Complete vineyard floor cover cropping and root pruning (RP) were evaluated for their ability to regulate excessive vegetative growth and improve berry and wine composition of ‘Cabernet Sauvignon’ (Vitis vinifera L.). Treatments were: tall fescue (Festuca arundinacea Shreb.) ‘KY-31’ and ‘Elite II’, hard fescue (Festuca ovina L.) ‘Aurora Gold’, perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), and an under-trellis herbicide strip combined with KY-31fescue interrows. Compared to herbicide strip/non-root pruned (NRP), Elite II fescue reduced vine pruning weight (kg/vine) 28%, individual cane weight (g) 20%, and canopy leaf layer number 25%. KY-31 fescue/RP lowered vine pruning weights 29% compared to an 8% reduction in pruning weights of vines grown in herbicide strip/NRP plots from 2005 to 2010. KY-31 fescue produced the greatest biomass and stand density. With the exception of a yield reduction in vines grown with KY-31 fescue in 2006, cover crops minimally decreased grape yield. Yearly climatic variation had a greater effect on berry weight and composition (pH, TSS, TA) than did treatments. Limited treatment differences detected in chemical compounds by gas chromatography–mass spectrometry (GC-MS) analysis in wines made from treatment vines in 2010 were correlated to descriptive sensory terms. Cover crop water use, as evapotranspiration, determined by mini-lysimeter (ML), ranged from 3.28 mm/d for KY-31 fescue to 1.52 mm/d for herbicide-treated plots. In 2008, root biomass of vines grown on KY-31 fescue/RP was increased at the 60 to 80 and 80 to 100 cm soil depths compared to root biomass of KY-31 fescue/NRP vines at those depths. Cover crops minimally impacted vine water potential (ΨPD, Ψmd, Ψstem) and grapevine nitrogen levels relative to the herbicide strip, indicating that the grasses were not overly competitive with grapevines. Root pruning and complete vineyard floor cover crops favorably reduced grapevine vegetative growth, although treatment effects diminished over time, possibly in response to redistribution of grapevines’ roots and climatic variation at the site. / Ph. D.

Crown gall of grapevine (Vitis spp.) is a serious and economically important disease caused by the bacterial pathogen Rhizobium vitis, which transforms healthy plant cell genomes leading to hypertrophic and hyperplastic growth of affected plant cells. Recent studies have documented a strong inhibitory effect against Japanese tumorigenic R. vitis isolates by a newly identified non-tumorigenic strain of R. vitis, ARK-1. We conducted co-inoculation assays in tomato (Solanum lycopersicum) and wine grape cultivars (Vitis vinifera) with four tumorigenic isolates of R. vitis from Virginia. These tumorigenic isolates were co-inoculated with ARK-1 in various ratios and resulting gall incidence and gall size were measured. Analysis was conducted with the generalized linear mixed model (GLIMMIX) in SAS (ver. 9.4). ARK-1 significantly reduced both the mean probability of gall formation and the mean gall size (P < 0.05). ARK-1 efficacy against combinations of two or four tumorigenic isolates and up to twice as many cells of tumorigenic isolates was also significant. However, there was an indication of a loss of efficacy when ARK-1 was challenged with four isolates at four times the cell number of ARK-1. Also, the efficacy of ARK-1 was influenced by both the specific isolate and host plant used in the study. Our results suggest that ARK-1 has promising potential as an effective biological control agent for grapevine crown gall in the United States. / MSLFS / Crown gall of grapevine (Vitis species) is a serious and economically important disease to the grape production industry caused by the bacterium Rhizobium vitis. This pathogen alters the genetic material of plant cells leading to cancer-like growth of affected plant cells (tumors); which may lead to the death of a grapevine. Recently, a non-tumor inducing strain of R. vitis (ARK-1) was documented to inhibit gall induction by tumor-inducing R. vitis strains in Japan. To see if ARK-1 would be a good candidate for biological control of the tumor-causing strains of R. vitis in the US, we tested it against four tumor-inducing strains in both tomato (Solanum lycopersicum) and grapevine (Vitis vinifera). The tumor-inducing strains were mixed with ARK-1, injected into plant stems in various ratios, and resulting gall incidence and gall size were measured 42 to 90 days later. ARK-1 significantly reduced both the probability of gall formation and the gall size in both tomatoes and grapevines. ARK-1 was an effective agent against mixtures of one, two, or four tumor-inducing strains and provided control even when outnumbered two to one by cells of tumor-inducing strains. The efficacy of ARK-1 was influenced by the specific strain, relative cell number to tumor-inducing strains, and host plant used in the study. Our results suggest that ARK-1 has promising potential as an effective biological control agent for grapevine crown gall in the United States.

