This thesis explores the possibilities for ecocritical study in fiction through John Steinbeck’s 1939 novel The Grapes of Wrath. Major ecocritical interpretation has yet to gain much traction in novels; by focusing on human nature, this form’s “anthropocentric” posture seems itself to be antithetical to ecocritical efforts, which aim to unseat humans as the center of the moral universe. However, by analyzing The Grapes of Wrath’s formal, narratorial, and thematic valences, I argue that principles of social justice concurrently imply environmental justice in the philosophical currents of the text. Tenets of deep ecology and Aldo Leopold’s “land ethic” inform the novel’s overall environmental outlook. The key to my interpretation is the value of community at the center of Steinbeck’s world. To expand principles of the collectivism and compassion in the social community to include the broader ecological community, I focus on the narrative’s unique Judeo-Christian spirituality and humanistic discourse. Ultimately I identify cohesion in The Grapes of Wrath’s composition that makes a single narrative of both the natural and the human worlds, and that creates a moral universe that guides ethical behavior towards others, both human and non-human; in doing so, I argue Steinbeck’s novel both enacts and represents an ecologically minded ethic.

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Various studies revealed that Botrytis cinerea, the causal pathogen of Botrytis bunch rot, is mostly associated with pedicels, rachises, laterals and berry bases, and not with berry skins as previously understood. Provided that sufficient coverage of inner bunch parts was achieved, laboratory studies have shown that fungicides can effectively reduce the amount of B. cinerea at the various positions in bunches, and prevent infection and symptom expression at all growth stages. The same efficacy was, however, not achieved with the same fungicides when using conventional spraying methods in vineyards. Poor disease control on fruit and leaves in vineyards is attributed to inappropriate timing of fungicide applications and/or insufficient coverage of susceptible tissue. Previously, spray coverage evaluations in South Africa were based on the use of water-sensitive cards. A variety of other methods have been used to assess spray coverage in vineyards, but none of these methods could assess spray deposits on a very small, three-dimensional area of interest such as the susceptible grape bunch parts. The methods were furthermore dependent on human objectivity, which lacks quantitative measuring and speed of measurement. Suitable technology to determine spray coverage on susceptible bunch parts is, therefore, not available. The aim of this study was to develop a protocol to visualise and quantify spray deposits in grape bunches, specifically on the inner bunch parts and to use the protocol to determine the effect of different levels of spray cover on artificially inoculated B. cinerea grape bunches, in order to facilitate future determination of minimum effective coverage levels for effective B. cinerea control. A spray coverage assessment protocol using fluorometry, photomicrography and digital image analyses was developed to measure spray coverage on susceptible grape bunch parts. Among several fluorescent pigments tested, a yellow fluorescent pigment (SARDI Fluorescent Pigment) from Australia was selected on the basis of its small particle size (2.45 - 4.90 μm). Bunches were sprayed at pea size and bunch closure with different volumes of a mixture of fenhexamid and the yellow fluorescent pigment. Sprayed parts from bunches were illuminated under black light (UV-A light in the 365 nm region) and visualised under a stereo microscope at 20 x magnification. Photos of the berry skin, pedicel and rachis were taken with a digital camera (Nikon DMX 1200). Image analysis of photos was done with Image- Pro Discovery version 4.5 for Windows (Media Cybernetics) software. The total area of deposited pigment in selected areas of interest (AOI) was calculated. The percentage area covered was subsequently calculated for each AOI. Good correlation was evident between the parameters, sum of objects and percentage area covered. Bunch parts at pea size generally had higher coverage values than at bunch closure. Spray applications earlier in the season would therefore result in higher and more effective spray coverage of the susceptible bunch parts. Similar deposition trends were observed on the inner bunch parts (pedicel and rachis). These were, however, significantly different from berry skins, which had significantly higher levels of spray deposits than the inner bunch parts. The variance component analysis indicated that the highest variance was observed for berries and bunches, and substantially less for image readings. For the same accuracy, means for percentage coverage values of at least 10 bunches per treatment (1 part per bunch and 3 readings per part) will be sufficient. In order to determine the biological efficacy of different levels of spray coverage on B. cinerea incidence on grape bunches, bunches were sprayed at pea size and bunch closure with different volumes of a mixture of fenhexamid and a yellow fluorescent pigment and the percentage fluorescent pigment coverage on pedicels was determine. Bunches were subsequently dusted with dry airborne conidia of B. cinerea in a settling tower and incubated for 24 h at high relative humidity (98%). Infection was determined by estimating the amount of B. cinerea infections occurring on sprayed bunch parts with isolations on to paraquat and Kerssies mediums. Linear regressions for the part x stage combinations of percentage B. cinerea incidence on different bunch parts were fitted on mean coverage levels. An increase in spray cover caused linear reductions in levels of B. cinerea on susceptible bunch parts. Higher B. cinerea incidences were recorded at pea size. Furthermore, higher B. cinerea incidences were found on paraquat medium for both stages, than on Kerrsies medium. The information gathered from this study will be used to facilitate future determination of minimum effective coverage levels for effective B. cinerea control in grape bunches. In these validation experiments, the results clearly showed that the protocol can be used to determine the effect of different levels of spray coverage on B. cinerea incidence and that an increase in spray coverage will decrease B. cinerea incidence. The information gathered from this study will be used to facilitate future determination of minimum effective coverage levels for effective B. cinerea control in grape bunches and subsequently be used as benchmarks to evaluate spray application in vineyards. / AFRIKAANSE OPSOMMING: Vaalvrot by wingerde word veroorsaak deur Botrytis cinerea. Verskeie studies het getoon/gewys dat die oorsaaklike patogeen meestal geassosieer word met die pedisel, ragis, laterale en die korrelbasis, en nie met die korrelskil soos voorheen beweer nie. Laboratorium studies het getoon dat swamdoders wel effektief is om B. cinerea by alle trosdele te verminder en simptoomontwikkeling te voorkom tydens alle groeistadia, mits die binne-trosdele voldoende spuit bedekking ontvang het. Dieselfde effektiwiteit is egter nie gevind in wingerde met konvensionele spuittegnieke nie. Onvoldoende siektebeheer van vrugte en blare van wingerde kan toegeskryf word aan verkeerde spuit skedulering en/of swak spuitbedekking van vatbare gasheerweefsel. Evaluering van spuitbedekking is voorheen in Suid Afrika deur middel van water-sensitiewe papier gedoen. Verskeie ander metodes is al gebruik om spuitbedekking te evalueer in wingerde, maar nie een van hierdie metodes kan gebruik word om spuitbedekking op ’n baie klein, drie-dimensionele oppervlak, soos die vatbare