Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Poor colour development in bi-coloured pears is a big concern for the South African deciduous fruit industry, resulting in low Class 1 packouts with huge financial implications. The objective of this study was, therefore, to evaluate manipulation practices to improve colour development. The effect of summer pruning on the colour development of 'Rosemarie' pear fruit was studied over two seasons. Pruning consisted of removing the upright shoots of the current season's growth on the lateral branches. The effect of the time of summer pruning on Class 1 packout percentage and average fruit mass were determined. The percentage blushed fruit (colour grading 1-10) of the trees pruned in November or pruned repeatedly from November to just before harvest were significantly higher than for unpruned control trees or trees pruned at other times. Fruit mass was not affected by summer pruning. A second study was conducted on 'Rosemarie' and 'Forelle' pears and the treatments consisted of non-pinched and pinched, where the bourse shoots were cut back at petal drop. There were no significant differences in fruit colour, fruit size, flesh firmness and total soluble solids after pinching compared to the control. In a third study on 'Rosemarie' and 'Forelle' trees, bourse shoots were removed in combination with defoliation. Spur leaves were removed at different times throughout the season from petal drop towards harvest. Both bourse shoots (Rosemarie), or one bourse shoot (Forelle) per cluster was removed as control, one treatment where no bourse shoots were removed served as a secondary control. Spur leaf removal on 'Rosemarie' and 'Forelle' did not have any significant effect on fruit set, fruit size or total soluble solids. In 'Rosemarie', there was also no significant effect on fruit colour. In 'Forelle', colour improved significantly between unmanipulated branches (control 1) and branches were one bourse shoot was removed (control 2). However, all treatments compared to control 1, improved red colour, indicated by a significant decrease in the hue angle values and an increase in Class 1 packout. A fourth study was conducted on 'Flamingo', 'Forelle' and 'Rosemarie' pears. A number of urea applications were made onto the fruit. Fruit nitrogen content increased with urea sprays. Urea sprays did not affect red colour of 'Flamingo', 'Forelle' and 'Rosemarie' pears. Urea sprays had no effect on the anthocyanin concentration (ug.g") of 'Rosemarie' and 'Flamingo'. However, there was a quadratic relationship between number of urea sprays and anthocyanin concentration of 'Forelle'. There were not significant differences in the chlorophyll a and b concentrations of 'Flamingo' and 'Forelle'. Urea applications significantly increased the chlorophyll a concentration of 'Rosemarie'. In contrast there was no significant difference in the chlorophyll b concentration of 'Rosemarie'. The carotenoid concentration of 'Flamingo' and 'Forelle' was not affected by urea applications. In contrast the carotenoid concentration of 'Rosemarie' increased significantly after the urea applications. Overhead cooling was applied with a micro-irrigation system to 'Rosemarie' pears. The water was applied with pulsed irrigation for a three-week period (24 December 1998 to 14 January 1999) before harvest. The system was activated when internal fruit temperature reached 24°C (day) and 19°C (night), and irrigation continued until internal fruit temperature reached 21°C (day) and 16°C (night). No significant differences were found in colour, soluble solids; fruit size, fimmess or yields. A study was conducted on 'Bon Rouge', 'Red d' Anjou' and 'Forelle' pears to assess the effect of storage period for 6 and 8 weeks at -O.SoC and ripening at 21°C for 1 week on anthocyanins, carotenoids, chlorophyll a and chlorophyll b content. There were no significant differences in the anthocyanin concentration in 'Bon Rouge' after cold storage compared to fruit at harvest, whilst for 'Red d' Anjou' anthocyanin concentration increased significantly after cold storage. Results with 'Forelle' were inconsistent. During ripening anthocyanin of 'Red d' Anjou' did not change, whereas the results for 'Bon Rouge' and 'Forelle' were inconsistent. However, cold storage had no effect on the anthocyanin concentrations of 'Bon Rouge' and 'Forelle'. Cold