Graduation date: 1947

Thesis (Ph. D.)--Oregon State University, 1966. / Typescript. Includes bibliographical references (leaves 79-83). Also available on the World Wide Web.

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 (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: 'Forelle' is one of three blushed pear cultivars produced in South Africa. A mandatory minimum cold storage duration of 12 weeks at -0.5°C to ensure even ripening, prevents 'Forelle' from being marketed earlier. Since earlier marketing can result in premium prices (in excess of 50% morê per carton) research in recent years has been directed at reducing this 12 week cold storage period. Intermittent warming treatments, controlled atmosphere (CA) storage in combination with regular atmosphere (RA) storage intervals, and ethylene treatments, have been tested as alternatives to the 12 week cold requirement. However, none of these treatments delivered a better internal quality in terms of mealiness and astringency. Fruit harvested from the Warm Bokkeveld and Theewaterskloof areas at commercial maturity were stored at -0.5°C for up to 21 and 22 weeks, respectively, to understand the changes in ripening and mealiness of 'Forelle' pears after cold storage (Paper 1). Samples were removed every third weev, placed at 15°C, and maturity factors, total ACC concentration, ethylene production and respiration rates monitored every third day for 12 days. Fruit from the Warm Bokkeveld and the Theewaterskloof areas ripened after 6 and 7 weeks at -0.5°C, respectively. However, after 6 weeks of cold storage followed by 6 days at 15°C, all fruit harvested in the Warm Bokkeveld, and 70 % of the fruit harvested in the Theewaterskloof area, were mealy. With extended storage at -0.5°C (> 15 weeks) the incidence of mealiness declined in fruit from both areas, but never disappeared, when evaluated at 15°C over 12 days. Since harvest maturity affects the incidence of mealiness in other pear cultivars, the effect of harvest maturity on 'Forelle' pears with regard to mealiness development was examined (Paper 2). Fruit were harvested from the Ceres area, in weeks 8 (preoptimum), 10 (optimum), 12 and 14 (both post optimum). Maturity indices, juice content, mealiness, total ACC content, ethylene production and internal ethylene were monitored at harvest, after 6 weeks of storage at -0.5°C and again after 7 days at 15°C. Fruit harvested 2 weeks before commercial harvest (week 8) had the highest total ACC concentration, ethylene production and the potential to ripen, but also developed the highest incidence of mealiness (80%). However, fruit of all harvest maturities (except where contamination with 1-MCP occurred) were mealy. It would appear that factor(s), other than harvest maturity, play a more important role in the initiation of mealiness in 'Forelle' pears. Although ethylene has been shown to shorten the cold requirement of 'Forelle', there are conflicting reports as to its effectiveness in reducing mealiness. Consequently, the aim of the third paper was to evaluate the effect of ethylene on ripening and mealiness of 'Forelle' pears. Fruit harvested from the Elgin area at commercial maturity were stored for 3 weeks at -0.5°C, treated with ethylene (100 Jl L.L·l , 24h, 20°C) and held at 20°C for a further 2 days (without ethylene). Control fruit were held at 20°C for 3 days. Fruit were returned to -0.5°C for a further 3 weeks. After a subsequent 3 days at 20°C, flesh firmness was 4.6 kg in treated fruit compared to 6.1 kg for control fruit. At this point all fruit treated with ethylene were mealy. Control fruit all exhibited mealiness after a further 3 weeks at -0.5°C followed by 7 days at 15°C. Ethylene treatment advanced fruit maturity, but did not prevent or alleviate mealiness. Mealiness is a textural disorder recognized by a dry soft pulp. This has previously been recorded in 'd'Anjou' pears, as a