Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Within-vineyard variability in vigour and water status commonly occurs in South African
vineyards. Different soil types found over short distances are probably the main cause of vigour
variability, while differences in grapevine water status are commonly induced by lateral water
flow in the vineyard, blocked irrigation emitters and differences in soil water-holding capacity.
These factors can cause heterogeneous ripening and differences in fruit quality between
different parts of the vineyard, an aspect that needs to be avoided as far as possible in order to
produce quality wines. Measurements of carbon isotope discrimination (CID) have proved to be
a tool to assess grapevine physiology in order to study the effects of environmental parameters
on leaf carbon dioxide (CO2) gas exchange and stomatal conductance (gs). Grapevine water
deficit stress/strain in reaction to these environmental conditions can then be determined by
observing the amount of 13C absorbed by plant material after discrimination of 13C has taken
place, and this is influenced by the grapevine stress condition and can indicate water-use
efficiency.
In this study, the variability of grapevine water status and vigour was determined in order to
quantify these parameters in different parts of the vineyard. Two separate trials were conducted,
the first at Wellington, South Africa, where different irrigation regimes resulted in variability in
grapevine water status between plots. The second trial was at Stellenbosch, South Africa,
where plots were divided among different vigour classes and irrigation was applied in different
quantities for different irrigation treatments. Within-vineyard variability in water status
(Wellington and Stellenbosch) and vigour (Stellenbosch) were then quantified and the effects on
some grapevine physiological parameters and berry composition were measured.
The treatments in the Wellington trial led to differences in grapevine water status, which
could be quantified by measurements of stem water potential (SWP) and leaf water potential
(LWP). Soil variability also led to differences in grapevine vigour, which were quantified by
measurements of pruning mass, leaf area and shoot length. The effect of the variability in
grapevine water status on grapevine physiology was assessed by measuring CID, which was
the main focus of the study. Other physiological measurements, such as gs and leaf and
canopy temperature, were also conducted. The effect of these conditions on grape berry
composition was also studied.
In the Stellenbosch trial, soil water content, plant water status measurements (SWP, predawn
LWP and LWP), physiological measurements (CID and gs) and berry size measurements
were used to classify plots into water status treatments (“wet” and “dry” treatments). The effect
of vigour differences was analysed separately from these treatments by using pruning mass as
a covariate in the statistical analyses. The effect of vigour variability on the measurements was
studied by looking at the effect of the covariate on the measurements, while shoot growth rate,
shoot length and leaf area measurements were conducted as vegetative growth measurements.
Differences in measurements were then studied between the treatments and between the
vigour levels of the different plots.
In the Wellington trial, plant water status was determined by irrigation, showing increased
stress for treatments that received less irrigation. The differences in plant water status then
caused differences in grapevine physiology between the treatments, leading to increased gs for increased irrigation. This of course influenced leaf internal CO2 and therefore CID, although CID
was also clearly influenced by berry development. Berry size was influenced by irrigation, with
larger berries found in wetter treatments, while berry chemical composition was influenced by
the irrigation regime, with increased irrigation leading to increased pH and leading to trends
showing increased total soluble solids and malic acid, and reduced total and tartaric acid and
colour intensity.
In the Stellenbosch trial, plots with higher vigour had increased shoot growth rate, longer
shoots and increased leaf area, although topping influenced this. Wet treatment vines also
showed slightly longer shoots and larger leaf areas. There were differences in soil water content
between the wet and dry treatments, and this led to differences in plant water status. Vigour
also influenced pre-dawn LWP, especially in the 2007 season, as higher-vigour vines struggled
more to rehydrate through the night.
Differences in plant water potential led to differences in grapevine physiology, with
increased gs for vines from the wet treatment, while higher-vigour vines had slightly increased
gs. The differences in gs led to gas exchange differences and therefore differences in CID,
meaning that water status and vigour influenced CID. CID measurements illustrated the long
term effect of water status on plant physiology, while measurements such as SWP illustrated
the short term effects. CID measurements therefore proved to be accumulative over the season,
in contrast to SWP measurements that were much more dependent on the current state of
grapevine water status. Other physiological measurements showed that wet-treatment vines
had higher photosynthetic rates and evapotranspiration and lower leaf temperatures, while
higher-vigour vines had slightly increased evapotranspiration and decreased leaf temperatures.
Wet-treatment vines had larger berries, while a higher vigour also led to slightly larger berries.
Berry composition was influenced by treatment, where wet-treatment vines had increased pH
and total soluble solids, while higher-vigour vines had increased juice pH and, in the 2008
season, decreased total soluble solids.
Extremely stressed conditions did not show significant effects on plant water potential, but
SWP measurements indicated slightly higher stress for the extremely stressed vines and LWP
showed slightly less stressed conditions for these vines. Measurements of gs showed slightly
lower values for the extremely stressed vines, while measurements of CID showed large
significant differences, with the extremely stressed vines having measurements showing high
stress. The measurement therefore indicated highly stressed conditions accurately, while other
physiological measurements, such as photosynthetic rate, evapotranspiration and leaf
temperatures, only showed trends and no significant differences. Measurements of stomatal
conductance reacted to plant water status measurements throughout the diurnal measurement
days, while CID only reacted slightly with gs changes during these days and was perhaps
influenced more by berry chemical composition and development at this early stage of the
season.