storage significantly decreased the carotenoid concentrations of 'Bon Rouge', but not in 'Red d' Anjou' and 'Forelle'. The carotenoids of 'Bon Rouge', 'Red d' Anjou' and 'Forelle' decreased significantly more during ripening at 21°C. The chlorophyll concentrations of 'Bon Rouge' decreased significantly during storage at -O.SoC, compared to fruit at harvest, but not in 'Red d' Anjou' and 'Forelle'. During ripening at 21°C chlorophyll a and chlorophyll b decreased significantly in 'Bon Rouge', 'Red d' Anjou' and 'Forelle'. In conclusion it is clear from this study, that although light is important for initial colour development, high December and January temperatures remain the biggest problem in maintaining good red colour at harvest. Other factors, e.g. fertilisation are secondary. / AFRIKAANSE OPSOMMING: Kleurverbetering van twee-kleur pere Onvoldoende kleur ontwikkeling in twee-kleur pere is 'n groot probleem vir die Suid Afrikaanse sagtevrugtebedryf aangesien dit lae Klas l-uitpakke tot gevolg het. Die doel van hierdie studie was dus om manipulasie tegnieke te evalueer om sodoende kleur ontwikkeling te verbeter. Die effek van somersnoei op die kleur ontwikkeling van 'Rosemarie' pere is ondersoek oor twee seisoene. Die snoei het bestaan uit die verwydering van regop lote van die huidige seisoen se groei op laterale takke. Die effek van die tyd van somersnoei op Klas I-uitpakpersentasie en gemiddelde vrugmassa is bepaal. Die persentasie vrugte met 'n blos (kleur gradering 1-10) van die bome wat in November of voortdurend vanaf November tot net voor oes gesomersnoei is, was betekenisvol hoër as die onbehandelde bome of bome wat op ander tye gesnoei was. Vrugmassa was nie beïnvloed deur somersnoei nie. 'n Tweede studie is gedoen op 'Rosemarie' en 'Forelle' bome. Die behandelings was nie-getop of getop, waar die beurslote teruggesny is na blomblaarval. Daar was geen betekenisvolle verskille in vrugkleur, vruggrootte, vrugfermheid en totale oplosbare suikers tussen die getopte en onbehandelde bome se vrugte nie. In 'n derde studie op 'Rosemarie' en 'Forelle' is beurslote verwyder in kombinasie met die verwydering van spoorblare. Spoorblare is verwyder op verskillende tye gedurende die seisoen vanaf blomblaarval tot oes. By 'Rosemarie' (beide beurslote per tros) en by 'Forelle' (een beursloot per tros) is beurslote verwyder om te dien as die kontrole, een behandeling waar geen beurslote verwyder was nie het gedien as die sekondêre kontrole. Spoorblaarverwydering by 'Rosemarie' en by 'Forelle' het geen betekenisvolle effek op vrugset, vruggrootte of totale oplosbare suikers gehad nie. By 'Rosemarie' was daar ook geen betekenisvolle effek op vrugkleur nie. By 'Forelle' is vrugkleur betekenisvol verhoog tussen onbehandelde takke (kontrolel) en takke waar een beursloot verwyder was (kontrole 2). Alle behandelings het egter vrugkleur verhoog in vergelyking met kontrole 1. Dit is waarneembaar in 'n betekenisvolle verlaging in die kleurskakering en 'n verhoging in die Klas l-uitpakke. 'n Vierde studie is uitgevoer op 'Flamingo' en 'Forelle' en 'Rosemarie' pere. 'n Aantal ureumtoedienings is gemaak op die vrugte. Die stikstofinhoud van die vrugte is verhoog met ureumbespuitings. Ureum spuite het nie rooi vrugkleur van 'Flamingo', 'Forelle' of 'Rosemarie' pere beïnvloed nie. Ureumbespuiting het geen effek op die antosianienkonsentrasie (ug.g") van 'Rosemarie' en 'Flamingo' gehad nie. Daar was egter 'n kwadratiese verwantskap tussen die aantal ureumbespuitings en die antosianienkonsentrasie van 'Forelle'. Daar was geen betekenisvolle verskille in die chlorofiel a en b konsentrasies van 'Flamingo' en 'Forelle' nie. Ureumtoedienings het die chlorofiel a konsentrasie van 'Rosemarie' betekenisvol verhoog, daar was egter in teenstelling hiermee geen verskil in die chlorofiel b konsentrasie van 'Rosemarie' nie. Die karotenoiedkonsentrasie van 'Flamingo' en 'Forelle' is nie beïnvloed deur die ureum toedienings nie. In teenstelling hiermee het die karotenoiedkonsentrasie van 'Rosemarie' betekenisvol toegeneem na die ureum toedienings. Oorhoofse verkoeling is toegedien met 'n mikro-besproeiingsstelsel op 'Rosemarie' pere. Die water is toegedien met puls besproeiing vir 'n periode van drie weke (24 Desember 1998 tot 14 Januarie 1999) voor oes. Die stelsel is geaktiveer wanneer die interne vrugtemperatuur 24oe (dag) en 19°e (nag) bereik het, die besproeiing het aangehou totdat die interne vrugtemperatuur 21°e (dag) en 16°e (nag) bereik het. Daar was geen betekenisvolle verskil in kleur, totale oplosbare suikers, vruggrootte, vrugfermheid of opbrengs nie. 