Masters Degrees (Horticultural Science)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6628

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Abscisic acid metabolism in a Citrus Sinensis flavedo enzyme system.
(1998) Kalala, Maloji.; Cowan, Ashton Keith.
This research project had its major objective the unequivocal demonstration that the plant growth regulator, abscisic acid could be produced in vitro from labelled precursors. In addition, this project was intended to demonstrate the metabolic relationship between β, β-xanthophyll turnover and ABA biosynthesis. Finally attempts were made to isolate the enzyme responsible for the cleavage of the immediate xanthophyll precursor to ABA, 9'-cis-neoxanthin. This was achieved using a cell-free system developed from Citrus flavedo which demonstrated formation of xanthoxal and abscisic acid from zeaxanthin, antheraxanthin, violaxanthin and neoxanthin. In addition product abscisic acid was shown to incorporate label from mevalonic acid lactone establishing the terpenoid origin of this plant growth regulator. 9'-cis-neoxanthin cleavage enzyme was present in the Citrus cell-free system, partially purified, and separated from lipoxygenase activity and shown to convert 9'-cis-neoxanthin into xanthoxal and related but unidentified neutral products.
Antioxidants composition of moringa (moringa oleifera lam) in different plant organs.
(2015) Mohammed, Fatima Abdelkarim Abdelrahman.; Tesfay, Samson Zeray.
Moringa oleifera Lam. is a versatile plant with various benefits; different parts of the plant have different pharmacological activity such as flavonoid, alkaloids, phenol, and carotenoids. The aim of the seed study was to investigate phytochemicals composition change and their utilization during seed and seedling germination. Seeds were germinated using three different temperature regimes (30/20 °C, 25/15 °C and 20/10 °C). Spectrophotometric determination of proline and phenols was carried out, while sugars were analyzed using HPLC-RID. The data were collected and analyzed using statistical software GenStat 14.1. Results of seed showed significant differences on speed of seed germination at temperature of 30/20°C followed by 25/15°C and 20/10°C respectively. Seed carbohydrates composition changes were observed with germination hours sucrose concentrations peaked within 24h (16 mg/g DW) and the same sugar showed sharp decrease for 96h (6.4 mg/g DW). Glucose and fructose concentrations also increased for 96h (2-6 mg/g DW). Also temperature had significantly influenced the biosynthesis and accumulation of biochemical compounds in the seeds especially 30/20°C. Temperature 30/20°C, increased seed phenols and proline concentration. Phenols and proline started to accumulate at 72h, after seed germination presumed within 48h. Results of leaves showed that Temperature also had significant effect on phenols the proline concentration particularly, 35/18°C, followed by 30/15°C, 25/12°C. The antioxidant levels of post germination phase was investigated, the result showed significant differences in antioxidant concentrations and sugar distribution in various parts of Moringa seedling. The leaf was recorded the highest antioxidant concentration (1.7 mg g-1). Moringa leaf also recorded the highest total phenols. The highest sugar concentration was found in root (258.9 mg g-1), and stem (245.72mg g-1) followed by root and seed. The highest concentration of total crude protein (110.4mg g-1) and vitamin E (28.57 μg g-1) was found in seed. The carotenoids concentration was the highest in the root (29 mg g-1). The result also showed different nutrients at various concentrations on different parts of Moringa tree. High phosphorous accumulated in leaf and seed; Potassium accumulation was found in root, stem, and seed coat. It is concluded that temperature treatments of Moringa seed and leaves resulted in significant differences in the rate of germination and biochemical compounds. Furthermore, the present study showed that Temperature plays an important role in germination seed and development of M. oleifera and antioxidants, phenolic, proline and carbohydrates contents. Further research on the effect of temperature on germination of M. oleifera and biochemical compound is therefore recommended.
Aspects of improving cold hardiness of tomato (Lycopersicon esculentum) var. Rossol.
(2004) Ghebretinsae, Amanuel Ghebrehiwet.; Bertling, Isa.; Bower, John Patrick.
Tomatoes, particularly those of the determinate type, are one of the most popular vegetables in the East African country Eritrea. The crop is a source of income to small farm operators as well as commercial growers, and plays an important role in the nutritional supply of the population. Nonetheless, tomato production is limited during the cool season resulting - on the one hand - in a reduced nutritional supply during this period and - on the other hand - in an increased economic potential of the crop. Although performance of tomato plants under low temperature conditions is genetically influenced, prevailing temperatures as well as management practices also affect growth and development. In order to understand the long-term effects of a cold spell on tomato plants, experiments were carried out to determine the effect of a cold spell on plant vegetative and reproductive characteristics of determinate type ''Rossol'' tomatoes. Plants were moved for two to five subsequent nights from a tunnel to a cold room (4°C). The fruit set stage of "Rossol" tomatoes was found to be most sensitive to cold temperature, followed by the flowering stage. The juvenile stage was, of all the developmental stages examined, the least sensitive to cold. Furthermore, subjecting tomato plants for five subsequent nights (cumulative 60hrs) to 4°C resulted in a significant retardation of growth and development and in yield reduction. However, tomatoes exposed to a two-night cold spell during either the vegetative or the flowering stage recovered quickly and, ultimately, performed well. Furthermore, trials were carried out under tunnel and field conditions to investigate the impact of potassium application as well as mulching on cold tolerance of "Rossol" tomatoes. Under low temperature conditions, increasing the level of potassium to up to 150% of the recommended level (157.5kg*ha-1 ) resulted in quicker ontogenetic development and increased yields significantly. On the other hand, supplying tomato plants with 50% and 200% of the recommended potassium level reduced growth, delayed development and decreased yield and yield attributes. Using black plastic mulch also increased plant growth and speeded up plant development. Maize stover mulch, however, retarded plant growth and development so that certain stages ofthe phenological cycle were reached later than by non-mulched plants. However, yield and yield attributes increased significantly using stover mulch. Therefore, the management practises potassium fertilization and mulching provide excellent tools to increase the tolerance of tomato plants to low temperature conditions. Furthermore, organic mulches can be used to delay crop development and time maturity to achieve high retail process of the commodity in the cool winter months.
