Browsing by Author "Du Toit, Tharine"

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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.