trosdele, te evalueer nie. Verder was die tegnieke afhanklik van menslike objektiwiteit, en gevolglik ontbreek kwantitatiewe meting en metingspoed. Daar is dus nie geskikte tegnologie vir die evaluering van spuitbedekking op vatbare trosdele nie. Die doel van hierdie studie was die ontwikkeling van ‘n protokol vir die visualisering en kwantifisering van spuitbedekking op spesifiek die binne-tros dele en om die protokol dan te gebruik om die effek van verskillende vlakke van spuitbedekking op B. cinereageinokuleerde druiwetrosse te bepaal, Protokol vir evaluasie van spuitbedekking op vatbare druifdele is ontwikkel deur gebruik te maak van fluorometrie, fotomikrografie en digitale beeldanalise. Van die verskillende fluoresensie pigmente wat getoets is, is ‘n geel flouresensie pigment (SARDI Flourescent Pigment) van Australië gekies op grond van sy klein partikelgrootte (2.45 - 4.90 μm). Druiwetrosse is gespuit tydens ertjie- en trostoemaakstadia met verskillende volumes van ’n mengsel van fenheksamied en die geel fluorosensie pigment. Die gespuite druifdele is dan verlig onder swartlig buise (UV-A lig in die 365 nm spektrum) en gevisualiseer deur ’n stereo mikroskoop by 20x vergroting. Foto’s van die korrelskil, pedisel en ragis is met ‘n digitale kamera (Nikon DMX 1200) geneem. Beeldanalise is gedoen met ImagePro Discovery weergawe 4.5 vir Windows (Media Cybernetics) sagteware. Die totale area neerslag van die pigment is in geselekteerde areas bereken. Die presentasie area bedek is bereken vir elkeen van hierdie areas. Goeie korrelasie is gevind tussen die parameters aantal fluoresserende partikels en die persentasie bedekte area. Trosdele tydens ertjie-stadium het in die algemeen hoër waardes gehad as by trostoemaak. Dit blyk dus dat spuittoediening vroeg in die seisoen meer effektief sal wees vir die bedekking van vatbare trosdele. Soortgelyke bedekkings patrone is gevind by die binne trosdele (pedisel en ragis). Dit het egter betekenisvol verskil van die korrelskil, wat betekenisvol meer spuitbedekking as die binne trosdele gehad het. ’n Variasie komponent analise het getoon dat die meeste variasie gevind is tussen korrels en trosse, en heelwat minder vir die beeld analise lesings. Om dieselfde akkuraatheid te behou, is ten minste 10 trosse per behandeling (1 deel per tros en 3 lesings per deel) nodig. Vir die bepaling van biologiese effektiwiteit van verskillende vlakke van spuitbedekking op B. cinerea voorkoms op druiwe, is druiwe gespuit tydens ertjie- en trostoemaak-stadia met verskillende volumes van ’n mengsel van fenheksamied en die geel fluorosensie pigment. Die persentasie fluoresensie pigment is bepaal op die pedisels. Trosse is vervolgens geinokuleer met droë luggedraagde konidia van B. cinerea in ’n inokulasietoring en geïnkubeer vir 24 h by hoë relatiewe humiditeit (98%). Die voorkoms van B. cinerea infeksie op gespuite tros dele is bepaal deur middel van isolasies op paraquat en Kerssies medium. Liniêre regressies vir trosdeel x stadium kombinasies van persentasie B. cinerea voorkoms op verskillende trosdele is gepas vir gemiddelde bedekkings waardes. ’n Verhoging in spuit bedekking het ‘n liniêre vermindering van B. cinerea voorkoms op vatbare trosdele veroorsaak. Verder is hoër vlakke van B. cinerea op paraquat medium as op Kerssies medium vir beide die groeistadia gevind. Die kennis wat verkry is uit hierdie studie sal gebruik word om minimum effektiewe spuitbedekkingsvlakke vir die beheer van B. cinerea op druiwetrosse te bepaal.

Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Phaeomoniella chlamydospora is the main causal organism of Petri disease, which causes severe decline and dieback of young grapevines (1-7 years old) and also predisposes the wood for infection by other pathogens. Knowledge about the epidemiology and especially inoculum sources of this disease is imperative for subsequent development of management strategies. Through isolation studies it was shown that Pa. chlamydospora is mainly distributed through infected propagation material in South Africa. However, the infection pathways and inoculum sources in grapevine nurseries are still unclear. The only existing method to detect this pathogen in various media is by means of isolation onto artificial growth media. This has proven to be problematic since this fungus is extremely slow growing (up to 4 weeks from isolation to identification) and its cultures are often over-grown by co-isolated fungi and bacteria before it can be identified. The aim of this study was (i) to develop a protocol for the molecular detection of Pa. chlamydospora in grapevine wood, and (ii) to use this protocol along with others, to test different samples (water, soil, rootstock and scion cuttings and callusing medium) collected from nurseries in South Africa at different nursery stages for the presence of Pa. chlamydospora. A protocol was developed and validated for the molecular detection of Pa. chlamydospora in grapevine wood. Firstly, several previously published protocols were used to develop a cost-effective and time-efficient DNA extraction method from rootstock pieces of potted grapevines. Subsequently, PCR amplification using species-specific primers (Pch1 and Pch2) was found to be sensitive enough to detect as little as 1 pg of Pa. chlamydospora genomic DNA from grapevine wood. The protocol was validated using various grapevine material from 3 different rootstock cultivars (101-14 Mgt, Ramsey and Richter 99) collected from each of 3 different nurseries, including grapevines that were subjected to hot water treatment. The basal end of the rootstock was parallel analysed for Pa. chlamydospora using isolations onto artificial medium and molecular detection. The identity of PCR products obtained from a subset of samples, that only tested positive for Pa. chlamydospora based on molecular detection, was confirmed to be Pa. chlamydospora specific through restriction digestion with AatII. Molecular detection was found to be considerably more sensitive than isolations, detecting Pa. chlamydospora from samples with positive as well as negative isolations. On average, the molecular technique detected Pa. chlamydospora in 80.9% of the samples, whereas only 24.1% of the samples tested positive for Pa. chlamydospora by means of isolations. Pa. chlamydospora was not isolated from hot water treated samples. The results confirm the importance of hot water treatment for proactive management of Petri disease in grapevine nurseries. However, Pa. chlamydospora DNA was molecularly detected in hot water treated samples in frequencies similar to that detected in non-hot water treated samples. As expected, the DNA in hot water treated plants was not destroyed and could be detected by the developed molecular detection protocol. This is an important consideration when using molecular detection for disease diagnosis or pathogen detection and shows that these methods should be used in conjunction with other diagnostic tools. Most importantly, the DNA extraction protocol was shown to be 10 to 15 times cheaper than commercial DNA extraction kits. Preliminary studies showed that the aforementioned molecular detection technique was not specific and sensitive enough for detection of Pa. chlamydospora in soil and water (unpublished data). Therefore, a one-tube nested-PCR technique was optimised for detecting Pa. chlamydospora in DNA extracted from soil, water, callusing medium and grapevine wood. Rootstock cane sections and soil samples were taking from the mother blocks from several nurseries. Water samples were collected from hydration and fungicide tanks during pre-storage and grafting. Scion and rootstock cuttings were also collected during grafting and soil were collected from the nursery beds prior to planting. The one-tube nested-PCR was sensitive enough to detect as little