Browsing by Author "Steyn, Juan"
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- ItemInvestigating plant growth dynamics of selected southern highbush blueberry (V. corymbosum L. interspecific hybrids) cultivars under South African growing conditions(Stellenbosch : Stellenbosch University, 2022-12) Steyn, Juan; Lotze, Elmi; Hoffman, L. (Lynn) (Horticulturalist); Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture.ENGLISH ABSTRACT: In South Africa, southern highbush blueberry (SHB) cultivars exhibit an evergreen growth habit, due to the generally warmer climatic conditions. Two SHB cultivars, 8- 42 and 9-02, were selected based on their observed differences in their aboveground characteristics. Cultivar 9-02 has a more vigorous growth habit than 8-42, but yields are considerably lower in 9-02 than in 8-42, regardless of the larger plant structure. Therefore, the aim of the study was to quantify the above- and belowground phenology of these cultivars, along with non-structural carbohydrate allocation patterns to provide deeper insights into the observed difference in yield between the cultivars. In the first trial, the timing, duration and intensity of selected flower bud stages in ‘8-42’ and ‘9-02’ were determined at two production sites (Hex River and Wolseley) in the Western Cape, South Africa. Cultivar 8-42 flowered from April to mid-October and reached a peak during early August, while cultivar 9-02 flowered from April to late October but also reached a peak during early August at the Wolseley site. However, at the Hex River site, peak flowering occurred a month later, in September, thus indicating a possible genetic and climate-related interaction response. Fruit harvesting commenced in early August in ‘8-42’, at both sites, and at the Hex River site for ‘9-02’; however, harvest was advanced to the end of July, at the Wolseley site. Despite these early harvesting times, more than 90% of the crop was concentrated between late- September and mid-November, for both cultivars, at both sites. Furthermore, the study confirmed the challenges encountered when attempting phenological predictions for SHB grown in an evergreen production system, as flowering and harvest stages can occur continuously, across several weeks, within a single plant. In the second trial, the number and length of new root production were quantified in ‘8-42’ and ‘9-02’ at the Hex River site to describe the seasonal timing of new root production and root distribution patterns. New root production (number of additional roots recorded on consecutive evaluation dates) was evident throughout the study, with increased root production rates occurring at similar times, for both cultivars. A first root production peak occurred at the onset of early winter and coincided with flowering. New root production continued until increased fruit maturation and harvesting that commenced in early spring. A second root production peak coincided with mid-summer, approximately one month after fruit harvest. New root formation occurred simultaneous with active shoot growth, until shoot activity declined with the termination of shoot elongation during early May. In the third trial, non-structural carbohydrate allocation patterns were determined in bearing and non-bearing ‘8-42’ and ‘9-02’ plants, at selected phenological stages at the Hex River site, to gain a better understanding of the underlying causes of the reported differences in yield between the cultivars. Leaves were the major source of carbohydrates to support, not only reproductive development between 50% and 90% flowering in both cultivars, but also root growth, which was evident during this period. Thereafter, reproductive growth and new vegetative growth were sustained by all evaluated plant organs in ‘8-42’, during both seasons, whereas distinctly different results between seasons occurred during this period, in ‘9-02’. Leaf carbohydrates decreased between 90% flowering and peak harvest in the 2020 season, whereas it increased sharply in the 2021 season. It was suggested that this could indicate that ‘9-02’ had excess carbohydrates in the 2021 season which were not utilized to enhance reproductive growth and development.