Banana (Musa AAA; Cavendish sub-group) cultivar/density trials in three bioclimatic groups on the north coast of KwaZulu-Natal.
(1997) Lagerwall, Gary Brian.; Wolstenholme, B. Nigel.
The North Coast of KwaZulu-Natal is a relatively new banana production area, for which there is an absence of local norms, specifically for choice of cultivar and population density. Three cooperative split-plot banana cultivar/density trials were established in December 1991, January 1992 and February 1992 on farms at Eshowe, Nkwaleni and Mposa, respectively. These sites represent Phillips' (1973) Bioclimatic Groups 2,10 and 1 respectively, and have widely divergent climatic potential, ranging from cool, to warm, to hot subtropical. Each randomised trial block, 0.92 ha in extent, comprised five replications of five cultivar main plots, each of which was split into three density sub-plots. The five cultivars planted represent those registered at the time of planting, viz. 'Dwarf Cavendish', 'Williams', 'Grand Nain', 'Valery' and 'Chinese Cavendish'. Sub-plots were planted at 1 666, 2 105 and 2 500 plants ha(-1) and tissue culture plants were used to establish all three trials. The field trials were evaluated over three full cropping cycles and culminated in October 1996. Morphological differences such as pseudostem height and circumference, leaf length and width, number of functional leaves at flowering and harvest, as well as phenological differences such as monthly leaf emergence rates, emergence-to-harvest intervals and harvest cycles, were evaluated. The yield component data comprised measurements of bunch mass, number of hands per bunch and number, length and mass of fingers on the third hand. Productivity was expressed as tonnes per hectare per annum (t ha(-1) an(-1). Each cultivar and density treatment was evaluated independently. However, it was the evaluation of the cultivar/density interaction which formed the basis of the recommendations for the three different Bioclimatic Groups. At the relatively cool Eshowe site, 'Williams' proved to be the most productive cultivar (471 ha(-1) an(-1) over all densities. The highest production (49.8 t ha(-1) an(-1) was achieved from a density of 2 500 plants ha(-1), but due to lower costs per hectare, the intermediate density of 2 105 plants ha(-1) generated the highest gross margin. When the cultivar/density interaction was evaluated, the combination producing the highest gross margin was 'Williams' at 2 105 plants ha(-1). This substantiated the independent evaluations and is consequently the recommended combination for Bioclimatic Group 2. However, the faster cycling of 'Chinese Cavendish' could conceivably result in this cultivar outperforming 'Williams' in future ratoons. At the warmer Nkwaleni site, 'Grand Nain' (57.8 t ha(-1) an(-1) proved to be the most productive cultivar. The density of 2 500 plants ha(-1) was the most productive (64 t ha(-1) an(-1) and also generated the highest gross margin. However, the cultivar/density interaction indicated that 'Williams' at 2 500 plants ha(-1), was the highest producing combination yielding the highest gross margin, and is consequently the recommended combination for Bioclimatic Group 10. At the hot Mposa site, 'Chinese Cavendish' (54.21 ha(-1) an(-1) proved to be the most productive cultivar. The density of 2 500 plants ha(-1) outproduced (57.4 t ha(-1) an(-1) the lower densities and also generated the highest economic returns. However, when the cultivar/density interaction was evaluated, 'Chinese Cavendish' at the lower density of 2 105 plants ha(-1) realised the highest gross margin and is consequently the recommended combination for Bioclimatic Group 1.
The biochemical basis of colour as an aesthetic quality in Citrus sinensis.
(2001) Oberholster, Renate.; Cowan, Ashton Keith.
The development of fruit colour in the sweet orange (Citrus sinensis) is a cultivar characteristic affected by climate and environment. Although external colour is not always an indication of internal quality or maturity, it is probably the most important factor determining consumer acceptance. In the present investigation, efforts were made to determine the biochemical basis of colour as an aesthetic quality in C. sinensis 'Navel' and 'Valencia'. Furthermore, the changes in pigment content and composition during the period of colour development were recorded. Finally, in an attempt to manipulate citrus colour, the effect of dehydrating agents (alcohols), plant hormones, micro-nutrients and low temperature on flavedo carotenoid content was determined. Saponification of the two major colour-imparting components resolved by thin layer chromatography, followed by reversed-phase high performance liquid chromatography revealed that the principal colour-imparting pigments in C. sinensis flavedo are the yellow-coloured xanthophyll 9-Z-violaxanthin and the red C(30) apocarotenoid β-citraurin. Both pigments occur in the flavedo in esterified form. Identification of the chromophores was based on co-chromatography and online spectral analysis. The colour quality of mature fruit was dependant on the content and relative amounts of 9-Z-violaxanthin and Pcitraurin. Quantitative results revealed that increased colour intensity of citrus flavedo was associated with a decline in the 9-Z-violaxanthin : β-citraurin ratio from greater than 50 to below 10, and an increase in 9-Z-violaxanthin and β-citraurin content. Measurement of the mass and ratio of these pigments can be used to accurately colour-grade orange fruit for local and export markets. These parameters will also aid in the evaluation of colour manipulatory techniques. Visual colour break in C. sinensis appears to be associated with a minimum in total pigment as well as total carotenoid content. The period prior to colour break is characterised by a reduction in chlorophylls, carotenes and free xanthophylls usually associated with photosynthetic activity. Following colour break, a massive increase in xanthophyll acyl esters (particularly 9-Z-violaxanthin) is observed. Efforts were made to manipulate carotenoid content of citrus flavedo in vivo, with a view to manipulate fruit colour commercially. It was shown that the micro-nutrients tungsten and molybdenum, and the plant hormones abscisic acid and jasmonic acid increased carotenoid content of flavedo discs; whereas the plant hormone gibberellic acid decreased carotenoid levels. The dehydrating agents ethanol and butanol increased carotenoid content in whole fruit flavedo and flavedo discs. Optimum concentrations were shown to be 20-30% (v/v) for ethanol and 5-10% (v/v) for butanol.