as 1 fg of Pa. chlamydospora genomic DNA from water and 10 fg from wood, callusing medium and soil. PCR analyses of the different nursery samples revealed the presence of several putative Pa. chlamydospora specific bands (360 bp). Subsequent sequence analyses and/or restriction enzyme digestions of all 360 bp PCR bands confirmed that all bands were Pa. chlamydospora specific, except for five bands obtained from callusing media and one band from water. Considering only Pa. chlamydospora specific PCR bands, the molecular detection technique revealed the presence of Pa. chlamydospora in 25% of rootstock cane sections and 17% of the soil samples collected from mother blocks, 42% of rootstock cuttings collected during grafting, 16% of scion cuttings, 40% of water samples collected after the 12- hour pre-storage hydration period, 67% of water samples collected during grafting and 8% of the callusing medium samples. These media should therefore be considered as potential inoculum sources or infection points of the pathogen during the nursery stages. The results furthermore confirmed previous findings that Pa. chlamydospora is mainly distributed through infected rootstock canes and cuttings. Infected scion cuttings were also shown to be potential carriers of the pathogen. Management strategies should include wound protection of rootstock mother plants, eradicating this pathogen from rootstock-cuttings (e.g. hot water treatment), biological or chemical amendments in the hydration water and callusing medium and wound protection from soil borne infections. / AFRIKAANSE OPSOMMING: Phaeomoniella chlamydospora is die hoof veroorsakende organisme van Petri se siekte wat lei tot die agteruitgang en terugsterwing van jong wingerdplante (1-7 jaar oud) en veroorsaak verhoogde vatbaarheid van hout vir infeksie deur ander patogene. Kennis oor die epidemiologie en veral die inokulumbronne van die siekte is noodsaaklik vir die daaropvolgende ontwikkeling van beheerstrategieë. Isolasies het getoon dat Pa. chlamydospora meestal versprei deur middel van geïnfekteerde voortplantingsmateriaal in Suid-Afrika. Die infeksieweë en inokulumbronne in wingerdkwekerye is egter steeds onbekend. Die enigste bestaande metode vir die opsporing van die patogeen, in verskeie mediums, is deur middel van isolasie op kunsmatige groeimediums. Dit is egter gevind om problematies te wees aangesien die swam uiters stadig groei (dit vat tot 4 weke vanaf isolasie tot identifikasie) en die kulture is telkens oorgroei deur ander organismes voordat identifikasie kan plaasvind. Die doel van die studie was (i) om ‘n protokol te ontwikkel vir die molekulêre opsporing van Pa. chlamydospora in wingerdhout, en (ii) om die protokol te gebruik, saam met ander, om verskillende monsters (water, grond, onderstok- en bostok-ente en kallusmedium) te toets, wat versamel is van kwekerye in Suid- Afrika, tydens verskillende kwekerystadiums, vir die teenwoordigheid van Pa. chlamydospora. ‘n Protokol is ontwikkel en geverifieer vir die molekulêre opsporing van Pa. chlamydospora in wingerdhout. Eerstens is verskeie protokols wat voorheen gepubliseer is, is as grondslag gebruik vir die ontwikkeling van ‘n ekonomiese en tydbesparende DNA ekstraksie protokol. Hierna is PKR (polimerase ketting reaksie) amplifikasie met spesie-spesifieke inleiers (Pch1 en Pch2) gevind om sensitief genoeg te wees om so min as 1 pg van Pa. chlamydospora genomiese DNA van wingerdhout op te spoor. Die protokol is geverifieer deur verskeie wingerdhoutmateriaal van 3 verskillende onderstokkultivars (101-14 Mgt, Ramsey en Richter 99) te gebruik, wat elk versamel is van 3 verskillende kwekerye. ‘n Aantal van die wingerstokke is ook onderwerp aan warmwaterbehandeling. Die basale kant van die onderstok is parallel geanaliseer vir Pa. chlamydospora deur gebruik te maak van isolasies op kunsmatige groeimedium asook molekulêre opsporing. Die identiteit van ‘n submonster van PKR produkte van verskeie monsters, wat slegs positief getoets het vir Pa. chlamydospora met die molekulêre opsporing, is bevestig om Pa. chlamydospora spesifiek te wees. Dit is gedoen deur middel van restriksie ensiem analise met AatII. Molekulêre opsporing is gevind om aansienlik meer sensitief te wees as isolasies, deurdat Pa. chlamydospora opgespoor is van positiewe sowel as negatiewe isolasies. Die molekulêre tegniek het Pa. chlamydospora in ‘n gemiddeld van 80.9% van die monsters opgespoor, terwyl slegs ‘n gemiddeld van 24.1% van die monsters postief getoets het vir Pa. chlamydospora, deur middel van isolasies. Pa. chlamydospora is nie geïsoleer van die monsters wat warmwaterbehandeling ondergaan het nie. Die resultate bevestig hoe belangrik warmwaterbehandeling is vir die proaktiewe beheer van Petri se siekte in wingerdkwekerye. Pa. chlamydospora DNA is met die molekulêre tegniek opgespoor, in warmwaterbehandelde monsters, in getalle wat ooreenstemmend is met die van niewarmwaterbehandelde monsters. Soos verwag, is DNA in warmwaterbehandelde plante nie vernietig nie en kon dit telke male opgespoor word deur die ontwikkelde molekulêre opsporing protokol. Dit is ‘n belangrike feit wat in ag geneem moet word wanneer molekulêre opsporing gebruik word in siekte diagnose en opsporing van patogene en dit is ‘n aanduiding dat die metodes gebruik moet word in samewerking met ander diagnostiese tegnieke. Die DNA ekstraksie protokol het getoon om tot en met 10 tot 15 kere goedkoper te wees as kommersiële DNA ekstraksie pakkette. Voorlopige studies het getoon dat die bogenoemde molekulêre opsporings tegniek nie spesifiek en sensitief genoeg is vir die opsporing van Pa. chlamydospora uit grond en water nie (ongepubliseerde data). Daarom is ‘n enkel-buis geneste-PKR tegniek geoptimiseer vir die opsporing van Pa. chlamydospora DNA wat geëkstraheer is vanaf grond, water, kallusmedium en wingerdhout. Dele van onderstokke en grond monsters is geneem vanaf moederblokke van verskeie kwekerye. Gedurende die voor-opberging en enting periodes is watermonsters versamel vanaf hidrasie en fungisied tenke. Bostok- en onderstokente is ook versamel gedurende enting en grond is versamel vanaf kwekerybeddens net voor uitplanting. Die enkelbuis geneste-PKR was sensitief genoeg om so min as 1 fg van Pa. chlamydospora genomiese DNA vanaf water en 10 fg vanaf hout, kallusmedium en grond op te spoor. PKR analise van die verskillende kwekerymonsters het getoon dat daar ‘n teenwoordigheid is van verskeie putatiewe Pa. chlamydospora spesifieke bande (360 bp). Daaropvolgende analise deur middel van DNA volgordebepaling en restriksie ensiem analise het bevestig dat al die 360 bp PKR bande wel Pa. chlamydospora spesifiek is, behalwe vir vyf bande wat verkry is vanaf kallusmedium en een band verkry vanaf water. As slegs Pa. chlamydospora spesifieke bande in ag geneem word, is daar met molekulêre opsporing die teenwoordigheid van Pa. chlamydospora gevind in 25% van die onderstokke, 17 % van die grond versamel vanaf moederblokke, 42% van die onderstokente versamel tydens enting, 16% van die bostokente, 40% van die watermonsters versamel voor die 12-uur hidrasie periode, 67% van die watermonsters versamel gedurende enting en 8% van die kallusmediummonsters. Hierdie mediums moet dus beskou word as potensiële inokulumbronne of infeksiepunte van die patogeen gedurende die kwekerystadiums. Die resultate bevestig ook verdere bevindinge wat aandui dat Pa. chlamydospora meestal versprei word deur geïnfekteerde onderstokke en ente. Geïnfekteerde bostokente is ook aangedui om potensiële draers van die patogeen te wees. Beheerstrategieë moet dus wondbeskerming van onderstok moederplante insluit, asook uitwissing van die patogeen vanaf onderstokente (bv. warmwaterbehandeling), toediening van biologiese of chemiese stowwe in die hidrasie water en kallusmedium en wondbeskerming teen grondgedraagde infeksies.

