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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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| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1869484157458972672 |
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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 | 2026-07-01T04:10:25.897Z |
| 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. Citrus fruit industry -- South Africa Citrus fruits -- Effect of temperature on Phenology -- South Africa Fruit -- Quality -- South Africa Growth (Plants) Regulation Fruit thinning -- South Africa UCTD 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 Unpublished masters thesis.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 ENGLISH ABSTRACT: 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. AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse sitrusbedryf is hoofsaaklik op uitvoere gerig, wat vereis dat vrugte aan streng vereistes ten opsigte van grootte, eksterne voorkoms en interne gehalte moet voldoen. Groot vrugte lewer premiepryse, terwyl klein vrugte die winsgewendheid verlaag, wat die behoefte aan presisiemonitering en -bestuur beklemtoon. Hierdie strategieë word ondersteun deur twee sleutel praktyke – akkurate fenologiese kennis en doeltreffende produksiepraktyke soos uitdunning. Fenologie, die studie van seisoenale ontwikkelingsstadiums, bepaal die tydsberekening van bestuurspraktyke soos besproeiing en toediening van plantgroeireguleerders (PGR’s). Sintetiese ouksiene word wyd gebruik as chemiese uitdunningsmiddels om vruggrootte te verbeter, maar die doeltreffendheid daarvan is afhanklik van presiese tydsberekening, wat verskil tussen kultivars en streke. Hierdie studie het die fenologie van ‘Nadorcott’ mandaryn en ‘Midknight’ Valencia in drie groot sitrusproduksiestreke, naamlik Citrusdal, Kirkwood en Tshipise, gedokumenteer. Dit het ook die optimale tydsberekening van sintetiese ouksientoedienings op ‘Nules’ clementine en ‘Nadorcott’ mandaryn in Citrusdal oor twee seisoene geëvalueer. Die tydsberekening van fenologiese stadiums, naamlik dormansie, bot, ballonstadium, volblom en blomblaarval, is weekliks gemonitor en gedokumenteer, en die tydsberekening en duur van fisiologiese vrugval, kleurbreek en oes is ook vasgestel. Sintetiese ouksiene (2,4-DP en 3,5,6-TPA) is op vroeë en laat stadiums toegedien gebaseer op vruggrootte, asook in kombinasie met handuitdunning en dan ook handuitdunning alleenlik. Vruggroei, opbrengs en na-oes gehalte is gemeet. Fenologiese tydsberekening het gewissel tussen die streke, hoofsaaklik gedryf deur temperatuur. Tshipise het die vroegste aanvang van alle stadiums getoon weens hoër gemiddelde temperature, terwyl Citrusdal en Kirkwood soortgelyk was t.o.v. tydsverlope. Die duur van die volblom venster het tussen kultivars en streke verskil. Fisiologiese vrugval het teen hoër vlakke in Citrusdal as in Kirkwood voorgekom. Soortgelyke kleurbreek- en oespatrone is in alle streke gevind. Die uitdunningsproef het getoon variërende reaksies, volgens tydsberekening, aktiewe bestanddeel, kultivar en seisoen, getoon. Vir ‘Nules’ het laat 2,4-DP-toedienings die vruggrootte en opbrengs verbeter sonder om interne gehalte te benadeel, terwyl vroeë toedienings die risiko ingehou het om opbrengs en gehalte te benadeel. Alhoewel handuitdunning tot ‘n moontlik afname in opbrengs gelei het, bly dit steeds ’n betroubare alternatief vir chemiese uitdunning om vruggrootte te verhoog. Vir ‘Nadorcott’, het 3,5,6-TPA die vruggrootteverspreiding verbeter, maar interne gehalte benadeel en opbrengs verlaag, terwyl laat 2,4-DP-toedienings die vruggrootte, sapinhoud en skildikte verbeter het en goeie opbrengs behoue gebly het. Oor die algemeen het 2,4-DP groter potensiaal getoon om vruggrootte en opbrengs te verbeter met hanteerbare risiko’s, veral wanneer dit later toegedien word. Ten slotte is presisie deur akkurate tydsbeplanning van ingrypings, gegrond in fenologie en uitgevoer deur geteikende uitdunning, noodsaaklik vir die produksie van uitvoergehalte-sitrus in Suid-Afrika. Hierdie tesis bied praktiese insigte vir verskillende streke waarop kultivarspesifieke bestuurs- strategieë vasgestel kan word. Die bevindinge moet egter bevestig word deur multiseisoenale fenologie data, asook uitgebreide proewe oor die doeltreffendheid van die verskillende sintetiese ouksiene op meer verskillende toedieningstye. 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 : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Citrus fruit industry -- South Africa Citrus fruits -- Effect of temperature on Phenology -- South Africa Fruit -- Quality -- South Africa Growth (Plants) Regulation Fruit thinning -- South Africa UCTD 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 |
| topic | Citrus fruit industry -- South Africa Citrus fruits -- Effect of temperature on Phenology -- South Africa Fruit -- Quality -- South Africa Growth (Plants) Regulation Fruit thinning -- South Africa UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/136116 |
| work_keys_str_mv | AT naudenanjehannah establishingphenologicaldevelopmentacrossthreeclimaticregionsofsouthafricaandoptimisingsyntheticauxinuseondifferentcitrustypes |