Vigour and water status therefore influenced grapevine physiology, with a more direct effect
by water status and an indirect effect by vigour due to microclimatic differences. This also
influenced berry composition and therefore quality. In future studies, CID measurements should be done on juice from which organic acids have
been removed in order to eliminate the effect of seasonal berry composition on the
measurement.
Measurements of CID proved to be an integrative, but sensitive, indicator of grapevine
stress, especially at the end of the season. It might at best be useful as a post-harvest
management tool for producers or grape buyers, especially for irrigation control, as has also
been stated by Van Leeuwen et al. (2007). / AFRIKAANSE OPSOMMING: Binne-wingerd variasie in groeikrag en waterstatus is algemeen in Suid-Afrikaanse wingerde.
Verskillende grondsoorte wat na aan mekaar voorkom, is seker een van die vernaamste
oorsake van variasie in groeikrag, terwyl verskille in wingerdwaterstatus algemeen deur laterale
watervloei in die wingerd, verstopte besproeiingspuite en verskille in grond waterhouvermoë
geïnduseer word. Hierdie faktore kan aanleiding gee tot heterogene rypwording en verskille in
vrugkwaliteit tussen verskillende dele van die wingerd, ‘n aspek wat so ver moontlik vermy moet
word om kwaliteitwyne te kan produseer. Die meting van koolstof-isotoopdiskriminasie (KID) is
bewys om as gereedskap te kan dien vir die assessering van wingerdfisiologie om die effekte
van omgewingsparameters op blaar koolstofdioksied (CO2) - gasuitruiling en stomatale
geleiding (gs) te bestudeer. Die stres/stremming as gevolg van ‘n watertekort in die wingerd in
reaksie op hierdie omgewingstoestande kan dan bepaal word deur te kyk na hoeveel 13C deur
die plantmateriaal geabsorbeer word ná 13C-diskriminasie plaasgevind het, en dít word deur die
wingerdstrestoestande beïnvloed en kan ‘n aanduiding verskaf van die doeltreffendheid van
waterverbruik.
In hierdie studie is die variasie in wingerdwaterstatus en groeikrag bepaal om hierdie
parameters in verskillende dele van die wingerd te kwantifiseer. Twee afsonderlike proewe is
uitgevoer, die eerste by Wellington, Suid-Afrika, waar verskillende besproeiingsregimes gelei
het tot verskille in die wingerdwaterstatus tussen persele. Die tweede proef was by
Stellenbosch, Suid-Afrika, waar persele tussen verskillende groeikragklasse verdeel is en
besproeiing in verskillende hoeveelhede vir verskillende besproeiingsbehandelings toegepas is.
Binne-wingerd variasie in waterstatus (Wellington en Stellenbosch) en groeikrag (Stellenbosch)
is toe gekwantifiseer en die effekte op sekere wingerd-fisiologiese parameters en
korrelsamestelling is gemeet.
Die behandelings in die Wellington-proef het gelei tot verskille in wingerdwaterstatus, wat
deur metings van stamwaterpotensiaal (SWP) en blaarwaterpotensiaal (BWP) gekwantifiseer
kon word. Grondverskille het ook gelei tot verskille in wingerdgroeikrag, wat deur metings van
snoeimassa, blaaroppervlak en lootlengte gekwantifiseer is. Die effek van die variasie in
wingerdwaterstatus op wingerdfisiologie is deur metings van KID bepaal wat die hooffokus van
hierdie studie was. Ander fisiologiese metings, soos gs en blaar- en lowertemperatuur, is ook
gedoen. Die effekte van hierdie toestande op die samestelling van die druiwekorrels is ook
bestudeer.
In die Stellenbosch-proef is grondwaterinhoud, metings van plantwaterstatus (SWP, voorsonopgang
SWP en BWP), fisiologiese metings (KID en gs) en metings van korrelgrootte
gebruik om die persele in waterstatusbehandelings (“nat” en “droë” behandelings) te verdeel.
Die effek van verskille in groeikrag is apart van hierdie behandelings geanaliseer deur
snoeimassa as ‘n kovariaat in die statistiese analises te gebruik. Die effek van groeikragvariasie
op die metings is bestudeer deur ondersoek in te stel na die effek van die kovariaat op die
metings, terwyl lootgroeitempo-, lootlengte- en blaaroppervlakmetings as metings van
vegetatiewe groei uitgevoer is. Verskille in metings tussen die behandelings en tussen die
groeikragvlakke van die verskillende persele is toe bestudeer. In die Wellington-proef is plantwaterstatus deur besproeiing bepaal, met verhoogde stres in
behandelings waar daar minder besproeiing toegedien is. Die verskille in plantwaterstatus het
dan verskille in wingerdfisiologie tussen die behandelings veroorsaak, wat gelei het tot ‘n
verhoogde gs in die geval van verhoogde besproeiing. Dit het natuurlik ‘n effek op die interne
CO2 van die blaar en dus op KID gehad, hoewel KID ook duidelik deur korrelontwikkeling
beïnvloed is. Korrelgrootte is deur besproeiing beïnvloed, met groter korrels in die natter
behandelings, terwyl die chemiese samestelling van die korrel deur besproeiingsregime
beïnvloed is. Verhoogde besproeiing het pH verhoog en gelei na tendense wat verhoogde totale
oplosbare vaste stowwe en appelsuur, en verminderde totale suur, wynsteensuur en
kleurintensiteit getoon het.
