Thesis (M.Sc. (Horticulture)) -- University of Limpopo, 2022 / Cold storage is commonly used to prolong papaya fruit storability. Furthermore, the optimal recommended storage temperature is below 10℃ for export and distant market. However, chilling injury (CI) occurs at 10℃ or lower during prolonged cold storage. This condition hampered consumer acceptance, resulting in economic losses for producers and exporters. Therefore, the study aimed to investigate the potential of postharvest polyamine dips and storage conditions to improve the quality and shelf life of ‘Solo’ papaya fruit. The experiment was conducted as 4 x 2 factorial arranged in a completely randomised design (CRD) with eight replications. The fruits were treated with putrescine (PUT) (0 (control), 1, 2 and 3 mM) before storage for 21 days at 7.5 and 13℃ plus 5 days storage at ambient temperature. Additionally, the PUT effect on quality attributes and shelf-life were studied. The results showed that physiological and pathological disorders increased with progressive storage, irrespective of storage temperature. However, PUT treatment reduced the incidence of chilling injury and anthracnose at both 7.5 and 13℃. Additionally, the interaction of treatment and cold storage temperature significantly affected ‘Solo’ papaya fruit physical and biochemical quality attributes. Furthermore, treatment with 2 and 3 mM PUT concentration reduced changes in colour, mass, firmness, TA, and TSS compared to control. In conclusion, postharvest PUT improved ‘Solo’ papaya fruit quality and prolonged shelf-life. / AgriSETA (Agricultural Sector Training Authority)

There is a growing recognition globally that many agrochemicals are hazardous to humans, animals and the environment. Therefore, there is a need to substitute these chemical products with biological and physical treatments, and to change agronomic practices in order to control pests and diseases in agriculture. The primary objective of this thesis was to develop and test in laboratory, field and commercial packhouses trials as alternative control measures against green mould of citrus (caused by Penicillium digitatum Pers: Fr. Sacc) and Penicillium molds of litchi (caused by several Penicillium). A South African isolate of P. digitatum, isolated from an infected orange fruit, was found to be resistant to imazalil (the standard postharvest fungicide used in South Africa). Sixty yeast and 92 Bacillus strains were screened for their antagonistic activity against this isolate of P. digitatum. None of the yeasts or Bacillus isolates produced a curative action against P. digitatum on oranges. However, yeast Isolate B13 provided excellent preventative control of P. digitatum, superior to all the Bacillus isolates, when it was applied to citrus fruit prior to artificial inoculation with P. digitatum. Electron microscopy showed that yeast Isolate B13 inhibited conidial germination of P. digitatum. For the control of P. digitatum pre-harvest, trees were sprayed with a yeast, Isolate B13, a few months or a few days before harvest. However, this treatment alone proved to be ineffective in providing preventative control of green mould on Valencia oranges. For the control of P. digitatum preharvest, trees were treated with potassium silicate for a full season. Regular potassium silicate treatments resulted in a significant preventative control of P. digitatum infection on both navel and Valencia oranges. Treatment of Eureka lemons with potassium silicate as a postharvest treatment for the control of P. digitatum resulted in reduced disease lesion diameters when applied preventatively or curatively. Electron microscopy showed that potassium silicate inhibited germination of P. digitatum conidia and growth of its mycelium. Hot-water dip treatment at 50-58°C for 60-180 seconds (in increments of 15 seconds), significantly reduced infection development in inoculated wounds of Valencia oranges compared with control fruit treated with tap water, without causing any rind damage. The integration of the yeast, a hot water dip and potassium silicate pre-and postharvest applications provided control of P. digitatum control in multiple packhouse trials. The control achieved by the yeast Isolate B13 or hot-water, and potassium silicate in the packhouse alone was superior or equivalent to that provided by imazalil. A similar study was also carried out to determine possible control measures for Penicillium sp. on litchis. In this study, a total of 23 yeast and 13 Bacillus isolates were obtained from litchi fruit surfaces. Ten yeast and 10 Bacillus isolates that had shown good efficacy against P. digitatum of citrus were added to these for screening against Penicillium sp. of litchis. None of the yeasts or Bacillus isolates produced a curative action against Penicillium sp. infection on litchis. However, several yeast isolates (YL4, YL10, YLH and B13) resulted in reduced severity of the pathogen, when