No description available.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: In order to develop a novel pink- or red-fleshed apple for the fresh consumer market,the red-fleshed genotype, ‘KAZ 91’ (Malus niedzwetzkyana Dieck.), was crossed with ‘Meran’ (M. domestica Borkh) at the Agricultural Research Council (ARC) apple breeding programme in South Africa. The objective of this study was to evaluate and quantify colour variability in the flesh and peel of this progeny (Family 1), to assess quality traits (i.e., acidity and total soluble solids) and phenolic levels in fruit peel and flesh, and to investigate consumer preference for the taste and appearance of redfleshed apples. All data, except for consumer preference, were also collected on two white-fleshed M. domestica Borkh families, i.e., ‘Reinette Burchardt’ x ‘Treco Red Gala’ (Family 2) and ‘Meran’ x ‘Treco Red Gala’ (Family 3). Fruit of Family 1 seedlings were on average darker red with greater blush coverage and higher anthocyanin and phenolic levels compared to fruits of Family 2 and 3. The proportion of bearing trees with red-fleshed fruits in Family 1 increased from 25% in 2007 to 35% in 2008. The intensity and distribution of red pigmentation in the flesh varied considerably between seedlings and even between individual apples from the same tree. A high intraclass correlation coefficient was found for red-flesh coverage within Family 1, indicating a high level of genetic determination that can be used in breeding. When only red-fleshed seedlings were considered, an intermediate repeatability coefficient (0.54) for red-flesh coverage indicates that the extent of red flesh coverage varies to some extent between seasons. The effect of environmental factors on red flesh colour needs to be assessed and breeders need to take care to select for genotypes with stable flesh colour intensity and coverage. Small intraclass correlations were found between families for other traits. No correlation was found for anthocyanin and total phenolics in both peel and flesh or between anthocyanin levels in the peel and flesh of Family 1 fruit. This suggests that red-fleshed fruit will not necessarily be high in antioxidants – since phenolics is by far the greatest contributor to fruit antioxidant capacity. The lack of a correlation between peel and flesh anthocyanin levels also suggest that fruit with dark red flesh will not necessarily have a dark red skin colour. Family 1 fruit were more prone to flesh browning and were more acidic compared to fruit of Families 2 and 3. With regard to consumer preference for flesh colour, 74% of South African consumers preferred white flesh while 64% preferred an attractive “floral” pattern created by the combination of a red cortex and white core. Consumers indicated a much lower liking for other distribution patterns and lower intensities of red flesh colour. Consumers preferred the taste of apples that were crisp, crunchy and high in apple flavour irrespective of flesh colour. Red-fleshed fruit were generally acidic or had poor texture, and some were also astringent. However, despite a general dislike in acidic fruit, consumers showed a preference for acidic fruit if that fruit also had high red-flesh coverage. / AFRIKAANSE OPSOMMING: Appeltelers van die Suid-Afrikaanse Landbounavorsingsraad (LNR) Infruitec- Nietvoorbij poog om unieke appelkultivars met ‘n pienk of rooi vleiskleur te ontwikkel. Vir hierdie doel het hulle die rooivleis genotipe, ‘KAZ 91’ (Malus niedzwetzkyana Dieck), gekruis met ‘Meran’ (M. domestica Borkh). Hierdie studie is uitgevoer ten einde kleurvariasie, interne kwaliteitseienskappe (i.e., suurheid en totale oplosbare vastestowwe) en vlakke van fenole in die vleis en skil van bogenoemde kruisingkombinasie se nageslag (Familie 1) te evalueer en te kwantifiseer asook om verbruikersvoorkeure vir die smaak en voorkoms van rooivleis appels te bestudeer. Buiten vir verbruikersvoorkeure, is alle data ook ingesamel vir twee witvleis M. domestica families, naamlik ‘Reinette Burchardt’ x ‘Treco Red Gala’ (Familie 2) en ‘Meran’ x ‘Treco Red Gala’ (Familie 3). Familie 1 saailinge se vrugte was gemiddeld donkerder rooi met ‘n groter rooi blos en hoër antosianien- en fenoolvlakke in vergeleke met vrugte van Families 2 en 3. Van die Familie 1 saailinge wat wel vrugte gedra het, het 25% en 35% in onderskeidelik 2007 en 2008 vrugte met rooi vleis gehad. Die intensiteit en verspreiding van rooi pigmentasie in die vleis het aansienlik varieer tussen saailinge en selfs tussen individuele appels van dieselfde boom. ‘n Hoë intraklas korrelasie koëffisiënt is gevind vir die proporsie van die vleis met rooi pigmentasie in Familie 1 nageslag. Dit dui op ‘n hoë vlak van genetiese determinasie en vinnige vordering met teling vir hierdie eienskap. Indien net rooi-vleis saailinge egter oorweeg word, word ‘n intermediêre herhaalbaarheid