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.

Thesis (MScAgric)--Stellenbosch University, 2014 / ENGLISH ABSTRACT: The objective of the study was to determine combined effects of irrigation and canopy management practices on grapevine water status, growth, yield and juice characteristics. The field study was carried out with Shiraz/110R grapevines in the Breede River Valley. Grapevines were drip irrigated at 30%, 60% and 90% plant available water (PAW) depletion, respectively. For each PAW level, grapevines had (i) suckered, vertical shoot positioned (VSP), (ii) non-suckered, VSP and (iii) sprawling canopies. Treatments were replicated three times in a randomised block design and applied during the 2011/12 and 2012/13 seasons. Irrigation applied at low PAW depletion levels, i.e. high frequency irrigation, required substantially higher irrigation volumes compared to high depletion levels, i.e. low frequency irrigation. Low frequency irrigation increased grapevine water constraints compared to high frequency irrigation. Sprawling canopy grapevines experienced more water constraints than VSP grapevines. Grapevines irrigated at 90% PAW depletion experienced strong water constraints. Low frequency irrigation seemed to accelerate berry ripening compared to high frequencies, probably due to smaller berries and lower yields. Sprawling canopies consistently enhanced berry ripening due to more sunlight interception by the leaves. Berry ripening of VSP grapevines was slower, but inconsistent between seasons. Level of PAW depletion and canopy management practice did not affect number of leaves per primary shoot. Low frequency irrigation reduced number of leaves per secondary shoot. Leaf number per shoot contributed more to total leaf area than leaf size. Level of PAW depletion did not affect number of shoots per grapevine. Suckering reduced number of shoots per grapevine. Low frequency irrigation reduced total leaf area per grapevine compared to high frequency irrigation. Effects of canopy management practice were more pronounced in the case of high frequency irrigation compared to low frequency irrigation. At pruning, primary cane length was not affected by level of PAW depletion or canopy management practice. Secondary cane mass and diameter were not affected by canopy management practice. Multiple linear regression showed that cane mass was a function of cane length and diameter. Low frequency irrigation reduced berry mass compared to high frequency irrigation, irrespective of canopy management practice. However, at harvest there was no difference in berry mass between 30% and 60% PAW depletion. Low irrigation The objective of the study was to determine combined effects of irrigation and canopy management practices on grapevine water status, growth, yield and juice characteristics. The field study was carried out with Shiraz/110R grapevines in the Breede River Valley. Grapevines were drip irrigated at 30%, 60% and 90% plant available water (PAW) depletion, respectively. For each PAW level, grapevines had (i) suckered, vertical shoot positioned (VSP), (ii) non-suckered, VSP and (iii) sprawling canopies. Treatments were replicated three times in a randomised block design and applied during the 2011/12 and 2012/13 seasons. Irrigation applied at low PAW depletion levels, i.e. high frequency irrigation, required substantially higher irrigation volumes compared to high depletion levels, i.e. low frequency irrigation. Low frequency irrigation increased grapevine water constraints compared to high frequency irrigation. Sprawling canopy grapevines experienced more water constraints than VSP grapevines. Grapevines irrigated at 90% PAW depletion experienced strong water constraints. Low frequency irrigation seemed to accelerate berry ripening compared to high frequencies, probably due to smaller berries and lower yields. Sprawling canopies consistently enhanced berry ripening due to more sunlight interception by the leaves. Berry ripening of VSP grapevines was slower, but inconsistent between seasons. Level of PAW depletion and canopy management practice did not affect number of leaves per primary shoot. Low frequency irrigation reduced number of leaves per secondary shoot. Leaf number