Masters Degrees (Horticulture)

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Browsing Masters Degrees (Horticulture) by Subject "Almond -- Effect of global warming on"

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    Dormancy progression, artificial rest breaking and pollination of 'Independence' almonds under South African growing conditions.
    (Stellenbosch : Stellenbosch University, 2021-04) Du Toit, Tharine; Louw, Esme D.; Theron, K. I.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Almond (Prunus amygdalus Batsch) has grown in popularity with South African growers, as the need for better alternatives to marginal crops arose in the Western Cape. A failure to establish a local almond industry in the past was ascribed to limited local supply that did not justify investments in expensive machinery needed for almond processing, which further prevented the expansion of the South African almond industry. Since then, advances in almond breeding have offered a wider range of cultivars that are more suitable for production under South African conditions, such as ‘Independence’, a self-compatible almond cultivar characterized by a low chill requirement (400 Utah chill units) and late flowering. Dormancy progression and bud break patterns, together with chilling and heat requirements, were investigated in various ‘Independence’ almond orchards grown throughout the Western Cape. A low level of dormancy was depicted for this almond cultivar, showing endodormancy progression, irrespective of chill accumulation. Dormancy induction and chill requirements varied among orchards, while the release from dormancy seemed more comparable. Results suggest that ‘Independence’ is more reliant on sufficient heat accumulation to ensure successful dormancy release, rather than chill. Regarding climatic conditions, ‘Independence’ is suitable for commercial production under South African conditions. Even though dormancy progression models showed a more acceptable representation of endodormancy release, its ability to accurately represent dormancy induction remains questionable under mild winter conditions. Using chemical rest breaking agents (RBAs) have become standard practice in deciduous fruit production in South Africa. The efficacy of various RBAs in improving bud break and increasing possible bearing positions was evaluated on ‘Independence’ almond trees. None of the RBAs affected reproductive bud break, fruit set, yield and post-harvest quality parameters. However, oil containing treatments enhanced the onset of vegetative bud break, resulting in a greater overlap between reproductive and vegetative growth. As no obvious disadvantage was shown in reproductive development, earlier vegetative bud break could hold potential benefits due to an advanced photosynthetic ability. An increase in spur production was also evident in trees treated with RBAs containing oil. As almond predominantly bears on spurs, these treatments increased the bearing surface, possibly increasing yield potential in subsequent seasons. The 0.5% hydrogen cyanamide treatment, in combination with 2% mineral oil, proved to be the most effective RBA tested to enhance vegetative growth and increase the bearing surface of ‘Independence’ almond trees grown under South African conditions. The effect of commercial beehives and presence of a cross-pollinator (‘Nonpareil’) on fruit set and quality was evaluated. The presence of a compatible cross-pollinator did not have an effect on fruit set, yield efficiency and post-harvest quality parameters, demonstrating that single-cultivar orchards would not compromise yield potential due to a lack of cross-pollinators. Even though the epistigmatic flowers of ‘Independence’ almond trees have autogamic capacity, it was not efficient in ensuring maximum yield potential. The presence of pollen vectors is needed to ensure successful self-pollination and fertilization in this self-compatible almond cultivar, to obtain commercially acceptable crop loads.
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    Quantifying the potential of almond production in the Western Cape for future extension and high-density plantings in suitable climatic regions
    (Stellenbosch : Stellenbosch University, 2022-04) Du Toit, Nina; Lotze, Elmi; Hoffmann, Willem H.; Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Almond (Prunus amygdalus Batsch) has become popular as an alternative crop with South African growers as the need for marginal crops in the Western Cape increases. Growers are also seeking more efficient and sustainable production methods that will reduce inputs to remain globally competitive. High-density plantings proved to be more profitable in commercial crops like peach and nectarine than traditional low-density plantings, but proper canopy management and manipulations are required to maintain the efficiency of these systems. The aim of this study was to assess different spacing and training configurations with respect to maximizing future reproductive potential, for two commercial cultivars. The canopy development and performance of two newly established super- high-density (SHD) (2049 trees.ha -1) training systems in the Robertson region were evaluated for the Soleta cultivar on ‘Garnem’ rootstock. The study focused on the relationship between light interception (LI) and potential yield efficiency, as the orchard was in a vegetative phase during the first two seasons. The Open-Vase (OV) system showed more vigorous growth patterns than Bi-Axis (BA), resulting in a significantly higher stem circumference (in all three seasons), shoot growth and canopy volume (CV) after summer pruning (2020/21) and LI during full bloom (2020/21;2021/22). The OV had a significantly higher trunk cross-sectional area (TCSA), which translated into the significantly higher yield efficiency in the BA system, in 2020/21. The OV had a significantly higher in-shell and kernel weight, -length and -width. Initial results indicated that both systems are suitable for ‘Soleta’ at SHD, but the BA system outperformed the OV system with regard to yield efficiency at the first commercial harvest (three years after establishment). The effect of two alternative rootstocks, ‘Viking’ and ‘Flordaguard’, on the vegetative development of ‘Nonpareil’, was evaluated in the Durbanville region. Rootstock did not influence the stem circumference or the average annual shoot growth during the two consecutive seasons. However, rootstock affected CV, after shoot growth cessation, and LI, after leaf drop. ‘Nonpareil’ trees on ‘Flordaguard’ had a significantly higher CV and LI than trees on ‘Viking’, which indicated that ‘Flordaguard’ resulted in more vigorous growth of the ‘Nonpareil’ scion than ‘Viking’. Almond cultivation at higher densities is a relatively new concept than the historical, traditional systems currently under production. A financial comparison was conducted on the performance of the Soleta (more compact, self-fertilising) and Nonpareil (vigorous, self-infertile) cultivars in the Durbanville, Robertson and Montagu regions, planted in different orchard systems, with varying planting densities and training systems. For each system, the net present value (NPV) and modified internal rate of return (MIRR) were calculated. The NPV at a discount rate of 5% and 10% indicate that the low-density system is preferred for both cultivars. A sensitivity analysis was performed on the year that full production is achieved, as well as on the orchard's life expectancy. With the exception of the MIRR, which increased by 1% for a two-year decrease in the life expectancy of low-density orchard systems, both factors had a negative impact on the NPV and a negative or no impact on the MIRR.