Biosynthetic origin of abscisic acid in ripening avocado fruit.
(2000) Guillaume Maurel, J. C.; Cowan, Ashton Keith.
Mesocarp of ripening avocado fruit incorporated label from [2-(14)C]mevalonolactone, [1-(14)C] acetic acid, [1-(14)C] glucose and [1 -(14)C] pyruvate into ABA, although incorporation from mevalonolactone was significantly higher. Inhibition of the mevalonate pathway at the HMGR level using mevastatin reduced incorporation from acetate and MVL, while increasing incorporation from pyruvate and glucose. The carotenoid biosynthesis inhibitors AMO 1618 (inhibitor of lycopene cyclase) and fluridone (inhibitor of phytoene desaturase) both decreased incorporation of MVL into ABA, while the plant growth regulators ancymidol (inhibitor of GA synthesis and cytochrome P450) and jasmonic acid (senescence stimulator reducing the carotenoid content of plants) both increased incorporation of MVL into ABA. Tungstate was found to reduce incorporation from all four substrates into ABA, although more significantly from MVL and acetate. Further investigation revealed that the tungstate induced decrease in MVL incorporation into ABA occurred concomitantly with increased label incorporation into XAN. Cobalt, an inhibitor of ACC oxidase and therefore of ethylene production, increased incorporation of MVL into ABA. Nickel had a similar effect. Analysis of the methyl ester of ABA extracted from avocado mesocarp supplied with either [1-(13)C] acetic acid or [1-(13)C] glucose revealed incorporation of label from acetate consistent with formation of ABA via the acetate/mevalonate pathway whereas glucose was incorporated via the triose phosphate pathway of isopentenyl pyrophosphate formation. Methane, positive ion-chemical ionisation-mass spectrometry of the cis, trans and all- trans isomers of ABA indicated more intense labelling of trans, trans-ABA, irrespective of substrate used. These results indicate that trans, trans- and cis, trans-ABA are derived by different pathways and that ABA is formed in avocado by both the mevalonate and non-mevalonate pathways of isopentenyl diphosphate synthesis.
Bowen ratio and surface temperature techniques for measuring evaporation from cabbages.
(1997) Lukangu, Gastao.; Savage, Michael John.; Johnston, M. A.
Good irrigation water management requires accurate, automated, non-destructive and simple techniques to measure crop water consumption. The actual evaporation from a cabbage crop was measured using the Bowen ratio energy balance technique (BREB), the surface temperature technique and the Penman-monteith method. All models used the shortened energy balance equation to estimate latent heat in which the advected energy is assumed to be negligible. Four irrigations were applied and 17 rainfall events were recorded during the experiment. The soil at the experimental field was a clay loam. An attempt to detect and reduce measurement error that could result from using inaccurate sensors was performed by calibrating the sensors. Data from inaccurate sensors were not used to compute the latent heat. Error and sensitivity analyse were performed, and the integrity of the weather data using the estimates of weather data from an appropriate model were checked. In addition, a comparative study showed that, for daily totals, there was a very small error in the latent heat calculations when fixed "constants" (density of air, specific heat capacity of air, psychrometric constant, slope of the saturation water vapour pressure vs temperature relationship and specific heat capacity of soil) were used instead of calculated ones. The Bowen ratio (β), a fundamental input of the BREB technique, was estimated accepting the Similarity Principle and excluding nighttime data. However, an error in β was also observed during the daytime measurement of the profiles entities because the sensors were wet and the stability condition was different from neutral conditions under which the Similarity Principle could not be observed. Negative values of β were observed when there were strong winds advecting sensible heat into the field under study. Data were rejected during mornings, and during strong advection periods. Data were also rejected when the sensors were wet because of rain or irrigation. In this experiment, only 35 % of data were valid for determining latent and sensible heat estimated using the BREB technique. Comparative analysis showed that the BREB technique overestimated the latent heat by 17 % compared to the Penman-Monteith method. However, both the Penman-Monteith method and BREB technique could not be trusted because of the presence of advection, a component of the energy balance equation normally assumed to be negligible. Either the surface to air temperature differential or the aerodynamic resistance, or both, were the source of overestimation of latent heat using the surface temperature technique. The surface to air temperature differential was large in magnitude when there were high wind speeds and drier conditions in the upwind field . It was small with lighter wind speeds and wetter surface conditions. An error of less than 5 % was attributed to the use of fixed air density and specific heat capacity and acceptance of 2 % and 20 % error in measuring the net irradiance and soil heat flux density, respectively. A comparative study showed that the surface temperature latent heat was overestimated in relation to the Penman-Monteith and BREB latent heat. Generally, the technique has been reported to overestimate evaporation, although to a lesser extent than the 57 % error reported in this experiment when compared to the BREB technique. An analysis of the energy balance closure, taking the Penman-Monteith and BREB as standards, suggested that the surface temperature technique overestimated the consumption of sensible heat from the air. This observation was also confirmed when the eddy correlation technique was used to compare sensible heat estimated using the surface temperature technique. The effect of placement height of air temperature sensors suggested that the consumption of sensible heat would be overestimated if the sensor was placed far from the crop surface. This overestimation in consumption of sensible heat resulted in an overestimation of latent heat. Irrigation water management was analysed using the crop water stress index (CWSI). The CWSI was calculated using the actual to potential evaporation ratio estimated using the Penman-Monteith method and the surface temperature techniques. The estimated and measured actual surface to air temperature differential, and the estimated potential and non-transpiring surface to air temperature differential were also used to estimate the CWSI using the Penman-Monteith method, the surface temperature technique and empirical method. The estimates of the CWSI using these techniques were inaccurate because of the poor correlation between the surface to air temperature differential and the water vapour pressure deficit (or water vapour pressure deficit and net irradiance). However, use of the CWSI estimated using the actual to potential evaporation ratio (CWSI = 1 - λ(a)/ λE(p) compared well to the standard CWSI determined using the Penman-Monteith approach. The actual canopy resistance was estimated using an empirical equation based on the potential canopy resistance, solar irradiance, soil water content and the shelter factor. A value of 50 s m(-1) was estimated for potential (minimum) canopy resistance of the cabbage crop. The soil water content was poorly correlated to CWSI, while the canopy resistance was well correlated. Comparative analysis showed that the estimated soil water content using the soil water balance equation was underestimated in relation to the soil water content measured using the ThetaProbe (frequency domain reflectometry technique) when the evaporation component was overestimated, and vice versa. Soil water content was underestimated throughout the experiment when evaporation from the surface temperature technique was used. There was an underestimation of soil water content in the early stages and overestimation in later stages of the experiment when the BREB and Penman-Monteith evaporation were used. Use of the estimated soil water content using the soil water balance with the overestimated evaporation would result in an early date of irrigation application, an unnecessarily large irrigation amount and frequent irrigations. More research is needed to find the cause of overestimation of evaporation using the surface temperature technique. The robustness of the equipment allowed a long period of measurement without frequent maintenance, as was required when using the BREB technique. The technique can monitor evaporation and irrigation management aspects at a regional scale. A combination of the Penman-Monteith, surface temperature and empirical method can assist the estimation of the crop water requirement by determining the CWSI. Future research would focus on quantification of sensible and latent heat advection, and analysis of additional resistances to water vapour flow from the surface to the atmosphere. The equipment for the BREB should be refined so that it measures actual latent heat under adverse weather conditions for a protracted period. A precise use of the soil water balance equation for water management should take into consideration runoff, vertical flow of soil water through a profile, intercepted water on plant surfaces and an accurately determined evaporation.