per shoot contributed more to total leaf area than leaf size. Level of PAW depletion did not affect number of shoots per grapevine. Suckering reduced number of shoots per grapevine. Low frequency irrigation reduced total leaf area per grapevine compared to high frequency irrigation. Effects of canopy management practice were more pronounced in the case of high frequency irrigation compared to low frequency irrigation. At pruning, primary cane length was not affected by level of PAW depletion or canopy management practice. Secondary cane mass and diameter were not affected by canopy management practice. Multiple linear regression showed that cane mass was a function of cane length and diameter. Low frequency irrigation reduced berry mass compared to high frequency irrigation, irrespective of canopy management practice. However, at harvest there was no difference in berry mass between 30% and 60% PAW depletion. Low irrigation. / AFRIKAANSE OPSOMMING: Die doelwit van hierdie studie was om die gekombineerde effek van besproeiing en lowerbestuurspraktyke op wingerd waterstatus, groei, opbrengs en druiwesap eienskappe te bepaal. Die veld studie is uitgevoer met Shiraz/110R wingerdstokke in die Breede Rivier Vallei. Wingerdstokke was d.m.v. drupbesproeiing teen 30%, 60% en 90% plant beskikbare water (PBW) ontrekking, onderskeidelik besproei. Vir elke PBW ontrekkingspeil, was wingerdstokke (i) gesuier en vertikale lootposisionering toegepas, (ii) ongesuier en vertikale lootposisionering toegepas en (iii) geen lowerbestuur toegepas nie (lowers wat oophang). Behandelings is drie keer in ‘n ewekansige blokontwerp herhaal en tydens die 2011/12 en 2012/13 seisoene toegepas. Besproeiing wat teen ‘n lae PBW ontrekkingspeil toegedien is, d.w.s. hoë frekwensie besproeiing, vereis aansienlik hoër besproeiings volumes i.v.m. hoë besproeiing ontrekkingspeile, d.w.s. lae frekwensie besproeiing. Wingerdstokke wat oopgehang het meer watertekorte as vertikaal lootgeposisioneerde wingerdstokke ervaar. Wingerdstokke wat teen 90% PBW ontrekking besproei was, het sterk watertekorte ervaar. Dit het voorgekom of lae frekwensie besproeiing korrelrypwording versnel het i.v.m. hoë frekwensie besproeiing. Dit was heelwaarskynlik a.g.v. kleiner korrels en laer opbrengste. Wingerdstokke wat oophang het, het konsekwent korrelrypwording versnel a.g.v. meer sonligonderskepping deur die blare. Korrelrypwording van vertikaal lootgeposisioneerde wingerdstokke was stadiger, maar teenstrydig tussen die seisoene. Plant beskikbare water ontrekkingspeil en lowerbestuurspraktyke het geen invoeld gehad op die aantal blare per primêre loot nie. Lae frekwensie besproeiing het die aantal blare per sekondêre loot verminder. Die hoeveelheid blare per loot het ‘n groter bygedra gemaak i.v.m. blaar grootte. Plant beskikbare water ontrekkingspeil het geen invloed gehad op die aantal lote per wingerdstok nie. Suier verminder die aantal lote per wingerdstok. Lae frekwensie besproeiing verminder die totale blaar oppervlak i.v.m. hoë frekwensie besproeiing. Die effek van lowerebestuurspraktyke is duideliker sigbaar by hoë frekwensie besproeiing i.v.m. lae frekwensie besproeiing. Primêre lootlengte was nie deur PBW ontrekkingspeil of lowerbestuurspraktyke beïnvloed nie. Sekondêre lootmassa en -deursnit is nie deur lowerbestuurspraktyk beïnvloed nie. Meervoudige lineêre regressie het getoon dat lootmassa ‘n funksie van lootlengte en -deursnit was. Lae frekwensie besproeiing het korrelmassa verminder ongeag die lowerbestuurspraktyk i.v.m. hoë frekwensie besproeiing. Daar was egter geen verskil in korrelmassa by oes tussen 30% en 60% PBW ontrekking nie. Lae frekwensie besproeiing was geneig om suiker akkumulasie te versnel i.v.m. hoë frekwensie besproeiing. Wingerdstokke wat oopgehang het, het veral by lae frekwensie besproeiing korrelrypwording versnel i.v.m. vertikaal lootgeposisioneeide wingerdstokke. Suikerinhoud per korrel het geneig om toe te neem totdat dit ‘n plato bereik het. Hierdie plato was meer prominent by hoë frekwensie besproeiing i.v.m. lae frekwensie besproeiing. Wingerdstokke wat oopgehang het, het ook hierdie plato vroeër bereik i.v.m. vertikaal lootgeposisioneerde wingerdstokke. By oes was die totale titreerbare suur (TTS) hoër vir wingerdstokke wat vroeër geoes was. As gevolg van versnelde rypwording was TTS van wingerdstokke wat teen lae frekwensie besproei is hoër i.v.m. hoë frekwensie besproeiing. ‘n Ligter oeslading in verhouding tot ‘n hoër blaaroppervlak het ook gelei tot hoër TTS by oes. Plant beskikbare water ontrekkingspeil en lowerbestuurspraktyke het geen invloed op die pH gehad met oes nie. Die hoeveelheid trosse per wingerdstok het nie duidelike tendense gewys wat verbind kon word met watertekorte wat deur die stokke ervaar is nie. Gesuierde vertikaal lootgeposisioneerde wingerdstokke het die hoeveelheid trosse per stok verminder i.v.m. die ongesuierde vertikaal lootgeposisioneerde wingerdstokke en wingerstokke wat oopgehang het. Trosmassa het dieselfde tendense as korrels per tros gevolg. Lae frekwensie besproeiing het opbrengs aansienlik verminder i.v.m. hoë frekwensie besproeiing. Gesuierde vertikaal lootgeposisioneerde wingerdstokke het geneig om opbrengste te verminder i.v.m. ongesuierde vertikaal lootgeposisioneerde wingerdstokke. Hierdie effek het egter verdwyn waar wingerdstokke teen 90% PBW ontrekking besproei was. Druif skade a.g.v. suurvrot was meer prominent by hoë frekwensie besproeiing, veral vir ongesuierde vertikaal lootgeposisioneerde wingerdstokke. Total opbrengs verlies, uitgedruk as ‘n persentasie, was hoofsaaklik ‘n funksie van sonbrand eerder as ‘n funksie van suurvrot.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Irrigation scheduling decisions are based either on the direct measurement of soil water status (SWS) or on physiological measurements like plant water status (PWS). Soil based measurements are quick and easily automated, but the plant response for a particular quantity of soil moisture varies as a complex function of evaporative demand. A plant-based approach measures the plant stress response directly, but is an integration of environmental effects as well. In contrary to soil-based methods, plant based measurements can indicate when to irrigate, but not the quantity. Pre-dawn leaf water potential (ΨPD) is determined mostly by the soil moisture level, and can serve as a measure of static water stress in plants and an index of bulk soil water availability or even as an estimate of soil water potential at the root surface. Therefore it should be possible to establish a link between SWS and PWS, but it is largely unknown how stable the link in a heterogeneous vineyard would be, and how the grapevine vegetative and reproductive response relates to this link. Plant water status plays a large role in determining vigour and yield of the plant. The levels of PWS are influenced by irrigation, but it was mostly affected by the season and vine location in the vineyard. More negative plant water potentials reduced vigour, but had a less pronounced effect on yield, while also reducing overall wine quality. Vigour variability in the vineyard was largely attributed to soil heterogeneity, which seemed to have a strong effect on SWS. SWS measurements were calibrated according to the observed variability, increasing the accuracy of measurements significantly. Soil water content values were used to establish a link between SWS and PWS. This link was determined over time using nine plots, consisting of rain-fed and irrigated regimes, in variable vigour areas. A non-linear relationship was found between ΨPD and percentage extraction of plant available water for rain-fed plots. When irrigation was applied, no correlation could be found. In this study, for Merlot in the Stellenbosch region, PWS differences affected vigour, and to a lesser extent yield, as well as wine quality. More negative plant water potentials reduced vigour more in high vigour areas than in lower vigour areas, which in turn led to unbalanced vegetative: reproductive ratios. This disturbed vine balance may have had a bigger impact on wine quality than PWS levels. Therefore a well-managed and balanced vine is able to withstand more stress, with less detrimental effects. This study also highlights the danger of limiting the assessment of soil and plant water status conditions to point measurements in vineyards with high levels of vigour variability. / AFRIKAANSE OPSOMMING: Besluite rakende