.m.v. PTGS. Die vervaardiging van virus spesifieke tranformasievektore vir die indusering van wingerdvirusweerstand was die primêre doelwit van hierdie studie. Die Waterhouse-sisteem was gebruik vir die konstruksie van drie transformasievektore, met die pHannibal vektor as basis. Elke vektor bevat homoloë virus kapsiedproteïen (CP) geensegmente, gekloneer in 'n komplementêre vorm stroom-op en stroom-af van 'n intronvolgorde. Die primêre vektor (pHann-SAScon) bevat komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, en was ontwerp vir die indusering van veelvoudige-virusweerstand. Die CP-geen van GRSPa V was vanuit RSP-geïnfekteerde wingerd geïsoleer, vir die konstruksie van die primêre vektor. 'n Kloon van die GLRa V-3 CP-geen was verkry. Die tweede vektor (pHann-LR3CPsas) bevat komplementêre CP geensegmente van GLRaV-3. Die derde vektor (pHann-LR2CPsas) bevat komplementêre CP geensegmente van GLRa V-2. Die kasset bestaande uit die komplementêre CP geensegmente van beide GRSPaV en GLRaV-3, was gekloneer in pART27 (pART27-HSAScon), en gebruik om N tabacum cv. Petit Havana (SRI) te transformeer d.m.v. A. tumefaciens bemiddelde transformasie. Ongelukkig het potensiële transformante nie geregenereer op bewortelingsmedia nie; gevolglik was geen molekulêre toetse gedoen om transformasie te bevestig nie. Na suksesvolle transformante gegenereer is, sal infeksie met 'n rekombinante-virusvektor (bestaande uit PYX, die GFP geen as waarneembare merker en die komplementêre CP geensegmente van beide GRSPa V en GLRa V-3) gebruik word om die effektiwiteit van die vektore as weerstandsinduseerders te toets. 'n Sekondêre doelwit is by die projek gevoeg toe 'n behoefte aan GRSPaV spesifieke teenliggame binne die Suid-Afrikaanse wynbedryf geïdentifiseer is, vir gebruik in serologiese toetsing. Om toekomstige serologiese toetsing van GRSPa V te bemiddel, was die CP-geen geïsoleer en in 'n bakteriële uitdrukkingsisteem (PETI4b) uitgedruk, in die E. coli BL21(DE3)pLysS sellyn. Die uitgedrukte proteïne sal gebruik word vir die vervaardiging van GRSPa V CP spesifieke antiliggame.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2007. / More and more markets develop around the world for South African grapes and it becomes a challenge to store grapes for longer and reach the market with superior quality. The most destructive decay fungus, Botrytis cinerea can cause huge economic losses and successful postharvest control in the table grape industry relies on SO2. This gas not only controls the fungus but also causes losses due to phytotoxicity. SO2 also creates allergic reactions amongst certain people. In modern times the focus is on food safety and governments consequently impose certain regulations and restrictions to restrict the use of chemicals and ensure “cleaner” produce. The objective of this study was to find a steriliser to reduce B. cinerea inoculum on the berry surface prior to storage,to be used in conjunction with the current method of control – the SO2 generator pad.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / The South African table grape industry exports approximately 60% of the table grapes produced. A major threat to the export of these grapes is the phytosanitary risk that insect pests pose. This study was conducted in the Hex River Valley, South Africa’s main table grape producing area. The aim of this study was to reduce the number of phytosanitary rejections from insects on table grapes from the Hex River Valley. Thus the main objectives of the study were to identify the most important phytosanitary pests in the Hex River Valley; the determination of their presence in the vineyards with possible means to control them; and to assess the possibility of using postharvest quarantine treatments in the Western Cape. Further aims were to determine the effect of different colour harvesting crates on the phytosanitary pests and whether the phytosanitary pests infested the grapes via packhouses. The most important phytosanitary pests of table grapes of the Hex River Valley are in order of importance: Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae), Epichoristodes acerbella Walker (Lepidoptera: Tortricidae), Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), Gonocephalum simplex Fabricius (Coleoptera: Tenebrionidae) and Dysdercus fasciatus Signoret (Hemiptera: Pyrrhocoridae). 