'Bon Rouge' 'Red d' Anjou' en 'Forelle' pere is gebruik om die effek van opbergingsperiodes van 6 en 8 weke by -O.5°e en rypwording by 21oe vir 1 week op die antosianiene, karotonoied, chlorofiel a en chlorofiel b konsentrasies te bepaal. Daar was geen betekenisvolle verskille in die antosienien konsentrasie van 'Bon Rouge' na koue opberging nie, terwyl die konsentrasie antosianien by 'Red d' Anjou' betekenisvol toegeneem het na koue opberging. Die resultate by 'Forelle' was nie konstant me. Gedurende rypwording was daar geen verskille in die antosianienkonsentrasie van 'Red d' Anjou' nie, die resultate by 'Bon Rouge' en 'Forelle' was nie konstant nie. Koue opberging het egter geen effek gehad op die antosianienkonsentrasies van 'Bon Rouge'en 'Forelle' nie. Die karonotoied- konsentrasies van 'Bon Rouge', 'Red d' Anjou' en 'Forelle' het betekenisvol meer afgeneem gedurend rypwording by 21°C. Die chlorofielkonsentrasies van 'Bon 'Rouge' het betekenisvol afgeneem gedurende opberging by -O.5°C teenoor die vrugte by oes, maar nie by 'Red d' Anjou' en 'Forelle' nie. Gedurende rypwording by 21°C het die chlorofiel a en chlorofiel b konsentrasies by 'Bon Rouge', Red 'd Anjou' en 'Forelle' betekenisvol afgeneem. Om op te som dit is duidelik uit hierdie studie dat alhoewel lig belangrik is vir vroeë kleurontwikkeling, hoë temperature gedurende Desember en Januarie steeds die grootste faktor is wat finale rooi vrugkleur by oes bepaal. Ander faktore soos bemesting is van sekondêre belang.

Thesis (PhD (Agric))--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Downgrading of fruit due to insufficient red colour has limited the profitability of lucrative blushed pear cultivars (Pyrus communis L.). In 'Rosemarie', poor fruit colour has been ascribed to pre-harvest red colour loss during periods of high temperature. The regulation of colour development in pears has not been studied and, in addition, little is known about anthocyanin degradation in attached fruit. Changes in colour were recorded and phenylalanine ammonia-lyase (PAL) and UDPGalactose: flavonoid-3-0-glycosyltransferase (UFGT) activities assessed in response to cold fronts and during fruit development in order to establish the regulation of colour development in red and blushed pear cultivars. Best red colour was generally attained a month or more before harvest whereafter red colour faded towards harvest. Unlike in some other fruits, UFGT activity apparently did not limit colour development whereas fading of red colour towards harvest might relate to decreasing PAL activity. 'Rosemarie' colour fluctuated considerably, increasing with cold fronts and decreasing during intermittent warmer periods, while red colour was more stable in other cultivars. PAL and UFGT activities in 'Rosemarie' increased in response to low temperatures, but were unaffected in 'Bon Rouge'. We concluded that anthocyanin synthesis in 'Rosemarie' requires low temperatures while colour development in 'Bon Rouge' and probably also other cultivars is primarily regulated by endogenous factors. Detached pome fruit were used to study temperature and light effects on anthocyanin degradation and fruit colour and to assess the modifying effect of anthocyanin concentration on colour loss. Anthocyanin degradation and red colour loss increased linearly between 10°C and 30°C. Irradiation further increased the rate of degradation and colour loss. The rate of colour loss depended on anthocyanin concentration, being much faster in fruit with high compared to fruit with low pigment levels. This was ascribed to the exponential relationship between anthocyanin concentration and hue at high pigment levels and the linear relationship at lower pigment levels. Anthocyanin degradation and pre-harvest red colour loss in 'Rosemarie' was quantitatively confirmed and corresponded with a warm period during fruit development. Based on these data, we attributed the susceptibility of 'Rosemarie' to pre-harvest colour loss to low anthocyanin concentrations in its peel that allow the visualisation of net anthocyanin degradation at high temperatures. Overhead evaporative cooling (EG) as measure to improve red colour in blushed pears was evaluated. 