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Aspects of fruit size and quality in citrusMzini, Loyiso L. 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the Western
Cape region of South Africa. Small fruit is not only unacceptable to the consumer but is also
more difficult and expensive to harvest. Means of alleviating this problem is to manage the
crop load. Hand thinning trials were conducted to evaluate the effect of timing and severity
thereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by a
heavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by a
reduction of total yield. Yield was reduced up to 30% when heavy thinning treatments were
applied. No effect on early or late treatments were obtained since the trial was conducted
rather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirable
results. However, better packouts are expected with thinning treatments since blemished fruit
are also removed.
The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were also
evaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, it
was observed that more than one spray was no better in improving fruit size. The use of
multiple dichlorprop sprays resulted in no additional yield reduction, while internal fruit
quality was also not affected. The best results were obtained with dichlorprop at 50 mg. L-1
•
The use of dichlorprop with different surfactants was evaluated in both 'Clementine'
mandarin and 'Valencia' orange. The fruit size was increased from 50 mg. L-1 up to 100 mg.
L-1
• Yield was usually not affected but, where reductions were experienced, yield of large
fruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the first
year, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield and
internal fruit quality effects were observed. The following year, when early and late sprays (fruit diameter at spray time = 8 and 12 mm, respectively) were evaluated, it was observed
that late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) was
significantly increased by early sprays. This implies that the dichlorprop effect on fruit size
is during the early stages of fruit development, just after or during the late stage of the
physiological fruit drop period. Yield was drastically reduced by up to 35%, which affected
the actual kilograms of large fruit adversely in some treatments. Juice percentage was
inconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended to
increase TSS slightly in year one and significantly so in year two, but did not affect the
TSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effective
and seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemed
to show potential in enhancing dichlorprop efficiency to reduce the application cost.
The dichlorprop-sprayed fruit was used to measure carotenoid content of the rind during the
later stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50
mg. L-1 obtained better carotenoid content in both 'Clementines' mandarin and 'Valencia'
orange. Also, fruit exposed to light had higher carotenoid levels as compared to fruit shaded
with brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1
, even though
exposed to light did not show significant differences with unsprayed in both shaded and
exposed conditions. Therefore, no consistent effect of dichlorprop was established on total
carotenoid content of the rind. / AFRIKAANSE OPSOMMING: Vruggrootte van 'Clementine' mandaryn en 'Valencia' lemoene kan 'n probleem wees in die
Wes Kaap area van Suid Afrika. Klein vrugte is nie net onaanvaarbaar vir die verbruiker nie,
maar is ook moeilik om te oes. Vrugdrag manipulasie is een manier om hierdie probleem te
beheer. Hand uitdunningsproewe is uitgevoer om die effek van tyd en graad van uitdunning
op vruggrootte te bepaal. Strawwe vruguitdunning (60% van vruggies verwyder) het groter
vrugte tot gevolg gehad maar het gelei tot 'n verlaagde opbrengs. Opbrengs is tot soveel as
30% verlaag met die strawwe vruguitdunning. Vroeë en laat behandelings het egter geen
effek gehad nie, aangesien die proewe te laat uitgevoer is (4 tot 6 weke na die fisiologiese
vrugvalperiode) om die gewenste effek te verkry. Beter uitpak word verwag na uitdunning,
aangesien vrugte met letsels ook verwyder word.
Die effek van veelvuldige 2,4-dichlorofenoksie-propioonsuur (dichlorprop) spuite IS ook
geëvalueer op 'Nules Clementine' mandaryn. Daar is geen verskil gevind tussen enkel en
veelvuldige spuite in terme van vruggrootteverbetering nie. Die gebruik van veelvuldige
dichlorprop spuite het nie tot 'n verlaging in opbrengs gelei nie, en interne vrugkwaliteit is
ook nie beïnvloed me. Die beste resultate is verkry met die 50 mg. L-1 dichlorprop
behandeling.