Thesis (MScAgric (Plant Pathology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A survey was undertaken on apple and pear trees in the Western Cape Province to determine the aetiology of trunk diseases with reference to trunk diseases occurring on grapevine. Grapevine trunk diseases cause the gradual decline and dieback of vines resulting in a decrease in the vine’s capability to carry and ripen fruit. In recent years, viticulture has been expanding into several of the well established pome fruit growing areas. The presence of trunk pathogens in pome fruit orchards may affect the health of the pome fruit trees as well as cause a threat to young vineyards planted in close proximity to these potential sources of viable inoculum. Several genera containing species known to be involved in trunk disease on pome fruit and grapevine were found, including Diplodia, Neofusicoccum, Eutypa, Phaeoacremonium and Phomopsis. Diplodia seriata and D. pyricolum, were isolated along with N. australe and N. vitifusiforme. Four Phaeoacremonium species, P. aleophilum, P. iranianum, P. mortoniae and P. viticola, two Phomopsis species linked to clades identified in former studies as Phomopsis sp. 1 and Phomopsis sp. 7, and Eutypa lata were found. In addition, Paraconiothyrium brasiliense and Pa. variabile, and an unidentified Pyrenochaetalike species were found. Of these the Phaeoacremonium species have not been found on pear wood and it is a first report of P. aleophilum occurring on apple. This is also a first report of the Phomopsis species and Eutypa lata found occurring on pome trees in South Africa Two new coelomycetous fungi were also found including a Diplodia species, Diplodia pyricolum sp. nov., and a new genus, Pyrenochaetoides gen. nov. with the type species, Pyrenochaetoides mali sp. nov., were described from necrotic pear and apple wood. The combined ITS and EF1-α phylogeny supported the new Diplodia species, which is closely related to D. mutila and D. africana. The new species is characterised by conidia that become pigmented and 1-septate within the pycnidium, and that are intermediate in size between the latter two Diplodia species. Phylogenetic inference of the SSU of the unknown coelomycete provided bootstrap support (100%) for a monophyletic clade unrelated to known genera, and basal to Phoma and its relatives. Morphologically the new genus is characterised by pycnidial with elongated necks that lack setae, cylindrical conidiophores that are seldomly branched at the base, and Phoma-like conidia. The phylogenetic results combined with its dissimilarity from genera allied to Phoma, lead to the conclusion that this species represents a new genus. A pathogenicity trial was undertaken to examine the role of these species on apple, pear and grapevine shoots. N. australe caused the longest lesions on grapevine shoots, while Pyrenochaetoides mali, Pa. variabile, D. seriata and P. mortoniae caused lesions that were significantly longer than the control inoculations. On pears, D. pyricolum and N. australe caused the longest lesions, followed by D. seriata and E. lata. On apples, the longest lesions were caused by N. australe and P. iranianum. D. seriata, D. pyricolum, E. lata, N. vitifusiforme, Pa. brasiliense, P. aleophilum and P. mortoniae also caused lesions on apple that were significantly longer than the control. The study demonstrated that close cultivation of grapevine to apple and pear orchards may have inherent risks in terms of the free availability of viable inoculum of trunk disease pathogens. / No Afrikaans abstract available.

Thesis MSc(Agric)--Stellenbosch University, 1973. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (PhD(Agric))--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A lack of defects is required for successful table grape marketing, which pre-suppose optimal vine performance, berry development and post-harvest quality. The supply of mineral nutrients affects vine development, physiology and berry quality. Despite a vast amount of research conducted over decades, there remain many unresolved issues regarding table grape vine nutrition to ensure optimal table grape quality and shelve-life. Unjustified fertilisation practices often include excessive applications of nitrogen (N), potassium (K) and calcium (Ca). A four-year field trial was therefore conducted on a sandy soil in the Paarl district of South Africa, using grafted on Ramsey, and trained to a gable trellis system. Nitrogen, potassium and calcium were applied, singular or in combination, at rates up to 300% the calculated annual nutritional requirement. The effect of these excessive applications on table grape performance under typical South African cultivation conditions was investigated for Vitis vinifera L. cv. Prime Seedless, a very early seedless table cultivar that is produced with minimum berry diameter of 18mm, with special reference to 1) vegetative growth, 2) expression of grapevine nutrient availability through foliar analyses, 3) berry nutrient accumulation patterns of this early cultivar, 4) manipulation of berry nutrient content through soil and bunch directed applications and 5) the effect of berry nutrient content on its quality. No definite vegetative growth responses (expressed as shoot length, leaf surface area and shoot mass) and leaf chlorophyll content differences were obtained for all the treatments. These results were obtained in a vineyard on a sandy soil where excessive N fertilisation caused a reduction of soil pH to detrimentally low levels and where the excessive N, K and Ca applications reduced mutual concentrations and that of Mg, in the soil. A lack of stimulation in vegetative growth may therefore be ascribed to the combined negative effect of these excessive applications on soil pH and vine nutrition. Although the N content of petioles was higher for treatments where N was applied, consistent significant increases in petiole N with N fertilisation were not observed. Petiole N concentration showed a decreasing trend throughout the season. Petiole K concentrations were significantly increased by the K fertilisation at all phenological stages. None of the K fertilisation treatments, however, succeeded to raise petiole K concentrations above the accepted maximum norms and petiole K concentration at a specific sampling stage varied significantly between the four seasons. A general decrease in petiole K concentration was found for all seasons. Calcium fertilisation did not increase soil Ca content, resulting in a lack of differences in petiole Ca concentrations between treatments. An increase in petiole Ca concentration towards harvest was obtained. Correlations between petiole nutrient concentration and berry mineral content at harvest were poor. The only way of knowing the mineral content of berries would seem to be by measuring it directly instead of deducing it from the results of leaf or petiole analyses. The dynamics of berry growth impacted on berry nutrient concentration. Early rapid berry growth, predominantly due to cell division and cell growth, was associated with the most rapid decreases in N, P and Ca concentration. Due to mobility of K and Mg in the plant, that exceeds other nutrients, the decrease in concentration of these two mineral elements was not as pronounced as that of the others. Nutrient accumulation was most rapid during the pre-véraison period, but only Ca showed a definite termination during the early ripening period. The continued inflow of N, P, K and Mg, albeit at slower rates immediately after véraison, should be taken into consideration when fertilisation is applied. As a table grape, total accumulation of each nutrient in Prime Seedless berries also far exceeded that of other cultivars studied thus far. A particular difference is that the berry flesh:skin ratio is much higher than that of previously studied cultivars, leading to higher levels of nutrient accumulation in the flesh. Slightly larger berry size was obtained for N applications and is ascribed to slight increases in early vegetative growth, allowing a better response to GA3 treatments. The use of GA3 for berry enlargement is also considered the reason why K fertilisation, resulting in increased berry K levels, did not affect berry size, as is often found for wine grapes. Higher available NO3 - in the soil on account of excessive N applications resulted in higher levels of berry N, despite sub-optimal soil pH regimes that were created by these treatments. Berry K concentration and content were increased by K fertilisation. Rapid vine K uptake and translocation to the berries seem to negate the reduced vine nutritional status as observed in petioles for situations of over-fertilisation with N. Berry Ca levels were not increased by Ca fertilisation or by bunch applied Ca. The rapid rates of berry growth, together with low rates of berry Ca uptake and Ca uptake that terminates at the onset of ripening, are assumed to be the main reasons