'Rosemarie' fruit that received pulsed EG applications from two weeks before harvest at air temperatures exceeding 28°G were redder than control fruit at harvest. EG had no effect on 'Forelle' colour. Though EG could be used to improve 'Rosemarie' fruit colour in warm production areas, its effect was relatively small compared to colour change in response to temperature. Lastly, we assessed the photoprotective function of anthocyanin in pear peel. Photoinhibition was evident in exposed faces of pears under natural conditions. The extent of photoinhibition increased with decreasing redness of peel and was maintained after photoinhibitory treatment. Although anthocyanin was apparently able to afford photoprotection at 40oG, we argued against this as a general function. There were indications that photoprotection was associated, but not necessarily due to light attenuation by anthocyanin. / AFRIKAANSE OPSOMMING: Afgradering van vrugte vanweë onvoldoende rooi kleur beperk die winsgewendheid van blospeercultivars (Pyrus communis L.). In die geval van 'Rosemarie' word swak kleur toegeskryf aan vooroes rooikleurverlies gedurende warm periodes. Die regulering van kleurontwikkelling in pere is nog nie ondersoek nie terwyl min bekend is oor antosianiendegradasie aan die boom. Om die regulering van kleurontwikkelling in rooi- en blospeercultivars vas te stel, is veranderinge in kleur en in die aktiwiteit van fenielalanien ammonia-liase (FAL) en UDPGalaktose: flavonoied-3-o-glikosieltransferase (UFGT) gemeet gedurende vrugontwikkelling en in reaksie op koue fronte. Pere was op hul rooiste 'n maand of langer voor oes. Hierna het rooi kleur afgeneem tot met oes. Anders as in sommige ander vrugsoorte het UFGT aktiwiteit nie kleurontwikkeling beperk nie. Die afname in rooi kleur tot met oes mag egter verband hou met 'n gelyktydige afname in FAL aktiwiteit. 'Rosemarie' kleur het aansienlik gefluktueer in reaksie op temperatuur. Rooi kleur het toegeneem met koue fronte en afgeneem in die warmer periodes tussen fronte. Rooi kleur was meer stabiel en klaarblyklik minder afhanlik van lae temperature in ander peercultivars. Die noodsaaklikheid van lae temperature vir kleurontwikkelling in 'Rosemarie' is bevestig deur 'n toename in ensiemaktiwiteit in reaksie op koue fronte. Lae temperature het geen effek gehad op ensiemaktiwiteit in 'Bon Rouge' nie. Appels en pere is gebruik om die effek van temperatuur en lig op antosianiendegradasie en vrugkleur te ondersoek. Die modifiserende effek van antosianienkonsentrasie op kleurverlies is ook ondersoek. Antosianiendegradasie en rooi kleurverlies het lineêr toegeneem tussen 10° en 30°C. Beligting het degradasie en kleurverlies verder versnel. Die tempo van kleurverlies was afhanklik van antosianienkonsentrasie. Kleurverlies was aansienlik vinniger in vrugte met hoë pigmentvlakke, in vergelyking met vrugte met lae pigmentvlakke vanweë die eksponensiële verwantskap tussen antosianienkonsentrasie en kleurskakeringswaardes (hue values) by hoë pigmentvlakke en die lineêre verwantskap by lae pigmentvlakke. Antosianiendegradasie en vooroes rooikleurverlies in 'Rosemarie' is kwantitatief bevestig en het saamgeval met 'n warm periode tydens vrugontwikkelling. Gebaseer op hierdie data is die gevoeligheid van 'Rosemarie' vir vooroes rooikleurverlies toegeskryf aan lae antosianienkonsentrasies wat die sigbaarheid van netto antosianiendegradasie by hoë temperature verhoog. Die gebruik van oorhoofse evaporatiewe verkoeling (EG) om rooi kleur van blospere te verbeter is ge-evalueer. 'Rosemarie' vrugte wat evaporatief verkoel is bo 28°G vanaf twee weke voor oes, was rooier as kontrole vrugte by oes. 'Forelle' kleur het nie gereageer op EG nie. Die effek van EG op vrugkleur was relatief klein in vergelyking met die effek van temperatuur. AI kan EG 'Rosemarie' kleur verbeter in warm produksiestreke sou dit meer effektief wees om 'Rosemarie' se verbouing te beperk tot koeler klimaatstreke. Laastens is die vermoë van antosianien om peerskil teen fotoinhibisie te beskerm ondersoek. Fotoinhibisie was aanwesig in vrugskil wat direk blootgestel was aan sonlig in die boord. Die omvang van fotoinhibisie het toegeneem met 'n afname in rooi pigmentasie van vrugskil. Die verband tussen skilkleur en fotoinhibisie was steeds aanwesig na blootstelling aan ligstres by 10° en 400G. Ons het egter geredeneer teen 'n algemene funksie vir antosianien in fotobeskerming by hoë temperature. Verder was daar aanduidings dat, alhoewel geassossieer met rooi skilkleur, beskerming teen ligstres nie noodwendig te wyte was aan antosianien nie.

Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2009. / The aim of this research project was to determine the preference of pear appearance and taste among South African pear consumers using descriptive sensory analysis, consumer preference and physical maturity measurements. The preference of external pear appearance among European consumers was also established. The Agricultural Research Council (ARC) Infruitec-Nietvoorbij, South Africa, aims to breed new cultivars with a local as well as export market potential. They are focused on a range of blushed cultivars from early to late season which do not loose their skin colour. Important eating quality characteristics they are focused on are high sugar content (sweet taste) and a strong pear flavour. Both research studies performed on local South African consumers showed that these objectives align very well with consumer preference. Lightly coloured blushed pears were preferred and important sensory attributes were pear flavour, sweet taste, melt character, juiciness and a soft texture. Sour taste, astringency, mealiness and grittiness were negative attributes. The appearance preference conducted on European consumers determined that these consumers prefer a bright yellow or green colour with a light red or pink blush. Shape played a role and a typical pear shape was preferred. The outcomes of the research performed on local South African consumers were compared to results found internationally. The findings were consistent with important sensory attributes being pear flavour, sweetness and juiciness and yellow or green colours preferred or a light blush was also acceptable. Age and gender did not seem to play a role in the preference analyses. Therefore, preference studies can be conducted locally on new cultivars for the export market. Blushed cultivars are prone to red colour loss in high temperature conditions. Breeding of selections (e.g. ‘Cheeky’) that accumulate more red pigment and are therefore less prone to colour loss has been done to try to overcome this problem. However, these selections are redder and darker in colour and have a lower preference among consumers. A possible solution to this could be to breed light blushed pears (e.g. Rosemarie) but to market the cultivar, as is the case with Cripp’s Pink apples, with separate trademark names for fruit with adequate and inadequate blush development. Thereby, the producers will still receive compensation for their produce if the colour is lost but if not, a higher premium will be received.

Thesis (MScAgric)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Red colour development on bi-coloured apples and pears ensures better prices for producers. The use of postharvest irradiation to improve colour has been successful on apples, and the objectives of this thesis were to optimise conditions during irradiation for apples and to evaluate the effects of irradiation on pears. 'Cripp's Pink' apples responded to postharvest irradiation with high-pressure sodium (HPS) lights by developing a red blush, whereas the response to irradiation with UV 8 plus incandescent lights was less effective. '8raeburn' apples held at -0.5°C for 4 or 8 weeks prior to irradiation showed a decrease in hue angle and an increase in anthocyanin concentration after 72 hours of irradiation with HPS lamps. In 'Forelle' pears treated in the same way, neither colour development nor anthocyanin synthesis was affected by irradiation. '8raeburn' and 'Cripp's Pink' apples picked weekly for 5 weeks until the optimum harvest date were irradiated with HPS lights. A significant increase in fruit colour was only measured in mature fruit of both cultivars. 