Die gebruik van dichlorprop saam met verskillende benatters is op beide 'Clementine'
mandaryn en 'Valencia' lemoene geëvalueer. Vruggrootte het toegeneem vanaf 50 mg. L-1 tot
100 mg. L-1
• Opbrengs was net in sekere gevalle verlaag en dan sonder 'n betekenisvolle
verskil in groot-vrug produksie (>55 mm: Clementines). Tydens die eerste jaar van die
'Valencia' lemoen proef is die dichlorprop relatief laat gespuit (vrug deursneë: 19 mm). Daar
was geen effek op vruggrootte, opbrengs en interne vrugkwaliteit nie. Tydens evaluasie van vroeë en laat bespuitings die volgende jaar is waargeneem dat laat bespuitings geen effek op
vruggrootte gehad het nie, terwyl vruggrootte (48 vrugte per karton) betekenisvol verhoog is
deur die vroeë bespuitings (Vruggrootte voor bespuiting = 8 en 12 mm, onderskeidelik). Dit
impliseer dat dichlorprop se effek op vruggrootte gedurende die vroeë stadiums van
vrugontwikkeling is, net na of gedurende die laat stadiums van die fisiologiese
vrugvalperiode. Opbrengs is drasties verlaag deur dichlorprop, tot soveel as 35% wat die
kilogram groot vrugte negatief beïnvloed het in sommige behandelings. Sappersentasie was
nie konsekwent affekteer nie, maar is verlaag deur die dichlorprop bespuitings. Dichlorprop
het die TSS effens verhoog in beide jare, maar het geen effek gehad op die TSS:TA
verhouding nie. Die gebruik van Orchex minerale olie as benatter was effektief by 150 mL.
100 L-1
, en laat klaarblyklik die gebruik van dichlorprop by laer konsentrasies toe. Dus, kom
dit voor dat benatters die potensiaal het om die effektiwiteit van dichlorprop te verbeter wat
lei tot 'n verlaging in toedieningskoste.
Die dichlorprop gespuite vrugte is gebruik om karotenoïed-inhoud van die skil te meet tydens
die laat stadiums van vrugontwikkeling. Vrugte gespuit met dichlorprop teen 'n konsentrasie
van 50 mg. L-1 het 'n beter karotenoïed-inhoud in beide 'Clementine' mandaryn en 'Valencia'
lemoene tot gevolg gehad. Vrugte blootgestel aan lig het ook 'n hoër karatenoïedkonsentrasie
gehad as vrugte wat met bruin papiersakke bedek was. Dichlorprop bespuite
vrugte teen 100 mg. L-I, alhoewel blootgestel aan lig, het geen betekenisvolle verskil gehad
in vergelyking met onbespuite vrugte nie. Dus is daar geen konsekwente effek van
dichlorprop op karotenoïde inhoud van die skiI waargeneem nie.
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Ecophysiological responses of citrus trees and sugar accumulation of fruit in response to altered plant water relationsPrinsloo, Johan Andries 03 1900 (has links)
Thesis (MSc (Horticulture))--University of Stellenbosch, 2007. / This study was undertaken to quantify some of the effects of daily fertigation on ecophysiological responses in citrus trees (Citrus spp.). Initial research was conducted to optimise and standardise the sampling procedure to quantify stem water potential (ψstem) in citrus trees. To reliably determine the plant water status of citrus trees, the following conditions are required to minimise unwanted variation in ψstem measurements. Bagging of leaves with black polyethylene envelopes covered with aluminium foil 3 to 4 hours prior to measuring ψstem allows the plant water status in those leaves to equilibrate with whole-tree plant water status, thereby providing a realistic measurement of the current water status. The use of aluminium foil to cover the bagged leaves, reduces unwanted heat stress by reflecting sunlight, and dramatically reduced variation in ψstem. The time of day at which ψstem measurements are made is important to ensure consistency in comparisons among treatments and interpretation of irrigation treatment effects. “Physiological midday” is the preferred time of day to measure ψstem, i.e. 1100 HR. Transpiring leaves with open stomata would be in sun-exposed positions on the east side of trees and should be used for making ψstem measurements. Under similar experimental conditions as those used here, only three leaves per replicate are required to detect a difference of 0.05 MPa in ψstem between treatment means. Plant water status categories were developed which may have useful practical applications, i.e. >-1.0 MPa = no water deficit; -1.0 to -1.2 MPa = low water deficit; -1.2 to -1.4 MPa = moderate water deficit; <-1.4 to -1.6 MPa = high water deficit; and <-1.6 MPa = severe water deficit.