applied preventatively, compared with an untreated control. The yeast isolates were superior to all the Bacillus isolates, when applied to litchis prior to artificial inoculation by Penicillium infection on litchis. Potassium silicate as a postharvest treatment for the control of the pathogen caused reduced lesion diameters when applied preventatively or curatively to naturally infected litchis. The results presented in this thesis highlight the use of biological, physical and agronomic practices singly or in combination as an alternative control strategy against citrus postharvest green mould. This thesis also provides an insight into expanding these strategies, partly or fully, for the control of other postharvest Penicillium infections using litchi as an example. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / The South African table grape industry exports approximately 60% of the table grapes produced. A major threat to the export of these grapes is the phytosanitary risk that insect pests pose. This study was conducted in the Hex River Valley, South Africa’s main table grape producing area. The aim of this study was to reduce the number of phytosanitary rejections from insects on table grapes from the Hex River Valley. Thus the main objectives of the study were to identify the most important phytosanitary pests in the Hex River Valley; the determination of their presence in the vineyards with possible means to control them; and to assess the possibility of using postharvest quarantine treatments in the Western Cape. Further aims were to determine the effect of different colour harvesting crates on the phytosanitary pests and whether the phytosanitary pests infested the grapes via packhouses. The most important phytosanitary pests of table grapes of the Hex River Valley are in order of importance: Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae), Epichoristodes acerbella Walker (Lepidoptera: Tortricidae), Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), Gonocephalum simplex Fabricius (Coleoptera: Tenebrionidae) and Dysdercus fasciatus Signoret (Hemiptera: Pyrrhocoridae). 12.71% of rejections were from species that were not identified, while a further 33% of the rejections were possibly identified incorrectly. Phytosanitary control of P. callosus appeared to be far more effective using Plantex® than pesticides. Weather conditions appeared to affect the abundance of P. callosus, especially warm weather, while bunches harboured less P. callosus later in the day. Control of E. acerbella with DiPel® (Bacillus thuringiensis var. kurstaki) appeared to at least reduce the population within the vineyards, and so its use is recommended. P. ficus is a non-actionable species for the USA market and is not listed as a phytosanitary pest for the Israeli market and so should not be causing any phytosanitary rejections. C. capitata appeared to be successfully controlled by the fruit fly sterile release program and the cold sterilisation it currently undergoes. G. simplex caused few rejections. It is still unclear where this pest infests the grapes, as it was found in both the field and in the packhouses. D. fasciatus occurrence on grapes was probably accidental. It was shown that picking during the early and late parts of the day, when this species was less active, reduced its occurrence in bunches. Gryllus bimaculatus (De Geer) (Orthoptera: Gryllidae), although not reported as a reason for rejections in table grapes for the past two years, was an actionable species that was present in large numbers in the Hex River Valley. There was a strong correlation between increasing quantities of pesticides and higher abundances of G. bimaculatus. It appeared to be an indicator of the overuse of pesticides. Results of this study showed that infestation by the phytosanitary pests came from neighbouring vineyards. The creation of barriers to prevent the movement of these pests between vineyards is suggested. Methyl bromide is the most commonly used postharvest quarantine treatment. Owing to the ozone-depleting properties of methyl bromide, it is scheduled to be outlawed in many countries from 2005. Alternative postharvest treatments are irradiation, extreme temperatures, forced air, vapour-heat treatments and the use of controlled atmospheres. Irradiation treatments appeared to control the pests at doses that do not damage the grapes. Controlled atmosphere treatments also have a high probability of success, although more research is required on this treatment. Low temperature treatments are relatively cheap as most exported fruit already undergoes cold storage, and appears to control species in the families Pseudococcidae and Tephritidae, although further research is required for the other pest. Colour or location of the harvesting crates in the vineyards appeared not to influence the number of phytosanitary pests collected, as they were not attracted to these crates.