'Cripp's Pink' apples were harvested from two production areas with different microclimates, namely, Ceres and Grabouw, and stored for 0, 2 or 5 days at -0.5 °C before irradiation for 120 hours at either 6°C or 20°C. Fruit from Ceres that were irradiated immediately after harvest developed better colour at 6 °C than at 20°C. The differences between fruit irradiated at the two temperatures were no longer significant after 5 days of cold storage prior to irradiation. Fruit from Grabouw consistently developed better colour when irradiated at 6°C than at 20°C. Colour development slightly after 5 days of cold storage prior to irradiation. In another experiment, fruit from both areas were stored at -0.5°C for 20 days before irradiation at either 6°C or 6/20°C. The fluctuating temperature regime resulted in decreases in hue angle of 70° and 65° for the fruit from Grabouw and Ceres, respectively. The decreases were smaller (±200) when fruit were irradiated at 6°C. The hue angle value of well-coloured 'Cripp's Pink' apples held at 3rC under HPS lights for 144 hours increased from 29.3° to 48.3°, and anthocyanin concentration decreased from 739.9 IJg·g·1to 283.6 IJg·g·1. Control fruit held at the same temperature in the dark did not show any change in hue angle value or anthocyanin concentration. 'Bon Rouge' and 'Red d' Anjou', two full red pear cultivars, irradiated with HPS lights for 72 hours, showed no significant changes in hue angle. 'Forelle' pears, harvested with or without attached leaves, were irradiated with HPS at two temperature regimes, 20°C and 200/6°C. The resulting decreases in hue angle were attributed to yellowing and not red colour formation. In conclusion, the response of apples to postharvest irradiation was affected by maturity and temperature, while pears failed to respond at all. / AFRIKAANSE OPSOMMING: Rooikleurontwikkeling van twee-kleur appels en pere verseker beter pryse vir die produsente. Na-oesbestraling om kleur te verbeter is al suksesvol uitgevoer op appels, en die doelwit van hierdie tesis was om die kondisies vir appels gedurende bestraling te optimaliseer en om die effek van bestraling op pere te evalueer. 'Cripp's Pink' appels het reageer op na-oesbestraling met hoëdruk-natriumligte (HDN) deur 'n rooi blos te ontwikkel, terwyl die reaksie op bestraling met UV-B plus gloeilamplig minder effektief was. 'Braebum' appels opgeberg by -O.5aC vir 4 of 8 weke voor bestraling het 'n afname in die kleurskakeringswaarde getoon, asook 'n toename in antosianienkonsentrasie na 72 uur se bestraling met HDN ligte. 'Forelle' pere wat dieselfde behandeling ontvang het, het geen kleurontwikkeling en geen antosianienontwikkeling getoon na bestraling nie. 'Braebum' en 'Cripp's Pink' appels wat weekliks geoes is vir 5 weke tot die optimum oesdatum is bestraal met HDN ligte. Slegs die volwasse vrugte van beide kultivars het 'n betekenisvolle toename in kleur getoon. 'Cripp's Pink' appels is geoes in twee produksie areas met verskillende mikroklimate, naamlik Ceres en Grabouw. Vrugte is opgeberg vir 0, 2 of 5 dae by -O.5aC voor bestraling vir 120 uur by of 6aC of 20aC. Vrugte van Ceres wat onmiddellik na oes bestraal is het beter kleur ontwikkel by 6aC as by 20aC. Kleurontwikkeling by vrugte bestraal by 6 of 20aC het nie verskil wanneer vrugte vooraf opgeberg was by -~5ac vir 5 dae nie. Vrugte van Grabouw het konstant beter kleur pntwikkel wanneer bestraling by 6°C eerder as 20°C plaasgevind het. In die volgende eksperiment, was beide die vrugte van Ceres en Grabouw vir 20 dae opgeberg by -o.soC voor bestraling by 6°C of 6°/20°C. Die flukturerende temperatuur regime het afnames van 70° en 65° in kleurskakeringswaarde getoon vir die vrugte van Grabouw en Ceres, respektiewelik. Die afname was kleiner (±200)wanneer vrugte by 6°C bestraal is. 'Cripp's Pink' appels wat goed gekleur was en opgeberg is by 3rC terwyl dit blootgestel is aan HDN ligte vir 144 uur, het 'n toename van 29.30 tot 48.3° getoon vir die kleurskakeringswaarde, en antosianienkonsentrasie het afgeneem van 739 I'g.g-1 tot 283.6 I1g.g-1. Die kontrole vrugte opgeberg by dieselfde temperatuur in die donker het geen verandering in beide die kleurskakeringswaarde of die antosianienkonsentrasie getoon nie. 'Bon Rouge' en 'Red d' Anjou', twee volrooi peerkultivars, is bestraal met HDN ligte vir 72 uur en het geen betekenisvolle verandering in kleur getoon nie. 'Forelle' pere, geoes met of sonder 'n aangehegte stingelsegment, is bestraal met HDN ligte by twee verskillende temperatuur regimes, nl. 20°C of 20/6°C. Die afname in kleurskakeringswaarde is aan vergeling toegeskryf eerder as aan rooikleurontwikkeling. Ter opsomming, die reaksie van appels op na-oes bestraling is beïnvloed deur rypheid en temperatuur, terwyl pere geen reaksie getoon het nie.