koëffisiënt (0.54) vir die proporsie van die vleis wat rooi is verkry, wat dui op aansienlike variasie tussen seisoene in die omvang van rooi pigmentasie. Die effek van omgewingsfaktore op rooi vleiskleur behoort dus bestudeer te word en telers moet let daarop om te selekteer vir genotipes met stabiele vleiskleur intensiteit en bedekking. Die intraklas korrelasies tussen families vir ander vrugeienskappe was klein. Antosianienvlakke en totale fenole in die skil en vleis van Familie 1 vrugte het nie gekorreleer nie. Dit dui daarop dat rooivleis appels nie noodwendig ‘n hoër antioksidantkapasiteit het nie – fenole maak by verre die grootste bydrae tot die antioksidantkapisiteit van vrugte. Antosianienvlakke in die skil en vleis van Familie 1 vrugte het ook nie gekorreleer nie wat daarop dui dat vrugte met ‘n donker rooi vleis nie noodwendig ook ‘n donker skilkleur sal hê nie. Familie 1 vrugte was gemiddeld suurder as vrugte van Families 2 en 3 en Familie 1 vrugte se vleis het gemiddeld ook meer verbruining ondergaan. Ten opsigte van verbruikersvoorkeur vir vleiskleur is gevind dat 74% van verbruikers ‘n wit vleiskleur verkies het terwyl 64% gehou het van die aantreklike “blom” patroon gevorm deur ‘n rooi korteks en wit kern. Verbruikers het aansienlik minder gehou van enige ander verspreiding van rooi pigment in die vleis of van ‘n laer intensiteit rooi kleur. In terme van smaak is geurige appels met ‘n bros tekstuur verkies ongeag hul vleiskleur. Rooivleisappels was oor die algemeen suur met ‘n swak tekstuur. Sommige rooivleisappels was ook frank. Tog, ten spyte van ‘n algemene afkeur in suur appels, het verbruikers ‘n voorkeur getoon vir vrugte met ‘n kombinasie van hoë suur en ‘n hoë proporsie vleis met rooi pigmentasie.

Limes (Citrus latifolia Tanaka) are an attractive fruit crop but generally suffer a loss in value as their colour changes from green to yellow. Various approaches were taken to slow degreening including low temperature storage, use of controlled atmosphere (CA) environments, and treatment of fruit with physiologically active agents such as gibberellic acid (GA3). However, the cold storage life of lime fruit can also be restricted by a number of factors including chilling injury (CI) and rots. Various pretreatments such as the use of fungicide (thiabendazole, TBZ) and hot water dipping (HWD) and several postharvest regimes based on temperature conditioning (step down technique) and intermittent warming (IW) regimes were further investigated to protect the fruit against rots and CI during cold storage. The objective of this study was to determine what storage conditions and pretreatments would permit long term storage of NZ limes with minimal loss of quality. CA storage (10% O2 with 0 or 3% CO2) was compared to regular air storage (RA) and IW (varying durations) treatments across a range of temperatures. Although some CA storage regimes could assist in delaying degreening, none of the treatments provided protection against CI. CA storage at 3% CO2 delayed yellowing and gave better fruit quality than the low CO2 treatment. High CO2 CA treatments at 5 or 7°C decreased the rate of colour change compared to other constant temperature treatments but did not protect against CI. CI limited storage of fruit under all conditions at constant low temperatures. Including fungicide (TBZ) in the dip water reduced the incidence of rots and had a secondary effect on protection against CI of lime fruit. However, fungicide use may sometimes exacerbate stresses such as heat injury on lime peel. Hot water dipping has been shown previously to hold potential as a storage pretreatment, but this technique may give risk of damage on produce if it is dipped at too high a temperature. Some HWD treatments did delay degreening, but there was no major effect on CI. HWD at > 47°C for = 4 min caused heat injury to NZ limes. All HWD treatments showed severe CI (>15%) after 10 weeks of cold storage; and HWD fruit stored under RA at 13°C did not show any CI but showed some pitting (= 10%) and degreened rapidly. Overall no suitable HWD treatment for limes was identified in this trial. This project identified the critical periods and temperature conditions for successful IW of limes. The IW conditions successfully delayed losses in quality of lime fruit provided the first warming period was applied within the first 20 days of storage. At least 2-cycle IW was required to maintain lime quality during long term storage. Some benefits were found after just one cycle of IW treatment but there were not enough to extend storage life. IW storage benefited fruit quality and provided the highest overall fruit quality of all postharvest treatments tested. The degreening of lime during cold storage at 5°C could be delayed by IW treatments in which the fruit were stored at 5°C for 12, 16 or 20 days then moved to 15°C for 2 