Attempts are being made to develop systems that improve crop management and enhance citrus fruit production through efficient and timeous application of water and mineral nutrients which has led to the use of daily drip fertigation or the open hydroponics system (OHS). However, the perceived benefits are not necessarily supported by facts. Fruit size and yield are apparently enhanced, but possible negative aspects of the system have not been quantified. Fruit produced on trees grown under daily drip fertigation generally have a lower total soluble solids concentration than on trees under micro-sprinkler irrigation. This is mainly due to a dilution effect that is caused by the greater availability of water and the uptake thereof. Sugar accumulation can be optimised by controlling the amount of water that the plant receives at different developmental stages. Therefore, it is essential to quantify the ecophysiological responses and benefits of OHS/daily fertigation, as well as the effects of this technology on fruit quality. ‘Nules Clementine’ mandarin (C. reticulata Blanco) trees in two commercial orchards in Simondium, Western Cape province, South Africa, received differential irrigation treatments. The treatments were applied at the end of stage I (± mid December) of fruit development. Stem water potential, fruit size and internal fruit quality were determined. Water-deficit stress enhanced sugar accumulation of ‘Nules Clementine’ mandarin by 0.3 to 0.6 °Brix under certain conditions. These conditions require that the difference in ψstem should be of a sufficient intensity of between 0.16 and 0.3 MPa, and this difference should be maintained for a sufficient duration of between 4 and 6 weeks. Furthermore, deficit irrigation should be applied relatively early in fruit development, namely during the sugar accumulation stage which starts within 4 weeks of the end of the fruit drop period and continues until harvest.
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Yield and fruit quality of citrus species relative to foliar sprays of macronutrientsMudau, N. Fhatuwani (Nixwell Fhatuwani) 03 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Yield and fruit quality of Citrus species relative to foliar sprays of macronutrients
Marginal fruit colour and poor internal quality have been primary problems in the production of
early-maturing mandarins in the Western Cape region (34 Os t 9°E). This leads to a reduction in the
percentage of exportable fruit, a delay in the picking and consequent reduction in internal quality
due to over-maturity. Therefore, a well-developed rind colour and internal quality of citrus are
quality parameters of major importance in the fruit market.
The effect of soil-applied limestone ammonium nitrate (LAN) and foliar low-biuret on fruit colour,
yield and internal fruit quality of 'Mihowase' Satsuma on 'Troyer' citrange rootstock were
evaluated. A significant reduction in leaf N levels was recorded where soil N has been reduced
from 168 kg N/ha per annum to 126 kg Nlha per annum. Nitrogen applications influenced internal
quality, although differences between treatments were too small to be of commercial importance.
Despite tree appearance being more yellow in some years where N was predominantly applied as
foliar spray, no consistent reduction in fruit size or yield was found. There were no clear significant
differences in fruit colour, probably due to the fact that leaf N-Ievels were still within or below the
norms suggested for Satsuma.
The effect of Seniphosf , a mineral mixture of 31Og/L P20S, 56g/L CaO and 30g/L total N, and
mono-potassium phosphate (MKP) [52% P20Sand 34% K20] on fruit colour, yield and internal fruit
quality of mandarins, viz., 'Mihowase' Satsuma and 'Nules' Clementine on 'Troyer' citrange
rootstock were evaluated. Seniphos'" and MKP applied during autumn colour break also did not
influence fruit colour, yield and internal fruit quality, viz., juice content (%), total soluble solids
(TSS), titratable acid (TA) and TSS:TA ratio of 'Nules' Clementine and 'Mihowase' Satsuma. In the Citrusdal region of South Africa (Western Cape Province), rind roughness is a general
problem which often limits the percentage of exportable fruits. The effect of foliar mono-potassium
phosphate (MKP) applied at 3% or 5% and urea ammonium phosphate (UAP) at 2% at 4 or 6
weeks, respectively, after full bloom (AFB) on yield, internal and external fruit quality (rind
texture) of Citrus spp on rough lemon rootstock were evaluated. MKP and UAP had no consistent
effect on yield, juice content (%), TSS, TA and TSS:TA ratio of 'Nouvelle' tangor, 'Valencia'
orange, 'Shamouti' midseason and 'Oroval' Clementine. MKP and UAP sprays significantly, but
inconsistently improved rind texture of 'Nouvelle' tangor, 'Shamouti' midseason and 'Valencia'
orange. However, no positive effect was found on rind texture of 'Oroval' Clementine and
'Eureka' lemon. Inconsistent effects ofMKP and UAP sprays were also found on % leafN, P and
K. / AFRIKAANSE OPSOMMING: Opbrengs en vrugkwaliteit van sitrus spesies relatief tat blaar toedienings van makroelemente
Marginale vrugkleur en swak interne kwaliteit is die prim ere produksieprobleme in vroee seisoen
mandaryne in die Wes-Kaap (34 Os 19°E). Die gevolg is 'n lae persentasie uitvoerbare vrugte
omdat die oesdatum uitgestel word wat 'n afname in interne kwaliteit veroorsaak weens oorrypheid.