for this result. Low levels of decay as well as a lack of consistently increased decay were obtained for N containing treatments. Nitrogen levels in the berries above which their susceptibility to fungal infection is increased, should be established. Information on specific N compounds that may lead to more susceptibility is required. Potentially increased berry browning on account of high rates of K fertilisation needs to be further investigated; indications that this may occur were observed. Neither soil applied Ca nor bunch applied Ca improved berry quality, although Ca treatments seemed to reduce decay during the only season that significant differences were obtained. The negative effect of excessive fertilisation on soil chemistry of sandy soils has again been highlighted by this study. This annuls the fertilisation, leading to inefficient fertilisation and a lack of the desired responses. As indicator of vine nutrient availability, petiole analysis, was proven unreliable and should be evaluated in parallel with soil analyses, taking seasonal variation into consideration. The danger of being only guided by published norms for leaf nutrient concentrations when establishing fertilisation practices has again been highlighted by this study. This research indicated that for a very early cultivar like Prime Seedless, nutrient accumulation dynamics can already start to change during the pre-véraison period in some seasons. This is due to different edaphic and climatic conditions as well as berry size, which leads to much higher flesh:skin ratios. Future research on table grapes would need to develop an understanding of the various factors and dynamics that determine berry nutrient concentration and accumulation of early ripening, large berry sized, seedless table grape cultivars. / AFRIKAANSE OPSOMMING: Suksesvolle bemarking van tafeldruiwe is ten nouste afhanklik van die beskikbaarheid van druiwe sonder defekte, wat ‘n direkte verband met optimale wingerdprestasie, korrelontwikkeling en na-oes kwaliteit inhou. Voorsiening van minerale voedingstowwe beïnvloed die stok se groei, fisiologie en korrelgehalte. Ten spyte van ‘n oorweldigende hoeveelheid navorsing wat oor dekades reeds gedoen is, is daar steeds onopgeloste kwessies aangaande bemesting van tafeldruiwe vir optimale druifgehalte en houvermoë. Die gevolg is onoordeelkundige bemestingspraktyke wat o.a. aanleiding gee tot oorbemesting met stikstof (N), kalium (K) en kalsium (Ca). ‘n Vier-jaar-lange veldproef is gevolglik op ‘n sandgrond in die Paarl distrik (Suid-Afrika) onderneem deur gebruik te maak van Vitis vinifera L. cv. Prime Seedless geënt op Ramsey en op ‘n dubbel-gewel prieelstelsel opgelei is. Stikstof, K en Ca is alleen, of in kombinasie, toegedien teen hoeveelhede gelykstaande aan 300% van die wingerd se jaarlikse behoefte. Die effek van hierdie oormatige toedienings op tafeldruif prestasie onder Suid-Afrikaanse verbouingstoestande is ondersoek, met spesiale verwysing na 1) vegetatiewe groei, 2) uitdrukking van voedingstofbeskikbaarheid deur blaarontledings, 3) die voedingstof akkumulasie patrone van korrels van hierdie vroeë kultivar, 4) manipulasie van korrel voedingstofinhoud deur grond en trosgerigte toedienings en 5) die effek van korrel voedingstofinhoud op kwaliteit. Die doel van die proef was om bemestinspraktyke van Prime Seedless, ‘n baie vroeë pitlose tafeldruifkultivar met ‘n minimum korrelgrootte van 18 mm, te verfyn. Deur die akkumulasie patrone van die druiwe uit te klaar is daar ook ondersoek ingestel of oestyd en na-oes gehalte deur oormatige toediening van voedingstowwe affekteer word. Geen duidelike verskille betreffende vegetatiewe groeireaksies (uitgedruk as lootlengte, blaaroppervlaktes en lootmassas) asook verskille in blaar chlorofilinhoud is vir die behandelings verkry nie. Hierdie resultate is verkry in ‘n wingerd op ‘n sandgrond, waar oormatige N-bemesting aanleiding gegee het tot grond pH verlagings tot die peil van nadelige vlakke. Verder het die oormatige N, K en Ca toedienings wederkerige verlagings in konsentrasies, asook op dié van Mg, in die grond teweeggebring. Die tekort aan vegetatiewe groeiresponse op die behandelings kon dus toegeskryf word aan ‘n gekombineerde effek van die oormatige toedienings op grond pH en voedingstofbalanse. Hoewel die N-inhoud van bladstele hoër was vir behandelings wat N toediening ingesluit het, was daar nie konstante toenames in die vlakke verkry nie. Bladskyf N-konsentrasie het afgeneem deur die loop van die groeiseisoen. Vir alle fenologiese stadiums was bladskyf Kkonsentrasies betekenisvol verhoog deur K-bemesting. Nie een van die Kbemestingsbehandelings het egter daarin geslaag om bladskyf K inhoud vir enige monstertyd bo die algemeen aanvaarde maksimum norms te lig nie. Verder het bladskyf K inhoud by ‘n spesifieke fenologiese stadium ook betekenisvol tussen seisoene verskil. Die K-inhoud van bladskywe het afgeneem met verloop van die seisoen. Kalsiumbemesting het nie die grond se Ca inhoud deurgans verhoog nie, wat dus die tekort aan verskille in Ca konsentrasies tussen die behandelings verklaar. ‘n Toename in Ca konsentrasie en korrel Ca inhoud is vanaf set tot oes waargeneem. Swak korrelasies tussen bladskywe se voedingstofinhoude en korrels se voedingstofinhoude is verkry. Die enigste manier waarop korrels se voedingstofinhoude dus afgelei kan word, blyk te wees deur direkte bepaling daarvan. Voedingstofinhoude van korrels is deur groeipatrone daarvan beïnvloed. Vroeë korrelgroei, hoofsaaklik a.g.v. seldeling en selgroei, het met die vinnigste afnametempo van N, P en Ca gepaard gegaan. As gevolg van die hoër beweeglikheid van K en Mg in die plant in vergelyking met ander voedingstowwe, was die afname in konsentrasie van hierdie twee elemente nie so groot soos vir die ander nie. Voedingstofakkumulasie was die vinnigste in die periode voor deurslaan. Slegs Ca het ‘n beeïndiging van opname aan die einde van hierdie periode getoon. Die voortgesette opname van N, P, K en Mg, alhoewel stadiger kort na deurslaan, moet in ag geneem word wanneer bemesting toegedien word. Vir hierdie kultivar het die totale opname van elke bemestingstof dié van die ander kultivars wat tot hede bestudeer is, ver oorskry. ‘n Spesifieke verskil is ‘n baie hoër vleis:dop verhouding as wat vir ander kultivars verkry is. Dit gee aanleiding tot baie hoër vlakke van voedingstofakkumulasie in die vleis. Effens groter korrelgroottes is verkry waar N toedienings gemaak is. Dit word toegeskryf aan klein toenames in vroeë vegetatiewe groei, wat dus beter reaksie op GA3 behandelings tot gevolg gehad het. Die gebruik van GA3 vir korrelvergroting word ook beskou as die rede waarom K-bemesting, wat tot hoër vlakke van K in die korrels aanleiding gegee het, nie korrelgrootte, soos by wyndruiwe, bevorder het nie. Hoër NO3 - in die grond (water), na aanleiding van N toedienings, het aanleiding gegee tot hoer vlakke van N in die korrels. Dit het plaasgevind ten spyte van sub-optimale grond pH wat deur die oormatige N toedienings veroorsaak is. Korrel K konsentrasie en -inhoud is deur K-bemesting verhoog. Vinnige opname en translokasie van K na die korrels het ook geblyk die rede te wees waarom die verlaagde voedingstatus van die stokke a.g.v. oorbemesting met N nie die korrels se K inhoud geaffekteer het nie. Die vinnige groeitempo van die korrels, tesame met lae vlakke van Ca opname, asook korrels se Ca opname wat tydens rypwording ophou, word as die redes vir die tekorte aan behandelingseffekte beskou. Lae vlakke van bederf, asook ‘n tekort aan betroubare tendense dat bederf deur Nbemesting verhoog word, is verkry. Daar moet vasgestel word of daar N vlakke in die korrels is waarbo hul vatbaarheid vir swaminfeksies verhoog word, en of daar spesifieke N verbindings is wat die korrels meer vatbaar maak vir bederf. Indikasies dat K-bemesting interne verbruiningsvlakke verhoog het, regverdig verdere ondersoek. Korrelkwaliteit is nie deur grond- of trosgerigte toedienings bevoordeel nie. Die negatiewe effek van oormatige bemesting op die chemiese samestelling van sandgronde is weer deur hierdie navorsing uitgelig. Dit lei tot oneffektiewe bemesting en ‘n tekort aan die verlangde effekte. Blaarontledings blyk onbetroubaar te wees as aanduiding van voedingstof beskikbaarheid. Dit moet evalueer word saam met grondontledings en ook seisoenale variasie in ag neem. Die gevaar om slegs deur gepubliseerde norme gelei te word wanneer bemestingspraktyke bepaal word, is weer deur hierdie navorsing uitgelig. Voorst is daar in hierdie navorsing gevind dat voedingstof akkumulasiepatrone van ‘n baie vroeë kultivar soos Prime Seedless alreeds voor deurslaan begin verander a.g.v. omgewingstoestande en korrelgroei wat tot ‘n veel hoër vleis:dop verhouding aanleiding gee. Toekomstige navorsing op tafeldruiwe behoort die faktore en dinamika wat voedingstofkonsentrasie en -akkumulasie in korrels van vroeë, groot korrel, pitlose tafeldruifkultivars beïnvloed verder te ondersoek.