days. Both 2- and 6-cycle IW treatments proved satisfactory for maintaining colour on the green and yellow side of lime for 12 weeks of storage. IW treatments in which fruit were warmed within 20 day of cold storage did not show significant CI symptoms after 12 weeks of storage, and the 2-cycle IW treatment showed only a low percentage of CI fruit at this time. A 2-cycle IW treatment was almost as effective as 6 cycles, and a step down treatment also showed some promising results, indicating that it may be possible to further optimize the time and duration of variable temperature storage regimes to meet both quality requirements and the constraints of temperature management in commercial coolstores. The application of these regimes to other citrus species may also be beneficial. There are a number of physiological explanations that may account for the effectiveness of IW including positive effects on heat shock protein (HSP) and cell membranes. Nutritional factors such as vitamin C and flavonoid compositions were also investigated and fruit that did not show visible CI were found to retain at-harvest levels of these factors. Practical ways of implementing IW are discussed. In order to understand the effectiveness of IW on degreening, I used a logistic model to describe degreening of lime peel. This modelling approach demonstrated that IW did not change the mechanism of lime degreening based on the similarity between the hue values predicted by the model and the actual hue values measured during lime storage. The activation energy (Ea) for degreening based on either hue angle (H°) or colour score (CS) during air storage was estimated to be ~53 and ~86 KJ.mol-1, respectively. Relationship between colour (H° and CS) and chlorophyll content, relationship between reflectance spectra (%), chlorophyll content and H° of lime fruit stored under different conditions are presented and discussed. This data allowed deduction to be made about the changes in individual pigments that are driving colour change during “good” and “bad” storage.

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.

It has been suggested that fruit features such as nutrient content, size and colour have co-evolved with dispersal agent behaviour, physiology and morphology. Avian nectarivore feeding ecology is relatively well studied; however, less is known about fruit selection in avian frugivores. Previous work highlights the importance of individual factors that contribute towards fruit preferences, but few studies bring these factors together. Consequently the aim of this dissertation was to attempt this in terms of frugivory by investigating behavioural, physiological and morphological aspects of fruit selection in generalist avian dispersers. This was achieved by manipulating the nutritional content, size and colour of fruits (artificial fruits) under controlled conditions. The first part of the dissertation addresses physiological aspects of fruit selection in Red-winged Starling Onychognathus morio, Speckled Mousebird Colius striatus and Dark-Capped Bulbul Pycnonotus tricolor. Assimilation efficiency of birds fed glucose and sucrose diet treatments of varying concentration was observed. All study species showed high apparent assimilation efficiency irrespective of artificial fruit sugar concentration and type (with the exception of Red-winged Starlings on an all sucrose diet). The second part of the dissertation addresses behavioural aspects of fruit selection in the same three species by observing selective preferences between glucose and sucrose fruits of varying concentration and molarity. While Mousebirds displayed no preference for any of the diet treatments, Bulbuls occasionally favoured glucose diets over sucrose diets and Starlings always favoured glucose diets over sucrose diets. Another behavioural aspect of fruit selection was addressed in the third part of the dissertation. Colour preferences of Red-winged Starling and Speckled Mousebird were observed. Although study species did not conform to trends by favouring black and red fruits, they did show avoidance of green fruits and (Starlings) presented evidence of learning. A morphological aspect of fruit selection is presented in the fourth part of the dissertation. Starlings, Bulbuls and Mousebird beak morphology was measured to investigate if this has an effect on fruit size preferences. Starlings with the largest beak dimensions were more selective of fruit size classes than Bulbuls and Mousebirds which displayed the importance of feeding method (thrashing/swallowing/mashing) to compensate for larger fruit sizes. The final section of this dissertation is a synthesis of the observed behavioural, physiological and morphological aspects of fruit selection in Red-winged Starlings, Dark-capped Bulbuls and Speckled-Mousebirds. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.