Goed ontwikkelde skilkleur en interne kwaliteit is dus van groot belang vir bemarking van die
vrugte.
Grond-toegediende kalksteen-ammonium-nitraat (KAN) en lae biuret ureum se effek op vrugkleur,
oesgrootte en interne vrugkwaliteit van 'Mihowase' Satsuma op 'Troyer citrange' onderstamme is
ge-evalueer. 'n Betekenisvolle afname van die N viakke in die blare is gevind nadat grondtoediening
van N vanaf 168 kg N/ha/jaar na 126 kg N/ha/jaar venninder is. N toedienings het
interne kwaliteit beinvloed, maar die verskille tussen die behandelings was nie van kornmersiele
waarde nie. Al was die boomvoorkoms geler in sommige jare waarin N hoofsaaklik as
blaarvoedings toegedien is, was daar nie konstante afnames in vrug-of oesgrootte nie. Daar was
geen betekenisvolle verskille in vrugkieur nie, waarskynlik omdat die blaarvlakke van N steeds
binne die nonne daarvoor in Satsumas was.
Die effek van Seniphos ('n minerale mengsel van 310g/L P20S, 56g/L CaO en 30g/L totaal N en
monokaliumfosfaat (MKP) [52% P20S en 34% K20] op vrugkleur, oesgrootte en interne
vrugkwaliteit van 'Mihowase' Satsumas en 'Nules' Clementine op Troyer citrange onderstarnme is
geevalueer. Seniphos en MKP, toegedien tydens kleurbreek in die herfs, het ook nie skilkleur of
interne vrugkwaliteit (sappersentasie, totale oplosbare vaste stowwe (TOV), suurheid (TS) en
TOV:TS) betekenisvol bemvloed nie. In die Citrusdal-omgewing in die Wes-Kaap Provinsie (Suid-Afrika) is skilgrofheid 'n algemene
probleem wat die hoeveelheid uitvoerbare vrugte beperk. Die effek van blaartoegediende MKP teen
3 en 5% en ureum-amrnoniurn-fosfaat (UAP) teen 2%, op onderskeidelik 4 of 6 weke na volblom, is
geevalueer ten opsigte van oesgrootte, interne en ekstenne (skil grofheid) vrug kwaliteit in Citrus
spp op growweskilsuurlemoen onderstam. Nie MKP of UAP het konsekwente verskille getoon
t.o.v. oesgrootte, sappersentasie, TOV, TS, of TOV:TS in 'Nouvelle' tangor, 'Valencia' orange,
'Shamouti' midseison of 'Oroval' Clementine nie. Skiltekstuur is egter betekenisvol, hoewel
inkonsekwent, verbeter in laasgenoemde drie. Skiltekstuur van 'Oroval' Clementine en 'Eureka'
suurlemoen is nie bemvloed nie. Blaarpersentasies van N, P en K is ook inkonsekwent deur MKP
en UAP beinvloed.
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Genetic variation and fruit quality in sea buckthorn and black chokeberry /Jeppsson, Niklas, January 1900 (has links) (PDF)
Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 9 uppsatser.
