Masters Degrees (Horticulture)

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Now showing 1 - 5 of 163
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    Investigating sustainable approaches to late maturity and fungal infection of organic ‘Medjool’ date palm (Phoenix dactylifera L.) fruit in the Western Cape, South Africa
    (Stellenbosch : Stellenbosch University, 2023-03) Peddie, Rude Jo-Anne; Lotze, Elmi; Brink, Casper; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The commercial production of date palm in South Africa was established approximately 50 years ago in the Northern Cape with the largest orchard stretching over 100 hectares. The province has a hot and dry climate, similar to the regions of the Middle East and North Africa where date palms are traditionally produced. These conditions result in little to no issues regarding the growth and development of the fruit, the presence of pests and/or diseases during its cultivation. Date palm cultivation has since spread to climatically suitable regions in the Western Cape, which is one of the richest fruit-growing regions in the country. However, on one of the farms (approximately 30 hectares in the Hermon region), irregular ripening and high incidences of microbial spoilage were observed soon after cropping. Since the specific farm employs organic agriculture, a sustainable approach is required to address these two challenges to enable marketing of the crop. The aim of this study was to investigate the application of preharvest fruit bunch bagging as an environmentally sustainable approach to the acceleration of date fruit ripening, as well as the control of fungal infections in an organic date orchard in the Western Cape. During the 2022 season on the Kleinplasie organic date orchard near Hermon in the Western Cape, ‘Medjool’ date palm trees underwent three different non-perforated bagging treatments (no bag, blue low-density polyethylene bag, white high-density polyethylene abg) at two different phenologically important times (Khalal at 17 February 2022, Khimri at 31 March 2022) during the fruit ripening period. Preharvest analyses found that the technique, particularly the blue low-density polyethylene bags implemented later in the fruit ripening process, significantly increased fruit weight, size, and improved fruit colour at harvest. However, the microbial load was found to significantly increase at harvest, leading to higher rates of fungal infection, when compared to the other bagged treatments (p = 0.034). Postharvest analyses concluded that bunch bagging, particularly blue low-density polyethylene bags implemented earlier in the fruit ripening process, could have a positive effect on ripening of fruit under the appropriate storage conditions, and the organoleptic properties of the fruit was significantly different between treatments. According to the results of the study, it was recommended that implementing a blue low-density polyethylene bag later in the ripening process at Khalal until harvest could result in the accelerated ripening of date fruit, while applying a white high density polyethylene bag applied earlier at Khimri could aid in the control of fungal infection. This is due to the colour of the bagging material acting as a filter of photosynthetically active radiation, which refers to the range of wavelengths that aid in photosynthesis.
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    The impact of protective netting on reproductive bud development, flowering, fruit set and fruit quality in apple trees
    (Stellenbosch : Stellenbosch University, 2023-03) Jordaan, Stephen Christiaan; Midgley, S. J. E.; Lotze, Elmi; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The overall objective of this study was to determine how yield, fruit quality and maturity, reproductive bud development, flowering, fruit set and early fruit growth of apple orchards are impacted by two types of protective netting compared to open orchards, in the Western Cape Province of South Africa. The study also aimed to investigate the interactive effects between black draped netting and various levels of crop load on reproductive processes of ‘Golden Delicious’ trees. To achieve these aims, three trials were conducted over two seasons. In the first trial, fixed white (20%) netting over ‘Rosy Glow’ resulted in improved fruit growth rate, increased fruit diameter and mass, lighter green ground colour, less peel red colour, lower viable seed count, and less sunburn and hail damage in two consecutive seasons. The netting did not induce any significant effect on percentage reproductive buds (R-buds), R-bud progression for different shoot types, flower progression, flower quality, and early fruit growth. A small but significant reduction in fruit set percentage under netting was, however, found. In the second trial, black draped netting (end-November to end-February) over ‘Golden Delicious Reinders’ resulted in greener fruit, less sunburn and hail damage, reduced firmness, and reduced ratio of total soluble solids (TSS) to titratable acidity (TA). R-bud percentage was promoted under the netting; however, R-bud progression was delayed after net removal. The latter effect may have culminated in delayed flowering, lowered fruit set (farm data) and reduced early fruit growth. In the third trial, black draped netting (mid-December to early March) over ‘Golden Delicious’ resulted in more stem-end russet, greener ground colour, lower firmness and advanced starch breakdown, fewer viable seed, less sunburn, and lower TSS and TA. Significant interactions between net/control and crop load treatments were found for ground colour, TA and TSS:TA. R-bud percentage was higher and more uniform across all crop loads and shoot types under the netting, while the control treatment displayed an increasing R-bud percentage for decreasing crop load level across most shoot types. After the harvest and net removal, R-bud progression was slightly but significantly delayed. Flower progression was unaffected by the netting. For flower quality, significant interaction between flower type and netting was found for pedicel length, receptacle length and number of locules. In addition, significant interaction between net/control and crop load treatments was found for ovule length. Fruit set percentage improved under netting. The different crop load levels did not have a significant impact on flower progression, flower quality and fruit set. The use of both fixed and draped netting in apple orchards has the potential to improve apple fruit quality. However, caution is required based on the impact of draped netting on flowering and reproductive growth during the following season in ‘Golden Delicious’ and its strains. Crop load adjustments are recommended in ‘Golden Delicious’ and its strains to minimise the impact of netting on reproductive growth during the current and following season.