12.71% of rejections were from species that were not identified, while a further 33% of the rejections were possibly identified incorrectly. Phytosanitary control of P. callosus appeared to be far more effective using Plantex® than pesticides. Weather conditions appeared to affect the abundance of P. callosus, especially warm weather, while bunches harboured less P. callosus later in the day. Control of E. acerbella with DiPel® (Bacillus thuringiensis var. kurstaki) appeared to at least reduce the population within the vineyards, and so its use is recommended. P. ficus is a non-actionable species for the USA market and is not listed as a phytosanitary pest for the Israeli market and so should not be causing any phytosanitary rejections. C. capitata appeared to be successfully controlled by the fruit fly sterile release program and the cold sterilisation it currently undergoes. G. simplex caused few rejections. It is still unclear where this pest infests the grapes, as it was found in both the field and in the packhouses. D. fasciatus occurrence on grapes was probably accidental. It was shown that picking during the early and late parts of the day, when this species was less active, reduced its occurrence in bunches. Gryllus bimaculatus (De Geer) (Orthoptera: Gryllidae), although not reported as a reason for rejections in table grapes for the past two years, was an actionable species that was present in large numbers in the Hex River Valley. There was a strong correlation between increasing quantities of pesticides and higher abundances of G. bimaculatus. It appeared to be an indicator of the overuse of pesticides. Results of this study showed that infestation by the phytosanitary pests came from neighbouring vineyards. The creation of barriers to prevent the movement of these pests between vineyards is suggested. Methyl bromide is the most commonly used postharvest quarantine treatment. Owing to the ozone-depleting properties of methyl bromide, it is scheduled to be outlawed in many countries from 2005. Alternative postharvest treatments are irradiation, extreme temperatures, forced air, vapour-heat treatments and the use of controlled atmospheres. Irradiation treatments appeared to control the pests at doses that do not damage the grapes. Controlled atmosphere treatments also have a high probability of success, although more research is required on this treatment. Low temperature treatments are relatively cheap as most exported fruit already undergoes cold storage, and appears to control species in the families Pseudococcidae and Tephritidae, although further research is required for the other pest. Colour or location of the harvesting crates in the vineyards appeared not to influence the number of phytosanitary pests collected, as they were not attracted to these crates.

Graduation date: 2004

Thesis (MScAgric)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: Phaeomoniella chlamydospora, Eutypa lata, Phomopsis, Phaeoacremonium, and Botryosphaeria spp. are important trunk disease pathogens that cause premature decline and dieback of grapevine. Previous research has focused primarily on wine grapes and the incidence and symptomatology of these pathogens on table grapes were largely unknown. A survey was therefore conducted to determine the status and distribution of these pathogens and associated symptoms in climatically diverse table grape growing regions. Fifteen farms were identified in the winter rainfall (De Doorns, Paarl and Trawal) and summer rainfall (Upington and Groblersdal) areas. Samples were taken in July and August 2004 from Dan-ben-Hannah vineyards that were 8 years and older. Distal ends of arms were removed from 20 randomly selected plants in each vineyard. These sections were dissected and isolations were made from each of the various symptom types observed: brown or black vascular streaking, brown internal necrosis, wedge-shaped necrosis, watery necrosis, esca-like brown and yellow soft wood rot, as well as asymptomatic wood. Fungal isolates were identified using molecular and morphological techniques. Pa. chlamydospora was most frequently isolated (46.0%), followed by Phaeoacremonium aleophilum (10.0%), Phomopsis viticola (3.0%), Botryosphaeria obtusa (3.0%), B. rhodina (2.2%), B. parva (2.0%), Fusicoccum vitifusiforme (0.6%), B. australis, B. dothidea and an undescribed Diplodia sp. (0.2% each), while E. lata was not found. Most of these pathogens were isolated from a variety of symptom types, indicating that disease diagnosis can not be based on symptomatology alone. Pa. chlamydospora was isolated from all areas sampled, although most frequently from the winter rainfall region. Pm. aleophilum was found predominantly in Paarl, while P. viticola only occurred in this area. Although B. obtusa was not isolated from samples taken in De Doorns and Groblersdal, it was the most commonly isolated Botryosphaeria sp., being isolated from Upington, Paarl and Trawal. B. rhodina occurred only in Groblersdal and B. parva in Paarl, Trawal and Groblersdal, while B. australis was isolated from Paarl only. The rest of the isolates (33%) consisted of sterile cultures, Exochalara, Cephalosporium, Wangiella, Scytalidium, Penicillium