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Improvement of cluster quality of Cardinal grapesTrue, Lowell Francis, 1930- January 1963 (has links)
No description available.
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The effects of gibberellin on berry quality of several ungirdled grape varietiesJones, Larry Warner, 1934- January 1959 (has links)
No description available.
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Effects of packaging and postharvest cooling on quality of table grapes (Vitis vinifera L.)Du Plessis, S. F. (Stephanus Francois) 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The table grape industry uses rapid cooling and packaging to protect grapes from desiccation
and decay. Numerous packaging methods and combinations are used in the industry with
each having their own advantages and disadvantages.
Inferior postharvest grape quality can usually be ascribed to either deficient or excessive
moisture in the carton. Berry split, decay and S02 damage are all disorders that are either
caused or aggravated by wet berries in conjunction with elevated temperature. On the other
hand, grapes that are exposed to desiccating conditions will develop brown stems and cause
ineffective control by S02 gas generators. Moisture management is governed by perforated
or non-perforated liners and/or by placing moisture absorbing materials inside the liners. To
find the optimum liner perforation or moisture sheet combination, 'Thompson Seedless' and
'Red Globe' (Vitis vinifera Linnaeus) table grape quality was evaluated in various trials.
The investigation of non-perforated liners compared to liners with different degrees of
perforation concluded the following: Perforated liners benefit grape quality by decreasing
S02 damage and berry split due to less moisture in the carton. These benefits, however, also
lead to loss in quality due to increased stem desiccation and a lower S02 concentration in the
packaging. The lower moisture content in the carton compensates for the lower S02
concentration, creating an environment less favourable for decay development. S02 damage
and berry split decreased with an increase in degree of liner perforation, irrespective of the
cultivars sensitivity to the disorder. Optimum level of perforation depends on the specific
sensitivity of a cultivar to certain quality disorders and the characteristics of the quality
disorders associated with a cultivar. Additionally, packing conditions such as product
temperature and humidity should be considered. The specific costs associated with the
advantages and disadvantages influenced by the degree of liner perforation will be the
deciding factor in liner selection.
The investigation of a clay-containing, moisture absorbing sheet emphasized the benefits and
risks of absorbing large amounts of water within the packaging. Irrespective of using a
perforated or non-perforated liner the influence of the desiccant sheet was evident throughout
the trials. It benefited grape quality by lowering the incidence of berry split and S02 damage. However, decay control was impaired by the desiccant sheet, and stem desiccation was
aggravated.
The comparison of non-perforated liners with liners of various degrees of perforation showed
the benefit of faster cooling rates of perforated liners. The various perforated liners showed
little variation in airflow and cooling times.
Morphological studies of various cultivars could not ascribe differences in stem condition to
anatomical dissimilarities between various cultivars. It was found that 'Red Globe' had a
much larger berry volume to stem weight ratio contributing to a high rate of water loss and
stem dehydration. Stem visibility is high in 'Red Globe' due to the straggly, loose nature of
the bunches. This heightens the perception of dry, brown stems and overemphasizes the
actual severity of the disorder. / AFRIKAANSE OPSOMMING: Die tafeldruifbedryf gebruik versnelde verkoeling en verpakking om druiwe te beskerm teen
uitdroging en bederf. Verskeie verpakkingsmetodes word gebruik in die industrie waarvan
elkeen sy eie voor- en nadele het.
Ondergeskikte na-oes kwaliteit kan gewoonlik toegeskryf word aan óf te min óf te veel vog
in die karton. Korrelbars, S02 skade en bederf is almal kwaliteitsdefekte wat óf veroorsaak
word, óf vererger word deur nat korrels, saam met 'n verhoging in temperatuur. In
teenstelling hiermee sal druiwe wat blootgestel word aan droë toestande, bruin stingels
ontwikkel en S02 beheer salook ondoeltreffend wees. Vog in verpakking word beheer deur
geperforeerde of nie-geperforeerde binnesakke en/of deur vogabsorberende materiaal binne
die binnesak te plaas. Om die optimum binnesak perforasie of vogabsorberende vel
kombinasie te vind is 'Thompson Seedless' en 'Red Globe' (Vitis vinifera Linnaeus)
tafeldruif kwaliteit ge-evalueer in verskeie proewe.
