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Studies on the seedless fruit set of Valencia oranges
Thesis (MScAgric)--Stellenbosch University, 2021.
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| Format: | Thesis |
| Language: | af_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867614114464923648 |
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| access_status_str | Open Access |
| author | Van Zyl, Carel Petrus |
| author2 | Cronje, Paul J. R. |
| author_browse | Cronje, Paul J. R. Van Zyl, Carel Petrus |
| author_facet | Cronje, Paul J. R. Van Zyl, Carel Petrus |
| author_sort | Van Zyl, Carel Petrus |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/124255 |
| institution | Stellenbosch University (South Africa) |
| language | af_ZA |
| last_indexed | 2026-06-10T12:46:53.692Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/124255 Studies on the seedless fruit set of Valencia oranges Van Zyl, Carel Petrus Cronje, Paul J. R. Theron, K. Stander, O. P. J. Stellenbosch University. Faculty of Agrisciences. Dept. of Horticulture. Valencia oranges -- Quality -- South Africa Growth (Plants) -- Effect of chemicals on Citrus fruits -- Breeding Valencia oranges -- Economic aspects -- South Africa Citrus -- Effect of temperature on Fruit trees -- Climatic factors Soils -- Classification Oranges -- South Africa -- Marketing Uniconazole Nitrogen-fixing trees UCTD Thesis (MScAgric)--Stellenbosch University, 2021. ENGLISH ABSTRACT: The profitability of a citrus orchard is determined by consistent fruit quality and yield, but seedless Valencia oranges have variation in this regard due to irregular fruit set. Environmental factors and cultural practices on Valencia fruit set under South African conditions are not well understood, and contradictory results between climatic regions exist. This study assessed factors that may influence the fruit set of seedless Valencia oranges. A review of weather conditions and production trends in two climatically diverse seedless Valencia production regions of South African (Kirkwood and Letsitele) revealed that tracking weather extremes help explain the variation in yield between orchards during growing seasons and shed some light on when the weather or the tree's physiology is the cause of a poor yield. Even so, the study highlighted the lack of targeted climatic studies in the various South African citrus-producing regions to identify possible weather factors contributing to inconsistent fruit set in these regions. Improved understanding should help manage their financial risk in high-value orchards by allowing them to take preventative measures. Secondly, the study included research into the cost of low set and yield of seedless Valencia cultivars in the Letsitele area Limpopo, using the orchard level budget model. The model highlighted that high fruit prices would decrease the possible financial loss an orchard incurs, but to reach these high fruit prices for high-quality fruit, the producers must use innovative horticultural practices in the orchard. This reduces the risk of the orchard not sustainably producing economically viable levels of high-quality seedless Valencia oranges. The effects of nitrogen (N), GA3 and uniconazole on ‘Midknight’ and ‘Delta’ Valencia to improve fruit set were tested and delivered inconsistent results but indicated that GA₃ application should be applied as standard practice to seedless Valencia oranges. Uniconazole applications can increase the yield, and if high N applications were made, it should be applied to counteract the possible excessive vegetative growth that it may cause. Higher levels N consistently led to the production of seedless Valencia oranges with a decreased internal quality. Finally, the study aimed to measure the effect of the soil potential and root development on fruit set of seedless Valencia oranges and provide an accurate classification system specifically for citrus, which should help the producer’s decision making, especially in making pre-establishment corrections, the optimisation of fertilisation and irrigation. The study also showed that higher potential soils improved the fruit size distribution produced, improving the orchards profitability. The improvement is possible because of improved nutrients, oxygen and water allocation to the root zone, and the tree and fruit itself during fruit development. AFRIKAANSE OPSOMMING: Die winsgewendheid