Can plant extracts enhance growth and development, yield and simultaneously sustaining the post-harvest quality and shelf-life of potatoes (solanum tuberosum L.)?
(2023) Mbuyisa, Siphokuhle.; Bertling, Isa.; Ngcobo, Bonga Lewis.
Abstract available in PDF.
The combined effects of daylength and temperature on onion bulb when grown under greenhouse environment.
(2017) Mpanza, Felicia Nobuhle.; Tesfay, Samson Zeray.
Abstract available in PDF file.
A comparative study of antioxidant potentials of some leafy vegetables : emphasis on African leafy vegetable and exotic vegetables.
(2014) Mathe, Sakhile.; Tesfay, Samson Zeray.
Due to malnutrition and food insecurity problem around the globe, mainly in developing countries, cheap nutritional food sources are required. In South Africa, a large proportion of the population is considered “poor” and with limited resources. However, South Africa as a whole is rich in indigenous leafy vegetables which have the capacity to help mitigate the problem of malnutrition and food insecurity. Amaranthus hybridus, an African indigenous leafy vegetable was tested for seed quality and potential essential antioxidants. Exotic (to Africa) leafy vegetables (Brassica oleracea and Brassica oleracea var. capitata f. rubra) were used as references for potential antioxidants. Amaranthus hybridus seed quality was tested using two different coloured seeds, red and white gold. Seed viability and vigor were tested using germination, electrolyte leakage and antioxidant content. Data recorded indicated better seed quality for red seeds than white gold seeds; therefore red coloured seeds were planted along with purchased Brassica oleracea and Brassica oleracea var. capitata f. rubra for quantifying antioxidant content. Selected antioxidant types were measured on weekly harvests of the studied vegetables. From the results it was evident that the indigenous leafy vegetable amaranth with total antioxidants [FRAP(3174.91 mmol Fe2 SO4 100g-1 DW) and DPPH(8.3 mmol trollox 100g-1)], proteins (6.88 mg.g-1 DW), total phenols ( 345 mg 100g-1 DW), flavonoids (79 mg 100g-1 DW), Chlorophyll and carotenoids (2.8 mg 100g-1 DW), ascorbic acid (86 mg 100g-1 DW) and soluble sugars (1.07 Brix %), could be used in conjunction with available commercial leafy vegetables to combat malnutrition and food security problems. Further, these results indicate that in resource limited regions this vegetable can act as a main source of nutrients and a supplement in resource abundant regions of the country and/or continent. Further, analysis of selected enzymatic antioxidants was carried-out on leaf material of the studied vegetable to evaluate the capability of indigenous leafy vegetables to protect themselves against oxidative damage. Indigenous leafy vegetables exhibited high antioxidant activity against lipid peroxidation at early stages of growth and high antioxidant enzyme activity at similar stages thus high capability of mitigating ROS effect. Data obtained from the study indicated that indigenous vegetables are a good source of essential antioxidants which are beneficial to human health; therefore the intensity of their use needs to be increased, especially in areas of high prevalence of malnutrition and diseases.
A comparative study on carbohydrates and antioxidants of indigenous crop black jack (Bidens pilosa L.) and selected commercial vegetable crops.
(2014) Mbokazi, Nelani Simon.; Tesfay, Samson Zeray.
