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Masters Degrees (Horticultural Science)

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    The effect of edible coatings and ZnO nanoparticles based on Moringa extracts on the postharvest quality of avocado (persea americana mill.) fruit.
    (2024) Ngubane, Sibonelo.; Tesfay, Samson Zeray.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.
    Abstract available in PDF.
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    Responses of cabbage (brassica oleracea var. capitata), swiss chard (beta vulgaris), and pepper (capsicum annuum) seedlings to growing media pre-enriched with vermicompost.
    (2021) Sokhela, Nkosikhona Brian.; Bertling, Isa.
    Seedling production is mainly achieved by using growing media as substrates; most nurseries in South Africa use pine bark and vermiculite in their ‘in-house’ medium. For the growing medium to effectively anchor and yield healthy and sound seedlings to develop into a mature vegetable crop, it must have a balance of certain physical, chemical and nutritional properties. The study was conducted concurrently at two nurseries (Top Crop Nursery and Sunshine Seedlings®) differing in nursery management and growing media types to investigate physical, chemical, and nutritional properties of growing media to develop various growing media mixes. These media were tested for their suitability for vegetable seed propagation, by monitoring and recording seedling growth parameters from sowing to the saleable seedling stage. Top Crop Nursery used the wattle and pine bark, whereas Sunshine Seedlings® used their standard growing media (75% Coir, 13% Peat, 12% Vermiculite + 0.2% Osmocote®). The study then tested the responses of cabbage (Brassica oleracea var. capitata), Swiss chard (Beta vulgaris var. cicla), and pepper (Capsicum annuum) seedlings. When developing growing media mixes, the pre-enrichment of growing media with vermicompost at varying levels of 0-20% was practiced at both nurseries. Top Crop Nursery had 15 treatments, with three controls (treatment 1, 2, and 3), where treatment 1 was pure pine bark, treatment 2 was pure wattle bark, treatment 3 was 50% pine bark and 50% wattle bark. Treatments 4 to 7 were pure pine bark with vermicompost pre-enrichment ranging from 5 to 20%. Treatment 8 to 11 were pure wattle bark with compost pre-enrichment ranging from 5 to 20%, whilst treatment 12 to 15 were 50% wattle bark + 50% pine bark with the same pre-enrichment ranging from 5 to 20%. Sunshine Seedlings® had 6 treatments with two controls (treatment 1 and 6), where treatment 1 was Sunshine Seedlings® Seedling Mix with 0% vermicompost, and treatment 6 being the Sunshine Seedlings® Mix without Osmocote®, with 0% vermicompost. From sowing, emergence was recorded daily, until all replications showed no further germination. Other parameters (root development, leaf number, seedling height, pest and diseases, general appearance of the seedlings) were recorded on a weekly basis throughout the seven weeks of each experiment. Measuring chlorophyll and seedling mass was carried out at the saleable seedling stage, at week 7. Seedlings were randomly sampled for seedling mass (wet mass taken in field, dry mass taken after laboratory oven drying). From both nursery sites, statistical analysis for days to emergence, leaf number and seedling height showed no significant differences. Seedling mass, chlorophyll content and nutrient uptake showed significant differences, with cabbage showing greater mass gains over the seedling growing period, up to 10.46 g per 20 seedling tops. Statistical analysis revealed differences in nutrient uptake by the three crops at both nurseries. Pepper showed higher nitrogen, potassium and boron uptake than Swiss Chard and cabbage, with the most significant nutrient uptake noticed in treatment 2 (Wattle bark = 0% vermicompost), treatment 3 (Pine bark + Wattle bark + 0% vermicompost), treatment 4, 5, 6, 7 (Pine bark + 5 to 20% vermicompost), treatment 9, 11 (Wattle bark + 10 to 20% vermicompost), treatment 14, and 15 (Pine + Wattle bark + 15 to 20% vermicompost). In most treatments, especially in treatment 5, 7 (Pine bark + 10 & 20% vermicompost), 8, 9 (Wattle bark + 5 to 10% vermicompost) and 15 (Pine + Wattle bark + 20% vermicompost), Swiss Chard had the highest uptake of phosphorus, iron, magnesium, aluminium, zinc, and manganese. Cabbage only showed a high uptake of calcium and sulphur, especially with treatment 2 (Wattle bark + 0% vermicompost), 10, 11 (Wattle bark + 15 & 20% vermicompost), 12, 13 (Pine + Wattle bark + 5 & 10% vermicompost), and 15 (Pine + Wattle bark + 20% vermicompost). The study demonstrated that wattle bark affects seedling growth more so positively than pine bark; however, the Sunshine Seedlings® mix produced much more desired growing media attributes for almost seedling growth parameters, more especially the root development. The addition of vermicompost had very little to no effect on plant growth; however, the effect of the slow-release fertilizer, Osmocote® made a noticeable impact. Conducting this study in two separate nurseries did not allow for precise comparisons, therefore, a similar study should be conducted at one site, to compare treatments under similar growing conditions.
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    Investigating the antifungal efficacy of moringa leaf extracts against Fusarium oxysporum, a causal agent of fusarium dry rot.
    (2021) Mncube, Carren Nonhlahla.; Bertling, Isa.; Yobo, Kwasi Sackey.
