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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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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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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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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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