The adequate consumption of African leafy vegetables has been closely associated with a strong reduction of chronically disease such as cancer, diabetes and cardiovascular diseases. The health benefits provided by African leafy vegetables are due to the presence of various primary and secondary metabolites. However, most of the epidemiological studies have indicated that very little is known about the antioxidant activity of African leafy vegetables, which is believed to be responsible for their therapeutic effect. In this present study the physiochemical and antioxidant properties were examined, in relation to other Asteraceae, commercial vegetables (lettuce and chicory). Firstly, the study investigated the physicochemical and antioxidant compounds during seed germination in black jack. Secondly examined the non-enzymatic and enzymatic antioxidants in black jack and compared them with lettuce and chicory. In seed germination test, physicochemical seed quality properties for African leafy vegetable, black jack antioxidants accumulation during seed imbibition were reported. The results revealed that soaking of black jack seeds in water before sowing, induces germination. In this study black jack seeds that were soaked for 15 hours before germinating, showed a highest percentage of germination (72 %) in 5 days. The seeds also showed high considerable total antioxidants capacity of antioxidants (DPPH) and phenols (0.69±0.44 mg/g and 56.45±0.08 mg/g DW). The protein content was also high on the seeds (0.328±0.17 mg/g DW). However, there were high amounts of anti-nutritional factors noticed on the seeds, where the total tannins content was (416.36±1.14 mg/g DW). The results further revealed that African leafy vegetable, black jack contained significant amount of non-enzymatic antioxidants at the early stages of growth than other leafy vegetables. The plant biomass per plant increased with the number of harvests. The plant DPPH antioxidant assay recorded black jack (0.73 ± 0.13mg/g DW - 0.29±0.083mg/g DW), lettuce (0.10±0.64mg/g DW - 0.29±0.03mg/g DW) and chicory (0.35±0.72 - 0.20±0.11mg/g DW). The plant phenolic content recorded black jack (155.46±0.07mg/g DW - 73.11±0.02mg/g DW) for lettuce it was found to be (13.24±0.05mg/g DW - 44.92±0.07mg/g DW) and for chicory (97.09±0.37mg/g DW - 17.88±0.22mg/g DW). However, as black jack all of the secondary metabolites were decreasing drastically when it was reaching maturity, while the phenols were increasing. For carbohydrates, black jack had the lowest concentration of the soluble sugars (glucose, sucrose and fructose). The enzymatic antioxidants of black jack were the lowest for most of enzymes, but SOD activity was higher. Although it decreased as the plant approaches maturity. In conclusion, black jack accumulates different types of antioxidants and their concentration varied over plant developmental stages. The key findings of this study are; the African leafy vegetables have different antioxidant production trends compared to exotic vegetables. Depending on leaf positions and leaf stage, preferably young leaves of the ALVs, there might be sequential harvests, increases the food access for extended period for household consumption. The ALVs also experience higher SOD, CAT, POD activities during early growth stage. These plants have also displayed the highest antioxidant capacity during the early plant development, early stage high accumulation of the studied antioxidants most likely contribute to this antioxidant strength. Furthermore there adaptation to wild environment, exposed to various harsh conditions, their tolerance to survive to this condition probably attributed to plants’ antioxidant production characteristics.
Development of a sulphur free litchi storage protocol using sealed polypropylene bags.
(2006) Archibald, Alison Joy.; Bower, John Patrick.; Bertling, Isa.
The use of sulphur as a method of postharvest disease control and colour retention in litchis is soon to be restricted by the European Union. It is therefore essential that new postharvest treatments and packaging techniques be developed in order to retain internal and external fruit qualities and thus allow for export. Good litchi quality is not only important for the export market but also for use on the local market. In this study, alternative methods for postharvest quality control were investigated with the aim of extending the litchi storage life to 40 days under modified storage. Packaging the fruit in polypropylene bags significantly decreased fruit water loss and resulted in an increase in shelf life, as determined by red colour and overall rind appearance. There was no distinct advantage of amodified atmosphere. The use of a punnet, lined with absorbent sheeting and placed within the sealed polypropylene bag, further improved the shelf life. The absorbent sheeting reduced the amount of free water and resulted in little pathogen infection, while the punnet was effective in protecting the fruit from damage. It was notable that most water loss occurred within the first 10 days of storage and that the majority would actually take place during the cooling phase. A hydrocooling technique was therefore investigated and was found to not significantly decrease water loss, possibly due to not hydrocooling the fruit for a long enough period of time. Temperature management was extremely important for both colour retention and pathogen control. It was found that treatments stored at 5.5QC showed better colour retention after the 40 days storage than the 1QC storage treatment. The higher storage temperature, however, enhances the potential for postharvest diseases. Three compounds, namely ISR 2000, 'Biosave' and F10, were tested for pathogen control. 'Biosave' showed the best results with the most effective concentration being 100 mill water and good pathogen control occurred when storage was at 10 C. Polyphenol oxidase (PPO) activity in the litchi rind was evaluated as it is thought to be closely related to browning of litchi fruit, probably due to the degradation of phenolics by PPO. Brown fruit had a high PPO activity whilst red fruit had much lower activity. It was also shown that PPO activity decrease over storage time, possibly due to product inhibition of the enzyme. The internal quality of the fruit was determined using the T88: acid ratio of the pulp, as it is well correlated to mean eating quality. For fruit to have excellent taste, it must have a T88: acid ratio of between 31:1 and 60:1. All the fruit had a ratio that met this criterion and would therefore ensure good eating quality.
The development of indigenous marula (sclerocarya birrea) fruit leather : effect of drying temperature and sugar concentration on the drying characteristics, physico-chemical and consumer sensory properties of marula fruit leathers.
(2016) Ndlovu, Phindile Faith.; Tesfay, Samson Zeray.; Ngcobo, Mduduzi Elijah Khulekani.