    Fungal diseases are amongst the most-destructive potato pathogens worldwide. Potato (Solanum tuberosum L.) is one of the most-common and -widely consumed crops in South Africa (SA). Population growth in SA is continuously putting pressure on the potato production, which has subsequently accelerated mono-cropping and chemical use, particularly in an attempt to control fungal diseases. There are currently no fusarium dry rot- resistant cultivars and no commercial biological control agents available to reduce occurrence of this disease. In an attempt to reduce agricultural pollution, and effectively control fusarium dry rot, plant extracts have been investigated for their antifungal properties. Moringa oleifera Lam. (moringa) is a tree well-known for its wide phytochemical composition and its antifungal abilities have been documented, but not on potato dry rot. This study was, therefore, carried out to investigate the antifungal potential of moringa leaf extracts against Fusarium oxysporum, the causal agent of fusarium dry rot of potato. Various potato cultivars were used, based on seasonal availability. Since the moringa plant is containing high amounts of secondary metabolites, in this study, first, the phytochemical composition of Moringa leaf excracts (MLEs) and the effect of MLE treatment on the phenolic concentration of tubers were analysed. The Moringa leaf powder was extracted with either (30%, 50% or 80%) of acetone, ethyl acetate, methanol and the other moringa powder eas extracted with distilled water. Various MLEs were tested for their capability to improve tuber quality post- harvest by assessing potato quality parameters, such as percentage mass loss and firmness. An in vitro assay was carried out to evaluate the moringa leaf extracts’ (MLEs’) inhibition activity on F. oxysporum using a disc diffusion method. The ability of MLEs to prevent fusarium dry rot development and to delay disease progression was also investigated in in vivo assays. Phytochemical analysis of MLEs revealed the presence of tannins, phenolics, flavonoids and glycosides. Tannins were, however, absent in ethyl acetate MLEs. Treatment with MLEs enhanced the concentration of free and bound phenolics in ‘BP1’ and ‘Mondial’ potatoes. Tubers coated with methanol-MLE had the highest concentration of both, free and bound phenolics. Treatment with MLEs slowed down average percentage mass loss (seemingly water loss) in both cultivars. Treatment with 70% ethyl acetate MLE, however, accelerated this water loss in both cultivars, but particularly in ‘Mondial’. This average reduction in mass was slightly less than the ii average reduction in mass of control tubers. Moringa treatment also preserved the healthy appearance of tuber skin and tuber firmness more so than the control. Macroscopic characteristics of F. oxysporum were pinkish colonies and a dark pigmentation, as observed on the PDA plates. The conodogenous cell was long and branched and the macroconidia had three to five septations. The fungus was found to be pathogenic on both cultivars used in this experiment, as tubers had dark depressions, typical for fusarium dry rot, and a white mycelium on the tuber surface. The efficacy of MLEs as antifungal agents was tested using a disc diffusion method. Three solvents were used to produce MLE stock solutions, namely acetone, ethyl acetate, ethanol, at three concentrations (30%, 50% and 70%). These solvent solutions were each further diluted to yield 2% and 4% concentrations, yielding eight MLE treatments. The dilutions of the MLEs produced with lower solvent concentrations (30% and 50%) had 100% fungal inhibition activity, while dilutions of MLEs extracted with the higher solvent concentration (70%) inhibited fungal development to a lesser degree. The 2% and 4% dilutions of 70% acetone, 70% ethyl acetate, and 70% methanol; resulted in 95.0%, 86.3% and 90.3% inhibition, respectively. Water-MLE, on the other hand, inhibited the fungus only by 87.5%. These results indicate that the extraction solvent and its concentration influence the antifungal efficiency of MLEs. In vivo assays demonstrated that MLEs were able to prevent disease development to a certain extent. Solvent type and concentration were influential in preventing fusarium dry rot development, as tubers treated with either 30% and 50% of acetone-MLE and methanol-MLE concentrations had the smallest average lesion diameter (3.7 mm and 3.4 mm for ‘Valor’ and ‘Mondial’, respectively). The 70% Ethyl acetate-MLE, on the other hand, was ineffective in controlling fusarium dry rot in both cultivars, resulting in an average lesion diameter of 14 mm; this was not significantly different from the control, which had an average lesion diameter of 15 mm (P>0.05) in ‘Valor’ tubers. In ‘Mondial’, 70% ethyl acetate-MLE treatment resulted in an average lesion diameter of 11 mm. Further, tubers of both cultivars treated with 50% and 70% ethyl acetate-MLE were prone to secondary infections by bacterial soft rot. The ability of MLE to delay and slow fusarium dry rot development is an indication of its antifungal potential. Response to MLE treatment was found to be cultivar-dependent, as following MLE treatment, ‘Mondial’ was more tolerant to fusarium dry rot than ‘Valor’. Solvent type and concentration were also found to influence MLE antifungal activity. Tubers treated with MLEs extracted with higher solvent concentrations (70%) as well as those treated with ethyl acetate MLEs were less tolerant to fusarium dry rot. This research, therefore, demonstrates that lower organic solvent (30% and 50%) concentrations should be used, when preparing antifungal extracts of moringa leaf powder.
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    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.
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    Postharvest technologies for predicting and reducing susceptibility of ‘Marsh’ grapefruit (Citrus paradisi MacFad.) to rind pitting disorder.
    (2019) Shinga, Mawande Hugh.; Mditshwa, Asanda.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.