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: For many apple (Malus domestica Borkh.) and pear (Pyrus communis L.) cultivars, attractive colour is essential to their profitability on export markets. This study focuses on problems related to poor green colour of ‘Granny Smith’ apples and insufficient red colour of bi-coloured pear cultivars. ‘Granny Smith’ apples often suffer from poor green colour. Green colour of fruit from various orchards was already found to differ midway through fruit development, with these differences being carried through to harvest. In a trial where nitrogen (N) fertilisers were applied using different forms at different times, there was no improvement in green colour. In another trial, artificial shading was applied to fruit only during their early development. Fruit that were shaded during this time were less green at harvest than unshaded fruit. Additional N applications may only improve colour where a deficiency exists. However, green colour may be improved by increasing light distribution early during fruit development. Bi-coloured pears attain their maximum red colour midway through their development, and this desired red colour is mostly lost prior to harvest. Red colour can also increase transiently with the passing of cold fronts. Anthocyanins, responsible for this red colour, may have a photoprotective function which would explain this pigmentation pattern, as photosystems are particularly sensitive to light damage at low temperatures. As ‘Rosemarie’ fruit bent over from a vertical to hanging position during development, peel photoinhibition was reduced as anthocyanins were synthesised. ‘Forelle’ peel was found to be very sensitive to high light levels at low temperatures. Substantial anthocyanin development took place in ‘Cripps’ Pink’ apples when weather conditions were cold, but clear following a cold front. A photoprotective role seems to explain daily changes in anthocyanins in response to temperature, but not the seasonal progression of colour development. For many apple (Malus domestica Borkh.) and pear (Pyrus communis L.) cultivars, attractive colour is essential to their profitability on export markets. This study focuses on problems related to poor green colour of ‘Granny Smith’ apples and insufficient red colour of bi-coloured pear cultivars. ‘Granny Smith’ apples often suffer from poor green colour. Green colour of fruit from various orchards was already found to differ midway through fruit development, with these differences being carried through to harvest. In a trial where nitrogen (N) fertilisers were applied using different forms at different times, there was no improvement in green colour. In another trial, artificial shading was applied to fruit only during their early development. Fruit that were shaded during this time were less green at harvest than unshaded fruit. Additional N applications may only improve colour where a deficiency exists. However, green colour may be improved by increasing light distribution early during fruit development. Bi-coloured pears attain their maximum red colour midway through their development, and this desired red colour is mostly lost prior to harvest. Red colour can also increase transiently with the passing of cold fronts. Anthocyanins, responsible for this red colour, may have a photoprotective function which would explain this pigmentation pattern, as photosystems are particularly sensitive to light damage at low temperatures. As ‘Rosemarie’ fruit bent over from a vertical to hanging position during development, peel photoinhibition was reduced as anthocyanins were synthesised. ‘Forelle’ peel was found to be very sensitive to high light levels at low temperatures. Substantial anthocyanin development took place in ‘Cripps’ Pink’ apples when weather conditions were cold, but clear following a cold front. A photoprotective role seems to explain daily changes in anthocyanins in response to temperature, but not the seasonal progression of colour development. Dwarfing rootstocks are known to improve red colour of bi-coloured pears due to improved light distribution. ‘Forelle’ fruit from six rootstocks of varying vigour were harvested from exposed positions only, so as to establish the effect of rootstock on red colour development independent of the effect of rootstock on canopy light distribution. Fruit from trees on quince (Cydonia oblonga Mill.) rootstocks were found to have redder fruit than those from