Die bestudering van nie-geperforeerde binnesakke teenoor binnesakke met verskillende grade
van perforasies het die volgende resultate gelewer: Geperforeerde binnesakke bevoordeel
druif kwaliteit deur die vermindering van S02 skade en korrelbars weens minder vog in die
karton. Hierdie voordele sal egter lei tot verlies in kwaliteit weens die vinniger uitdroging
van stingels en die verlaging van S02 konsentrasie in die verpakking. Die laer vog inhoud in
die karton vergoed vir die vermindering van S02 konsentrasie, omdat minder gunstige
toestande vir die ontwikkeling van bederf geskep word. S02 skade en korrelbars het
verminder met 'n vermeerdering van perforasies, ongeag die kultivar se sensitiwiteit vir die
defekte. Optimum vlakke van perforasie is afhanklik van die spesifieke sensititiwiteit van 'n
kultivar tot sekere kwaliteitsdefekte, en eienskappe van die kwaliteitsdefekte wat geassosieer
word met die kultivar. Boonop moet verpakkingsomstandighede soos produktemperatuur en
humiditeit ook in gedagte gehou word. Die spesifieke koste verbonde aan die voor- en nadele
wat beïnvloed word deur die graad van perforasie sal die bepalende faktor wees wanneer 'n
binnesak gekies word.
Die bestudering van 'n klei-bevattende, vogabsorberende vel het bewys dat dit voordele en
risiko's inhou om groot hoeveelhede vog te absorbeer. Ongeag die gebruik van 'n geperforeerde of nie-geperforeerde binnesak, was die invloed van die desikkante vel duidelik
in al die proewe. Dit was voordelig vir druif kwaliteit deurdat dit korrelbars en S02 skade
verminder het. Bederfbeheer is egter verswak deur die desikkante vel, en stingel uitdroging
IS vererger.
Die vergelyking van nie-geperforeerde binnesakke met verskillende grade van geperforeerde
binnesakke het die voordeel bewys van vinniger verkoelinstempo's van die geperforeerde
binnesak. Verskille in die graad van perforasie het 'n klein invloed gehad op die lugvloei en
verkoelingstempo 's.
Bestudering van verskeie kultivars kon geen morfologiese verskille uitwys wat variasie in
stingelkwaliteit tussen kultivars kan verklaar nie. Dit is bevind dat 'Red Globe' 'n baie groter
korrelvolume tot stingelgewig verhouding het. Stingels is meer sigbaar by 'Red Globe'
weens die yl, los aard van die trosse. Dit verhoog die persepsie van droë, bruin stingels en dit
oorbeklemtoon die voorkoms van die defek.
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Korrelasies tussen gesondheidstoestand van steendruiwe, chemiese samestelling van die mos en organoleptiese beoordeling van die wynVos, P. J. A. (Petrus Johannes Andreas) 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 1966. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming
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Postharvest berry split and abscission in 'Thompson Seedless' and 'Waltham Cross' table grapesBurger, D. A. (Dirk Albert) 12 1900 (has links)
Thesis (MScAgric) -- University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Postharvest berry split and abscission are prevailing physiological disorders that negatively
impact on the quality of table grapes exported from South Africa. Inferior grape quality due to
these disorders results in a considerable decline in consumer confidence in the branded
product, which leads to a drop in demand, and consequently, lower prices. Since information
concerning postharvest factors influencing postharvest berry split and abscission is limited, the
search for reliable methods to adequately control these problems remains elusive. In an
attempt to obtain the required information, the influence of harvest temperature, harvest
maturity, perforated liners, field heat removal prior to packing, delay periods before and after
packing, storage duration and the elevation of storage temperature on the development of berry
split and abscission in 'Thompson Seedless' (Vitis vinifera Linnaeus) table grapes was
investigated. Changes in abscission related factors during berry development, and the influence
of pre-and postharvest ethylene inhibitors on the development of berry abscission in 'Waltham
Cross' table grapes, was also studied.
Berry split was aggravated by packing 'Thompson Seedless' grapes at high pulp temperatures
of approximately 30°C, especially if the grapes were packed in non-perforated bags. The
incidence of berry split could be reduced by between 80 and 90% by packing grapes in
perforated instead of non-perforated liners. Perforated bags also reduced levels of S02
damage. However, due to significantly more moisture loss from grapes in perforated bags,
compared to non-perforated bags, the risk of higher fruit and stem desiccation and softer berries
existed. Optimum size and density of perforations needs to be determined to reduce berry split
without excessive loss of moisture from the grapes, and S02gas from the air space surrounding
the product. The influence of harvest temperature and liner type on berry abscission was not
conclusive. Advanced maturity increased grape resistance to berry split. However, grapes
harvested too mature were prone to stem desiccation and the development of Botrytis decay.
The occurrence of berry abscission also appeared to increase with advanced harvest maturity.
Consequently, to ensure optimal post-storage quality, 'Thompson Seedless' grapes should be
harvested as soon as horticultural maturity has been reached, which appears to be at
approximately 18°Brix.