result of storing the fruit for too long at -1.1°C, but has also been the result of a chilling injury in fruit like nectarines, kiwi and persimmon. The role of storage temperature on ripening, and specifically mealiness, of 'Forelle' was thus investigated (Paper 4). Fruit harvested from the Elgin area at commercial maturity were stored at -0.5°C, 4.0°C and 7.5°C for 0, 3 and 6 weeks. Samples were removed every third week, placed at 15°C, and maturity indices, extractable juice content, mealiness, total ACC content, internal ethylene concentration and ethylene production were monitored on removal and after 7 days. Flesh firmness of the 4°C stored fruit was 0.5 kg lower than fruit stored at -0.5°C, on removal from storage. Fruit stored at 4°C and 7.5°C ripened with little to no mealiness (0 and 8% respectively) in contrast to fruit stored at -0.5°C (70% mealy). Total ACC accumulation and ethylene production were higher for fruit stored at 4°C and 7.5°C than fruit stored at -0.5°C. Storage temperature appears to playa role in the development of mealiness. Although storage temperatures influenced mealiness development, this research should be repeated before this can recommended as a commercial treatment. The underlying mechanism of action in the development of mealiness should be investigated. By examining fruit grown in different climatical areas, harvested at different maturities, treated with exogenous ethylene and stored at different temperatures, this research has helped to a better understanding of the role of factors affecting ripening and development of mealiness in 'Forelle'. / AFRIKAANSE OPSOMMING: Forelle' is een van drie blos peer kultivars wat in Suid Afrika geproduseer word. 'n Minimum van 12 weke by -0.5°C opberging, is deur wetgewing vasgestel, om eweredige rypheid van 'Forelle' te verseker. Vroeër bemarking van 'Forelle' kan daartoe lei dat vrugte premium pryse, van 50% meer per karton behaal. Aangesien die vasgestelde koue periode verhoed dat 'Forelle' vroeër bemark kan word, het onlangse navorsing gefokus op vermindering van die vasgestelde opberging van 12 weke by -0.5°C. Afwisselende verwarmmgs behandelings gedurende koue opberging, beheerde atmosfeer (BA) opberging in kombinasie met gewone atmosfeer (GA) opbergings intervalle, en etileen behandelings, is _getoets as alternatiewe vir die 12 weke opbergings vereiste by -0.5°C. Geen van die bogenoemde behandelings kon egter 'n beter interne kwaliteit in terme van meleringheid en frankheid as 'n alternatief verseker nie. Die doel van die eerste proef was om die invloed van koue opberging by -0.5°C op rypwording en melerigheid van 'Forelle' te bepaal. Vrugte is in die Warm Bokkeveld and Theewaterskloof areas geoes tydens kommersiële oesrypheid, waarna hulle vir 21 en 22 weke, respektiewelik, by -0.5°C opgeberg is. Monsters is elke derde week vanaf die -0.5°C koue opberging geneem en by 15°C geplaas, waarna rypheids indeksering, totale ACC konsentrasie, etileen produksie and respirasie tempos elke derde dag vir 12 dae gemonitor is. Vrugte wat in dieWarm Bokkeveld en Theewaterskloof areas geoes is, het rypgeword by 15°C, na 6 and 7 weke by -0.5°C, respektiewelik. Alle vrugte vanaf die Warm Bokkeveld en 70% vrugte vanaf die Theewaterskloof area, het egter na die 6 en 7 weke by -0.5°C, respektiewelik, en 6 dae by 15°C, melerigheid ontwikkel. Vrugte wat vir langer as 15 weke by -0.5°C opgeberg is, het in albei areas 'n afname in melerigheid getoon, maar die defek het nooit heeltemal verdwyn tydens evaluasie by 15°C nie. Oes rypheid affekteer die ontwikkeling van melerigheid in ander peer kultivars. Die tweede proef was dus gefokus op dip. invloed van oes rypheid op 'Forelle' se ontwikkeling van melerigheid. Vrugte is in die Warm Bokkeveld area geoes in week 8 (pre-optimum), 10 (optimum), 12 and 14 (albei post-optimum). Rypheids indekse, uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke en etileen produksie is gemonitor, na opberging vir 6 weke by -0.5°C en 7 dae by 15°C. Vrugte wat 2 weke voor kommersiële rypheid geoes is (week 8) het die hoogste totale ACC konsentrasie en etileen produksie gehad, en het reeds die potensiaal gehad om ryp te word. Die hoogste vlakke van melerigheid (80%) is ook in vrugte wat tydens hierdie oes verkry is, waargeneem. Vrugte wat op alle tye geoes is, het melerigheid ontwikkel, behalwe waar kontaminasie met 1-MCP plaasgevind het. Dit wil voorkom asof 'n ander faktor 'n belangriker rol in die ontwikkeling van melerigheid in 'Forelle' speel as oes rypheid. Etileen is bewys om die vereiste koue opberging vir 'Forelle' te kan verkort, maar daar is konflik oor die effektiwiteit van etileen op die verlaging van melerigheid in 'Forelle'. Die doel van die derde proef was dus om die effek van eksterne etileen behandeling op rypheid en melerigheid van 'Forelle' te toets. Vrugte wat in die Elgin area by kommersiële oesrypheid geoes is, is vir 3 weke gestoor by -0.5°C, met etileen behandel (100 Il L.L-1, 24h, 20°C) en vir 'n verdere 2 dae by 20°C gehou (sonder etileen). Kontrole vrugte is vir 3 dae by 20°C gehou. Daarna is vrugte weer vir 'n verdere 3 weke by -0.5°C opgeberg. Na 'n verdere 3 dae by 20°C, was vlees fermheid van etileen behandelde vrugte 4.6 kg .n vergelyking met 6.1 kg vir die kontrole vrugte. Alle vrugte wat met etileen behandel is, was melerig op hierdie stadium. Die kontrole vrugte het ook almal melerig geword, maar slegs na 'n verdere 3 weke by -0.5°C en 7 dae by 15°C. Etileen behandeling het dus die rypheid van 'Forelle' bevorder, maar het nie melerigheid voorkom nie. Melerigheid is 'n tekstuur probleem, wat gekenmerk word aan sagte droë pulp. Hierdie tekstuur probleem is voorheen waargeneem in 'd'Anjou' pere wat te lank by -Ll=C opgeberg is, maar is ook kenmerkend by vrugte soos nektariens, kiwi en persimmon wat aan koue skade ly. Lie gevolg is dat die effek van opbergings temperatuur op 'Forelle' rypwording en melerigheid getoets moes word. Vrugte is geoes van die Elgin area tydens kommersiële oesrypheid en gestoor by -0.5°C, 4.0°C en 7.5°C vir 0, 3 en 6 weke. Vrug monsters is geneem, na verwydering van bogenoemde stoor temperature en na 7 dae by 15°C, waarby rypheids indekse, uitdrukbare sapinhoud, meleringheid, totale ACC konsentrasie, interne etileen vlakke en etileen produksie gemonitor is. Vlees fermheid van vrugte wat vir 6 weke by 4°C opgeberg was, was 0.5 kg laer as vrugte wat by -0.5°C opgeberg was. Vrugte wat by 4°C and 7.5°C vir 6 weke gestoor is en by 15°C ryp geword het, het min tot geen melerigheid ontwikkel (0 and 8%, respektiewelik) nie. Vrugte wat by -0.5°C opgeberg was het egter hoë vlakke van melerigheid bereik (70% melerig). Totale ACC akkumulasie en etileen produksie was hoër vir vrugte wat by 4°C en 7.5°C gestoor was, teenoor vrugte wat gestoor was by -0.5°C. Dit wil voorkom asof na-oes opbergings temperature wel 'n rol speel in die ontwikkeling van melerigheid. Alhoewel dit voorkom asof na-oes temperature wel 'n rol speel in die ontwikkeling van melerigheid in 'Forelle' pere, is meer basiese navorsing nodig om die meganisme van werking in melerigheid ontwikkeling te verstaan. Na-oes temperatuur as 'n faktor wat melerigheid kan beïnvloed, moet oor 'n reeks van seisoene nagevors word. Laasgenoemde is van uiterste belang aangesien die invloed van seisoenale variasies op melerigheid nog nie gekwantifiseer is nie. Die navorsing was gefokus daarop om vas te stel watter faktore 'n fisiologiese rol speel in rypwording en melerigheid van 'Forelle' pere. Deurdat vrugte van twee areas met verskillende klimate, vrugte met verskye oesryphede, ekterne etileen behandeling, en vrugte van verskillende opbergings temperature ondersoek is, het hierdie navorsing gehelp om 'n beter begrip te vorm van die rol van hierdie faktore op die rypwording en die ontwikkeling van melerigheid in 'Forelle'.