Fruits indigenous to African countries are highly recognised and valued by rural communities for food security purposes. An examples of such fruits include but not limited to marula fruits (Sclerocarya birrea), which is indigenous to many parts of Southern Africa. In some parts of the continent, the role and usefulness of indigenous fruit species still receives little attention in agricultural research. Amongst others, this results from the magnitude postharvest quality losses due to the high moisture content characteristic of these fruits and a lack of access to required postharvest infrastructure by small-scale farmers. The processing of high moisture content commodities offers a convenient way of preserving their quality. The main aim of this research was to develop fruit leathers from the indigenous marula fruits as means of quality preservation. The development of new products from indigenous fruit crops as a means of preserving the fruits quality (nutrients) has a potential of enabling farmers, particularly small-scale farmers, to diversify on their on-farm business and farming activities. It also has the potential of improving the nutrition security and economy of the rural communities. Marula fruit are normally processed and conserved into various product forms (e.g. jams, juice, flavoured water, sweets, essential oils, traditional beer and world exported beverages such as Amarula Cream) which are readily available in the market. The production of such products from the indigenous fruits involves different processing techniques and these techniques ranges from highly sophisticated processes to simple traditional ones. The choice of the processing technique used is dependent on the characteristics of the intended product. Drying is one of the techniques that have not been widely applied in the processing of indigenous fruits. The application of this technique offers the potential to produce healthy, nutritious and flavourful ready to eat snack from the indigenous fruits such as fruit energy bars and fruit rolls which can be accessible and available throughout the year. Very little information have been reported on product development of indigenous marula fruit in previous years. The study conducted independent drying experiments to evaluate the effects of different drying temperature (50, 60 and 70 °C) and different added sugar concentrations (0, 5 and 10% w/w) on the drying kinetics of the marula fruits pulp. Moisture loss from the fruits’ pulp and different drying models in explaining the heat and mass transfer processes and for predicting the drying behaviour of the fruit leathers during drying were assessed. The textural, colour and consumer sensory attributes of the dried fruit leathers were also evaluated. The moisture loss and drying behaviour of the marula fruit leathers were significantly (p ≤ 0.05) affected by the drying temperature and added sugar content. During the evaluation of the colour properties, the drying temperature and the added sugar content increased significantly (p ≤ 0.05) the colour of the fruit leathers. However, the colour properties of fruit leathers with high added sugar concentration for each drying temperature were significantly (p ≤ 0.05) reduced. The texture attributes of the marula fruit leather significantly (p ≤ 0.05) increased with drying temperature (50 and 60 °C) and sugar concentration (0, 5 and 10% w/w), but significantly decreased at 70 °C for 10% w/w treated fruit leathers. The consumer sensory evaluation was also conducted to assess the acceptability of the fruit leathers. In general, all fruit leathers were accepted by panellists, and this demonstrated that marula fruit leather would form an acceptable new product. The sensory analysis showed that the mostly liked and preferred fruit leathers by the panellists were the ones prepared at 50 °C with 10% w/w added sugar.
Effect of coloured shade nets and plastics on Eucalyptus hybrid mini-hedge stock plant morphology and subsequent cuttings rooting potential.
(2014) Gilbert, Donna Louise.; Bertling, Isa.
Eucalyptus grandis (W. Hill) × E. nitens (Maiden) (G × N) clonal hybrids are bred to produce trees more cold-tolerant than E. grandis alone due to the cold-resistant E. nitens parent. Some of these selected hybrid clones have superior wood and pulp properties but are considered “difficult-to-root”; thus, any technique that improves their rooting percentage is valuable to the industry. As the radiation spectrum can affect growth and development of plants, manipulation of the spectrum received by mini-hedge stock plants through cultivating them under certain shade nets and plastics could alter the rooting potential of the subsequent mini-cuttings. Therefore, the effects of the covering factor at eight levels (shade nets: black 30 %, green 40 %, Apple blue 20 %, Photo red 30 % and silver Aluminet® 40 % and plastics: Clarix E Blue® as well as Patilite®, plus the control (no covering)) on morphology and subsequent rooting potential on the G x N clone factor at two levels (GN018B: difficult-to-root or PP2107: easy-to-root) were evaluated. A further factor, fertilizer, at two levels (inorganic or organic) was also evaluated. Statistical analysis was carried out using GenStat®. Data were analysed using analysis of variance (ANOVA) where data were orthogonally distributed. Where data were not orthogonally distributed the algorithm restricted maximum likelihood (REML) was used to estimate variance parameters in the multivariate linear mixed model. To pinpoint the effect of the covering employed, firstly, the alteration of environmental parameters (temperature, relative humidity (RH) and radiation spectrum) were analysed as well as the seasonal effect on stock plants and rooting of mini-cuttings and root system quality of mini-cuttings were analysed. One greenhouse was used for stock plants and one for mini-cuttings. In the stock plant tunnel the shade nets and plastic were draped over wire trellising over bricked beds where the top and two sides were covered but the ends left open to allow sufficient ventilation. Thermometers and HOBOs® were hung above the plants and a spectroradiometer placed centrally under a specific covering to measure environmental parameters. It was found that Aluminet® and black nets and Patilite® plastic act as neutral covers with regard to radiation transmission, while the blue, red and green shade nets as well as Clarix E Blue® plastic covers altered the transmission spectrum; thus, they can be considered photoselective. Similarly, the red to near infrared ratios (R:NIR) were altered significantly by the coverings, however, this did not significantly affect the shoot internode length or leaf area (LA) of stock plants. Leaf area was determined with a leaf area meter using ten of the first fully expanded leaves collected per treatment and averaging them to run analyses based on LA per leaf. The irradiance levels in the stock plant tunnel were lowest under Aluminet® 40 % (PPFD of 204.6 μmol s-1 m2) during winter, resulting in low rooting percentages, while higher irradiance under blue 20 % shade net and control (no cover) (PPFD 604.4 and 931.5 μmol s-1 m-2, respectively) during spring 2011, achieved average rooting percentages. There was no clear trend of an optimal radiation intensity to expose G × N stock plants to, in order to achieve high rooting percentages; however, a tendency was documented, whereby black 30 % and green 40 % at 200 to 450 μmol s-1 m-2 PPFD gave good rooting percentages.
Effect of elevated CO2 concentration on growth, development and postharvest characteristics of sweetcorn (Zea mays L. var. saccharata)
(2022) Dlulisa, Balungile Precious.; Bertling, Isa.; Clulow, Alistair David.
Abstract available in PDF.
Effect of methyl jasmonate and salicyclic acid on chilling injury of 'eureka' lemons.
(2010) Siboza, Xolani Irvin.; Bower, John Patrick.; Bertling, Isa.