Field heat removal for 1.5 hours at 19°C prior to packing had no beneficial or adverse effect on
berry split and abscission. Delay periods prior to packing aggravated berry abscission, but did
not influence berry split significantly. Grapes delayed for 12 hours showed a significant increase
in berry abscission and Botrytis decay, compared to grapes delayed for only 3 or 8 hours. Considering that the absence of fungal decay is the most important quality prerequisite in table
grapes, it is of vital importance to pack grapes with as short a delay period as possible. Grapes
packed in non-perforated liners and delayed for different durations after packing, before the
onset of forced-air cooling (FAC), showed significant differences regarding the incidence of
berry split. Grapes delayed for 18 hours had significantly higher levels of berry split directly after
the delay period, compared to grapes delayed for 6 or 12 hours. No significant difference in
berry abscission occurred between grapes delayed for different periods. To minimise the
amount of berry split, FAC should be applied as rapidly as possible after the packing of grapes
in non-perforated liners.
Two storage related factors significantly influenced the incidence of berry split in 'Thompson
Seedless' grapes during cold storage significantly, viz. the duration of storage at -O.soC,and the
increase in temperature after low temperature storage. Berry split increased almost linearly with
prolonged storage at -O.soC. An elevation of storage temperature from -O.soC to 10°C any time
during the cold storage period, further aggravated the split problem. Consequently, the
reduction of berry split in 'Thompson Seedless' table grapes during cold storage requires (a) the
shortest possible cold storage period, and (b) good temperature management throughout
distribution, from initiation of cooling until the final point of sale.
The grape berry abscission potential, as quantitatively indexed by the measurement of the fruit
removal force (FRF), showed significant changes during berry development of 'Waltham Cross'
table grapes, from 27 to 111 days after full bloom (OAFB). This showed that at certain stages of
fruit growth, 'Waltham Cross' grapes are more prone to berry abscission. At 27 OAFB, when the
berries had an average diameter of 6.6mm, the grape bunches showed a significantly higher
potential for berry abscission, compared to grapes sampled at a later stage. 'Waltham Cross'
has inherently straggly bunches with bare shoulders. Therefore, any abscission during berry
development will aggravate the problem. Consequently, it is of vital importance that any
adverse factors such as moisture stress be avoided, especially during the period when
'Waltham Cross' grapes appear to be very susceptible to berry abscission. Of all parameters
measured, moisture loss showed the best correlation with abscission. Grapes harvested with
total soluble solids (TSS) of 12.3°Brix, 83 OAFB, had a significantly higher abscission potential
than grapes harvested more mature. Therefore, by harvesting 'Waltham Cross' grapes at
optimum maturity, at a TSS of approximately 16.4°Brix, berry abscission can be reduced to a
great extent. It was evident that at veraison, the metabolism of grape berries changes
drastically, and additional to the rapid increase in sugars and the rapid decrease in acidity, a
decrease in FRF occurs. Preharvest sprays of ReTain™ (a derivative of aminoethoxyvinylglycine), which inhibits ethylene
synthesis, showed no promise as a means to reduce postharvest berry abscission. A
postharvest treatment with EthylBloc® (1-methylcyclopropene), which inhibits ethylene action,
only reduced berry abscission during one season. / AFRIKAANSE OPSOMMING: Die fisiologiese defekte korrelbars en los korrels wat algemeen voorkom tydens opberging van
sekere tafeldruif-kultivars, het 'n negatiewe invloed op tafeldruiwe wat uitgevoer word vanaf
Suid-Afrika. Minderwaardige kwaliteit as gevolg van hierdie defekte het 'n aansienlike afname
in verbruikers-vertroue tot gevolg wat aanleiding gee tot 'n ooreenkomstige afname in aanvraag
en prys van die produk. Inligting rakende na-oes faktore wat die voorkoms van korrelbars en los
korrels beïnvloed is beperk, en geen gewaarborgde metode bestaan om hierdie twee defekte
volkome te beheer nie. In 'n poging om dié gewenste inligting te bekom, is ondersoek ingestel
na die effek van oes-temperatuur, oes-rypheid, geperforeerde sakke, veldhitte verwydering voor
verpakking, vertragingsperiodes voor en na verpakking, tydsduur van opberging, en die
verhoging van die opbergingstemperatuur, op die voorkoms van korrelbars en los korrels by
'Thompson Seedless' (Vitis vinifera Linnaeus) druiwe. Daar is ook ondersoek ingestel na
veranderings in afsnoering verwante faktore tydens korrel-ontwikkeling, en die invloed van vooren
na-oes toedienings van etileen inhibeerders op die ontwikkeling van los korrels by 'Waltham
Cross'tafeldruiwe.
Korrelbars is vererger deur 'Thompson Seedless' met hoë pulptemperature van ongeveer
29.5°C te verpak, veral indien dit in 'n riie-geperforeerde sak verpak is. Die voorkoms van
korrelbars kon tussen 80 en 90% verminder word deur 'Thompson Seedless' druiwe in
geperforeerde sakke te verpak, in plaas van nie-geperforeerde sakke. Geperforeerde sakke het
ook S02 skade op die druiwe verminder. Tog, as gevolg van betekenisvol meer vogverlies
vanaf druiwe in geperforeerde sakke as vanaf druiwe in nie-geperforeerde sakke, bestaan die
risiko van meer stingel-uitdroging en minder ferm korrels indien druiwe in geperforeerde sakke
verpak word. Optimale grootte en digtheid van perforasies moet bepaal word om korrelbars te
verminder, maar sonder oormatige vogverlies vanaf die druiwe en oormatige verlies aan S02.
