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Manipulation of internal fruit quality in citrus

dc.contributor.advisorRabe, E.en_ZA
dc.contributor.advisorTheron, K. I.en_ZA
dc.contributor.authorVerreynne, Johannes S.en_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science.
dc.date.accessioned2012-08-27T11:34:27Z
dc.date.available2012-08-27T11:34:27Z
dc.date.issued1999-12
dc.identifier.urihttp://hdl.handle.net/10019.1/51334
dc.descriptionThesis (M.Sc. Agric.) -- University of Stellenbosch, 1999.
dc.description.abstractENGLISH SUMMARY: Internal fruit quality in citrus IS becoming an important Issue in the deregulated marketing environment. Fruit with poor and variable taste would lead to low prices on the markets and loss of market share. Internal fruit quality is determined by a few parameters such as the sugar content (determined as total soluble solids (TSS)), titratable acid (TA) content, the TSS:TA ratio and juice percentage. The objective of this study was to manipulate these parameters by means of cultural practices in order to improve the internal quality of citrus fruit. The separate and combined effects of summer trunk girdling and deficit irrigation on internal fruit quality of 'Delta' Valencia and 'Marisol' Clementine trees were investigated over two consecutive seasons. On 'Marisol' Clementines, four trials were conducted over two seasons, at two different sites, Somerset West and Citrusdal. Girdling increased the TSS, although not always significantly, but there were no trends observed for T A and TSS:TA ratios. Deficit irrigation increased the TSS and the T A levels in both seasons and at both sites. On 'Delta' Valencias, deficit irrigation increased the TSS of fruit in 1998, but decreased the TSS in 1999. Deficit irrigation decreased the TA levels and increased the TSS:TA ratio in both years. Summer trunk girdling, performed at different times after the physiological fruit drop period, had no significant effect on the TSS and TA levels and consequently the TSS:TA ratios in both years. The timing of summer trunk girdling, perforn1ed at different times after the physiological fruit drop period on the internal fruit quality of 'Temple' tangor trees, was evaluated over two consecutive years. Girdling significantly decreased the TSS in the first year, but had no significant effect on the TA level and the TSS:TA ratio of the fruit. In the second year there was, however, a tendency towards an increase in TSS and TA levels with the later girdling treatments, although this was not significant. The effect of exposing internally-borne fruit to direct sunlight, by means of summer pruning, on the internal fruit quality of these normally-shaded fruit was evaluated on 'Mihowase' Satsuma and 'Nules' Clementine trees over two consecutive years. Summer pruning had no significant effect on fruit quality of 'Mihowase' Satsumas in the first year. In the second year, pruning significantly decreased T A levels and increased the TSS:TA ratio, but had no significant effect on fruit colour and TSS. Pruning on 'Nules' Clementines significantly increased the TSS:TA ratio of fruit in the first year, but had no significant effect on the colour, TSS and TA levels. In the second year, pruning had no significant effect on the colour, but significantly decreased the T A levels and increased the TSS levels and the TSS:TA ratio. Fruit quality differences between fruit from different sectors of 'Mihowase' Satsuma, 'Nules' Clementine, 'Fairchild' and 'Temple' tangor trees were investigated. In Satsumas, Clementines and 'Temple' tangors the top fruit were the largest and inside bottom fruit the smallest, but the opposite was true in 'Fairchild'. The TSS in all four cultivars was the highest in top fruit and the lowest in inside bottom fruit. Outside bottom fruit (Satsumas) or top fruit (Clementines, 'Fairchild' and 'Temple') had the highest TSS:TA ratios and inside bottom fruit had the lowest ratios. The north sector in all the cultivars had higher TSS:TA ratios than the south sector. The accumulation of reducing and non-reducing sugars in 'Mihowase' Satsuma and 'Nules' Clementine fruit from physiological fruit drop to maturation were quantified. In Satsumas, reducing and non-reducing sugars increased linearly over time, but plateaued out towards the last sampling date. In Clementines, reducing sugars increased cubically over time with a rapid decrease towards maturity and non-reducing sugars also increased over time until maturity. The timing of girdling and the type of girdling tool used on the healing ability of the girdle on 'Nules' Clementine trees were investigated in two trials. Slow healing and essentially at the same rate, took place when trees were girdled with a Stanley carpet knife in September, October and November, faster healing when girdled in December and January (the hottest period), followed by slower healing when girdled in February. The Outspan girdling tool resulted in girdles which took more days to heal than the Stanley carpet knife. The effect of ridging on the internal quality of fruit from 'Bahianinha' Navel trees was evaluated over two consecutive years. Ridging increased the TSS and the TSS:TA ratio of fruit in both years.