    Citrus fruit is globally one of the most important fruit due to their nutritional value and sensorial attributes, however, they were susceptible to various postharvest disorders, especially during shipping period. Therefore, the aim of this study was to determine the effect of edible coating, carboxymethyl cellulose (CMC) infused with moringa leaf extracts (MLE) on reducing postharvest physiological rind pitting disorder in ‘Marsh’ grapefruit (Citrus paradisi MacFad.). The study also reviewed the literatures on the ability of edible coatings to improve fruit quality and extend shelf life of citrus fruit. Edible coatings recently received attention due to their ability to enhance fruit quality without compromising human health. The first experimental chapter was conducted to evaluate the ability of CMC and MLE as edible coatings to control the disorder in ‘Marsh’ grapefruit. A total of 300 fruit (150 from outside canopy and 150 from inside canopy) were harvested from a commercial orchard at Dole Bolton Citrus Estate in Nkwalini at Showe, KwaZulu Natal, South Africa. Fruit were subjected to different treatments, control (untreated), CMC (0.5%) + MLE (10%), CMC (1%) + MLE (10%), CMC 0.5% and CMC 1%. Treatments were organised in a factorial design. Fruit were stored at 3 ± 0.5 °C and 90-95 % relative humidity (RH), for nine weeks and thereafter taken to room temperature (22 ± 2 °C) for two weeks to simulate shelf life. The physicochemical attributes (total soluble solids. titratable acidity, maturity index, fruit mass loss, fruit colour, rind dry matter) of the fruit were analysed during this period. Rind pitting as well as sensory quality was evaluated at the end of storage period. This study identified that CMC 0.5% + MLE 10% and CMC 1% + MLE 10% reduced postharvest rind pitting disorder incidence compared to CMC 0.5%, CMC 1% and the control treatment. High mass loss contributes largely to rind pitting development, however, edible coatings managed to provide semi-permeable barrier to the fruit. Uncoated fruit had high mass loss which may be due to high water loss from the rind, most probably rind cell collapsed thereby leading to visible pitting in fruit rind. Coated fruit with low rind pitting incidence had low rind dry matter (RDM) compared to uncoated fruit with high rind pitting incidence. This study reported that total soluble solids (TSS) increased with storage time, however, low rate of increase was noticed in coated fruit compared to uncoated fruit. Fruit with higher TSS at the end of storage had high rind pitting incidence compared to fruit with low TSS. Rind colour was expressed as citrus colour index (CCI). Citrus colour index was noticed to increase with storage, however, the rate of increase in coated fruit was lower than that of uncoated fruit. At the end of storage, CCI was therefore higher in uncoated fruit than coated fruit, while higher CCI was correlated with high rind pitting incidence. These physicochemical quality parameters can be used to predict rind pitting occurrence in ‘Marsh’ grapefruit. The second experimental chapter investigated rind phytochemical quality attributes that can be used as pre-symptomatic markers of rind pitting disorder in ‘Marsh’ grapefruit. Treatments used for this chapter were similar to the abovementioned. Treatments were organised in a factorial design. Visible to near infrared spectroscopy (Vis/NIRS) as a non-destructive technique was used to develop models that can assist in rind pitting disorder prediction. Partial least square (PLS) regression models were developed to predict rind phytochemical quality attributes such as ascorbic acid, phenolics, flavonoids, antioxidant capacity and activity, pigments (chlorophyll a and b, β carotene and total carotenoids) and sugars (sucrose, glucose and fructose), and these models were developed to predict rind pitting disorder of ‘Marsh’ grapefruit. Noticeably, CMC when combined with MLE were able to reduce the incidence of rind pitting disorder when compared to their counterparts. This could be due to the fact that moringa is believed to have high content of flavonoids, phenolics and antioxidants, which may be released to fruit and act as free radical scavengers from the cell matrix and protect fruit from external stress. These studies further investigated the effect of canopy position on susceptibility of rind pitting development. It was found that outside canopy (OC) fruit were more susceptible to rind pitting disorder compared to fruit from inside canopy (IC). This may be due to that OC fruit are exposed to different climate during fruit growth and development which could lead to rind quality stress and damage rind cells. Since OC fruit were more prone to disorder development than IC fruit, it would make financial sense to export fruit to the low demanding market with less penalties if fruit develop pitting prior to destination. Alternatively, fruit with higher chances of developing disorders (OC fruit) must be sent to local markets or fruit may be processed to other sellable products such as juices and dried fruits.
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    Evaluating the efficacy of formulations containing hexanal, moringa leaf extracts, and carboxy methylcellulose as postharvest treatments for fresh tomatoes (Solanum lycopersicum L.).
    (2020) Mthembu, Sisanda Sibusiso Luyanda.; Tesfay, Samson Zeray.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.
    Tomato fruit have a relatively short shelf life due to their highly perishable nature. This presents a challenge for long distance transportation of tomatoes. The use of non-refrigerated trucks (used by most commercial entities in South Africa) for transportation exacerbates the loss of fresh tomatoes. The adoption of low temperature storage units during transit is an expensive technology for farmers in developing countries. The application of postharvest treatments such as chemical treatments is used to reduce these losses. However, chemical treatments contain residues that negatively impact the environmental and human health. In addition, it causes off-flavours which negatively affects consumer acceptability and market value of tomatoes. The inefficiency of chemical treatments and the pressure experienced by producers to meet the increase in demand for fresh tomatoes without any hazardous residues by both consumers and regulatory agencies, encourages further research to investigate eco-friendly and sustainable treatments as an alternative to chemical treatments. The use of total soluble solids as a predictor of tomato quality does not provide an accurate description of internal biochemical changes. The use of accurate predictors such as sugar content and sweetness indices, provides a precise description of internal quality and estimation of shelf-life capacity. However, conventional measurements of these parameters are laborious. Thus, probing the use of a rapid and non-destructive technology (Vis/NIRS) to predict and determine sugar content and sweetness indices, in order to facilitate quality management and accurate grading of tomato produce along the supply chain. The research findings obtained in this present study, demonstrated the ability of the hexanal formulation and moringa based edible coating to optimise organoleptic quality and improve the nutritional quality of tomato fruit, harvested at different maturity stages. Vis/NIRS accurately predicted important internal quality parameters relating to the market value of tomatoes such as sugar content and sweetness indices. Results obtained by evaluating the effects of these treatments to extend shelf life and reduce losses of tomato show the potential of adopting these treatments to serve as an alternative to the currently used treatments in the tomato industry. The successful prediction and accurate determination of sugar content and sweetness indices using Vis/NIRS, has the potential to enable rapid and precise grading of tomato produce.