Die invloed van oes-temperatuur en sak-tipe op los korrels was nie oortuigend nie. Gevorderde
oes-rypheid het die druif se weerstand teen korrelbars verhoog. Daarteenoor was druiwe wat té
ryp geoes is, meer gevoelig vir stingel-uitdroging en Botrytis bederf. Dit wilook voorkom of die
voorkoms van los korrels toeneem met gevorderde rypheid. Dus, om optimum kwaliteit na
opberging te verseker, moet 'Thompson Seedless' geoes word sodra hortologiese rypheid
bereik word, wat blyk om by 'n totale opgeloste vaste stof-inhoud (TOVS) van ongeveer 18°Brix
te wees.
Veldhitte verwydering voor verpakking, vir 1.5 uur by 19°C, het geen effek gehad op die
voorkoms van korrelbars en los korrels nie. 'n Vertragingsperiode voor verpakking het die los korrel-probleem vererger, alhoewel dit geen betekenisvolle invloed op die voorkoms van
korrelbars gehad het nie. Druiwe wat vir 12 uur voor verpakking vertraag is, het betekenisvol
meer los korrels en Botrytis bederf getoon, in vergelyking met druiwe wat slegs 'n
vertragingsperiode van 3 of 8 uur ondergaan het. Aangesien die afwesigheid van bederf die
belangrikste kwaliteits-vereiste vir tafeldruiwe is, is dit van kardinale belang om druiwe so gou as
moontlik na oes te verpak. Druiwe, verpak in nie-geperforeerde sakke, wat vir verskillende
periodes vertraag is voor geforseerde-lug verkoeling, het betekenisvolle verskille getoon
betreffende die voorkoms van korrelbars. Druiwe vertraag vir 18 ure voor verkoeling, het
betekenisvol meer korrelbars getoon, soos gemeet onmiddellik na die vertragingsperiode, in
vergelyking met druiwe wat slegs vir 6 of 12 ure vertraag was. Geen betekenisvolle verskille in
los korrels het voorgekom tussen druiwe wat verskillende vertragingsperiodes ondergaan het
nie. Om korrelbars te verminder, moet geforseerde-lug verkoeling so gou as moontlik na
verpakking van druiwe in nie-geperforeerde sakke toegepas word.
Twee opbergings-verwante faktore beïnvloed die voorkoms van korrelbars by 'Thompson
Seedless' druiwe tydens koelopberging, naamlik die tydsduur van opberging by -O.soC,asook 'n
styging in temperatuur vanaf -O.soC tot 1DoC. Korrelbars het feitlik liniêr toegeneem met
verlengde opberging by -O.soC. 'n Styging in temperatuur vanaf -O.SoCtot 1DoCop enige tydstip
gedurende die koelopbergingsperiode, het korrelbars verder vererger. Dus, om korrelbars by
'Thompson Seedless' tydens opberging tot die minimum te beperk, moet die tydsduur van
opberging so kort as moontlik wees, en moet die koue ketting regdeur die distribusie-proses
gehandhaaf word, vanaf inisiëring van verkoeling tot en met die uiteindelike verkoop van die
produk.
Die afsnoerings-potensiaal van druiwe, soos kwantitatief geïndekseer is deur meting van die
vrug-verwyderings-vermoë (VVV), het betekenisvol verander gedurende korrel-ontwikkeling van
'Waltham Cross' tafeldruiwe, vanaf 27 tot 111 dae na volblom (DNVB). Dit het getoon dat
'Waltham Cross' druiwe by sekere stadiums van vrug-groei meer gevoelig is vir korrel
afsnoering. By 27 DNVB, wanneer die korrels 'n gemiddelde deursnee van 6.6mm gehad het,
het die druiwe 'n betekenisvolle hoër potensiaal vir afsnoering getoon, in vergelyking met druiwe
wat op 'n latere stadium getoets is. 'Waltham Cross' is inherent geneig tot yl trosse met kaal
skouers, gevolglik sal enige afsnoering tydens korrel-ontwikkeling die probleem vererger. Dus
is dit van kardinale belang dat enige nadelige faktor, soos byvoorbeeld vogstres, vermy moet
word, veral gedurende periodes wanneer dit wil voorkom of 'Waltham Cross' baie vatbaar is vir
korrel afsnoering. Van al die parameters wat gemeet is, het vogverlies die beste korrelasie met
korrel afsnoering getoon. Druiwe wat 83 DNVB, by 'n TOVS van 12.3°Brix geoes is, het 'n betekenisvol hoër potensiaal vir korrel afsnoering getoon, in vergelyking met druiwe wat ryper
geoes is. Dus, deur 'Waltham Cross' druiwe by optimum rypheid te oes, by 'n TOVS van
ongeveer 16.4°Brix, kan korrelbars in 'n groot mate verminder word. Tydens verelson, wanneer
die metabolisme van die druiwe drasties verander, was daar gepaardgaande met die drastiese
toename in TOVS en die drastiese afname in totale titreerbare sure (TSS), ook 'n afname in
Voor-oes bespuitings met ReTain™, wat etileen sintese inhibeer, het geen potensiaal getoon
om los korrels by 'Waltham Cross' te verminder nie. 'n Na-oes behandeling met EthyIBloc®,
wat etileen werking inhibeer, het slegs korrel afsnoering in een van die seisoene effens
verminder.