South Africa is the second largest exporter of citrus fruit in the world. There has recently emerged a strong demand for lemons in the world market due to their nutritional value, culinary and non-culinary uses. During exportation, fruit are subjected to low temperature (-0.5°C) for varying periods of time as an obligatory quarantine treatment. However, lemons are sensitive to low temperatures and easily develop chilling injury during this obligatory quarantine treatment. This has become a major limitation to the expansion of South Africa’s lemon industry. Postharvest treatments with methyl jasmonate (MJ) and / or salicylic acid (SA) have been successfully used in horticultural crops to reduce chilling injury. A similar treatment was applied to ‘Eureka’ lemons. During the 2008 harvest season, postharvest fruit were either dipped in 10 or 50 μM MJ or 2 or 2.5 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. During the 2009 harvest season the following postharvest treatments were applied as dips: 10 μM MJ, 2 mM SA, 10 μM MJ & 2 mM SA, 1 μM MJ & 0.2 mM SA, or 0.1 μM MJ & 0.02 mM SA solutions. A control or no dip treatment was also applied. Three replicates of 15 fruits per treatment were used. Subsequently fruit were stored at -0.5ºC for 0, 7, 14, 21, 28, 35, and 42 days, before being transferred to room temperature (25°C) for 7 days where after chilling injury was rated. Treatments with 10 μM MJ and / or 2 mM SA reduced chilling injury symptoms in lemons harvested during the 2009 season. Although no visual symptoms of chilling injury were observed during the 2008 harvest season, treatments with 10 μM MJ and / or 2 mM SA reduced fruit mass loss, delayed the occurrence of stress symptoms such as lipid peroxidation and suppressed accumulation of ROS in the rind. Treatments with 10 μM MJ and / or 2 mM SA were more effective in inducing antioxidant capacity and other defence compounds such as phenolics, ascorbic acid, carbohydrates and chilling injury responses such as accumulation of proline in the rind. This may have increased the chilling tolerance of fruit during the cold storage. Therefore, this study revealed that MJ and SA have the potential to reduce and delay symptoms of chilling injury in lemons. This lead to the suggestion that both, MJ and SA dips should be further tested as treatments to mitigate chilling injury in lemons. Future studies should focus more on preventing the injury itself or preventing the primary event of chilling injury. This could probably reduce the chances of secondary events to take place.
The effect of moringa leaf extract (MLE) on growth and development, mineral composition and antioxidant properties of radish (raphanus sativus) and green beans (phaseolus vulgaris)
(2019) Mabaso, Makungu Charmaine.; Bertling, Isa.
Besides enhancing food production, one of the major challenges of the agricultural sector is to provide essential minerals and nutrients to humans for the maintenance of a healthy body, not only from a caloric perspective, but also through the provision of antioxidant compounds. It is believed that two-thirds of the world’s plants have medicinal properties and many of these plants have high antioxidant potential. Natural antioxidants, such as flavonoids, vitamin C, tocopherols and other phenolic compounds are known to be present in many plants. Moringa oleifera is one of such plants that has been identified to contain natural antioxidants; particularly the leaves of moringa are a good source of natural antioxidants due to the presence of phenolics, carotenoids, ascorbic acid and flavonoids. While the effect of such plant material on human health has become common subject of investigation, little is known on the effect of moringa leaf extracts applied to plants to enhance their resistance and antioxidant potential. The aim of the experiment was to evaluate the effect of moringa leaf extract (MLE) on the growth and development, mineral composition and antioxidant properties of radish (Raphanus sativus) and green beans (Phaseolus vulgaris). The experiment was laid out in a completely randomized design with five replications and comprised of three treatments, viz. (Control, only inorganic fertilizer Calmag+B (5 g/plant) (T1), common fertilizer plus MLE 100% (T2) (20 g/L dried moringa powder (obtained from Run KZN, Pietermaritzburg, South Africa)) and MLE 50% (T3) (T2 diluted to 50% with 100% methanol). Applications of MLE was carried out during the flowering stage, pod formation stage and prior to harvest. The obtained results demonstrate that MLE applications increased growth and development of both crops (leaf size, pod size, number of flowers, number of matured leaves and, at final harvest, above and below ground fresh and dry mass). Among the various MLE treatments, MLE 50% resulted in higher growth development and yield parameters on both radish and green bean plants compared with the MLE 100% and control plants. The mineral composition of radish leaves, storage roots and green bean pods was carried out by an independent laboratory. Applications of the treatments had significant influence (p < 0.05) on plants, with MLE-treated plants obtaining higher mineral concentrations compared with the control plants. Treatment with MLE also significantly (p < 0.05) increased antioxidant properties, particularly total antioxidants, anthocyanin, ascorbic acid and total chlorophyll concentrations, with MLE 50% producing plants of the highest overall antioxidant properties. This treatment could, therefore, be possibly employed as a method to obtain healthier, organic vegetables.
Effect of postharvest silicon application on 'hass' avocado (Persea americana Mill.) fruit quality.
(2010) Kaluwa, Kamukota.; Bertling, Isa.