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    Investigating the effect of trellising and stem training methods on the horticultural performance of indeterminate tomatoes grown in dome shape tunnels.
    (2020) Mngoma, Mlungisi Fihlane.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.; Sithole, Nkanyiso Justice.; Mditshwa, Asanda.; Magwaza, Shirly Tentile.
    Growing of tomato in open field in South Africa is very challenging due to unfavorable environmental conditions, pests and diseases. This has resulted to an increased hydroponic production of tomatoes in protected cultivation. However, protected cultivation require many horticultural practices for optimum production. The first experiment of the study was conducted to evaluate the effect of different trellising methods namely, early layering, late layering and vertical trellising in response to leaf gas exchange and chlorophyll fluorescence of indeterminate tomato produced in tunnels. The second experiment was conducted to assess the effect of trellising method on growth, yield and quality parameters of indeterminate tomato. The third experiment investigated effects of different stem training methods namely, single stem, double stem and two plant per pot in line with growth, yield and physiological responses of indeterminate tomato grown in dome shape tunnels.The results of the first study showed that early and late layering increase photosynthetic rate (A), transpiration rate (T), the effective quantum efficiency of photosystem II photochemistry (ФPSII) and electron transportation rate (ETR) compare to vertical trellising. The second study revealed that early and later layering increase plant height, number of fruit and fruit mass compare to vertical trellising. However observed results showed no variation among trellising methods with quality parameters. The third experiment on leaf gas exchange results showed high photosynthetic rate (A) and stomatal conductance (gs) in single and two plants per pot stem. Single stem exhibited high plant height and stem diameter with double and two plants per pot stem. Single stem and double stem showed high number of fruits, and fruits mass compare to two plants per pot stem training. The study also showed high colour index, total soluble solids (TSS), titratable acids (TA), and BrimA with double stem and two plants per pot than single stem. Therefore, the presented results revealed that early and late layering trellising methods can be the best methods that can be used by resource-constrained farmers in dome shape tunnel to increase physiological efficiency, growth and yield. On the other hand double stem and two plants per pot training method can had a potential to improve yield and quality of indeterminate tomato grown in tunnel.
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    Physiological and biochemical effect of biostimulants on Abelmoschus esculentus (L.) and Cleome gynandra (L.)
    (2021) Makhaye, Gugulethu.; Tesfay, Samson Zeray.; Amoo, Stephen Oluwaseun.; Aremu, Adeyemi Oladapo.
    Abelmoschus esculentus (L.) and Cleome gynandra (L.) are neglected plants, often collected from the wild, with dual benefits of nutritional and medicinal values, especially in rural communities. Biostimulants are well-known for their stimulatory effect on plant physiological processes, from germination to full maturity. In the current study, the effect of biostimulant application was investigated on the germination, growth, yield and biochemical quality of selected A. esculentus and C. gynandra genotypes, as a tool for improving their physiological and biochemical aspects. The study involved two biostimulants [Kelpak® (1:100, 1:40 and 1:20, dilutions)] and plant growth promoting rhizobacteria = PGPR (1:5, 1:10 and 1:15, dilutions)] as well as their interaction effect on the different genotypes of A. esculentus (Okra PB1, PB2, PB3, PB4 and PB5) and C. gynandra (TOT10212, TOT8420, Cleome 3, CleomeMaseno and Cleome Arusha). The parameters evaluated were seed germination, vegetative growth, yield, biochemical (ꞵ-carotene, vitamin C, total phenolic, flavonoids and condensed tannins) and mineral elements content (Ca, Fe, K, Mg, Na and Zn). Germination of A. esculentus and C. gynandra was influenced by different genotypes and biostimulants. Okra PB2 and Okra PB4 had significantly enhanced Final Germination Percentage (FGP), Germination index (GI) and Germination Rate Index (GRI). Similarly, genotype TOT10212 had significantly increased FGP, GI and GRI while Cleome 3 had least FGP, GI, GRI and Coefficient of Velocity of Germination (CVG). The effect of Kelpak® treatments on FGP, GI, Mean Germination Time (MGT) and GRI was significantly comparable to that of control. The effect of PGPR treatments on FGP, GI and GRI significantly increased with increasing PGPR dilutions. In A. esculentus, the interaction of Kelpak® (1:100) and genotype OkraPB1 significantly improved germination parameters (FGP, GI and GRI) while no stimulatory effect was observed on the interaction of biostimulants and Okra PB2, PB3, PB4 and PB5. In C. gynandra, the biostimulants especially PGPR (1:5, 1:10 and 1:15), inhibited germination parameters (FGP, GI and GRI) of genotype TOT10212. A. esculentus genotypes showed different growth parameters. For instance, Okra PB5 had significantly higher plant height while Okra PB4 had least plant height. Biostimulants further influenced the vegetative growth and yield of A. esculentus and C. gynandra genotypes. Plant height, chlorophyll content and stem diameter of A. esculentus genotypes was significantly enhanced by PGPR (1:5, 1:10 and 1:15) application. The yield (number of pods, total fresh weight and total dry weight) of A. esculentus was enhanced by PGPR (1:5, 1:10 and 1:15) application. Plant growth promoting rhizobacteria (1:5, and 1:10) enhanced the chlorophyll content, stem diameter and yield (total fresh and total dry weight of leaves) of C. gynandra genotypes. No inhibitory effect was observed on the growth and yield of A. esculentus and C. gynandra genotypes following biostimulant treatments. Interaction of biostimulants with A. esculentus and C. gynandra genotypes had no significant effect on growth and yield parameters. The biochemical and mineral elements content of A. esculentus and C. gynandra genotypes was influenced by genotype and biostimulant (both