Peanuts contribute significantly to food security in western Kenya due to their high nutritional value and cash crop potential. However, the crop is highly susceptible to aflatoxin contamination. Yet little information is available on the extent of contamination in the region. This study explores the level and extent of contamination of peanuts by aflatoxins, Aspergillus section Flavi, Rhizopus and Penicillium spp. in western Kenya. A survey of 769 households was carried out in the Busia and Homa bay districts of Kenya. Information on peanut pre- and post-harvest practices was collected through person-to-person interviews. Aflatoxin levels of samples collected from each household were determined by indirect competitive ELISA method. Isolation of Aspergillus section Flavi, Penicillium and Rhizopus spp. was done on Modified Dichloran Rose Bengal (MDRB) agar, while identification of specific fungal species was done on Czapek yeast extract agar (CYA). Screening isolates of A. flavus and A. parasiticus for aflatoxin production was done in high sucrose yeast extract (YES) liquid medium, and the aflatoxin types identified on TLC plates, using analytical grades of aflatoxin B1, B2, G1 and G2 as reference standards. Common household preparation techniques (roasting, making peanut paste and boiling peanuts) were evaluated for effectiveness in reducing aflatoxin levels in peanuts. The boiling procedure was modified to test the effect of magadi (locally available salt used mainly to soften legumes, vegetables or maize while cooking), ammonium persulphate and sodium hypochlorite during soaking. Magadi, sodium bicarbonate and locally prepared ash was subsequently used to boil the nuts after soaking. Aflatoxin levels ranged from zero to 7525 ìg/kg. Most samples were safe to consume, based on the European Union and Kenya Bureau of Standards tolerance levels, with 63.7 per cent of all samples having undetectable levels, and only 7.54 per cent being contaminated based on KEBS standards. Peanuts from the Busia district, which has more of Lower Midland 1 (mean annual rainfall of 1600-1800 mm) and Lower Midland 2 (mean annual rainfall of 1300-1700 mm) agro-ecological zones had significantly (÷2=14.172; P=0.0002) higher levels of aflatoxin compared to the Homa bay district, that has more of the drier Lower Midland 3 agroecological zone (mean annual rainfall of 900-1500mm). Improved cultivars had significantly (÷2=9.748; P=0.0018) lower levels of aflatoxin compared to local cultivars. Over 60 per cent of all samples had A. flavus S-strain, A. flavus L-strain and A. niger. A. flavus S-strain was positively correlated with aflatoxin levels. As expected, grading of peanuts post-harvest significantly reduced the incidence of A. flavus S- and L-strains, while peanuts collected from farmers who belonged to producer marketing groups had a significantly lower incidence of A. flavus S- and L-strains, A. niger and Rhizopus spp. The incidence of A. flavus L-strain, A. niger and Rhizopus spp. was significantly higher in local landraces compared to the improved cultivars. Over 60 per cent of isolates produced Aflatoxin B1. Intermediate processes such as sorting and dehusking led to a significant decline in levels of aflatoxin. Soaking peanuts in water, magadi, NaOCl and ammonium persulphate significantly reduced aflatoxin levels by 27.7, 18.4, 18.3 and 1.6 per cent respectively; while boiling the peanuts in magadi, local ash, baking powder and water reduced aflatoxin levels by 43.8, 41.8, 28.9 and 11.7 per cent respectively. Using magadi during boiling increased the acceptability of the boiled peanuts while reducing the aflatoxin levels. The impact of aflatoxin levels in peanuts studied in this research is within safe limits except a few samples, and therefore aflatoxin contamination of peanuts at household level is not a serious threat. Contamination by aflatoxin and post-harvest fungi can be reduced by focusing on improved control strategies for wetter and more humid zones such as planting improved peanut cultivars and controlling pre-harvest pest damage. Conventional household peanut preparation techniques should be explored as possible aflatoxin management strategies in Kenya. The aflatoxin binding properties of locally available salts such as magadi and locally prepared ash should be further investigated. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

The susceptibility of the 'Pinkerton' avocado cultivar to mesocarp discolouration, after storage, has seriously threatened its export from South Africa. This disorder has proven to be complex, requiring a better understanding of the fruit's physiology. The purposes of this study were to identify the role of pre- and postharvest factors, or their interactions, in the development of the problem. This was done by obtaining fruit from several production areas of varying mesocarp discolouration histories (referred to as "high", "medium" or "Iow risk" areas) during the 2000 and 2001 seasons. Fruit were stored at 8, 5.5 and 2°C for 30 days, as well as ambient (20°C). Evaluations of fruit quality were made before and after storage, as well as after softening. Once removed from storage the weight loss (during storage) was determined, and fruit firmness and carbon dioxide (C02) production rates monitored daily. It was found that temperatures below the recommended shipping temperature of 5.5°C, i.e. 2°C, produced the best internal fruit quality. This was supported by the membrane integrity studies that showed less membrane stability at the warmer storage temperature of 8°C. Furthermore, remained hard during storage and subsequently had an extended shelf life. Fruit origin was also found to play a major role in browning potential, with discolouration being consistently more severe in fruit from "high risk" areas and increasing