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    Investigating the potential of medicinal perennial species as permanent cover crops in deciduous orchards and vineyards
    (Stellenbosch : Stellenbosch University, 2023-03) Petzer, Heleen; Stone, Wendy; Lotze, Elmi; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Two intercropping trials were conducted, one was on Welgevallen research Farm in Stellenbosch in a plum orchard (Prunus salicina), on a heavy clay soil with limited irrigation during 2022, with a selection of five commercially available medicinal cover crop species (Salvia rosemarinus, Artemisia afra, Pelargonium capitatum, Helichrysum crispum and Eriocephalus africanus). The other was an established trial on Bon Vallon Farm in Robertson (2019) in a Chardonnay vineyard, on a sandy clay loam soil with limited irrigation during its establishment and a selection of four fynbos medicinal cover crop species (Salvia rosemarinus, Artemisia afra, Helichrysum crispum and Eriocephalus africanus). The trial at Welgevallen investigated cover crops during establishment, while the Robertson trial investigated an already-established cover cropping system. Similar parameters were investigated to evaluate the scientific impact and economic potential of both. A literature review was conducted to evaluate how medicinal cover crops affect soil health, and how they contribute to a more sustainable and low input agricultural system. The contrast between conventional farming and diversified farming practices was investigated, focusing on the use of perennial medicinal species as a more sustainable approach for crop production systems. The effect of the different medicinal cover crop species was quantified using several parameters including evaporation rates, soil temperature, chemical parameters and soil nutrients, survival rates, plant cover, weed density, climate, snail presence and the harvest of medicinal cover crop biomass for a potential secondary income. Findings showed that in a deciduous orchard, A. afra and S. rosemarinus were the most successful medicinal species at establishment. A. afra was the most efficient in weed suppression. A. afra resulted in a significantly higher biomass return per hectare, although none of the treatments resulted in a secondary income with regard to the calculations in our study. The three-year established trial showed that the efficiency of all medicinal cover crops for weed suppression increased as the season progressed. Both S. rosemarinus and H. crispum had significant effects on the evaporation rates compared to the control treatment. For soil temperature, there was a significant difference between the control compared to all other treatments. No treatments resulted in a secondary income after one harvest, although A. afra and S. rosemarinus were the most beneficial medicinal species over both trials regarding environmental and economic sustainability in the long-term.
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    The effect of prohexadione-calcium application in ‘Fuji’ apple trees in South Africa
    (Stellenbosch : Stellenbosch University, 2023-03) Horne, Aldo; Siboza, Xolani; Theron, Karen; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: South African apple [Malus x domestica Borkh.] producers have observed that shoot regrowth occurs in vigorous ‘Fuji’ apple trees after applying the registered treatment of prohexadione-calcium (calcium 3-hydroxy-5-oxo-4-propionyl-cyclohex-3-enecarboxylate; Pro-Ca). The registered treatment includes two applications of Pro-Ca during the first four weeks after full bloom (WAFB). The first applied at 70 mg.L⁻¹ and a rate of 80% tree row volume (TRV) when shoots are 3 – 5 cm long in spring. The second application should occur at the same concentration, but four weeks later at 100% TRV. The effect of Pro-Ca treatments applied at different timings and rates on shoot growth and shoot regrowth in ‘Fuji’ apple trees in South Africa is unknown. The Pro-Ca treatments were applied to ‘Fuji’ Kiku® and ‘Fuji’ Akifu® apple trees in the Vyeboom and Witzenberg Valley regions, respectively. Trees were randomly selected and treated with Pro-Ca according to the TRV. Nine Pro-Ca treatments were used with Pro-Ca applied up to six times during the growing season, but no later than 6 WAFB. These treatments were compared to an untreated control (UTC). The application of 70 mg.L⁻¹ Pro-Ca (80% TRV) at full bloom, followed by 70 mg.L⁻¹ (100% TRV) four and six WAFB; or five 70 mg.L⁻¹ (40% TRV) applications applied from full bloom until four WAFB, suppressed shoot growth in ‘Fuji’ Akifu® trees without increasing shoot regrowth, but did not significantly suppress final shoot length in ‘Fuji’ Kiku® trees. The current registered treatment of Pro-Ca in South Africa may cause shoot regrowth to occur, which may negatively affect flowering, fruit yield and quality. The Pro-Ca treatments that included an initial 70 mg.L⁻¹ (80% TRV) at full bloom followed