Thesis (MScAgric)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The declaration of Namibia’s independence from South Africa in 1990 has seen the Namibian government aim to plan and implement development programmes that enhance a growing agricultural sector. The new government is facing challenges regarding the addressing of inequalities of income and the allocation and distribution of resources, which have resulted in implementation of the land reform programmes. On the international front, Namibia is a member country of various trade arrangements, such as the WTO, the SADC and SACU. The main driving force behind Namibia’s joining the international communities chiefly has been market access and trade policy reforms. The country’s agricultural sector, in particular the horticultural industry, in regards to table grape production, has been significantly affected by both domestic and regional policies, as well as by the WTO rules. The aim of this study is to determine the environmental factors that create a competitive advantage for the Namibian table grape industry in the international market. A detailed supply-chain analysis, augmented by Porter’s ‘diamond’ model, is used in this study to assess the determinants of the competitiveness of fresh table grapes. Interviews were conducted in informal, semi-structured questions. The questionnaires were mailed to several producers within the table grape-growing industry. Secondary information was obtained from reports, articles and research publications, among other sources. An expert assessment was used to verify information based on the reference methods. Consultations took place in the form of office visits and, in some cases, telephone interviews were held with different experts. The finding of the study shows that Namibia can supply the European markets during the northern hemisphere off-season with quality fresh table grapes. However, industry growth in the European Union (EU) market is constrained by limited free import quotas and high tariffs, specifically as regards seeded fresh table grapes, which are not exempt from such duties. Such constraints are in place despite Namibia’s meeting of international set quality standards, such as EUREPGAP. Moreover, there is potential for increasing supplies to the regional and Asian markets as well as the US market albeit to the lesser extent. Finally, Namibian fresh table grapes profitability is significantly affected by the high production and transaction costs incurred, as well as by the decline in business and the depreciation of the US Dollar against the Namibian Dollar. The study makes the general recommendation that producers should significantly reduce their transaction costs within the chain, by means of vertical co-ordination and integration. / AFRIKAANSE OPSOMMING: Met die verklaring van Namibië se onafhanklikheid van Suid-Afrika in 1990 het die Namibiese regering hulle dit ten doel gestel om ontwikkelingsprogramme te beplan en in werking te stel ten einde daardie land se groeiende landbousektor te versterk. Die nuwe regering moet tans uitdagings met betrekking tot inkomsteongelykhede en die toekenning en verspreiding van hulpbronne die hoof bied wat tot die inwerkingstelling van grondhervormingsprogramme aanleiding gegee het. Internasionaal is Namibië 'n lidland van verskeie handelsreëlings soos die Wêreldhandelsorganisasie (WHO), die Suider-Afrikaanse Ontwikkelingsgemeenskap (SAOG) en die Suider-Afrikaanse Doeane-unie (SADU). Die twee hooffaktore wat daartoe gelei het dat Namibië hom by die internasionale gemeenskappe skaar, is marktoegang en handelsbeleidhervormings. Die land se landbousektor, in besonder die tuinboukundige bedryf met die klem op tafeldruifproduksie, is aansienlik deur binnelandse en streeksbeleid asook deur die WHO-reëls geraak. Die doel van hierdie studie is om die omgewingsfaktore te bepaal wat in die internasionale mark aan die Namibiese tafeldruifbedryf 'n mededingende voordeel gee. Derhalwe gebruik die navorser 'n gedetailleerde aanvoerkettingontleding, ondersteun deur Porter se “diamantmodel”, om die beslissende faktore vir die mededingendheid van vars tafeldruiwe te evalueer. Onderhoude is met behulp van informele, semigestruktureerde vrae gevoer. Die vraelyste is aan verskeie produsente op die gebied van tafeldruifboerdery gepos. Sekondêre inligting is ook onder andere uit verslae, artikels en navorsingspublikasies verkry. Met behulp van 'n kundige evaluering is inligting op grond van die verwysingsmetodes geverifieer. Oorlegpleging met verskeie kundiges het in die vorm van kantoorbesoeke en in sommige gevalle deur middel van telefoononderhoude plaasgevind. Die studiebevinding toon dat Namibië die Europese markte gedurende die noordelike halfrond se tussenseisoen van gehalte- vars tafeldruiwe kan voorsien. Die uitbreiding van die bedryf in die Europese Unie (EU-) mark word egter deur beperkte gratis invoerkwotas en hoë tariewe aan bande gelê, in besonder met betrekking tot pitlose, vars tafeldruiwe wat nie van invoerbelasting vrygestel is nie. Hierdie beperkinge word opgelê ten spyte daarvan dat Namibië aan vasgestelde internasionale gehaltestandaarde soos EUREPGAP voldoen. Die moontlikheid bestaan boonop om lewering aan die streeks- en Asiatiese markte asook die VS-mark te verhoog, hoewel in 'n mindere mate. Laastens word die winsgewendheid van Namibiese vars tafeldruiwe beduidend deur hoë produksie- en transaksiekoste, asook deur die afname in sake en die waardevermindering van die Amerikaanse teenoor die Namibiese dollar geraak. Die studie maak die algemene aanbeveling dat produsente hulle transaksiekoste binne die ketting aansienlik met behulp van vertikale koördinering en integrasie moet verminder.

Thesis (MBA (Business Management))--University of Stellenbosch, 2010.