Kelpak® and PGPR dilutions) application. In C. gynandra, biostimulants enhanced the ꞵ-carotene, total flavonoid and total phenolic content. Okra PB4 had significantly enhanced vitamin C and total phenolic content while Okra PB5 had significantly higher total flavonoid content. Genotype TOT10212 had significantly increased Ca, Fe, Mg and Na content. However, the content of condensed tannins together with Fe and Mg of C. gynandra genotypes was inhibited by biostimulants application. Application of PGPR-1:5, Kelpak®-1:40 and Kelpak®-1:20 significantly enhanced total phenolic, total flavonoid and condensed tannins of A. esculentus genotypes. Furthermore, biostimulants had varying effects on the mineral element content. A significant increase was observed on Fe content when A. esculentus genotypes were treated PGPR (1:10). Application of Kelpak® (1:100 and 1:40) caused a significant decrease on the Ca content of A. esculentus genotypes. The interaction effect of biostimulants application and genotypes significantly inhibited the mineral elements of C. gynandra genotypes while significantly enhancing the vitamin C and condensed tannins of Okra PB3. The current study demonstrated the differential effect of biostimulants application (Kelpak® and PGPR) on A. esculentus and C. gynandra genotypes. The application of biostimulants can therefore, be used to enhance germination, growth, yield, biochemical content and mineral elements, depending on the crop genotype, and hence assist in combatting food insecurity in food insecure communities.
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    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.
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    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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    Effects of Litsea glutinosa (Lour.) C.B. Rob. plant biowaste-derived media on plant growth and development of thyme and rocket.
    (2020) Anumanthoo, Thagen.; Bertling, Isa.
    Enhancing and sustaining agricultural productivity is critical, as soil quality in many parts of the world deteriorates becoming unsuitable for agriculture. Plant bio-waste derived from composted alien invasives could be recycled and reused to enrich media used for plant production. This bio-waste could improve soil fertility and thereby enhance agricultural productivity. KwaZulu-Natal (KZN) is threatened by numerous alien invasive plants which negatively impact on the natural environment, human welfare and quality of life. Biological plant invasion is a natural process; however, human intervention has accelerated the rate of spread and naturalisation of many species across a multitude of landscapes. Composting some species of such alien invasives into bio-waste has been reported as a viable source of nutrients and organic matter. Farmers can, therefore, use these outputs as livestock-feed products and/or fertilizer for crops. The purpose of this study was to assess the effects of compost, derived from the IAPs (invasive alien plant species) - Litsea glutinosa – (Lour.) C.B. Rob., as enrichment for plant growth and development of two herb species, Thymus vulgaris (thyme) and Eruca sativa (rocket). This experimental study was conducted using three media into which rocket and thyme were planted: control medium (Gromor® Potting Soil, PS); experimental medium (composted Litsea, EM) and a combination (1:1) of control and enriched medium (PSEM). This study was carried out over three growing periods: eight-week experiments between April and May (autumn to winter), between September and October (winter into spring) and between February and March (summer into autumn). Composting of Litsea glutinosa plants was started at a vacant site in Verulam (KZN) before being moved to the experimental study site, at the Durban University of Technology Horticultural Practical Centre. Five replicates per treatment of the rocket and thyme plants were planted in the three media (PS, EM and PSEM). The following measurements were taken to assess plant growth and development: leaf diameter and plant height (rocket) and length of side shoot and plant height (thyme). Fresh and dry mass (g) were determined and the concentrations of total chlorophylls and carotenoids were measured spectrophotometrically. The growth of the thyme plants was positively influenced by cultivating the plants in EM and PSEM media resulting in increased plant height and length of side shoots, growth parameters significant for the culinary and cosmetic thyme industry. The leaf diameter of rocket was positively influenced when grown in the winter to spring period, particularly when cultivated in the PSEM medium compared with PS. Rocket displayed the most vigorous growth (fresh and dry mass of rocket leaves) during the winter to spring period when grown in PSEM. Results showed that herbs grew similarly in PS and PSEM media. It is, therefore, feasible to use PSEM as a medium for thyme production. Thyme grew best in EM in the autumn season (April-May), while PSEM performed best when used in summer/autumn (February-March). Thyme, therefore, grows well in this composted IAP in the summer and autumn months, rather than in winter or spring. The chlorophyll concentration of rocket plants was also affected by the season (highest concentration in plants grown during summer months) and medium (highest concentration in plants grown in PS) compared with PSEM and EM, as plants grew slowly and showed low values of pigment concentrations. Growing rocket and thyme in the composted Litsea glutinosa did not affect the taste and texture of the leaves determined by the consumer evaluation panel. Litsea glutinosa compost used to enrich potting soil (PSEM) was beneficial to the growth and development of rocket as well as thyme. Therefore, this study recommends the use of composted IAPs mixed in a 1:1 ratio with a general potting soil which would benefit the environment, the ornamental industry, as well as nurseries/wholesalers. A higher dosage of the composted Litsea glutinosa in a PSEM medium should be experimented with to grow thyme plants, while the potting soil is better suited to grow rocket plants. This study, therefore, highlights the usefulness of composted plant bio-waste derived from alien invasive plants as enrichment of media for growing herbs for human consumption.