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Effect of varying levels of nitrogen, potassium and calcium nutrition on table grape vine physiology and berry qualityRaath, P. J. ( Pieter Johannes) 03 1900 (has links)
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.
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The effect of partial rootzone drying and foliar nutrition on water use efficiency and quality of table grape cultivars Crimson seedless and DauphineVan Zyl, Tinake 12 1900 (has links)
Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / The South African and international table grape industries are growing rapidly, which
necessitates the production of high quality export fruit at competitive production costs.
For this reason, alternative irrigation methods are required to utilise water optimally
while still attaining good quality table grapes. An increase in agricultural productivity
may be dependent on either the availability of more water for irrigation or an increase in
the efficiency of water use.
The first aim of this study was to evaluate the effectiveness of the Partial Rootzone
Drying (PRD) irrigation strategy in Crimson Seedless and Dauphine table grape
production. This irrigation system is based on the drying of half of the vine roots,
thereby allowing the plant to produce hormones like abscisic acid (ABA) in reaction to
water stress. The hormone production in turn results in stomatal closure and the
reduction of water loss via transpiration. The drying cycle is then repeated after 10 to 15
days on the other side of the vine, irrigating the previously dried roots. PRD will
encourage a consistent production of the stress hormone abscisic acid (ABA), without
actual water stress. This strategy reduces the amount of water used for irrigation,
without an accompanying loss in fruit yield, as compared to conventional techniques. In
this study, conventionally treated vines were irrigated according to historical block data
and PRD-treated vines were irrigated at the same times.
The second aim of this study was to monitor the efficacy of a foliar nutrient, Croplife.
This foliar nutrient allegedly improves the uptake of foliar applied nutrients, assists with
transport of all minerals through the leaves and enables the plant to attain higher pest
and disease resistance thresholds. Conventionally treated vines that did not receive
foliar nutrient treatment were compared to vines that received foliar nutrients as
prescribed by the manufacturer.
Vine cultivars Crimson Seedless and Dauphine, were grown under open hydroponic
principles with drip and drip irrigation respectively in this experiment. For the hydroponic
vines (Crimson Seedless), all vines were situated in the same row and 72 vines were
divided into mini-plots of three vines. Treatments were then assigned to an equal
number of plots at random. The same procedure was followed for the drip irrigated
vines (Dauphine) but the vines were situated in two rows of equal length. Treatment effects were followed from budburst until harvest, where after post-harvest analyses
were conducted.
The first aim, namely to show that PRD is an effective irrigation strategy for table grape
production in Crimson Seedless and Dauphine cultivars , has shown that vines did not
exhibit signs of stress even though they received only half the conventional amount of
water. This study was conducted over only one growth season and therefore no definite
conclusions could be drawn about the long term effectiveness of PRD on table grapes.
It did, however, confirm numerous results obtained from different studies on the use of
PRD in wine grape production.
The results obtained in the second part of the study were inconclusive and could not
show that Croplife is effective in improving the uptake and transport of applied foliar
nutrients. Because Crimson Seedless is cultivated under open hydroponic principles,
nutrients can be absorbed by the roots via the soil and micronutrients are also available
from chemical sprays during the season. There was no evidence to indicate that the use
of Croplife increased nutrient absorption and transport, neither did it supplement or
detract form the observed effect of PRD.
Despite the limitations experienced during this study, it has shown that the use of PRD
for table grape production may be a useful tool for improving water utilisation efficiency
in future. The strategy will have to be developed systematically through experimentation
to fully unlock the potential of the PRD management system for table grape production.
This study provides a good starting point for future research required to elucidate
numerous aspects of the PRD system and has clearly shown that established vineyards
can be switched to a PRD system without a loss in table grape quality. It is envisaged
that the advantages of this system could have a positive effect on the production of high
quality fruit for the international market.