vigorous BP pear rootstocks. This may be due to higher chlorophyll and carotenoid concentrations present in the peel of fruit from BP rootstocks, whose leaf and peel N were also high. The use of quince rootstocks is recommended where red colour development of bi-coloured pears is a problem. An early season bi-coloured cultivar with good red colour is required. Breeding trials to find such a cultivar are resource intensive. To streamline the process, a method to preselect immature seedlings for their future fruit colour is required. Fruit colour from bearing seedlings was compared with colour of their immature leaves. Trees with red leaves were likely to produce fruit that were too red for the breeders’ requirements. Trees with green or blushed leaves were capable of producing blushed fruit. It would be feasible to cull red-leaved seedlings with minimal risk of losing potential bi-coloured cultivars. / AFRIKAANSE OPSOMMING: Verskeie appel (Malus domestica Borkh.) en peer (Pyrus communis L.) kultivars se winsgewendheid word bepaal deur hul aantreklike kleur. In hierdie studie word die swak groen kleur van ‘Granny Smith’ appels asook rooi kleurontwikkeling van blospere ondersoek. Die groen kleur van ‘Granny Smith’ appels is dikwels onvoldoende. Verskille in groen kleur tussen boorde was reeds gedurende vroeë vrugontwikkeling aanwesig, en hierdie verskille het voortgeduur tot met oes. Groen kleur kon nie deur verskillende bronne en tye van stikstofbemesting verbeter word nie. Stikstofbemesting verbeter groen kleur moontlik net in boorde met ‘n stikstoftekort. Vrugte wat gedurende hul vroeë ontwikkeling oorskadu is, se groen kleur was swakker by oes in vergelyking met vrugte wat nie oorskadu is nie. Groen kleur kan moontlik verbeter word deur ligverspreiding tydens vroeë vrugontwikkeling deur middel van snoei aksies te verhoog. Blospeerkultivars bereik hul maksimum rooi kleur halfpad deur hul ontwikkeling, maar is geneig om hul rooi kleur grootliks voor oes te verloor. Rooi kleur mag egter kortstondig toeneem in reaksie op die lae temperature gepaardgaande met koue fronte. Antosianiene, wat verantwoordelik is vir die rooi kleur, het moontlik ‘n beskermende funksie teen hoë ligvlakke, en hierdie funksie mag moontlik die bogenoemde patroon van rooikleurontwikkeling verklaar. Die natuurlike buiging van ‘Rosemarie’ pere van hul aanvanklike regop oriëntasie tot hul karakteristieke hangende posisie, is gekenmerk deur ‘n afname in fotoinhibisie van die skil en ‘n gelyklopende sintese van antosianien. ‘Forelle’ skil was uiters sensitief vir hoë ligvlakke in kombinasie met lae temperature (16 ºC). ‘Cripps’ Pink’ appels het ‘n vinnig toename in rooi kleur getoon met die koue, maar helder, weerstoestande wat gevolg het op ‘n kouefront. Dit is welbekend dat dwergende onderstamme die rooi kleur van blospere verbeter deur ligverspreiding in die boom te verhoog. Ten einde die effek van onderstam op rooi kleurontwikkeling onafhanklik van die effek van onderstam op ligverspreiding te ondersoek, is ‘Forelle’ pere wat blootgestel was aan vol son geoes van bome geënt op ses onderstamme met verskillende groeikrag. Kweperonderstamme (Cydonia oblonga Mill.) het rooi kleur verbeter in vergelyking met die groeikragtige BP peeronderstamme. ‘n Moontlike rede vir die verbetering is die laer chlorofiel- en karotenoïedkonsentrasies in die skil van vrugte op kweperonderstamme. Bome op peeronderstamme het ook hoër blaaren skil stikstofvlakke gehad. Kweperonderstamme word aanbeveel in gevalle waar rooi kleurontwikkeling van blospere ‘n probleem mag wees. Die RSA vrugtebedryf benodig ‘n vroeë blospeerkultivar met goeie rooi kleurontwikkeling. Die teling van so ‘n kultivar is hulpbronintensief en baie duur. Ten einde die teelproses meer effektief te maak, word ‘n metode benodig om saailinge al voor uitplanting in die boord te selekteer na gelang van hul toekomstige vrugkleur. Die vrugkleur van oesryp pere van draende saailinge is vergelyk met die kleur van hul onvolwasse blare. Bome met rooi blare is geneig om vrugte te dra wat té rooi is om te kwalifiseer as blospere. Die meerderheid blospere is afkomstig van bome met blos of groen onvolwasse blare. Dit is prakties haalbaar om rooiblaarsaailinge uit te dun, met net ‘n klein, aanvaarbare risiko om ‘n moontlike blospeerkultivar in die proses te verloor. / medg2010-1 / Imported from http://etd.sun.ac.za April 2010.