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    Effects of edible coatings and moringa extracts on postharvest quality of papaya fruits.
    (2018) Langa, Sabeliwe.; Tesfay, Samson Zeray.; Mditshwa, Asanda.
    Carica papaya L., known as papaya is a member of the small family Caricaceae. It is an important fruit for both fresh and processed products. It is a good source of vitamin A, lycopene, polysaccharides and proteins. High consumption of papaya is known to contribute to the prevention of the chronic diseases such as cardiovascular disease. About 30-50% of the harvested papaya is reported to never reach the consumers due to postharvest spoilage. Postharvest spoilage can be attributed to the fact that it is perishable after harvesting. The level of spoilage depends on the management of pre-harvest (environment and cultural practices) and postharvest factors (handling, environmental conditions). The factors contribute largely to papaya quality deterioration by stimulating physiological/biochemical processes (respiration, transpiration) and microbial growth. Also, some of the factors affect papaya fruit quality at maturity stage, time of harvest and the harvest method. Various fungicides have been used to reduce postharvest spoilage. However, the negative effects on human health and the environment, accompanied with high costs, residues in plants has encouraged development of alternative approaches. The development of new natural preservatives and antimicrobials has increased as alternatives for fruit quality preservation. Edible coatings are amongst the natural methods of fruit quality preservation and protecting perishable food products from deterioration by retarding dehydration, suppressing respiration, improving textural quality, helping retain volatile flavour compounds and reducing microbial growth. The study evaluated the effect of edible coatings on papaya fruit quality, and antifungal activity of plant extracts against fungal pathogens that affect postharvest quality of fruits. In the first section of the study, Moringa oleifera extracts (leaf and seed) incorporated with chitosan and CMC (MLE+CH, MSE+CH, MLE+CMC and MSE+CMC) were used as an alternative for synthetic fungicides. The quality parameters were measured to observe the effect of treatments. The quality parameters that were assessed under cold and ambient storage conditions included pH, total titratable acidity, total soluble sugars, weight loss, firmness, peel colour, vitamin C, total flavonoids, total phenols, antioxidants and soluble sugars. Inhibitory effects of Moringa oleifera aqueous and ethanolic leaf and seed extracts (MLWE, MSWE, MLEE and MSEE) was evaluated in-vitro. Treatments applied (MLE+CH, MSE+CH, MLE+CMC and MSE+CMC) maintained papaya fruit quality compared to the control under both ambient and cold storage conditions. Treatment MSE+CMC showed better fruit quality maintenance compared to other treatments. MLWE, MSWE, MLEE and MSEE had relatively high inhibitory potential in all tested concentrations (10%, 20% and 30%) compared to the control treatment. A 100% mycelial growth inhibition in PDA agar amended with moringa extracted with ethanol was observed.
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    Efficacy of carboxymethyl cellulose and gum arabic edible coatings in combination with moringa leaf extract in improving postharvest quality of new avocado (Persea americana Mill.) cultivar, ‘Maluma’.
    (2018) Kubheka, Sanele Fana.; Tesfay, Samson Zeray.; Magwaza, Lembe Samukelo.; Mditshwa, Asanda.
    There is growing trend towards an increase in demand for environmental friendly and sustainable postharvest treatments for fresh horticultural produce. This trend is also coupled by the recent increase in demand for ‘organic’ fresh products. In response to these demands, fresh produce industry together with researchers in the postharvest biology and technology have identified polymers such as polysaccharides, proteins and waxes to develop what is known as edible coatings. Edible coatings have been successful in reducing mass loss, delaying senescence thus prolonging shelf life of fresh produce. In addition, edible coatings have proven to be excellent carriers of active ingredients such as colourants, antimicrobials which helps alleviate antimicrobials properties of coated produce. The application edible coatings can also provide relief to both producers and consumers as they are economical affordable compared to other techniques. This review looks at formulation of edible coatings with focused on maintenance of postharvest quality. Recent advances in application and their effect on phytochemicals and sensory properties is also discussed. Furthermore, this review makes recommendations that could of assistance in the future, whilst assisting in future research.
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    Effects of organic and inorganic fertilisers on the growth of pseuderanthemum atropurpureum, soil fertility and leachate composition.
    (2018) Constance, Duane Wayne.; Bertling, Isa.; Odindo, Alfred Oduor.