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Cellular factors that affect table grape berry firmnessDu Plessis, Beatrix W. 03 1900 (has links)
Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / The South African table grape industry is under great pressure to produce table grapes
of the best quality for the export markets. Quality defects such as poor colour,
inadequate berry firmness, browning and soft tissue breakdown cause great losses in
export. The firmness of table grapes is one of the major factors determining the eating
quality of grapes. Consumers prefer grapes with a firmer flesh above those with soft
flesh. Firmer berries are commonly accepted to have better eating quality and longer
cold storage capacity. Factors that promote and maintain berry firmness are only
speculated about; therefore producers cannot effectively control the development of
firmer berries by managerial practises or by applying specific sprays.
The study was done on Redglobe and two Waltham Cross clones (the firmer Clone
8 and softer Clone 13). The aim of this study was two-fold. Firstly the cellular and
ultracellular differences between the tissues of firm and soft berries were determined.
The effect of gibberellic acid (GA3), synthetic cytokinin (CPPU) and bunch applied
calcium sprays on the cellular and ultracellular structure of berry tissues were also
under investigation. Secondly, the effects of GA3, CPPU and bunch directed calcium
sprays on berry firmness, eating quality and storage capacity were determined.
To determine the cellular and ultracelular structure of berry tissues, light microscope
(LM) and transmission electron (TEM) studies were done. In order to investigate the
effect of different sprays on berry firmness, 20 mg/L GA3 (GA3 treatment) was applied at
10mm average berry size; 20 mg/L GA3 plus 3 mg/L CPPU (CPPU treatment) was
applied at 10 mm average berry size; and a mixture of 8 L/ha Stopit® and 5 L/ha
Caltrac® (calcium treatment) was applied directly to the bunches every two weeks from
berry set till veraison for the calcium treatments. The control received no plant
bioregulators (PBR’s). The treatments were the same for both cultivars.
Grapes were stored three weeks at 0 °C and one week at 10 °C after which it was
evaluated for loose berries, botrytis infections, rachis browning and berry split.
Afterwards it was tasted by an independent tasting panel.
Firm berries were found to have an opaque coloured flesh while soft berries had a
gel-like translucent flesh. For berries with normal firmness, the opaque flesh is limited to
the outer mesocarp of the berry. Extremely firm berries’ whole mesocarp consisted of
the opaque coloured flesh while soft berries’ mesocarp consisted of mostly the gel-like
translucent flesh with, in some cases, a very thin layer of opaque flesh just under the
skin.
Berry firmness was not related to cell size as the cell size of the tissues in the firm
and soft berries were identical. Cell shape seems to play an important role in berry
firmness. The cells in the opaque coloured flesh of the outer mesocarp are more turgid
and oval than those in the gel-like flesh of the inner mesocarp. Berry firmness is
therefore determined by the thickness of the outer mesocarp with the opaque coloured
flesh that contains turgid cells. The thickness of cell walls between the different tissues did not differ. There was however a difference between the cell contents and the
plasmalemmas of the inner and outer mesocarp. The plasmalemma and tonoplast of
the outer mesocarp cells was more intact than those of the inner mesocarp. The
membranes in the inner mesocarp are more subtracted form the cell wall than in the
outer mesocarp.
Both the PBR’s and calcium treatments cause a delay in sugar accumulation in the
case of Redglobe and Waltham Cross. The CPPU treatment results in significantly
bigger and firmer berries for both cultivars. In the case of Redglobe, this treatment
cause bigger cells in the outer mesocarp suggesting a correlation between berry
firmness and cell size. In the case of Waltham Cross, however, cell size did not play a
role in berry size and firmness; instead the rate of cell division earlier in berry
development. The CPPU treatment was the only treatment that maintains berry
firmness during cold storage for Redglobe while GA3 and CPPU did so in the case of
Waltham Cross.
PBR’s seems to have no effect on cell wall thickness. In the case of Redglobe, the
calcium treatments resulted in significantly thinner cell walls, but this can not be
explained.
Calcium and GA3 treatments had a negative effect on grape quality after cold
storage of both Redglobe and Waltham Cross. The Waltham Cross CPPU treatment
results in better taste and colour as observed by the tasting panel, while in the case of
Redglobe, the tasting panel preferred the control.
It is found that the use of CPPU in combination with GA3 had the best effect on the
eating quality, storage capacity, berry size and firmness. When a producer decides to
use the CPPU treatment in order to improve berry firmness, he must realize that it can
cause delayed ripening which can affect the export of the fruit.