by 70 mg.L⁻¹ (100% TRV) four WAFB; or five 70 mg.L⁻¹ (40% TRV) applications within the first six WAFB, increased fruit diameter in ‘Fuji’ Kiku® trees without significantly affecting fruit yield. The application of Pro-Ca had no significant effect on return bloom, fruit set, fruit yield or quality in either ‘Fuji’ Kiku® or Akifu® apple trees. Few studies have shown that the application of Pro-Ca at full bloom on the vigorous ‘Fuji’ apple cultivar may suppress shoot regrowth and improve fruit quality. However, these studies were conducted over a single growing season. No study has observed the cumulative effect of Pro-Ca applied over two consecutive seasons in ‘Fuji’ apple trees in South Africa. The application of 70 mg.L⁻¹ Pro-Ca (80% TRV) at full bloom, followed by 70 mg.L⁻¹ (100% TRV) four and six WAFB on the same ‘Fuji’ Kiku® trees over two consecutive seasons suppressed shoot growth and improved fruit yield efficiency without significantly increasing shoot regrowth, or negatively affecting fruit set, fruit size or return bloom. The application 70 mg.L⁻¹ (80% TRV) at full bloom, followed by 70 mg.L⁻¹ (100% TRV) four and six WAFB, applied over two consecutive seasons to the same ‘Fuji’ Akifu® trees, suppressed shoot growth without significantly increasing shoot regrowth, or negatively affecting fruit set, fruit yield, fruit quality, or return bloom.
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    Improving crop load and fruit quality in deciduous fruit using plant growth regulators
    (Stellenbosch : Stellenbosch University, 2023-03) Dippenaar, Charlize; Theron, K. I. ; Steyn, Wiehann ; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Crop load in deciduous fruit trees plays an important role in fruit quality, yield and alternate bearing. Young ‘Packham’s Triumph’ trees fail to achieve adequate yields, while apple, peach, and nectarine trees, set fruit abundantly, requiring annual thinning. Crop load can be manipulated using plant growth regulators to enhance or reduce abscission. Hand thinning remains the popular thinning method in stone fruit. Due to increasing labor costs alternatives are needed. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) has recently shown potential as a chemical thinner. While ACC thinned at various phenological stages (pink bud, balloon, early flower and late flower), later stages produced more ethylene resulting in greater thinning. In ‘Keisie’, ACC at 450 µl.L⁻¹ applied when fruitlets were 8-10 mm in diameter achieved adequate thinning, leading to an increased fruit weight but a slight reduction in yield. In nectarine (‘Alpine’, ‘August Red’, ‘Zee Fire’, ‘Ruby Rose’ and ‘Luciana’), ACC thinned successfully when applied at pink bud – 20% flowering to a greater or lesser extent. Second applications to the upper ⅓ of the canopy can enhance thinning, if applied at the correct phenological stage. Where ACC successfully thinned, an increase in fruit weight was observed. ACC did not affect yield or harvest distribution. Generally, two applications at 450 + 225 µl.L⁻¹ ACC or a single application at 450 µl.L⁻¹ ACC where trees bloom uniform, seems promising in nectarine. No leaf toxicity or split pit was induced by ACC. Future studies in stone fruit should evaluate ACC closer to full bloom. In apple, chemical thinners are considered standard commercial practice. However, existing thinners are only effective until 15 mm fruitlet diameter and therefore the need remains for a reliable “rescue thinner”. Recently, ACC has shown thinning potential in this late window. When 450 µl.L⁻¹ ACC was applied at 15-20 mm fruitlet diameter it successfully thinned ‘Royal Gala’, ‘Cripps’ Pink’, ‘Rosy Glow’, ‘Royal Beaut’ (Gala type) and at 560 µl.L⁻¹ ACC in ‘Cripps’ Red’. Results in ‘Fuji’ varied between seasons, although a full bloom application seemed promising in one trial. ACC was combined with existing thinners but did not always thin additively. At the recommended rates, ACC sometimes affected yield, ground color, blush intensity and percentage, seed number or stem-end russet, but variable results were observed between trials. Fruit weight was improved in some, but not all trials. Trees treated with ACC tended to have a better return bloom the following spring. Aminoethoxyvinylglycine (AVG) is an inhibitor of ethylene biosynthesis and can reduce premature fruitlet abscission in young ‘Packham’s Triumph’. The effect of AVG varied between trials due to weather conditions during and after AVG application. Generally, an increase in final fruit set and/or yield was observed when AVG was applied during cool, damp conditions. AVG at rates between 125 mg.L⁻¹ and 250 mg.L⁻¹ was effective one or two weeks after full bloom, therefore application timing should be altered according to weather conditions. An expected decrease in fruit weight was observed in trials were fruit set and/or yield was increased. AVG did not affect fruit firmness, the occurrence of retiform russet or skew calyx-ends.