In die Stellenbosch-proef het persele met hoër groeikrag ook verhoogde lootgroeitempo,
langer lote en verhoogde blaaroppervlak getoon, hoewel dit deur top beïnvloed is.
Wingerdstokke van die nat behandeling het ook effe langer lote en groter blaaroppervlakke
getoon. Daar was verskille in grondwaterinhoud tussen die nat en droë behandelings en dit het
verskille in plantwaterstatus veroorsaak. Groeikrag is ook deur voor-sonopgang BWP beïnvloed,
veral in die 2007-seisoen, aangesien stokke met hoër groeikrag meer gesukkel het om in die
nag te rehidreer.
Verskille in plantwaterpotensiaal het gelei tot verskille in wingerdfisiologie, met ‘n verhoogde
gs vir stokke in die nat behandeling, terwyl stokke met hoër groeikrag ‘n effens verhoogde gs
getoon het. Die verskille in gs het gelei tot verskille in gasuitruiling en dus verskille in KID, wat
beteken dat waterstatus en groeikrag ‘n invloed op KID het. KID was meer verteenwoordigend
van die langtermyneffekte van water status op plantfisiologie, terwyl metings soos SWP die
korttermyneffekte weerspieël het. KID metings was dus akkumalatief oor die seisoen, terwyl
SWP metings meer ‘n weerspieëling was van die huidige toestand van plantwaterpotensiaal.
Ander fisiologiese metings het getoon dat stokke in die nat behandeling ‘n hoër fotosintesetempo
en evapotranspirasie sowel as laer blaartemperature ondervind het, terwyl die stokke
met hoër groeikrag effe verhoogde evapotranspirasie en verminderde blaartemperature getoon
het. Stokke in die nat behandeling het groter korrels gehad, terwyl hoër groeikrag ook effens
groter korrels veroorsaak het. Korrelsamestelling is deur die behandelings beïnvloed, met
stokke in die nat behandeling wat verhoogde pH en totale oplosbare vaste stowwe getoon het,
terwyl stokke met hoër groeikrag verhoogde pH van die sap en verminderde totale oplosbare
vaste stowwe (laasgenoemde in die 2008-seisoen) gehad het.
Uitermate toestande van stres het geen beduidende effekte op plantwaterpotensiaal getoon
nie, hoewel SWP-metings effens hoër stres vir die uitermate gestresde wingerde getoon het en
BWP effens minder gestresde toestande vir hierdie stokke getoon het. Metings van gs het
effens laer waardes vir die uitermate gestresde stokke getoon, terwyl metings van KID groot
noemenswaardige verskille getoon het, met die metings vir die uitermate gestresde wingerde
wat hoër stres aangedui het. Dié meting het dus hoogs gestresde toestande akkuraat aangedui,
terwyl ander fisiologiese metings, soos tempo van fotosintese, evapotranspirasie en
blaartemperature net tendense en nie beduidende verskille aangedui het nie. Metings van
stomatale geleiding het dwarsdeur die dae waarop daaglikse metings gedoen is op
plantwaterstatusmetings gereageer, terwyl KID net effens met gs-veranderinge op hierdie dae gereageer het en moontlik meer deur die chemiese samestelling en ontwikkeling van die korrel
in hierdie vroeë stadium van die seisoen beïnvloed is.
Groeikrag en waterstatus het dus wingerdfisiologie beïnvloed, met ‘n meer direkte effek deur
waterstatus en ‘n indirekte effek deur groeikrag as gevolg van mikroklimaatsverskille. Dit het
ook korrelsamestelling en dus kwaliteit beïnvloed.
In toekomstige studies moet KID-metings gedoen word op sap waarvan die organiese sure
verwyder is om die effek van seisoenale korrelsamestelling op die meting uit te sluit.
Metings van KID is getoon om ‘n integrerende, maar gevoelige, aanduider van wingerdstres
te wees, veral aan die einde van die seisoen. Dit is ten beste miskien bruikbaar as naoesbestuursgereedskap
vir produsente of druiwekopers, veral vir besproeiingsbeheer, soos ook
reeds deur Van Leeuwen et al. (2007) aangedui is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4345 |
| Date | 03 1900 |
| Creators | Rossouw, Gerhard C. |
| Contributors | Strever, A. E., University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 118 p. : ill. |
| Rights | University of Stellenbosch |
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