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Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types
Thesis (MScAgric)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613784243175424 |
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| access_status_str | Open Access |
| author | Naude, Nanje Hannah |
| author2 | Raath, Pieter J. |
| author_browse | Naude, Nanje Hannah Raath, Pieter J. |
| author_facet | Raath, Pieter J. Naude, Nanje Hannah |
| author_sort | Naude, Nanje Hannah |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/136116 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:41:38.867Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/136116 Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types Naude, Nanje Hannah Raath, Pieter J. Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science. Thesis (MScAgric)--Stellenbosch University, 2026. Naude, N. H. 2026. Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/21fefb3e-d9e0-4389-b09f-784375d6789c The South African citrus industry is primarily export-oriented, requiring fruit to meet strict standards for size, external appearance, and internal quality. Large fruit earn premium prices, while undersized fruit reduces profitability, highlighting the need for precision management. Two key factors underpin these strategies – accurate phenology knowledge and effective production practices such as thinning. Phenology, the study of seasonal developmental stages, guides the timing of management practices such as irrigation and plant growth regulator (PGR) applications. Synthetic auxins are widely used as chemical thinning agents to improve fruit size, yet efficacy is dependent on precise timing of application, which varies by cultivars and regions. This study documented the phenology of ‘Nadorcott’ mandarin and ‘Midknight’ Valencia across three major citrus-producing regions – Citrusdal, Kirkwood and Tshipise, and evaluated optimal timing of synthetic auxin applications on ‘Nules’ clementine and ‘Nadorcott’ mandarin in Citrusdal over two seasons. Timing of the phenological stages, i.e., dormancy, sprouting, balloon stage, full bloom and petal drop was monitored and documented weekly and the timing and duration of physiological fruit drop, colour break and harvest documented. Synthetic auxin treatments (2,4-DP and 3,5,6-TPA) were applied at early and late timings based on fruitlet size, as well as in combination with hand thinning and hand thinning alone, and the fruit growth, yield, and postharvest quality was measured. Phenological timing varied across the regions, primarily driven by temperature. Tshipise exhibited the earliest onset for all stages due to higher ambient temperatures, while Citrusdal and Kirkwood showed similar timing trends. Full bloom windows varied in duration based on cultivar and regional differences. Physiological fruit drop occurred at elevated rates in Citrusdal compared to Kirkwood. Similar colour break and harvest trends were found in all regions. The thinning trial demonstrated that responses vary by timing, active ingredient, cultivar and season. For ‘Nules’ clementine, late 2,4-DP applications improved fruit size and yield without compromising internal quality, while early applications posed the risk of compromising yield and quality. Hand thinning proved to remain a reliable alternative to chemical thinning in increasing fruit size but could lead to a decrease in yield. For ‘Nadorcott’ mandarin, 3,5,6-TPA improved fruit size distribution, yet compromised internal quality and decreased yield, whereas late 2,4-DP applications improved fruit size, juice content and decreased rind thickness, while maintaining yield. Overall, 2,4-DP showed greater potential for improving fruit size and yield with manageable risks, particularly when applied later. In conclusion, precision through accurately timed interventions, grounded in phenology and executed through targeted thinning, is essential for producing export-quality citrus in South Africa. This thesis provides practical insights for different regions on which cultivar-specific management strategies can be built. The reported findings, however, must be corroborated through multi-season detail of phenology, as well as extended trials on the effectiveness of the different synthetic auxins at more timings. Masters 2026-04-22T13:27:32Z 2026-04-22T13:27:32Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/136116 en Stellenbosch University 104 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Naude, Nanje Hannah Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title | Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title_full | Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title_fullStr | Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title_full_unstemmed | Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title_short | Establishing phenological development across three climatic regions of South Africa and optimising synthetic auxin use on different citrus types |
| title_sort | establishing phenological development across three climatic regions of south africa and optimising synthetic auxin use on different citrus types |
| url | https://scholar.sun.ac.za/handle/10019.1/136116 |
| work_keys_str_mv | AT naudenanjehannah establishingphenologicaldevelopmentacrossthreeclimaticregionsofsouthafricaandoptimisingsyntheticauxinuseondifferentcitrustypes |