Masters Degrees (Horticulture)

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Browsing Masters Degrees (Horticulture) by Subject "Aminoethoxyvinylglycine (AVG)"

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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.
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    Investigating the reproductive potential and yield of pecans [Carya illinoinensis (Wangenh. K. Koch)] under South African conditions.
    (Stellenbosch : Stellenbosch University, 2021-12) Snyman, Tertius Jacobus; Lotze, Elmi; Theron, K. I.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Successful pecan [Carya illinoinensis (Wangenh. K. Koch)] production is highly dependent on the effective management of pollination related crop losses (e.g. Stage-II fruit drop). Pecan nut production has seen a rapid increase in the last century and focus has steadily shifted towards retaining fruit that has set. Pecans are known to suffer drastically from fruit drop, which has introduced new avenues of research opportunities to increase fruit retention. The effectiveness of aminoethoxyvinylglycine (AVG; formulated as ReTain®) to increase fruit retention of two commercial pecan cultivars (‘Wichita’ and ‘Navaho’) in Prieska, Northern Cape, was evaluated over a period of three seasons. AVG was applied at 125 mg.L-1 and 250 mg.L-1 at various phenological stages: 20 -30% flowering, 60 - 80% flowering, 7 DAFB (Days After Full Bloom), 14 DAFB and 21 DAFB (‘Wichita’ only). The application of AVG decreased nut retention in a season with high fruit set (> 80%) and low crop load (< 300kg.ha-1) in ‘Wichita’ site B. AVG application did however significantly increase nut retention in one ‘Wichita’ site, in the third season, when applied under a lower fruit set (< 60%) and higher crop load (> 700kg.ha-1) condition. Therefore, the use of AVG as a cropload management tool may be limited to similar conditions. Lastly, the use of AVG with the intent to decrease Stage-II fruit drop did not result in a significant yield increase compared to the control. Thus, under the Northern Cape climatic conditions, for ‘Wichita’ and ‘Navaho and with the recommended dosages, there was no economic advantage to apply AVG to improve nut retention. The nutrient reserve status of a tree is invaluable in increasing nut retention of pecan. Therefore, the mid-season application of a commercially available foliar nutrient product (Top Groei® - Supreme) was evaluated. Top Groei® - Supreme was applied at a rate of 2 ml.L-1 during pistillate flower differentiation (March) for two consecutive seasons on young, bearing ‘Wichita’ trees. In addition, Top Groei® - RootAktiv and Top Groei® - Vigor were applied once off, during the beginning of the 2nd season, as a soil drench at 2.5 L.ha-1 and 5 L.ha-1 respectively, on the treatment trees. Nut retention was unaffected in both seasons. However, a significant increase in yield efficiency (kg.cm-2) was observed during the 2nd season, after the additional soil nutrient amendment was included. It is speculated that this result indicated a potential ‘hidden nutrient/reserve requirement’ in bearing ‘Wichita’ trees and that trees may react positively towards additional nutrient applications, even though no deficiencies were recorded in foliar analyses to result in an increase in yield. Pecan tree architecture is an often-overlooked aspect of pecan production due to most producers adopting the “hedging” technique. Young trees are often left to fill their space with little to no tree training, where after trees are pruned mechanically. This technique results in a complex canopy resulting in shading within the internal tree canopy, which could lead to reduced reproductive development due to a lack of sufficient light distribution. The management practice of pinching the terminal section of vegetative shoots to increase potential bearing positions was evaluated on young, non-bearing ‘Wichita’ trees in the Villiersdorp, South Africa. Selected shoots of 22 cm length and longer were pinched in November 2017 and 2018. A follow-up pinch should have been conducted, but due to the unforeseen three-year drought, shoots did not grow sufficiently after the first pinch. Pinching resulted in a consistent increase in the number and length of laterals on the current season’s growth, compared to the non-pinched control trees, which produced long and unproductive current season’s shoots. At a young, non-bearing tree age, when bearing positions are not required yet, pinching may also serve as a means to induce lateral growth positions which could then be selected, based on crotch angle etc., to create an ideal framework.