in severity as the season progressed. The rate of CO2 production was found to follow a similar trend, with rates increasing as the season progressed, and also being slightly higher in fruit from "high risk" areas. The higher CO2 production rates were thought to be related to a decrease in membrane integrity as the season progressed. While storage temperature was not found to have a significant effect on the rate of CO2 production after storage, it did affect the time taken to reach the maximum rate, with fruit stored at 2°C taking longer. Biochemical analyses to determine the concentration of total phenolics and the activity of the enzyme polyphenol oxidase (PPO) also showed that the potential for browning was initiated by preharvest conditions. While no significant differences were found between growers with regards to total phenol concentrations, the PPO activity was found to be higher in fruit from poor quality areas, and subsequently browning potential was expected to be higher in these fruit. It was, however, found that the potential for browning could be reduced by storing fruit at 2°C, as this decreased the total phenolics concentration. This evidence further emphasized the idea that storage at 2°C could be highly advantageous. Fruit mineral analysis showed that certain key elements played a significant role in the severity of mesocarp discolouration, with excessive fruit nitrogen and decreasing copper and manganese concentrations appearing to play major roles. The high fruit nitrogen concentrations were suspected to reflect fruit grown on very vigorous trees, resulting in shoots competing with fruit for available reserves. It is suggested that 'Pinkerton' of a quality acceptable to the market, can be produced by manipulating source:sink relationships, particularly through decreasing the availability of nitrogen, followed by low temperature (24° C) shipping. Future work should concentrate on manipulation of source:sink relationships, to take account of both climatic conditions and leaf to fruit ratios. The evaluation of chlorophyll fluorescence as a tool for predicting mesocarp discolouration potential in 'Pinkerton' proved to be unsuccessful in this study and future studies may require modifications to the current technique. It is suspected that differences in chlorophyll content, for example, between fruit from different origins, will have to be taken into account when interpreting results. The success of using 2°C storage to improve the internal quality on 'Pinkerton' fruit prompted further studies, during 2004, to ensure that the development of external chilling injury would not decrease the marketability of the cultivar. Low temperature conditioning treatments, prior to storage, proved to be highly successful in reducing the development of external chilling injury, thus further improving fruit quality as a whole. Preconditioning treatments consisted of fruit that were kept at either 10°C, 15°C or 20°C for 1 or 2 days before being placed into storage for 30 days at 2°C or 5.5°C. All preconditioning treatments were compared to fruit that were placed directly into storage. The effect of fruit packaging on moisture loss (as determined by weight loss) and chilling injury was also investigated using unwaxed fruit, commercially waxed and unwaxed fruit individually sealed in micro-perforated polypropylene bags with an anti-mist coating on the inside (polybags). Holding 'Pinkerton' fruit, regardless of packaging treatment, at 10°C for 2 days prior to storage at 2°C or 5.5°C significantly decreased the severity of external chilling injury. The use of polybags during preconditioning and storage showed potential in further reducing the development of external chilling injury, although the higher incidence of fungal infections in these fruit needs to be addressed. The determination of proline concentrations in fruit exocarp tissue after storage was helpful in determining the level of stress experienced by fruit that were subjected to different packaging and preconditioning treatments. In this study waxed fruit subjected to 1 d preconditioning at 10°C, 15°C or 20°C or placed directly into storage at 2°C showed very high proline concentrations and also displayed more severe external chilling injury, despite unwaxed fruit losing more weight during these treatments. The role of moisture loss thus needs further investigation. The thickness and method of wax application was thought to play an important role in the higher external chilling injury ratings in this study as waxed fruit often developed chilling injury symptoms around the lenticels and it was suspected that either the lenticels were damaged by the brushes used to apply the wax or that the lenticels became clogged thus resulting in reduced gaseous exchange. Nevertheless, the success of low temperature conditioning in reducing external chilling injury, while maintaining sound internal quality, may enable storage temperatures to be dropped even further, thus enabling South Africa to export avocados to countries that require a cold disinfestation period prior to entry to eliminate quarantine pests (e.g. fruit fly). / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