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.

Different concentrations of various browning inhibitors and a firming agent were evaluated to prevent browning and softening of Bartlett, Bosc and Anjou pear slices during cold storage at 2-4°C. Browning inhibition effect of Semperfresh, Snow Fresh and cysteine were compared with that of 4-hexylresorcinol (4-HR). The effect of ripeness on color and texture changes as well as the influence of storage temperature on texture and color retention was investigated. 4-HR residual content under different treatment conditions and its sensory properties were analyzed. 4-HR was an effective browning inhibitor at concentration as low as 0.005% when combined with 0.5% ascorbic acid (AA). Cysteine (0.5%) with 0.5% ascorbic acid (AA) effectively inhibited Anjou and Bosc pear slice browning for 25 days and its sensory properties merit further study. A combination of 1.0% AA and 1.0% calcium lactate prevented Anjou pear slices from discoloration, but also caused tissue leaking and softening. Semperfresh and Snow Fresh did not maintain flesh color effectively. 1.0% calcium lactate maintained slice firmness at an acceptable level for 30 days when the average firmness of whole pears at slicing was 49, 38 and 43 Newton (N) for Bartlett, Bosc and Anjou respectively. A storage temperature of 0°C significantly retained better texture than the control of 2-4°C. Slices with acceptable texture and color were achieved by treatment with a solution of 0.01% 4-HR, 0.5% AA, and 1.0% calcium lactate for 2 min, vacuum packaging, and storage at 2-4°C for 30 days for Bartlett and Bosc, and 15 days for Anjou. 4-HR residual content increased with increasing dipping times and concentrations, with the latter being the major factor. The 4-HR residual decreased with storage time for all the treatments. Sensory tests indicated that panelists detected the overall differences between 0.01% 4-HR treated samples and the controls for both Bartlett and Anjou pears (P<0.01). There were no significant differences in preference between treated sample and control for Anjou pears. / Graduation date: 1999

Thesis (M.S.)--Oregon State University, 1963. / Typescript. Includes bibliographical references (leaves 104-106). Also available on the World Wide Web.

Thesis (MScAgric)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

This creative project explored the visual characteristics of the transitions found in the decay of the pear. The project consisted of oil paintings, watercolors and prints. I found that what is normally viewed as ugly can be visually stimulating or actually beautiful. These images were produced to communicate the visual changes which occure with the characteristics of the fruit through the passage of time. / Department of Art

The nutrient elements needed for the optimum growth and yield of pear trees is vitally important to the pear growers. The knowledge of the amounts and kinds of fertilizer to apply to obtain this growth could increase the production and cut the costs for these growers. Field experiments have been made on the nutritional elements needed for pears, but the results were affected by many variants, such as the availability of the elements and rainfall. The growing of fruit trees in sand with controlled nutrient solutions added had been used to obtain data not possible to obtain under field conditions. Since other factors affect the absorption of the nutrient elements in the field experiments, an experiment for the application of varied nutrient solutions on one year old Anjou pear trees, grown in sand culture, was undertaken. The purpose was to try to determine the influence that the concentration and the ratio of nitrogen and phosphorus in the nutrient solutions would have on the amount of nitrogen and phosphorus which the pear trees would absorb into the leaves. One year old pear trees were grown in a sand culture in a greenhouse through one growth period. The experiment was set up as a factrial with three levels each of nitrogen and phosphorus. The solutions were applied through an automatic system which irrigated the trees every hour. The solutions were checked daily and were changed once every week. The trees were harvested and the leaves were analyzed for nitrogen and phosphorus. The results indicated that the supply of nitrogen was adequate at all levels to support normal development of the leaves of the trees. The supply of nitrogen in the nutrient solution did not cause the percent of nitrogen in the leaves to vary by a statistically significant amount. The analysis of the variations of the percent of phosphorus in the leaves showed significant differences between treatments. The main effect of the phosphorus in the nutrient solution was to increase the phosphorus content of the leaves as the supply of phosphorus was increased. The main effect of phosphorus on nitrogen was negative at all levels. This effect was noticeable at the highest phosphorus level, but it was not statistically significant. The ability of the Anjou pear tree, to absorb both nitrogen and phosphorus from a nutrient solution with very low levels of each of the elements, implies that heavy fertilization with either of these elements may not be necessary for normal, vigorous growth; this is especially true in the case of phosphorus. / Graduation date: 1960