van 'n boord word bepaal deur die kwaliteit en volume van die vrugte wat dit produseer, maar saadlose Valencia-lemoene word deur variasie in vrug set beïnvloed. Die invloed van omgewingsfaktore asook verbouingspraktyke op die vrugset en - kwaliteit, onder Suid- Afrikaanse toestande, word nie goed begryp nie en daar bestaan teenstrydige resultate tussen klimaat streke. Die doel van die studie was om faktore te identifiseer wat die hoeveelheid en kwaliteit van saadlose Valencias kan beïnvloed. Die studie het 'n oorsig van weerstoestande en produksietendense in twee saadlose Valencia-produksiestreke van Suid-Afrika (Kirkwood in die Oos Kaap en Letsitele in Limpopo provinsies) ingesluit, wat aangetoon het dat weer die opbrengste in boorde gedurende die seisoene kan help verklaar. Die studie het egter die gebrek aan geteikende klimaatstudies, om klimaatsfaktore te identifiseer wat kan bydra tot 'n inkonsekwente vrugset in die verskillende Suid-Afrikaanse sitrusproduserende streke, uitgelig. Sulke studies behoort produsente te help om hul finansiële risiko in hoë waarde boorde te bestuur, deur dit moontlik te maak om aktief voorsorg maatreëls te tref, hul besproeiings- en voedingsskedule te beplan, en om hulle te help om die beste verbouingspraktyke te kies. Die studie het ook, met die gebruik van 'n boordvlak-begrotingsmodel, die feit beklemtoon dat hoë vrugpryse die moontlike finansiële verlies wat 'n boord kan ly deur lae set, sal verminder. Hierdie hoër vrugpryse word egter slegs bereik indien vrugte van hoë gehalte geproduseer word en dien as motivering vir produsente om innoverende praktyke gebruik om die oes te manipuleer. Die invloed van stikstof, GA3 en uniconazole op 'Midknight' en 'Delta' Valencias om vrugset te verbeter, is getoets, maar inkonsekwente resultate is gelewer. Die studie het getoon dat ten minste GA₃ as ʼn standaard op saadlose Valencias toegedien moet word. ‘n Uniconazole toediening kan egter die opbrengs van 'n boom verhoog, en indien hoë N toedien was kan die uniconazole die moontlike oormatige vegetatiewe groei inhibeer. Die hoë N het deurgaans gelei tot die produksie van saadlose Valencia- lemoene met 'n laer interne gehalte. Laastens het die studie die invloed van die grond - en wortel ontwikkeling op vrugset van saadlose Valencia-lemoene bepaal. 'n Akkurate klassifikasiestelsel spesifiek vir sitrus is voorgestel, wat die produsent se besluitneming kan verbeter, in terme van tydige regstellings voor vestiging aan te bring en om bemesting en besproeiing effektiwiteit te verbeter. Die studie het ook getoon dat hoër potensiaal grond die vruggrootte verspreiding verbeter, wat die winsgewendheid van boorde sal verbeter. Die verbetering is moontlik as gevolg van verbeterde opname van voedingstowwe, suurstof en water in die wortelsone en dus die boom en vrugte self tydens vrugontwikkeling. Master 2021-11-29T19:49:04Z 2022-02-22T10:20:17Z 2021-11-29T19:49:04Z 2021-12 Thesis http://hdl.handle.net/10019.1/124255 af_ZA Stellenbosch University vii, 183 pages : illustrations (some color) application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Valencia oranges -- Quality -- South Africa Growth (Plants) -- Effect of chemicals on Citrus fruits -- Breeding Valencia oranges -- Economic aspects -- South Africa Citrus -- Effect of temperature on Fruit trees -- Climatic factors Soils -- Classification Oranges -- South Africa -- Marketing Uniconazole Nitrogen-fixing trees UCTD Van Zyl, Carel Petrus Studies on the seedless fruit set of Valencia oranges |
| title | Studies on the seedless fruit set of Valencia oranges |
| title_full | Studies on the seedless fruit set of Valencia oranges |
| title_fullStr | Studies on the seedless fruit set of Valencia oranges |
| title_full_unstemmed | Studies on the seedless fruit set of Valencia oranges |
| title_short | Studies on the seedless fruit set of Valencia oranges |
| title_sort | studies on the seedless fruit set of valencia oranges |
| topic | Valencia oranges -- Quality -- South Africa Growth (Plants) -- Effect of chemicals on Citrus fruits -- Breeding Valencia oranges -- Economic aspects -- South Africa Citrus -- Effect of temperature on Fruit trees -- Climatic factors Soils -- Classification Oranges -- South Africa -- Marketing Uniconazole Nitrogen-fixing trees UCTD |
| url | http://hdl.handle.net/10019.1/124255 |
| work_keys_str_mv | AT vanzylcarelpetrus studiesontheseedlessfruitsetofvalenciaoranges |