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: In the field of agriculture, plant pathogens are a major concern because of the severe damage these organisms cause to crops yearly. Fundamental studies regarding plant pathogens and their modes of action made it possible for researchers in the field of molecular biology to investigate pathogens further on a molecular level. Botrytis cinerea, has been used to great effect as a model system to investigate various aspects regarding pathogenesis, also on a molecular level. Molecular research done on B. cinerea over the last few years has shown that the endopolygalacturonases (EPGs) of this fungus are key role players in pathogenesis. This hydrolytic enzyme family of six members, encoded by the Bcpg1-6 genes, are important in breaking down the complex cell wall polymers of host plants, enabling the fungus to penetrate its host sufficiently. It has been shown that both BcPG1 and 2 are crucial for virulence of B. cinerea. A leucine-rich repeat inhibitor protein situated in the cell wall of various plant species, the polygalacturonase-inhibiting protein (PGIP), has been proven to interact with and inhibit EPGs, and thus the necrotic actions of B. cinerea. From literature it was clear that specific data regarding individual interactions of fungal EPGs with PGIPs are lacking currently. Furthermore, most experiments regarding the effects of EPG as well as interaction and inhibition studies of EPGs and PGIPs, rely on in vitro methods, without the possibility to contextualize the results on an in vivo or in planta level. The scope of this study was to specifically address the issues of individual EPG:PGIP interactions and the use of possible in vivo methodology by using EPGs from a highly virulent South African strain of B. cinerea and the grapevine VvPGIP1 that has been previously isolated in our laboratory. This PGIP, originally isolated from Vitis vinifera cv Pinotage, has been shown to inhibit a crude EPG extract from this strain with great efficiency. The approach taken relied on heterologous over-expression of the individual Bcpg genes and the isolation of pure and active enzymes to evaluate the inhibition of the EPGs with VvPGIP1. The genes were all successfully over-expressed in Saccharomyces cerevisiae with a strong and inducible promoter, but active enzyme preparations have been obtained only for the encoding Bcpg2 gene, as measured with an agarose diffusion assay. The in vitro PGIP inhibition assay is also based on the agarose diffusion assay and relies on activity of the EPGs to visualize the inhibiting effect of the PGIP being tested. The active EPG2, however, was not inhibited by VvPGIP1 when tested with this assay. The EPG encoding genes from B. cinerea were transiently over-expressed also in Nicotiana benthamiana by using the Agrobacterium-infiltration technique. Transgene expression was confirmed by Northern blot analysis and EPG-related symptoms were observed five to eight days post-infiltration. Differential symptoms appeared with the various EPGs, providing some evidence that the symptoms were not random events due to the infiltration or a hypersensitive response. Moreover, the symptoms observed for EPG2 was similar to those that were reported recently by another group on the same host. In spite of the expression data and the clear symptoms that developed, active preparations, as measured with the agarose diffusion plate asay, could only be obtained for EPG2 again. In our search for a possible in vivo method to detect and quantify EPG activity and inhibition by PGIPs, we tested and evaluated a technique based on chlorophyll fluorescence to detect the effect of EPGs on the rate of photosynthesis. Our results showed that the over-expression of these genes reduced the rate of electrons flowing through photosystem II, indicating metabolic stress occurring in the plant. We used the same technique to evaluate possible interaction between VvPGIP1 respectively with BcPG1 and 2 and found that the co-expressing of the Vvpgip1 gene caused protection of the infiltrated tissue, indicating inhibition of EPG1 and 2 by VvPGIP1. For EPG2, the observed interaction and possible inhibition by VvPGIP1 is the first report to our knowledge of an interaction between this specific EPG2 and a PGIP. Moreover, to further elucidate the in planta interaction between VvPGIP1 and the EPGs from the South African B. cinerea strain, we tested for possible interactions by making use of a plant two-hybrid fusion assay, but the results are inconclusive at this stage. Previous studies in our laboratory have shown that several natural mutations exist between PGIP encoding genes from different V. vinifera cultivars. Based on this finding and the fact that these natural mutations could result in changes with regard to EPG inhibition and ultimately disease susceptibility, we isolated an additional 37 PGIP encoding genes from various grapevine genotypes, some of which are known for their resistance to pathogens. Combined, these results make a valuable contribution to understand plant pathogen interactions, specifically in this case by modeling the interactions of pathogen and plant derived proteins. The possibility to use in vivo methods such as chlorophyll fluorescence to follow these interactions on an in planta level, provides exciting possibilities to strenghten and contextualize in vitro results. / AFRIKAANSE OPSOMMING: Plantpatogene organismes veroorsaak jaarliks erge skade aan landbougewasse en word dus as ’n ernstige probleem in die landbousektor beskou. Diepgaande studies wat handel oor plantpatogene en hul metodes van infeksie het dit vir molekulêre bioloë moontlik gemaak om patogene nou ook op molekulêre vlak verder te bestudeer. Botrytis cinerea is baie effektief as modelsisteem gebruik om verskeie aspekte van patogenese verder te bestudeer, ook op ‘n molekulêre vlak. Molekulêre navorsing op B. cinerea, het getoon dat die endopoligalakturonases (EPGs) van dié swam kernrolbelangrik in patogenese is. Hierdie sesledige hidrolitiese ensiemfamilie word gekodeer deur die Bcpg1-6 gene en is belangrik vir die afbraak van die komplekse selwandpolimere van plantgashere, om suksesvolle gasheerpenetrasie te veroorsaak. Daar is aangetoon dat beide BcPG1 en 2 essensieël vir virulensie van die patogeen is. ’n Leusienryke-herhalings inhibitorproteïen wat in die selwand van verskeie plantspesies voorkom, die poligalakturonase-inhiberende proteïen (PGIP), het interaksie met en inhibeer EPGs en gevolglik ook die nekrotiserende aksies van B. cinerea. Uit die literatuur is dit duidelik dat spesifieke inligting aangaande individuele interaksies van fungiese EPGs met PGIPs tans nog ontbreek. Verder word daar op in vitro metodologie staatgemaak wannneer die effekte van EPGs asook die interaksie en inhibisie met PGIPs bestudeer word, sonder om die konteks van die in vivo- of in planta-omgewing in ag te neem. Die fokus van hierdie studie was om aspekte van individuele EPG:PGIP interaksies, asook die moontlike gebruik van in vivo metodologie te bestudeer deur EPGs, afkomstig van ’n hoogs virulente Suid-Afrikaanse ras van B. cinerea en die wingerd VvPGIP1, wat vroeër in ons laboratorium geïsoleer is, te gebrruik. Hierdie PGIP wat uit Vitis vinifera cv Pinotage geïsoleer is, inhibeer ’n kru EPG-ekstrak van bogenoemde ras baie effektief. Die benadering wat gevolg is het op die ooruitdrukking van die individuele Bcpg-gene in heteroloë sisteme staatgemaak en die gevolglike isolering van suiwer en aktiewe ensieme om EPG-inhibisie deur VvPGIP1 te beoordeel. Al die gene is suksesvol in Saccharomyces cerevisiae ooruitgedruk onder ’n sterk induseerbare promotor, maar volgens ’n agarose-diffundeerbare toets kon aktiewe ensiempreparate slegs vir die enkoderende Bcpg2 verkry word. Die in vitro PGIP-inhibisie toets is ook op die gemelde toets gebasseer en vereis EPG-aktiwiteit om die inhiberende effek van die PGIP, te visualiseer. Die aktiewe EPG2 is egter nie deur VvPGIP1 geïnhibeer met die aanleg van hierdie toets nie. Die EPG-enkoderende gene van B. cinerea is ook tydelik in Nicotiana benthamiana ooruitgedruk deur gebruik te maak van ’n Agrobacterium-infiltrasietegniek. Transgeenuitdrukking kon met die Noordelike kladtegniek bevestig word en EPG-verwante simptome is vyf tot agt dae na infiltrasie waargeneem. Verskillende simptome vir die verskillende EPGs is waargeneem, wat aanduidend is dat die simptome nie lukrake gevolge van die infiltrasies, of ’n hipersensitiewe respons is nie. Verder kon die simptome wat EPG2 vertoon het, gekorreleer word met dié wat onlangs deur ’n ander groep op dieselfde gasheer waargeneem is. Ten spyte van die ekspressiedata en die waargenome simptome, kon aktiewe ensiempreparate op die agarose-diffundeerbare toets, weereens slegs vir EPG2 waargeneem word. ’n Metode wat gebasseer is op chlorofilfluoressensie is getoets en geëvalueer as ’n moontlike in vivo metode om EPG aktiwiteit en inhibisie deur PGIPs waar te neem en te kwantifiseer. Die