    The use of fertilisers in agricultural production systems, particularly nitrogen and phosphorous, has been shown to be one of the causes of eutrophication as a result of the excessive enrichment of freshwater systems through surface runoff and soil infiltration. The contamination of freshwater bodies from horticultural production systems in South Africa has, however, been rarely studied, although influx from such systems are considered highly polluting elsewhere. Eutrophication is particularly considered a major problem in areas with limited water resources. Phosphate is especially limiting in contributing to eutrophication in South African rivers and dams. The development of harmful algal blooms, particularly from cyanobacteria, has been a concern for a long time due to toxins introduced into freshwater systems from these algae. This study investigated whether the use of organic fertilisers compared with inorganic fertilisers was potentially less detrimental to freshwater systems as a result of leachate nutrient and algal microorganism composition; further it was examined, if organic fertiliser was more beneficial to plant growth of Pseuderanthemum atropurpureum. Liquid and soluble granular organic and inorganic N equilibrated fertiliser treatments were applied at low, medium and high concentrations based on recommended label rates. Plant growth parameters were determined from mean height, number of leaves, size of leaves, number of nodes, internode length and number of branches. The species was grown over a period of three months and the experiment was repeated three times. Leaf tissue was analysed for mineral nutrient content and chlorophyll a, b and total chlorophyll. Leachate was analysed for mineral nutrient content including total phosphate, orthophosphate and chlorophyll a. Growth media was analysed for total nitrogen, ammonium and nitrate. A phase contrast light microscope was used to identify larger algal microorganisms and a scanning electron microscope (SEM) to identify smaller algal microorganisms from growth media extracted leachate. One specimen of green algae and some diatoms were identified, including two which may be found in eutrophic waters, but would not pose a threat similar to some species of cyanobacteria, if leached into freshwater systems over a period of time. Further, results showed that total phosphate and orthophosphate concentrations were significantly higher in leachate extracts from bark-based growth media across all fertiliser treatments and at all rates of treatment compared with soil-based growth media. This may have been due to a lack of binding sites in soilless media such as bark. Nitrate concentrations from organic soluble granular treatments were higher in both growth media types, whilst other treatments were similar. Ammonium and leachate nitrogen concentrations were found to be also similar. This may explain why plant growth traits assessed together were similar across all parameters tested. No single fertiliser compared with any other, produced plants that were superior in all growth characteristics measured. It is, therefore, suggested that the fertiliser treatments used in this study be applied at the half rate and plants be rather grown in randles growth medium than gromor for the production of Pseuderanthemum atropurpureum.
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    Non-destructive determination of pre-symptomatic biochemical markers for Peteca spot and evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons
    (2019) Mbhoni, Rikhotso Muriel.; Magwaza, Lembe Samukelo.; Tesfay, Samson Zeray.; Mditshwa, Asanda.
    International markets that import citrus fruit from South Africa have imposed regulations that involve cold sterilization at low temperatures, which cause physiological disorders such as peteca spot in lemon. The aim of this study was to, non-destructively determine pre-symptomatic biochemical markers for Peteca spot and the evaluation of edible coatings for reducing the incidence of the disorder on ‘Eureka’ lemons. The first chapter is general background which introduces the key words and clearly outlines the aim and objectives of the study. The second chapter is review of literature, which motivated the three research chapters due to the gaps found. Presymptomatic biochemical markers that are related to peteca spot were evaluated in the third chapter. The Principal Component Analysis (PCA) was able to separate fruit harvested from the inside and outside canopy positions based on their susceptibility to the disorder. Fruit harvested in the inside canopy were more susceptible to peteca spot and these were correlated with physic-chemical properties, which were typically low in the inside canopy. The efficacy of carboxymethyl cellulose (CMC) and chitosan (CH) incorporated with moringa leaf extracts (M) edible coatings on reducing the incidence of peteca spot was also evaluated in the fourth chapter. Fruit harvested from inside and outside canopy positions were assigned to five coating treatments: control, M+CMC, CMC, CH and M+CH. The most effective coating treatment in reducing the susceptibility of ‘Eureka’ lemon to peteca spot was M+CMC followed by CMC and CH. The fifth chapter focused on, non-destructively predicting peteca spot using visible to near infrared spectroscopy (vis/NIRS). Presymptomatic biochemical markers that have been related to peteca spot were successfully predicted. Lastly, general discussions and conclusions were made in chapter six as well as recommendations.
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    Maintenance of carbon 7 sugar levels and effect on ripening of 'fuerte' and 'hass' avocado (Persea americana Mill.) fruit.
    (2018) Mathe, Sifundo.; Bertling, Isa.; Tesfay, Samson Zeray.
    Avocado fruit are susceptible to a large variety of disorders. These disorders may be a result of an inability of the mesocarp tissue to counteract or tolerate postharvest stress. The C7 sugars D-mannoheptulose and perseitol have been reported to form the predominant portion of antioxidants in the mesocarp and their presence has been associated with avocado fruit quality. It was, therefore, investigated, if mesocarp C7 sugar levels, particularly of D-mannoheptulose and perseitol, can be maintained through infusion of these sugars and further, if this C7 sugar level is associated with fruit quality and shelf life. Avocado fruit, harvested from ‘Hass’ and ‘Fuerte’ avocado orchards in the KwaZulu-Natal Midlands in three different season (early, middle, and late harvest) were infused with 1.5 mL water, 1.5 mL solution of (9.5 mM/fruit; 4.75 mM/fruit D-mannoheptulose), a C7 sugar solution (1.5 mL of 9.5 mM/fruit; 4.75 /fruit; 4.75 mM perseitol/fruit). Fruit quality parameters (firmness, CO2 production, soluble sugar concentrations, moisture content, dry matter, and oil content) were determined over the postharvest ripening period. Early-harvested fruit displayed more severe ripening heterogeneity, with high water loss. The infusion of D-mannoheptulose and perseitol prolonged the shelf life of avocado fruit compared to sucrose-infusion and untreated fruit (control) at different harvesting stages. Water infusion had a considerable effect on mid- and late-season fruit, regarding firmness and respiration rate. Infusion of D-mannoheptulose and perseitol improved the fruit quality attributes flesh firmness and fresh mass retention, and resulted in higher mesocarp C7 sugar concentrations than sucrose- and water-infusion. Regarding the concentration of C7 sugars, water-infused fruit contained the third-highest D-mannoheptulose and perseitol concentration. The oil content was not affected by sugar postharvest infusion, but noticeable differences in oil content were observed through the harvest seasons. Maintaining a certain level of these sugars in the avocado mesocarp tissue seems vital in ensuring a good fruit quality. These C7 sugars could be used as postharvest markers and determining their concentration could become a vital tool in the management of avocado postharvest quality.
