The manipulation of flowering time to produce lemon fruit out of season
| dc.contributor.advisor | Stander, Ockert P. J. | en_ZA |
| dc.contributor.advisor | Cronje, Paul J. R. | en_ZA |
| dc.contributor.advisor | Maree, H. J. | en_ZA |
| dc.contributor.advisor | Bester, Rachelle | en_ZA |
| dc.contributor.author | Krogsheepers, Cornelius | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. | en_ZA |
| dc.date.accessioned | 2020-02-03T06:13:37Z | |
| dc.date.accessioned | 2020-04-28T15:10:10Z | |
| dc.date.available | 2020-02-03T06:13:37Z | |
| dc.date.available | 2020-04-28T15:10:10Z | |
| dc.date.issued | 2020-04 | |
| dc.description | Thesis (MScAgric)--Stellenbosch University, 2020. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: South African lemon (Citrus limon) plantings have increased considerably during the past few years, leading to a possible oversupply of fruit in winter and subsequent declines in current export prices. To address this potential problem, an attempt was made to shift the major lemon fruit harvest to summer, a period during which prices are traditionally higher. This was done by physiologically manipulating the natural flowering habit of a lemon tree, firstly, through an inhibition of spring flowering with the application of foliar gibberellic acid (GA3) sprays during the floral induction period in autumn; and, secondly, to stimulate a late-summer or autumn flowering response through induced water-deficit stress in mid-summer in a manner similar to the Sicilian forzatura technique. An additional objective of the study was to evaluate the effect of these horticultural manipulations on the expression of key citrus flowering genes to shed light on how the reproductive processes are expressed at a molecular level. The lowest concentration of GA3 foliar sprays, viz. 10 mg·L⁻¹, consistently reduced spring flowering compared with untreated trees and to the same extent as the 20 and 40 mg·L⁻¹ treatments. Vegetative growth was stimulated in most cases compared with the control. The expression of the FLOWERING LOCUS T (FT) gene, which is known to integrate floral pathways to initiate the floral cascade, was decreased in buds of trees that received foliar GA3 treatments. Similarly, mRNA levels of APETALA 1 (AP1) were decreased in GA3 treated trees. As expected, AGAMOUS (AG) was not sufficiently expressed to quantify. Adaptation of the forzatura technique was however not consistently successful under South African conditions in this study. Varying climatic conditions across seasons and areas resulted in a lack of sufficient water-deficit stress, which translated in non-significant changes in the expression of citrus flowering genes and varying and limited floral induction. In cases where stem-water potential reached levels lower than -2.5 MPa, a significant flowering reaction was observed about three weeks after re-irrigation, similar to Sicilian observations. However, fruit set was very low due to rapid and extensive floral abscission, possibly as a result of low carbohydrate levels and/or wind and insect damage. This study confirmed the efficacy of GA3 in restricting lemon flowering, while proving that this inhibitive effect is due to downregulation of FT. Additionally, the forzatura technique was proven to be reproducible in Western Cape production regions, albeit with limited success. Future research focused on increasing fruit set after water-deficit stress conditions may support the practicality and commercial viability of the forzatura technique. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Nuwe aanplantings van suurlemoene in Suid-Afrika het toegeneem, met die gevolg dat ‘n moontlike ooraanbod van vrugte in die winter bemarkingsvenster kan ontstaan wat mag lei tot afname in prys. Om hierdie potensiële probleem aan te spreek is ‘n poging aangewend om die verwagte suurlemoen produksiepiek in die winter te skuif na die somer, ‘n periode waar pryse tradisioneel hoër is. Hierdie is gedoen deur om die natuurlike blompatroon te manipuleer. Twee afsonderlike eksperimente is uitgevoer om suurlemoenproduksie te manipuleer - eerstens was gepoog om die tradisionele lenteblom te inhibeer met behulp van gibberelliensuur (GA3) blaarspuite tydens blominduksie in die herfs en, tweedens was die Siciliaanse forzatura tegniek aangewend in mid-somer om ‘n blomreaksie in laatsomer of -herfs te stimuleer deur die induksie van gereguleerde vogstremming. Verder was die effek van hierdie hortologiese manipulasies op die uitdrukking van bekende sitrus-blomgene geëvalueer, om meer lig te werp op die geaffekteerde reproduktiewe prosesse op ‘n molekulêre vlak. Die laagste konsentrasie van GA3 blaartoedienings, naamlik 10 mg·L⁻¹, het lenteblom deurlopend inhibeer in vergeleke met die kontrole, met n soortgelyke intensiteit as die 20 en 40 mg·L⁻¹ GA3 behandelings. In die meeste gevalle is vegetatiewe groei in die lente ook gestimuleer vergeleke met die kontrole. Die uitdrukking van die geen FLOWERING LOCUS T (FT), wat verantwoordelik is vir die integrasie van blom padweë om die blomontwikkelings proses te inisieër, was verlaag in knoppe van bome wat GA3 toedienings ontvang het. mRNA vlakke van die geen APETALA1 (AP1) was soortgelyk onderdruk as die FT geen in behandelde bome. Soos verwag, was die uitdrukking van die geen AGAMOUS (AG) nie voldoende vir kwantifisering. Die poging om die forzatura tegniek toe te pas in plaaslike toestande was nie deurlopend suksesvol nie. Wisselende klimaatstoestande tussen seisoene en areas het die induksie van genoegsame droogtestres belemmer, met die gevolg dat geen beduidende verskille in uitdrukking van sitrus blomgene gevind is nie, asook ‘n varierende, beperkte blomreaksie. In gevalle waar stamwater- potensiaal gedaal het tot benede -2.5 MPa is ‘n beduidende blomreaksie nagenoeg drie weke ná her-besproeiing waargeneem, soortgelyk aan die Siciliaanse waarnemings. Vrugset was egter baie laag aangesien blomme spoedig en teen ‘n hoë intensiteit afgespeen het, waarskynlik as gevolg van lae koolhidraat vlakke en/of wind- en insek skade. Hierdie studie het die effektiwiteit van GA3 om suurlemoen blomvorming te inhibeer bevestig, terwyl dit bewys het dat hierdie inhiberende effek as gevolg van die onderdrukking van FT is. Daar is ook bewys dat die forzatura tegniek tot ‘n sekere mate in die Wes-Kaap reproduseerbaar is. Toekomstige navorsing sal egter moet gefokus wees om vrugset te verhoog ná die aanwending van droogtestres om die kommersiële vatbaarheid te toets. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | viii, 100 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/108334 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Lemon (Citrus limon) -- South Africa | en_ZA |
| dc.subject | Plants, Flowering of | en_ZA |
| dc.subject | Lemon -- Genetics | en_ZA |
| dc.subject | Lemon -- Effect of temperature on | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | The manipulation of flowering time to produce lemon fruit out of season | en_ZA |
| dc.type | Thesis | en_ZA |