dc.description.abstractAFRIKAANSE OPSOMMING: Interne vrugkwaliteit by sitrus is besig om belangrik te word in die gedereguleerde bemarkingsomgewing. Vrugte met swak en varierende smaak lei tot lae pryse op die markte en 'n verlies aan markaandeel. Interne vrugkwaliteit word bepaal deur 'n paar parameters, nl. suikerinhoud (bepaal as totale oplosbare vaste stowwe (TOV)), titreerbare suur (TS) vlakke, die TOVS:TS-verhouding en sappersentasie. Die doel van hierdie studie was om hierdie parameters te manipuleer deur verbouingspraktyke en so die interne kwaliteit van sitrusvrugte te verbeter. Die effek van somerringelering, stresbesproeiing en die kombinasie van beide op die interne vrugkwalitiet van 'Marisol' Clementine en 'Delta' Yalencias borne is ondersoek oor twee agtereenvolgende seisoene. Vier proewe is uitgevoer op 'Marisol' Clementines oor twee seisoene en by twee lokaliteite, t.w. Somerset-Wes en Citrusdal. Ringelering het die TOVS verhoog, alhoewel nie altyd betekenisvol nie, maar daar was geen tendense vir TS en TOYS:TS-verhouding nie. Stresbesproeiing het die TOYS-en die TS-vlakke in albei seisoene en by beide lokaliteite verhoog. Op 'Delta' Valencias het stresbesproeiing die TOVS van vrugte verhoog in 1998, maar dit verlaag in 1999. Stresbesproeiing het die TS-vlakke verlaag en die TOVS:TS-verhouding verhoog in albei jare. Somerringelering, uitgevoer op verskillende tye na die fisiologiese vrugvalperiode, het geen betekeisvolle verhoging in TOVS gehad nie en geen betekenisvoIIe effek op die TSvlakke en die TOVS:TS-verhouding in albei jare. Die effek van somerringelering, uitgevoer op verskiIIende tye na die fisiologiese vrugvalperiode op die interne vrugkwaliteit van 'Temple' tangor borne, is ondersoek oor twee agtereenvolgende jare. Ringelering het die TOVS betekenisvol verlaag in die eerste jaar, maar het geen betekenisvoIIe effek op die TS-vlakke en die TOVS:TS-verhouding van vrugte gehad nie. In die tweede jaar was daar egter 'n tend ens na verhoogde TOVS en TS-vlakke, met die latere behandelings, alhoewel dit nie betekenisvol was nie. Die effek van blootstelling van binnevrugte aan direkte sonlig, deur somersnoei, op die interne vrugkwaliteit van hierdie skaduvrugte is ondersoek op 'Mihowase' Satsuma en 'Nules' Clementine borne oor twee agtereenvolgende jare. Somersnoei in die eerste jaar het vrugkwaliteit van 'Mihowase' Satsumas nie betekenisvol belnvloed nie. In die tweede jaar het snoei die TS-vlakke betekenisvol verlaag en die TOVS:TS-verhouding verhoog, maar het geen betekenisvolle effek op kleur en TOVS gehad nie. Snoei op 'Nule's' Clementines het die TOVS:TS-verhouding in die eerste jaar betekenisvol verhoog, maar het geen betekenisvolle effek op kleur-, TOVS-en TS-vlakke gehad nie. In die tweede jaar het snoei geen betekenisvolle effek op kleur gehad nie, maar het die TS-vlakke verlaag en die TOVS en TOVS:TS-verhouding verhoog. Vrugkwaliteitsverskille tussen vrugte vanaf verskillende posisies in 'Mihowase' Satsuma, 'Nules' Clementine, 'Fairchild' and 'Temple' tangor borne is ondersoek. In Satsumas, Clementines, en 'Temples' was vrugte uit die boonste posisies die grootste en binnevrugte in die onderkant van die boom die kleinste, maar die teenoorgestelde het voorgekom by 'Fairchilds'. In al vier kultivars was die TOVS die hoogste in vrugte uit die boonste posisies en die laagste in binnevrugte aan die onderkant van die boom. Buitevrugte aan die onderkant van die boom (Satsumas) of vrugte in die boonste posisies (Clementines, 'Fairchilds' en 'Temples') het die hoogste TOVS:TS-verhoudings gehad en binnevrugte aan die onderkant van die boom die laagste verhoudings. Die noordelike sektor in al die kultivars het hoer TOVS:TS-verhoudings gehad as die suidelike sektor. Die akkumulasie van reduserende en nie-reduserende suikers in 'Mihowase' Satsuma en 'Nules' Clementine vrugte vanaf fisiologiese vrugval tot rypwording is gemonitor. In Satsumas het reduserende en nie-reduserende suikers lineer toegeneem oor tyd, maar het later afgeplat. In Clementines het reduserende suikers kubies toegeneem oor tyd met 'n skerp afname tot by rypwording en nie-reduserende suikers het ook toegeneem oor tyd tot by rypwording. Die effek van die tyd van ringelering en die tipe ringeleermes wat gebruik is op 'Nules' Clementine borne, op die tyd en tempo van wondgenesing, is ondersoek in twee studies. Stadige genesing, en teen dieselfde tempo, vind plaas wanneer borne geringeleer word met 'n Stanley-matmes in September, Oktober en November, vinniger genesing wanneer in Desember en lanuarie (die warmste periode) geringeleer word, gevolg deur stadiger genesing wanneer in Februarie geringeleer word. Die Outspan-ringeleermes veroorsaak ringeleerwonde wat langer neem om te genees as die Stanley-matmes. Die effek van operdwalle op die interne vrugkwaliteit van 'Bahianinha' nawelbome is ondersoek oor twee agtereenvolgende jare. Vrugte van borne op operdwalle het verhoogde TOVS en TOVS:TS-verhoudings in albei jare gehad.
dc.format.extent156 pages : ill.
dc.language.isoen_ZA
dc.publisherStellenbosch : Stellenbosch University
dc.subjectCitrus fruits -- Qualityen_ZA
dc.subjectDissertations -- Horticultureen_ZA
dc.titleManipulation of internal fruit quality in citrusen_ZA
dc.typeThesisen_ZA
dc.description.versionMaster
dc.rights.holderStellenbosch University


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