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The evaluation of Fourier transform infrared spectroscopy (FT-IR) for the determination of total phenolics and total anthocyanins concentrations of grapesLochner, Elana 03 1900 (has links)
Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2006. / The assessments of grape and wine quality are complex issues and the wine industry needs more objective analysis of grape and wine quality. The standard quality assessment protocol for grading grapes at most wine cellars in South Africa is based on viticultural practices and the determination of chemical parameters such as ºBrix, pH and titratable acidity (TA). Grape juice indices calculated by formulae such as ºBrix/pH, TA/pH, ºBrix/TA, ºBrix x (pH)2 have been used in the past but these approaches have had limited success. It was shown that the total anthocyanins and total phenolics of red grapes correlate with wine quality and provide additional objective measures of grape quality. Most methods for the quantification of total anthocyanins and total phenolics are complex and time consuming and therefore not easily implemented in the routine laboratory environment. Fourier transform infrared spectroscopy (FT-IR) is widely used in South African laboratories for the routine quantification of wine and grape parameters but the commercial calibration models supplied for the quantification of grape total anthocyanins and phenolics are not satisfactory. The focus of this study was to develop new FT-IR calibration models for the quantification of total anthocyanins and phenolics of grapes and to use the generated data during a preliminary evaluation of the implementation of these parameters as part of the grape quality control protocol at a commercial winery in South Africa.
The potential of Fourier transform infrared spectroscopy (FT-IR) for the rapid quantification of total anthocyanins and total phenolics in red grapes was investigated and evaluated for prediction accuracy with independent validation sets. The design of calibration sets aimed at capturing most of the variation due to vintage (2004 and 2005), cultivar (Cabernet Sauvignon, Merlot, Pinotage, and Shiraz) and sugar concentration. Best prediction accuracies were obtained for calibration sets using grapes from a single vintage or cultivar or approximately the same sugar concentration. The highest prediction accuracies were obtained for total anthocyanins calibration sets of grapes with sugar concentrations ≥ 23.5ºBrix (SEP = 0.13 mg/g; R2 validation set = 0.77) and for total phenolics calibration sets of grapes with sugar concentrations < 23.5ºBrix (SEP = 0.13 OD280/g; R2 validation set = 0.74). Strong correlations were found between the spectral data and the total anthocyanins (SEP = 0.12 mg/g; R2 validation set = 0.84) and total phenolics concentration data (SEP = 0.10 OD280/g; R2 validation set = 0.76) for 2005 Merlot calibration sets indicating that the FT-IR spectra captured most of the variation. Overall the RPD (ratio of the standard deviation of the reference data to the standard error of prediction) values of all calibration models were below 3 indicating that calibration models are fit for screening purposes. Spectroscopic absorbance at 280 nm is not specific enough for the quantification of total phenolics and the use of an alternative reference method such as high performance liquid chromatography (HPLC) will be considered in the future. Principal component analysis (PCA) revealed that the major sources of variation in the FT-IR spectra of grapes could be ascribed to vintage and grape sugar concentration and this had an effect on the accuracy of the analytical data generated when using FT-IR spectroscopy. This report is the first to our knowledge where FT-IR has been used for the quantification of total anthocyanins and phenolics of grapes.
The evaluation of the reference laboratory protocol for the quantification of total anthocyanins and total phenolics in grapes were evaluated in Chapter 4 and emphasized the importance of meticulous laboratory practices to obtain reliable reference data for calibration purposes.
This large scale investigation of the total anthocyanins and phenolics concentrations in grapes is the first of its kind in South Africa and a quantitative database containing analytical data of the anthocyanins and total phenolics concentrations of 692 grape samples representing a wide range of grape maturities of Vitis vinifera cultivars Cabernet Sauvignon, Merlot, Pinotage and Shiraz from the 2004 and 2005 vintages was established based on the reference values. The data were used in a preliminary investigation of the implementation of total anthocyanins and total phenolics concentrations as part of grape quality classification at a commercial South African winery (Chapter 5). The results showed that the total anthocyanins and total phenolics concentration in grapes increased with increasing grape maturity (measured as sugar concentration). ANOVA and post-hoc analysis (Bonferroni testing) revealed significant differences between the total anthocyanins and total phenolics concentrations of the four Vitis vinifera cultivars investigated. Grapes harvested earlier in the season had significantly higher (p≤0.05) total anthocyanins and total phenolics concentrations than grapes harvested later in the season. This implies that grapes harvested earlier in the harvest season could produce wines with higher quality. Grapes from regularly irrigated vineyards had lower total anthocyanins and total phenolics concentrations compared to dryland vineyards. The current grape grading system in use at the industrial cellar did not correlate well with the total anthocyanins and total phenolics concentrations of grapes which highlighted the need for the inclusion of more objective measures during grape grading. The information captured in the database can be used as a starting point to establish profiles of the typical anthocyanins and total phenolics of South African grapes and data from more vintages should be included and continually updated. These findings highlight the important contribution of the results obtained in this preliminary study for the incorporation of total anthocyanins and phenolics concentrations as objective parameters of grape quality. Finally multivariate data analysis of the FT-IR spectra revealed important information regarding factors (both physical and chemical) that contribute to the variation of the spectra. The main variation between the 2004 and 2005 samples can probably be interpreted in terms of the water content of the samples.