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Qualidade de maçãs Gala‟ e Fuji‟ em função da nutrição e das condições climáticas no Sul do Brasil / Quality of Gala and Fuji apples affectrred by nutrition and climatic conditions in Southern BrazilMacedo, Charle Kramer Borges de 31 July 2014 (has links)
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Previous issue date: 2014-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The diferences in climatic conditions and the appropriate nutritional management are crucial for productivity and fruit quality. Southern Brazil is the main apple production region, with the States of Rio Grande do Sul (RS) and Santa Catarina (SC) the major producers. The aim of this research was to evaluate the quality of apple fruits grown in Southern Brazil,considering the nutritional variables and weather conditions during the 2012-2013 season. The study was carried out in the regions of Vacaria-RS, Bom Jesus-RS, Caxias do Sul-RS, Fraiburgo-SC and São Joaquim-SC. Seventy-six orchards were selected. The concentrations of nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg) and calcium (Ca) were quantified in samples of leaves and fruits. The N/Ca and (K+Mg)/Ca ratios were also quantified in the fruit samples. Sulfur (S), cooper (Cu), zinc (Zn), iron (Fe), manganese (Mn) and boron (B) were quantified in leaf samples. At harvest, 20 fruits were ecaluate for flesh fiirmness (N), soluble solids (SS;%), titratable acidity (TA; % malic acid), iodine-starch, and transverse and longitudinal (mm) diameter. After refrigerated storage under air atmosphere (AA) for 120 days (0±1 °C/ RH of 90±5 %) followed by seven days at 20 °C, fruit were analyzes for flesh firmness, SS and AT. Climatic data of rainfall (mm), number of days of precipitation,temperatures (maximum, minimum and average) (°C) and Wind speed (m/s) were evaluated in the diferente regions. The averageconcentrations (mg kg¯¹ of fresh matter) in the fruit of de N, P, K,,Ca and Mg were, respectively, 295, 83, 1.399, 47 e 36 mg kg¯¹ in Fuji , the mean values of (K+Mg)/Ca andN/Ca relatios were 30 and 6,4 for Gala , and 35 and 6,7, for Fuji , respectively. Gala and Fuji apple fruits had P concentration below the lower minimum critical value (˃100 mg kg¯¹) and the N/Ca ratio was below the upper critical value (˂14 mg kg¯¹). Fuji apple fruit had Ca concntration below the lower critical value (˃40 mg kg¯¹), and the (K+Mg)/Ca ratio above the uppercritical value (˂30 mg kg¯¹). In Gala apples, colder regions favor the occurrence of lower N concentration, higher Ca concentration and lower N/Ca and (K+Mg)/Ca ratios in the fruit. The average concentration (g kg¯¹ of dry matter) in the leaves of N. P. K. Ca, and Mg were, respectively, 21, 2, 17, 10, 3 g kg¯¹ in Gala , and 23, 2, 16, 12, 3 g kg¯¹ in fuji . Apples harvested in diferente regions showed great variation in terms of starch-iodine index, and thus, the postharvest results were signicantly affected by fruit maturity at harvest. During the experimental period, there were substantial diferences of climatic conditions between regions. Fraiburgo had the lowest average anual rainfall (1,170 mm) and Bom Jesus the highest one (1,749 mm). The Monthly average temperatures were highest in Caxias do Sul and lowest in São Joaquim / As diferenças nas variáveis climáticas e o manejo nutricional adequado são fatores determinantes para produtividade e qualidade dos frutos. A região Sul do Brasil destaca-se no cultivo de macieiras, sendo os Estados do Rio Grande do Sul (RS) e Santa Catarina (SC) os principais produtores. Este trabalho teve por objetivo determinar a qualidade de frutos de macieira produzidas no Sul do Brasil, avaliando as variáveis nutricionais e as condições meteorológicas durante a safra 2012-2013. O estudo foi realizado nas regiões de Vacaria-RS, Bom Jesus-RS. Caxias do Sul-RS, Fraiburgo-SC e São Joaquim-SC. Selecionou-se 76 pomares. As concentrações de nitrogênio (N), fósforo (P), potássio (K), magnésio (Mg) e cálcio (Ca) foram determinadas em amostrar de folhas e frutos. Determinou-se também as relações N/Ca e (K+Mg)/Ca nas amostras de frutos. Enxofre (S), cobre (Cu), zinco (Zn), ferro (Fe), manganês (Mn) e boro (B) foram determinados nas amostras de folhas. Na colheita, 20 frutos foram avaliados quanto à firmeza da polpa (N), sólidos solúveis (SS; %), acidez titulável (AT; % ácido málico), índice de iodo-amido e diâmetro transversal e longitudinal (mm). Após a armazenagem refrigerada sob atmosfera