New emerging markets such as Japan and the United States require cold sterilisation of South African citrus fruit as a phytosanitary standard against fruit fly. However, citrus fruit are chilling susceptible, with lemons being the second-most chilling susceptible after grapefruit. Chilling injury is a physiological rind disorder; the occurrence of which is despite its prevalence in horticultural commodities, not well understood. Therefore, the aim of this study was to investigate physiological compounds regulating chilling susceptibility or resistance in citrus fruit, with special emphasis on lemons. Furthermore, the potential of hot water dips or “molybdenum soaks” to maintain a certain level of physiological compounds which determine manifestation of chilling injury symptoms in citrus fruit was investigated. Moreover, it was attempted to create an understanding of the order in which physiological compounds mitigate chilling injury. Lemon fruit from different farms known to be chilling susceptible or resistant were obtained during the 2007 and 2008 harvest season. Thereafter, fruit were treated by soaking for 30 min in 1μM NaMo04.2H20 solution followed by a 2 min HWD 47 or 53°C. Treated fruit were waxed, weighed and stored at -0.5°C for up to 28 days and sampled for chilling injury evaluation 7, 14, 21, or 28 days into cold storage. A second evaluation was carried out five days after withdrawal from cold storage to allow development of chilling injury symptoms as a shelf-life simulation. After the second evaluation fruit were peeled, peel freeze-dried, milled using mortar and pestle and stored at -21°C for further physiological analysis. Freeze-dried peel was analysed for soluble sugars (glucose, fructose, sucrose), vitamin C (ascorbic acid), vitamin E (α-tocopherol), β-carotene, polyamines (putrescine, spermine, spermidine), specific flavanones (naringin and hesperidin) using HPLC-UV-Vis detector and proline, total antioxidant assays (FRAP, ABTS, DPPH), total phenolics, total flavonoids, lipid peroxidation using spectrophotometry, as well as for the heat shock protein (HSP70) using electrophoresis and silver-staining. Chilling susceptibility of lemon fruit varied with fruit source; those sourced from Ukulinga and Eston Estates were chilling resistant, while fruit from Sun Valley Estates showed chilling injury symptoms after 28 days of cold storage plus five days shelf-life. Furthermore, hot water dips (HW) 53°C, 1 μM Molybdenum (Mo) and 10 μM Mo plus HW 53°C significantly reduced chilling injury symptoms compared with the control and HW 47°C. In addition, Sun Valley Estates fruit also showed higher fruit weight loss compared with non-chilling resistant lemons. The alignment of higher fruit weight loss during storage with chilling susceptibility ascertains the use of weight loss as a non-destructive parameter for chilling susceptibility. With respect to flavedo sugars, glucose was found to be the dominant soluble sugar with multi-functional roles during cold storage. This plays a significant role in mitigating cellular stress. Chilling susceptible lemons from Sun Valley Estates had low flavedo glucose concentrations and, therefore, little conversion of glucose to ascorbic acid was possible resulting in a low antioxidant capacity. However, treatments with HW 53°C and Mo soaks seemed to enhance the enzymatic conversion of glucose to ascorbic acid leading to a higher antioxidant capacity in the flavedo of such treated fruit. Furthermore, glucose also feeds into the pentose phosphate pathway which is coupled with the shikimate pathway synthesizing secondary metabolites, especially of the phenolics group. The decrease in glucose was aligned to the levels of total phenolics, but not to that of β-carotene, naringin and hesperidin through 28 days into cold storage period. Moreover, as glucose also feeds into shikimate pathway, simultaneously an increase in proline flavedo concentration was observed. Proline is an antioxidant synthesized from glutamate; as cellular glucose decreases so does the total antioxidant capacity during cold storage. Ascorbic acid is a dominant and potent antioxidant in lemon flavedo as proven with the FRAP, ABTS and DPPH assays. Chilling resistant fruit have significantly higher ascorbic acid conversion. Furthermore, ascorbic acid also acts to generate the α-tocopheroxy radical to further important membrane-bound antioxidant, vitamin E (α-tocopherol equivalent). Furthermore, the DPPH assay was found to be effective in quantifying total antioxidants in lemon flavedo since it detects both lipophilic and hydrophilic antioxidants compared with the ABTS and FRAP assays which are bias to the estimation of liphophilic or hydrophilic antioxidants, respectively. The hot water and molybdenum treatments increased total antioxidants (DPPH assay) with reduced lipid peroxidation 7 days into cold storage and therefore, reduced chilling symptoms in fruit from Sun Valley Estates. The capacity of antioxidant to scavenge reactive oxygen species (ROS) was increased during cold storage and membrane stability significantly improved. Furthermore, putrescine as low valency polyamine was reduced as such compound acted as precursor to the synthesis of the high valency polyamines, spermine and spermidine. Chilling susceptible lemons from Sun Valley Estates showed increased soluble-conjugated polyamines as a response to stress. Furthermore, HW 53°C, 1 μM Mo and 10 μM Mo plus HW 53°C significantly increased the protein concentration and, therefore, likely also the occurrence of proteins with 70kDa (as estimator of HSP70). Additionally, the concentration of conjugated high valency polyamines was also increased, resulting in reduced chilling injury symptoms. The effect of ROS has only been viewed as damaging, while recently their role has also been viewed as stress acclamatory signalling compounds when produced concentrations below critical damaging threshold. Therefore, hot water dips seems to signals synthesis of total protein which include HSPs which then act throughout cold stress to protect other protein and channel other damaged proteins towards proteolysis. While molybdenum increased ROS production below damaging critical threshold, with ROS signalling stress acclimation by further signalling production of bioactive compound with antioxidant properties. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

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.