spp. and two unidentified basidiomycetes, which were isolated from five samples with yellow esca-like symptoms from the Paarl area. These findings clearly illustrate that grapevine trunk diseases are caused by a complex of fungal pathogens, which has serious implications for disease diagnosis and management. Protection of wounds against infection by any of these trunk disease pathogens is the most efficient and cost-effective means to prevent grapevine trunk diseases. However, previous research on the effectiveness of chemical pruning wound protectants has mostly focused on the control of Eutypa dieback only. Fungicide sensitivity studies have been conducted for Pa. chlamydospora, P. viticola and Eutypa lata, but no such studies have been conducted for the pathogenic Botryosphaeria species from grapevine in South Africa. Ten fungicides were therefore tested in vitro for their efficacy on mycelial inhibition of the four most common and/or pathogenic Botryosphaeria species in South Africa, B. australis, B. obtusa, B. parva and B. rhodina. Iprodione, pyrimethanil, copper ammonium acetate, kresoxim-methyl and boscalid were ineffective in inhibiting the mycelial growth at the highest concentration tested (5 μg/ml; 20 μg/ml for copper ammonium acetate). Benomyl, tebuconazole, prochloraz manganese chloride and flusilazole were the most effective fungicides with EC50 values for the different species ranging from 0.36-0.55, 0.07-0.17, 0.07-1.15 and 0.04-0.36 μg/ml, respectively. These fungicides, except prochloraz manganese chloride, are registered on grapes in South Africa and were also reported to be effective against Pa. chlamydospora, P. viticola and E. lata. Results from bioassays on 1-year-old Chenin Blanc grapevine shoots indicated that benomyl, tebuconazole and prochloraz manganese chloride were most effective in limiting lesion length in pruning wounds that were inoculated with the Botryosphaeria spp after fungicide treatment. The bioassay findings were, however, inconclusive due to low and varied re-isolation data of the inoculated lesions. Benomyl, tebuconazole, prochloraz manganese chloride and flusilazole can nonetheless be identified as fungicides to be evaluated as pruning wound protectants in additional bioassays and vineyard trials against Botryosphaeria spp. as well as the other grapevine trunk disease pathogens. / AFRIKAANSE OPSOMMING: Phaeomoniella chlamydospora, Eutypa lata, Phomopsis, Phaeoacremonium, en Botryosphaeria spesies is die mees belangrikste stamsiekte patogene wat agteruitgang en vroeë terugsterwing van wingerd veroorsaak. Voorafgaande navorsing het hoofsaaklik gefokus op wyndruiwe en die voorkoms en simptomatologie van hierdie patogene op tafeldruiwe is dus grootliks onbekend. ‘n Opname is gevolglik gedoen in verskillende klimaaatsareas waar tafeldruiwe verbou word om die voorkoms en verspreiding, asook die simptome geassosieer met hierdie patogene, te bepaal. Vyftien plase is geïdentifiseer in die winter- (De Doorns, Paarl en Trawal) en somer-reënval (Upington en Groblersdal) streke. Wingerde (8 jaar en ouer) met die kultivar Dan-ben-Hannah is gekies vir opname en monsters is gedurende Julie en Augustus 2004 geneem. Die distale deel van ‘n arm is verwyder vanaf 20 lukraak gekose plante in elke wingerd. Hierdie dele is ontleed en isolasies is gemaak vanuit elke simptoomtipe wat beskryf is, naamlik bruin en swart vaskulêre verkleuring, bruin interne nekrose, wig-vormige nekrose, waterige nekrose, esca-geassosieerde bruin en geel sagte houtverrotting en asimptomatiese hout. Identifikasie van die swamagtige isolate is gedoen op grond van morfologiese eienskappe en molekulêre tegnieke. Pa. chlamydospora is die meeste geïsoleer (46.0%), gevolg deur Phaeoacremonium aleophilum (10.0%), Phomopsis viticola (3.0%), Botryosphaeria obtusa (3.0%), B. rhodina (2.2%), B. parva (2.0%), Fusicoccum vitifusiforme (0.6%), B. australis, B. dothidea en ‘n onbeskryfde Diplodia sp. (0.2% elk), terwyl E. lata nie geïsoleer is nie. Hierdie patogene is elk geïsoleer vanuit ‘n verskeidenheid simptoomtipes, wat daarop dui dat siektediagnose nie alleenlik op simptomatologie gebaseer kan word nie. Pa. chlamydospora is geïsoleer vanuit al die gebiede, alhoewel die patogeen opmerklik meer voorgekom het in die winter-reënval area. Pm. aleophilum het hoofsaaklik voorgekom in Paarl, terwyl P. viticola slegs in hierdie area voorgekom het. Alhoewel B. obtusa nie voorgekom het in die De Doorns en Groblersdal areas nie, was dit die mees algemeen geïsoleerde Botryosphaeria sp. en het in Upington, Paarl en Trawal voorgekom. B. rhodina het slegs in Groblersdal voorgekom, B. parva in Paarl, Groblersdal en Trawal en B. australis het slegs in Paarl voorgekom. Die res van die isolate (33%) het bestaan uit steriele