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Canopy manipulation practices for optimum colour of redglobe (V.Vinifera L.)Strydom, Janene 03 1900 (has links)
Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2006. / Under certain South African conditions, Redglobe develops a colour that is too dark
and thus unacceptable for the Far Eastern markets. These markets require a pink
colour instead of a dark red colour. The cultivation of grapes with an acceptable
colour involves amongst other, canopy management practices. This generally
includes the removal of leaves and/or lateral shoots. Hereby, the leaf area and the
microclimatic conditions in the canopy are altered.
The aim of this study was to test the usefulness of leaf and lateral shoot removal
at different defoliation times after anthesis in order to obtain a pink coloured
Redglobe crop. Other quality aspects, namely total soluble solids (TSS), total
titratable acidity (TTA), berry mass and total yield, were also evaluated.
A canopy management trial was conducted on six year old Redglobe vines with
moderate vigour. The treatment design was a 2 x 3 x 4 factorial and involved two
leaf removal (L) levels (L0 = 0% leaf removal; L33 = 33% leaf removal) in combination
with three lateral shoot removal (LS) levels (LS0 = 0 % lateral shoot removal; LS50 =
50% lateral shoot removal; LS100 = 100% lateral shoot removal). Four defoliation
times (DT) were selected: 36 (pea berry size), 69 (véraison), 76 (one week after
véraison) and 83 (two weeks after véraison) days after anthesis (DAA). A total of 24
treatment combinations, replicated in four blocks, were applied.
Generally, treatment combinations involving 33% leaf removal lowered the main
shoot leaf area. Likewise, the lateral shoot leaf area was decreased by increasing
levels of lateral shoot removal at any defoliation time. As expected, 33% leaf
removal applied in combination with any level of lateral shoot removal, always
resulted in a lower total vine leaf area compared to where 0% leaf removal was part
of the treatment combination. Compensation reactions occurred and in this regard
the main shoot leaf size increased due to 33% leaf removal applied at 1 week after
véraison and 2 weeks after véraison. Treatment combinations involving lateral shoot
removal increased the ratio of main shoot leaf area to the total leaf area. On the
other hand, the main shoot leaf area percentage was lowered by the application of
33% leaf removal at 2 weeks after véraison compared to no leaf removal at the same
defoliation time. It can therefore be assumed that the contribution of lateral shoot
leaves to grape composition might have increased in cases where the main shoot
leaf area was lowered at a later stage (e.g. 2 weeks after véraison).
The bunches were visually evaluated and divided into classes from dark (class
one) to light (class nine). This visual bunch evaluation showed that the mean bunch
colour was in class three (lighter than class two) due to the defoliation time. The
lateral shoot removal x leaf removal interaction resulted in a mean bunch colour that
was in classes 2 and 3. However, within these classes, there was a tendency that
bunch colour decreased for defoliation times later than pea berry size. The lateral
shoot removal x leaf removal interactions showed that bunch colour was darker when
the treatment combinations involved 0% leaf removal. The percentage of bunches
with the desired colour was increased by application of the treatments at véraison, compared to the other defoliation times, and also with 50% lateral shoot removal and
100% lateral shoot removal compared to 0% lateral shoot removal. Biochemical
analyses confirmed that increased levels of lateral shoot removal generally lowered
the anthocyanin concentration regardless of defoliation time.
A similar effect on TSS was observed, i.e. from véraison onwards, the application
of 50% lateral shoot removal and 100% lateral shoot removal tended to lower TSS.
The effect of these levels of lateral shoot removal at véraison was significant. The
role of the lateral shoots in colour development and sugar accumulation is therefore
emphasized.
Furthermore, the special role that lateral shoots also play in berry development is
illustrated in that berry mass tended to decrease when 100% lateral shoot removal in
combination with 33% leaf removal and 100% lateral shoot removal in combination
with 0% leaf removal were applied at véraison. This, together with the positive
relationship obtained between grape colour and the lateral shoot leaf area:fruit mass
ratio, accentuates the role of active leaf area during the ripening period.
The possible effect of the microclimatic light environment on colour must also be
considered. However, although the light intensity increased with increased levels of
LS, the colour that was obtained was probably not associated with the differences in
light intensity.
It was found that it is possible to manipulate the colour of Redglobe grapes with
defoliation treatments. However, the treatments that have a decreasing effect on
grape colour also affected other quality parameters like TSS and berry size
negatively.
Although, it is possible to reduce the colour of Redglobe through the application
of leaf and lateral shoot removal at different defoliation times, the question arises
whether the treatment combinations used in this study are worthwhile to pursue
because the mean bunch colour that was obtained was still too dark. However, it
was possible to increase the percentage of bunches with the desired colour.
Therefore, if such treatments are applied, it must be approached cautiously, keeping
in mind that assimilate supply has to be sustained throughout the ripening period.
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