resultate het bevestig dat die ooruitdrukking van hierdie gene die elektronvloeitempo deur fotosisteem II verminder het wat ’n aanduiding is dat metaboliese stres in die plant heers. Dieselfde tegniek is gebruik om die moontlike interaksies tussen BcPG1 en 2 en VvPGIP1 te bestudeer en het aangetoon dat die mede-uitdrukking van die Vvpgip1-geen aanleiding gee tot ’n beskermende effek van die geinfiltreerde weefsel, wat aanduidend is van inhibisie van EPG1 en 2 deur VvPGIP1. In die geval van EPG2 is hierdie interaksie en moontlike inhibisie met ’n PGIP die eerste waarneming in die verband. In ’n verdere poging om die in planta-interaksie tussen VvPGIP1 en die EPGs van die Suid-Afrikaanse B. cinerea ras uit te klaar, is ’n plantgebasseerde twee-hibriede toets aangelê, maar geen klinkklare resultate kon verkry word nie. Vorige werk het bevestig dat verskeie natuurlike mutasies in PGIP-enkoderende gene, afkomstig van verskillende V. vinifera kultivars, voorkom. Hierdie resultaat en die feit dat hierdie mutasies verskille in EPG inhibisie en uiteindelik vatbaarheid vir siektes kan beïnvloed, het aanleiding gegee tot die isolering van ’n verdere 37 PGIP-enkoderende gene uit ‘n verskeidenheid druifplantgenotipes, sommige waarvan juis bekend vir hul weerstand teen patogene is. Die gekombineerde resultate wat in dié studie verkry is, maak ’n waardevolle bydrae tot die verstaan van plant-patogeeninteraksies, spesifiek met die modelering van interaksies van patogeen- en plantgebasseerde proteïene. Die moontlikheid om in vivo-metodes soos chlorofilfluoressensie te gebruik in in planta-analises, is besonder bemoedigend om in vitro-resultate te versterk en ook in konteks te plaas.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Grapevine water status is considered to be the most important factor limiting plant growth and production in the Mediterranean zones. In these regions with limited summer rainfall and limited water resources for irrigation grapevines may experience water deficits for an extended period of time. The demand of water for agriculture is constantly increasing, and will continue to do so due to the rise in the world population and to the effects of climate change on rainfall and evaporative demand in these regions. The Western Cape wine region is also classified as Mediterranean and grapevines grown in this region are often exposed to water “stress” conditions due to high evaporative demand and low water availability in the soil. Plant water status of grapevines may dependent on, amongst other factors, the water potential of soil layers close to the root system, canopy size and evaporative demand. The canopy size of a grapevine can inherently be seen as a measure of grapevine vigour, and vigour variation among grapevines within a vineyard is a common phenomenon in the Western Cape. The importance of the contributions from several factors causing vigour variation within vineyards is still a subject of debate. This may be largely ascribed to the significant amount of variability in vineyards that researchers have to deal with during viticultural studies. However, the recent advances in remote sensing technology have established new methods to assess grapevine vigour variability. In the face of the recognized variation within vineyards and the importance of a sustained grapevine water status, for wine grape productivity and -quality, it is alarming to think that a vineyard block is generally managed as a homogeneous entity when it comes to irrigation scheduling. What is more alarming is the assumption that grape, juice and wine quality will be homogeneous throughout a vineyard block – even without irrigation. With this in mind, a study was conducted to study the interaction between grapevine vigour and grapevine water status within a commercial vineyard with variable vigour by implementing various irrigation regimes. Vigour variation was identified through multispectral aerial imagery and plant-based water status determinants were used to assess grapevine water status in plots of differing vigour within the vineyard. Soil water status was also assessed, and vegetative growth quantified to ultimately determine the variability in vigour and its possible contribution to the variability through the water status of the plant. Reproductive growth was monitored continually before evaluating the effect of water status and grapevine vigour on grape composition and subsequent wine quality. The various methods used to evaluate grapevine vigour showed good correspondence. Pruning mass measured at the end of the season confirmed leaf area measurement (main leaves and lateral leaves) during vegetative growth, and corresponded well, in terms of main vigour classifications with the NDVI images collected. Berry weight and volume responded to the various classifications, with a decrease in water deficits from one classification to the next accompanying an increase in berry weight and volume. Analyses of the berry composition and wines showed statistically significant differences between the classifications. This was found for sugar content per berry, total phenols, total red pigment, malic acid, nitrogen and pH for the grape juice analyses. Wine pH and total acidity also differed significantly. / AFRIKAANSE OPSOMMING: In die Mediterreense sones word plantwaterstatus beskou as `n hooffaktor wat groei en produksie van `n wingerdstok negatief beinvloed. In hierdie sones kan wingerdstokke vir lang periodes `n tekort aan water ervaar a.g.v `n tekort aan reënwater gedurende die somer en lae beskikbaarheid van besproeingswater. Die vraag na water vir landbou is ook konstant besig om toe te neem in dié sones en die tendens sal voorduur a.g.v die groei in die wêreldbevolking, die effek van klimaatsveranderig op reënvalpatrone en die hoë verdampingsfaktor. Die wingerd- en wynstreek van die Wes-Kaap word ook geklassifiseer as Mediterreens en wingerdstokke in hierdie streek ervaar dikwels waterspanning wat deur hoë evapotranspirasie en min beskikbare grondwater veroorsaak word. Van die faktore wat die waterstatus van `n wingerdstok bepaal is onder andere die waterpotensiaal van die grondlae rondom die wortelstelsel, die grootte van die wingerdlowerraamwerk en die evapotranspirasiebehoefte. Die omvang van `n wingerdstok se lower binne die prieel word beskou as `n aanduiding van wingerdstokgroeikrag en variasie in groeikrag tussen wingerdstokke is `n algemene verskynsel in die Wes-Kaap. Die rangorde, wat die effek van die verskeie faktore wat groeikragvariasie tussen wingerdstokke bepaal, word steeds gedebatteer. Die debat kan groottendeels toegeskryf word aan die beduidende hoeveelheid variasie tussen wingerde waarmee navorsers te doen kry in wingerdkundige studies. Hoewel, met onlangse vordering aangaande afstandswaarnemingstegnologie is daar nou nuwe metodes beskikbaar om wingerdgroeikrag te evalueer. Dit is kommerwekend om te dink dat `n wyndruifwingerd normaalweg as `n homogene eenheid bestuur word as dit kom by besproeiing. Veral met die wete dat groeikragvariasie tussen wingerde algemeen erken en aangeteken word, en dat volhoubare waterstatus van `n wingerdstok van kardinale belang is vir produksie en kwaliteit van wyndruiwe. Die aanname dat wyndruiwe, die sap- en ook wynkwaliteit homogeen sal wees regdeur `n wingerdblok is egter meer kommerwekkend. Na aanvang van dié denke is daar `n studie geloods om die interaksie tussen wingerdstokgroeikrag en wingerdstokwaterstatus te evalueer. Met die studie is verskeie besproeiingsregimes aangebring binne `n kommersiële wingerd wat interne groeikragvariasie tentoonstel. Groeikragvariasie was geïdentifiseer deur middel van multispektrale lugfotos terwyl die wingerdstok se waterstatus geëvalueer is met behulp van plantgebaseerde metings in die verskillende groeikragareas. Die waterstatus van die grond is geëvalueer tesame met die vegetatiewe groei van die wingerd sodat die groeikragvariasie en die invloed van die plantwaterstatus op die groeikrag bepaal kon word. Die reproduktiewe groei is deurlopend gemonitor voor die effek van wingerdstokwaterstatus en wingerdstokgroeikrag op druifsamestelling en wynkwaliteit bepaal is. Daar was `n goeie ooreenkoms tussen die verskeie metodes wat gebruik is om wingerdgroeikrag te bepaal. Snoeimassa aan die einde van die seisoen was ooreenkomstig met die blaaroppervakte (hooflootblare en sylootblare) wat tydens vegetatiewe groei gemeet is, en het ook goed korreleer, met die multispektrale lugfotos se hoof groeikragklassifikasie. Korrelgewig en -volume het reageer op die verskeie besproeiingsregimes, en daar was `n toename in korrelgewig en -volume saam met die afname in watertekort van een regime tot `n ander. Daar was beduidende verskille tussen die verskeie klassifikasies t.o.v. korrelsamestelling analise en wynevaluasie. Die suikerinhoud per korrel, totale fenole, totale rooi pigment, appelsuur, stikstof en pH het verskil in druiwesap analises. Die pH en suur van die wyne het ook beduidend verskil.