die skedulering van besproeiing word gewoonlik gebaseer op die direkte meting van grondwaterstatus (GWS), of op fisiologiese metings soos byvoorbeeld plantwaterstatus (PWS). Grond gebaseerde metings is relatief vinnig en maklik om te outomatiseer, maar die plantrespons vir ʼn spesifieke grondwaterinhoud varieer as ʼn komplekse funksie van dampdruktekorte. ‘n Plantgebaseerde benadering meet die plantstresreaksie direk, maar is ʼn integrasie van omgewingstoestande. In teenstelling met grondgebaseerde metodes, kan plantgebaseerde metodes aandui wanneer om te besproei, maar nie die hoeveelhede wat besproei moet word nie. Voorsonsopkoms blaarwaterpotensiaal (ΨPD) word grootliks deur die grondwaterinhoud bepaal, en kan as ʼn maatstaf van statiese waterspanning in plante en as ʼn indeks van bulk grondwaterbeskikbaarheid dien, of selfs as ʼn benadering van die grondwaterpotensiaal by die worteloppervlak. Dit behoort dus moontlik te wees om ʼn verwantskap te bepaal tussen GWS en PWS, maar dit is grootliks onbekend hoe stabiel hierdie verwantskap sal wees in ʼn heterogene wingerd, asook hoe die wingerdstok se vegetatiewe en reproduktiewe reaksie die verwantskap kan beïnvloed. Plantwaterstatus speel ʼn groot rol in die bepaling van groeikrag en opbrengs in die wingerdstok. Die vlakke van plantwaterstatus word deur besproeiing beïnvloed, maar word skynbaar meesal deur die seisoen en wingerdstok se ligging in die wingerd bepaal. Meer negatiewe plantwaterpotensiaalvlakke het gelei tot laer groeikrag, maar het ʼn minder uitgesproke effek gehad op opbrengs, terwyl dit in die algemeen wynkwaliteit verswak het. Groeikrag variasie in die wingerd kon grootliks aan grond heterogeniteit toegeskryf word, wat skynbaar ʼn sterk invloed op grondwaterstatus gehad het. Grondwaterstatus metings is gekalibreer volgens die variasie wat waargeneem is, wat die akkuraatheid van metings beduidend verhoog het. Grondwaterinhoud waardes is gebruik om ʼn verwantskap aan te dui tussen SWS en PWS. Hierdie verwantskap is oor tyd bepaal vir nege persele, wat bestaan het uit droëland asook besproeide persele, in areas waarvan die groeikrag verskil het. ʼn Nie-liniêre verband is gevind tussen ΨPD en die persentasie onttrekking van plantbeskikbare water vir die droëland persele. Waar besproei was, kon geen verband gevind word nie. In hierdie studie, vir Merlot in die Stellenbosch area, het PWS vlakke groeikrag en tot ʼn mindere mate opbrengs en wynkwaliteit beïnvloed. Meer negatiewe plantwaterpotensiaal vlakke het groeikrag meer beïnvloed in hoër groeikrag areas as in die laer groeikrag areas, wat ook gelei het tot ongebalanseerde vegetatiewe:reproduktiewe verhoudings. Hierdie versteurde balans in die wingerdstokke kon dalk ʼn groter impak op wynkwaliteit gehad het as PWS vlakke. Daar moet dus gepoog word om goed bestuurde en gebalanseerde wingerdstokke te hê, sodat strestoestande beter weerstaan kan word met minder nadelige gevolge. Die studie beklemtoon ook die gevaar verbonde daaraan om die bepaling van grond- en plantwaterstatus te beperk tot puntmetings in wingerde met groot variasie in groeikrag.

Made available in DSpace on 2010-04-20T20:14:49Z (GMT). No. of bitstreams: 0 Previous issue date: 1995-05-26T00:00:00Z / The main subject of this study, is the rádio peão, (the brasilian word to the american grapevine) and the rumor (or gossip) in organizations. It is basicaly a teory review, including the analysis of growing, transformations, types and classification of rumors, according to social and psycological approachs. It also analyses the research methods of studing. At the end, some organizational recomendations and sugestions of new approachs areavailable. / Esta dissertação tem como tema o estudo da rádio peão, equivalente brasileiro da grapevine americana e dos rumores e boatos que circulam nas organizações. O trabalho contém a revisão da teoria existente sobre o assunto, abrangendo seus principais mecanismos de . surgimento e transformação, a tipologia, e classificação dos rumores, segundo seus aspectos sociais e psicológicos. Também analisa as diversas metodologias de pesquisa do assunto. Ao final são feitas algumas recomendações para as empresas e sugeridos alguns temas para aprofundamento futuro do assunto.