The South African avocado industry is export-orientated with forty percent of total production sold overseas. The avocado fruit is a highly perishable product with a relatively high rate of respiration which results in the quick deterioration of fruit quality. Good phytosanitary procedures are a necessity in ensuring good product quality. Due to the threat of pests and diseases becoming resistant to the conventional chemicals currently used to control them, there has been a great need to diversify from their usage. Silicon (Si), being the second most abundant element (28%) in the earth’s crust after oxygen, is a major constituent of many soils and has been associated with disease resistance in plants for a long time. It has been used in a number of crop species to provide resistance against pathogenic agents. In some horticultural crops Si has been found to offer protection against fungal infections by strengthening cell walls, thus making it more difficult for the fungi to penetrate and colonize the plant. The aim of this research was to investigate the effects of postharvest silicon application on the quality of ‘Hass’ avocado fruit. The specific objectives included investigating the effect of silicon on the ripening pattern as well as the metabolic physiology of the avocado fruit. Avocado fruit were obtained from two locations in the KZN Midlands (Everdon Estate in Howick and Cooling Estate in Wartburg). Fruit were treated with different forms of Si (potassium silicate (KSil), calcium silicate (CaSil), sodium silicate (NaSil) and Nontox-silica® (NTS)) at concentrations ranging from 160 ppm to 2940 ppm. After dipping for 30 minutes in the silicon treatments, the fruit were stored at -0.5°C, 1°C, 5°C or at room temperature (25°C). Energy dispersive x-ray (EDAX) analysis was then conducted on the exocarp and mesocarp tissues to determine the extent of silicon infiltration within each treatment. Firmness measurements, ethylene evolution and CO2 production were recorded as fruit approached ripening. The CO2 production of fruit that were stored at room temperature was analysed daily until they had fully ripened, while fruit from cold storage were removed weekly to measure respiration. Mesocarp tissue from each fruit was extracted using a cork borer and subsequently freeze-dried and stored for physiological analysis. The freeze-dried mesocarp tissue was then finely ground and later analysed for sugar content, total anti-oxidant capacity (TAOC), total phenolic (TP) content and phenylalanine ammonia lyase (PAL) activity using their respective assays. Statistical analyses were carried out using GenStat® version 11 ANOVA. Treatment and storage temperature means were separated using least significant differences (LSD) at 5% (P = 0.05). The experimental design in this study was a split-plot design with the main effect being storage temperature and the sub-effect being treatments. Each replication was represented by a single fruit. EDAX analysis revealed that Si passed through the exocarp into the mesocarp tissue in fruit treated with high concentrations of silicon, i.e., KSil 2940 ppm. Significant differences (P < 0.001) were observed in temperature means with regards to firmness. Fruit treated with KSil and NTS only and stored at 5°C were firmer than fruit stored at other temperatures. Fruits treated with Si in the form of KSil 2940 produced the least amount of CO2, while non-treated fruits (Air) had the highest respiration rate. Fruit stored at room temperature (25°C) produced significantly higher amounts of CO2 and peaked much earlier than fruit stored at other temperatures. Ethylene results showed that there were differences (P < 0.05) between temperature means with the highest net ethylene being produced by fruit stored at 25°C. There were also significant differences amongst treatment means (P < 0.001), with fruits treated with KSil 2940 ppm producing the least ethylene. There were significant differences (P < 0.001) in temperature means with regards to the total phenolic concentration with fruits stored at 1°C having the highest TP concentration (26.4 mg L-1 gallic acid). Fruit treated with KSil 2940 ppm had the highest total phenolic concentration whilst the control fruit (Air and Water) had the lowest. There were also differences (P < 0.05) in storage temperature means with respect to the total antioxidant capacity. Fruit stored at -0.5°C had the highest TAOC (52.53 μmol FeSO4.7H2O g-1 DW). There were no significant differences in TAOC (P > 0.05) with regards to treatment means although fruit treated with KSil 2940 ppm and stored at -0.5°C showed the highest TAOC of 57.58 μmol FeSO4.7H2O g-1 DW. With regards to the concentration of major sugars in avocado, mannoheptulose and perseitol (mg g-1), no significant differences (P > 0.05) were observed in temperature means. However, fruit stored at -0.5°C had the highest concentration of these C7 sugars compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) showing that fruit treated with KSil 2940 ppm had the highest concentration of both mannoheptulose (18.92 mg g-1) and perseitol (15.93 mg g-1) in the mesocarp tissue. Biochemical analyses showed differences (P < 0.05) in storage temperature means with respect to PAL enzymatic activity. Fruit stored at 5°C had the highest PAL activity (18.61 mmol cinnamic acid g-1 DW h-1) in the mesocarp tissue compared with fruit stored at other temperatures. There were significant differences in treatment means (P < 0.001) with regard to PAL activity. Fruit treated with KSil 2940 ppm had the highest PAL activity (23.34 mmol cinnamic acid g-1 DW h-1). This research has demonstrated the beneficial effects, particularly applications of 2940 ppm Si in the form of KSil. This treatment successfully suppressed the respiration rate of avocado fruit. Biochemical analyses of total antioxidants, total phenolics and PAL activity in the mesocarp tissue have shown the usefulness of Si in improving the fruit’s metabolic processes. The C7 sugars (D-mannoheptulose and perseitol) also seem to be more prevalent in avocado fruit treated with Si (particularly KSil 2940 ppm) than in non-treated fruit. This suggests that an application of Si to avocado fruit can aid in the retention of vital antioxidants (C7 sugars).
The effect of shadenetting on ‘3-29-5’ avocado production under subtropical conditions.
(2016) Mazhawu, Evidence.; Savage, Michael John.; Blakey, Robert John.; Tesfay, Samson Zeray.
Abstract available in PDF file.
Effect of storage temperatures on the postharvest performance and sprouting of selected potato cultivars.
(2019) Ngceni, Xola.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
Sprouting, processing and nutritional quality of potato tubers are cultivar and storage dependent. Due to the extensive choice of potato cultivars currently available in South Africa, there is a limited information on their performance under the wide range of storage temperatures. This research investigated four objectives which were to: i) review the postharvest factors affecting the potato tuber quality; ii) investigate the effect of different storage temperatures on sprouting incidence and processing attributes of the selected potato cultivars; iii) determine the effect of different storage temperatures on nutritional quality parameters of selected potato cultivars; iv) develop prediction models using near infrared spectroscopy (NIRS) for determination of potato quality. In chapter 2, factors affecting postharvest quality of potato tubers were reviewed. It was observed that factors such as sprouting, mass loss, storage conditions and duration, and postharvest treatments have high influence on the postharvest quality of potato tubers. Sprouting was found to be the major cause of the high postharvest losses occurring in potato industry. Chapter 3 investigated the effect of storage temperatures on sprouting and processing attributes of potato tubers. The results clearly demonstrated that sprouting and processing attributes were both cultivar and storage dependent. For instance, sugars of some potato tubers were highly stimulated by cold storage whereas for sprouting it was vice-versa. The dry matter content and mass loss of potato cultivars slightly increased with storage time and temperature. In chapter 4, the effect of storage temperatures on the nutritional quality of potato tubers was investigated. In this chapter, the findings clearly proved that ascorbic acid and total phenolic content generally decreased while the antioxidant activity was increasing with storage time. Proteins in potato tuber varied based on storage temperature and cultivar. Chapter 5 sought to develop the predictive models for determination of the internal quality of potato tubers. Good models for ascorbic acid, mass loss and total phenolics for all the cultivars were developed. On the hand, poor models were developed for both sucrose and reducing sugars for all the cultivars.

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