do ar (AA) durante 120 dias (0±1°C/UR de 90±5%), seguido de mais sete dias a 20°C, foram realizadas análises de firmeza de polpa, SS e AT dos frutos. Dados climáticos de precipitação pluvoométrica (mm), número de dias de chuva, temperaturas máxima, mínima e média (°C) e velocidade do vento (m/s) foram avaliados nas diferentes regiões. As concentrações médias (mg kg¯¹ matéria fresca) de N, P, K, Ca e Mg nos frutos foram , respectivamente, 295, 83,1.299, 47 e 36 mg kg¯¹, para Gala , e 260, 73, 1.331, 39 e 28 mg kg¯¹, para Fuji . Os valores médios das relações (K+Mg)/Ca e N/Ca foram 30 e 6,4 para Gala , e 35 e 6,7 para Fuji , respectivamente Maçãs Gala e Fuji apresentaram concetração de P abaixo do nível crítico inferior (˃ 100 mg kg¯¹), e a relação N/Ca ficou abaixo do nível crítico superior (˂14 mg kg¯¹). Maçãs Fuji apresentaram valores de Ca abaixo do nível crítico inferior (˃40 mg kg¯¹), e a relação (K+Mg)/Ca acima do nível crítico superior (˂30 mg kg¯¹) em maçãs Gala , regiões mais frias favorecem a ocorrência de menores teores de N, maiores teores de Ca e menores relações N/Ca e (K+Mg)/Ca. As concentrações médias nas folhas (g Kg¯¹ matéria seca) de N, P, K, Ca, Mg foram, respectivamente, 21, 2, 17, 10, 3 g kg¯¹, para Gala , e 23, 2, 16, 12, 3 g kg¯¹, para Fuji . S maçãs colhidas nas diferentes regiçoes apresentaram grande variação no índice de iodo-amido, e assim, os resultados de pós-colheita foram afetados significativamente pelo ponto de colheita. Durante o período avaliado, houve diferença nas variáveis climáticas entre regiões. Fraiburgo apresentou os menores volumes médios de precipitação pluvial anual (1.170mm) e Bom Jesus os maiores valores (1.749 mm). As temperaturas médias mensais mais altas foram observadas em Caxias do Sul, e as menores em São Joaquim
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The potential of post-harvest potassium silicate dips to mitigate chilling injury on citrus fruit.Mditshwa, Asanda. January 2012 (has links)
The South African Citrus Industry is the second largest exporter of citrus, after Spain. The industry is under pressure to supply high quality fruit as well as to expand into new, high paying markets. However, high paying markets such as Japan and the USA require cold sterilised fruit as obligatory quarantine treatments against Mediterranean fruit fly (Ceratitis capitata) in order to reduce any possible spread of the pest. Citrus fruit originated from tropical climates and hence are chilling susceptible.
Chilling injury symptoms appear as dark brown spots, pitting and/or decay when fruit are transferred to shelf temperatures; thus reducing the marketability of citrus fruit. Therefore, there is need for methods to mitigate chilling injury. Previous studies have shown silicon to mitigate many forms of stress without any hazardous effect on human health. Thus, the aim of the study was to investigate the potential of post-harvest silicon dips in mitigating chilling symptoms in citrus fruit.
Briefly, fruit from two sources (Ukulinga Research Farm and Ithala Farm) were dipped in different silicon concentrations (0, 50, 150, and 250 mg ℓ-1) for 30 minutes and thereafter stored at -0.5 or 2⁰C for up to 28 days with weekly evaluation for chilling injury symptoms. Total antioxidants were determined using FRAP, ABTS, and DPPH assays under spectrophotometer. In addition, sugars, ascorbic acid, phenolics and flavonoids were analysed using High Performance Liquid Chromatography (HPLC).
Fruit from Ukulinga Research Farm showed significantly higher total antioxidants (ascorbic acid total phenolics and specific flavonoids hesperidin and naringin) and sugars relative to fruit from Ithala Farm. Low concentrations of silicon dips significantly reduced the appearance of chilling injury symptoms by inducing an enzymatic conversion of glucose to ascorbic acid, thereby increasing the antioxidant capacity of chilling susceptible fruit. Moreover, silicon increased the concentration of total antioxidants, total phenolics and total flavonoids. High silicon concentrations had a negative effect on post-harvest quality of lemons by increasing fruit weight loss and electrolyte leakage, resulting in appearance of chilling symptoms.
In conclusion, the study showed that silicon had potential to reduce chilling injury. However, high silicon concentrations raised concern, in particularly, on fruit appearance. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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