L’enroulement de la vigne cause des pertes de rendement et de la qualité des vins au niveau mondial. Il est causé par quatre espèces de Grapevine leafroll-associated virus(GLRaVs) ; GLRaV-1, -2, -3, -4-like. Si le GLRaV-2 (genre Closterovirus) ne possède pas de vecteur connu, les trois autres espèces (genre Ampelovirus) sont transmises par cochenilles(Coccoidea) qui contribuent à leur dispersion dans et entre les vignobles. Les vignobles de la France septentrionale (Alsace, Bourgogne, Champagne) sont les plus impactés par l’enroulement viral. Ce travail a porté sur le rôle vecteur de Phenacoccus aceris, espèce connue pour son efficacité de transmission et de dispersion des ampélovirus, ainsi que de vitivirus souvent associés. Les interactions cellulaires et moléculaires entre virus et cochenille restent peu connues. Une approche pluridisciplinaire combinant entomologie,virologie, biologie cellulaire et moléculaire a été développée pour étudier la biologie de la vection du GLRaV-1 et du Grapevine virus A (GVA) par P. aceris. Des expériences de transmission ont montré que ces virus sont transmis selon le mode semi-persistant non circulant. L’étude préliminaire du comportement alimentaire de P. aceris sur vigne par électropénétrographie a révélé une activité similaire à celle d'autres espèces de cochenilles déjà décrites et suggère un effet de l’infection sur le comportement alimentaire. L’anatomie des pièces buccales de P. aceris, organes directement impliqués dans la transmission et la rétention de virus non-circulants a été décrite et une méthode basée sur l’acquisition de virus purifié sur membrane a été développée pour rechercher les sites de rétention virale dans le vecteur. / Grapevine leafroll disease affects grape yield and wine quality worldwide. It is caused by four species of Grapevine leafroll-associated virus (GLRaVs) (GLRaV-1, -2, -3, -4-like).While GLRaV-2 (genus Closterovirus) has no known vector, the other three (genus Ampelovirus) are transmitted by mealybugs (Coccoidea) and thus prone to be dispersed within and between vineyards. In north-eastern France (Alsace, Bourgogne et Champagne),vineyards are more impacted by Grapevine leafroll disease. This thesis focusses on the vector role of the species Phenacoccus aceris, known for its efficiency in transmission and dissemination of ampeloviruses, as well as often associated vitiviruses. Molecular and cellular interactions between viruses and mealybugs remain poorly known. A multidisciplinary approach, combining entomology, virology, molecular and cellular biology, was developed to analyse the vector biology of GLRaV-1 and Grapevine virus A (GVA) by P. aceris.Transmission experiments showed that GLRaV-1 and GVA transmission follows the semipersistent non-circulative mode. A preliminary study of P. aceris feeding behavior on grape using electropenetrography revealed an activity similar to that of other mealybug species already described and suggested a potential effect of infection on Ph. aceris feeding behavior. The anatomy of mouth parts, directely implied in transmission and retention of non circulative viruses was described and a method for membrane acquisition of purified virus was developed to search for virus retention sites within the vector.

During the modern era, the urbanization of water has been facilitated by various privileged discourses, which valorize major engineering interventions for the sake of continued urban growth. This research examines discourse surrounding the 2-th Century proposal and construction of a reservoir near the then-tiny farming community of Grapevine, Texas, for the benefit of urban interests. I argue that urban interests produced Grapevine space as nothing more than a container for city water, by rendering meaningless any conception of space that was not directly articulated with urban economic networks. Modern discourse collapsed Denton Creek space from a watershed and landscape into a dimensionless node in the urban space of flows. In return, rural inhabitants were encouraged to progress and to modernize their own spaces: to become urban. Whereas urban discourse entails an implicit spatial imaginary of networks, I deploy the conceptual framework of settler colonialism to show that a core-periphery relationship remains relevant, and is not reducible to a network spatial ontology.