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    Evaluation of best practices for local chicory production.
    (2017) Manyoni, Nonduduzo Nelly.; Bertling, Isa.; Odindo, Alfred Oduor.
    Chicory roots obtained from Cichorium intybus are commonly used to produce a caffeine-free coffee substitute. Although the crop has been produced in South Africa for many decades, the country still relies on imported chicory roots to meet its chicory needs, as satisfactory yields are often not achieved. The low yields are associated with the use of poor quality seed, which often results in poor crop establishment. In addition, there are limited options for weed control in chicory since only one herbicide is currently registered for use with chicory in South Africa. Chicory seeds vary in seed coat colour and research has indicated that seed coat colour maybe associated with seed quality of chicory. Results by various authors showed dark chicory seeds to have better performance than light coloured seeds however, contrary findings showing poor performance of dark coloured seeds compared to light coloured seeds have also been reported. There is a need to gain a deeper understanding of the possible association between seed coat colour variation and seed performance in chicory so as to come up with best management practises in order to obtain maximum crop establishment and optimum yields. The aim of the study was to evaluate the use of the image analysis in determining seed coat colour differences in chicory and to gain a deeper understanding of possible associations between seed coat colour variation and seed quality with respect to germination and vigour. In addition, the study assessed the effect of seed coat colour on germination, seedling growth and development of chicory in response to different priming solutions and durations. Lastly, a field experiment was conducted to identify the optimal planting density of chicory with respect to seed coat colour and weed management strategies. Seeds (cv. Orchies) were obtained from Nestle®, KwaZulu-Natal. In the first experiment (chapter three) seeds were separated visually into eight seed colours and then separated and assigned to a certain group using an image analysis system. This analysis system indicated that two colour categories could be separated with respect to hue. These groups were categorized as light and dark coloured seeds. Results also showed significant interactions (P < 0.05) between seed colour and seed quality test with respect to germination percentage and mean germination time. There were highly significant interactions (P < 0.001) between seed coat colour and seed quality test as detected by the germination velocity index (GVI) and imbibition time. Electrolyte leakage from the seeds was not significantly different (P > 0.05) between the seed colour groups. Results from chapter four showed osmo- and hydro-priming to improve seed quality of chicory through improvements in germination velocity index (GVI) and mean germination time (MGT). Osmo-priming resulted in relatively high improvements in seed quality compared with hydro-priming. Priming improved seedling establishment (mean emergence time (MET), seedling length, shoot length, root length, fresh mass and, root/ shoot ratio). Results from the field trial showed the interaction of planting density, seed coat colour, and weeding method to be significant for total plot yield. This suggested that, no optimal crop stand exists with regards to weeding methods and seed coat colour. On the other hand, if the agronomic parameter of interest is biomass plot yield, the optimal plant density would be 200 000 plants ha-1. Herbicide application tended to reduce agronomic performance of dark coloured seeds.
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    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.
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    Evaluation of a low-cost energy-free evaporative cooling system for postharvest storage of perishable horticultural products produced by smallholder farmers of Umsinga in KwaZulu-Natal.
    (2017) Nkolisa, Ntombizandile Sylvia.; Magwaza, Lembe Samukelo.; Workneh, Tilahun Seyoum.; Chimphango, A.
    In this study, a low-cost energy-free evaporative cooling system for postharvest storage of perishable horticultural was investigated. The evaporative cooler is a cost effective, energy free and easy to maintain way of cooling fruit and vegetables. It is basically what smallholder farmers can use as a postharvest storage condition to maintain their fruits and vegetables. However, before the evaporative cooling system was selected, the area of Umsinga where the cooler was installed was studied. The first chapter is a general introductory chapter, which clearly explains problem statement, has justification, hypothesis and outlines the aims and objectives. The second chapter is a review of literature which gives a broad idea of cooling technologies used to preserve quality and reduce postharvest losses on horticultural products. Consequently, it also gives an overview of the causes of postharvest losses. The third chapter of the study assesses vegetable postharvest loss challenges of smallholder farmers in the rural area of Umsinga in KwaZulu-Natal. The assessment was carried out as survey questionnaires. The fourth chapter of the study was evaluating the evaporative cooling system as an energy-free method for postharvest storage of tomatoes for smallholder farmers. The fifth chapter is evaluating the effect of different storage conditions on biochemical quality of tomatoes. The last chapter of the study is chapter six which has the general discussion, conclusion and recommendations.