kulture, Exochalara, Cephalosporium, Wangiella, Scytalidium, en Penicillium spesies asook twee onbekende basidiomycete isolate, geïsoleer vanuit vyf monsters met geel eska-geassosieerde simptome vanuit die Paarl area. Hierdie resultate illustreer dus die feit dat wingerdstamsiektes deur ‘n kompleks van swampatogene veroorsaak word, wat belangrike implikasies het vir die bestuur en diagnose van hierdie siektes. Wondbeskerming teen infeksie van enige van hierdie stamsiekte patogene is die mees doeltreffende en koste-effektiewe manier om wingerdstamsiektes te voorkom. Vorige navorsing aangaande die effektiwiteit van chemiese wondbeskermingsmiddels het egter slegs gefokus op die beheer van Eutypa terugsterwing. In vitro swamdoder sensitiwiteitstoetse is gedoen vir Pa. chlamydospora, P. viticola en Eutypa lata, maar geen studies is al gedoen ten opsigte van die patogeniese Botryosphaeria spesies op wingerd in Suid-Afrika nie. Tien swamdoders is dus getoets vir inhibisie van in vitro miseliumgroei van die vier mees algemene en/of patogeniese Botryosphaeria spesies wat in Suid-Afrika voorkom, naamlik B. australis, B. obtusa, B. parva en B. rhodina. Iprodione, pyrimethanil, koper ammonium asetaat, kresoxim-metiel en boscalid was oneffektief by die hoogste konsentrasies getoets (5 μg/ml; 20 μg/ml vir koper ammonium asetaat). Benomyl, tebuconasool, prochloraz mangaan chloried en flusilasool was die mees effektiewe swamdoders met EC50 waardes tussen 0.36-0.55, 0.07-0.17, 0.07-1.15 en 0.04-0.36 μg/ml, onderskeidelik vir die verskillende spesies. Hierdie fungisiedes, behalwe prochloraz mangaan chloried, is geregistreer op druiwe in Suid-Afrika en is ook effektief gevind teenoor Pa. chlamydospora, P. viticola en E. lata. Resultate van biotoetse op 1-jaar-oue Chenin Blanc wingerd lote het getoon dat benomyl, tebuconasool en prochloraz mangaan chloried die effektiefste was om die lengte van letsels in snoeiwonde, geinokuleer met Botryosphaeria spesies na die aanwending van swamdoder behandelings, te verminder. Die bevindinge was egter onbeslis as gevolg van die lae en variërende her-isolerings data. Benomyl, tebuconasool, prochloraz mangaan chloried en flusilasool kan egter geïdentifiseer word as swamdoders wat verder geevalueer kan word as snoeiwond beskermingsmiddels teen Botryosphaeria spesies asook ander wingerd stamsiekte patogene in verdere biotoetse en wingerdproewe.

Thesis (MAgricAdmin (Agricultural Economics))--University of Stellenbosch, 2005. / The wine industry is one of the oldest commercial activities in South Africa. The South African wine grape industry annually produces more than a million tonnes of grapes, making the country the ninth largest producer in the world. The total area under wine grape production is divided into eight regions for administrative purposes. These boundaries are a legacy of the era of controlled marketing and there is continued meaningfulness of having various classifications such as ‘wine of origin’ scheme. The purpose of this study is to identify the factors that determine the producers’ choice of wine grape cultivars in the wine regions in South Africa. Time series data for the period 1990-2003 were used to estimate the parameters of linear regression models. Two equations for each wine grape cultivar in each region were postulated and estimated using Ordinary Least Squares as applied with Eviews. Further, a stepwise regression as applied in STATISTICA was used to eliminate the parameters that were not statistically significant at five percent significant level. In identifying the factors that determine the choice of wine grape cultivars in the regions, the results showed that each wine grape cultivar in each region has its own factors influencing the producers’ choice of that specific wine grape cultivar. Same wine grape cultivars in different regions similarly have its own factors determining the producers’ choice. The implication of this is that there are differences in terms of the requirements and types of crops and wine grape cultivars grown in each region. However, the most important result that emerged with regular frequency is that, the factors determining the producers’ choice of a specific wine grape cultivar for each region is price of other wine grape cultivars and competitive products in that wine region. The price of specific wine grape cultivars only had an influence on few wine grape cultivars. The implication is that the producers in South Africa appears to consider the prices of other wine grape cultivars and competitive products before making a choice of whether to plant or uproot a specific wine grape cultivar more than the price of the specific wine grape cultivar. This supports the theory that farm prices play a key role in allocating resources and in rewarding efficient producers.