Thesis (PhD(Agric))--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Water scarcity is a key limiting factor for viticulture in dry regions. Traditionally drought sensitive varieties have the potential to grow in dry areas, however in most situations, through the use of rootstocks. Drought-tolerant rootstocks are expected to improve grapevine response to water deficit by improving the water uptake and transport and by reducing the water loss in leaves by root-to-shoot signalling. The mechanisms of rootstocks’ tolerance to drought are not yet fully understood. The main aim of this study was to improve the understanding of the rootstock/scion-cultivar interaction in the regulation of grapevine water use and leaf stomatal behaviour. Irrigated field vines without any water constraint were compared to rain-fed grapevines subjected to moderate water constraint. To better manage vine water status, reduce variability, and compare more rootstocks, greenhouse trials were also conducted where plants were well watered or subjected to severe water constraints. Pinotage grapevines (Vitis vinifera L.) grafted onto 110 Richter, 140 Ruggeri and 1103 Paulsen rootstocks were used for field experiments whereas Pinotage grapevines grafted onto 99 Richter, 110 Richter, 140 Ruggeri, 1103 Paulsen and Ramsey were used for greenhouse experiments. Our study suggested the influence of rootstocks on scion-cultivar water status and leaf stomatal size and density and gas exchange of the scion, implying an influence on water uptake and transport and a tight regulation of the stomatal conductance. Our data supported the hypothesis that the influence of rootstock in response to drought seemed to be higher under increasing water deficit up to a point where the plant water status is the main driver of the stomatal conductance and therefore photosynthesis regulation, considering the plant water status thresholds. In addition, the results suggested that stomatal development is affected by light, drought and possibly by rootstocks. Nevertheless, it is still not clear how the rootstock affects stomatal development and the link with scion-cultivar water use. It seems that the transpiration rate of leaves is more related to stomatal size than density. Thus one possible mechanism of Pinotage leaf adaptation to water constraints was structural during leaf growth, with a reduction in pore size to reduce plant water loss. The results showed that the rootstock is regulating the cultivar's stomatal size (anatomical changes during leaf growth) and functioning (stomatal regulation) through a complex signalling process. The effect of light on stomatal development is interesting in the context of canopy microclimate and canopy manipulation (choice of the vine architecture vs canopy size, in the context of climate change versus the possible increase in drought and water scarcity). The use of rootstocks is a long term investment which aims to provide resistance to soil pests and pathogens and to confer to the scion-cultivar drought and salt tolerance. The use of drought tolerant rootstocks is actually one of the most relevant practical solutions in dry terroir – units and in situations where water availability is limited. The understanding of the physiological and genetic mechanisms which govern scion-cultivar drought tolerance/behaviour induced by rootstocks is critical in terms of rootstocks choice in interaction with the scion-cultivar and is critical to assist breeding programs to create/select drought tolerant rootstocks.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2006. / High potassium content in grape juice and wine are associated with low quality red wine in warm wine producing countries. In an attempt to reduce the potassium content of juice, must and wine, a field experiment was laid out on the farms Meerlus and Kersfontein in the Paardeberg area near Wellington in 1998 on granite derived soils to investigate the effect of canopy management and fertiliser applications on berry K accumulation and wine quality. Four fertiliser applications, three canopy treatments and a MgSO4 foliar spray were studied. The three fertiliser treatments being: none (control), CaSO4, Ca(OH)2, and MgSO4 applications. The canopy treatments were: thin to two shoots per bearer, tip, vertical shoot positioning (VSP) and the removal of yellow leaves and lateral shoots (canopy 1), thin to three shoots per bearer, top after véraison and VSP (canopy 2) and VSP with top after véraison (canopy 3/control). Magnesium sulfate sprays were applied at véraison for two seasons (1999/00 and 2000/01). Seasonal effects produced the most significant differences in this experiment. Canopy treatments did not affect juice K concentration at harvest. Canopy 1 and 2 produced significantly lower wine pH values at Kersfontein. Fertiliser treatments had no effect on juice K concentration nor did it affect wine quality. Magnesium sulphate foliar sprays did not affect juice K concentration at harvest but significantly lowered juice and wine pH, improved wine colour density and total phenolic content. It appears for this experiment that soil K content before véraison, shoot growth at and after véraison and water stress after véraison were the main factors determining juice K concentration at harvest.