Thesis (MSc)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: Sunburn on apple and pear fruit results in large losses of export volumes in South African orchards. Producers estimate that losses due to sunburn are often about 10- 20%. Knowledge of temperature thresholds for sunburn as well as technologies available to manage sunburn is important to increase producer earnings. The effect of evaporative cooling on fruit surface temperature and sunburn was evaluated on 'Cripps' Pink', 'Royal Gala' and 'Fuji' apples as well as 'Forelle' pears. Evaporative cooling was effective in reducing fruit surface temperature by 0.6-3.7°C. Apple fruit under evaporative cooling treatments appeared to have acclimatised and had significantly higher surface temperatures when dry (0.9-4.7°C) than non-cooled fruit. This acclimitasing effect could be due to a modification of the cuticular wax layer. Futher trials are needed to investigate the cause of this acclimatising effect. The acclimatising effect was not found on 'Forelle' pears. Sunburn was reduced significantly only on 'Royal Gala' apples. Spraying 'Braeburn', 'Granny Smith', and 'Fuji' apples with reflective kaolin-based particle film (Surround WP) significantly reduced sunburn on 'Braeburn', 'Granny Smith' and 'Fuji' apple cultivars. Surround WP applications reduced leaf stomatal conductance and photosynthetic rate. Four applications of Surround WP with a commercial blower sprayer increased total soluble solids in 'Braeburn' . Four applications with a blower and five applications with a tower sprayer resulted in increased fruit size, higher flesh firmness, and lower percentage starch breakdown in 'Granny Smith'. Surround WP treatments slightly improved fruit colour in 'Granny Smith' apples. Futher trials are needed to establish whether Surround WP can,be reliably and economically removed from apple fruit and to evaluate the storage quality of fruit cleansed in this way. The effect of fruit surface temperatures (24°C, 30°C, 33-35°C, 40-43°C and 48-49°C) for increasing periods of time (two, four, six or eight hours) on maximum quantum yield of fluorescence (Fv/Fm) was measured on exposed and shaded sides of detached 'Cripps' Pink' and 'Royal Gala' apples. Measurements were taken directly after removal from the chamber as well as 12 hours later to assess recovery. Permanent damage to Photo system II (PSII) occurred between 48-49°C irrespective of duration, with permanent damage possible at 42-43°C when exposure exceeded six hours. There were no meaningful differences in Fv/Fm between shaded and exposed sides of apple fruit after exposure to high temperature. Duration of exposure was important in lowering PSU efficiency in 'Cripps' Pink' but less so in 'Royal Gala'. 'Cripps' Pink' apples harvested later in the season appeared to be able to recover from heat stress better than apples harvested earlier in the season. However, we only studied the effects of high temperature on apple tissues. More research is needed to establish the reaction of apple tissues to high temperatures in the presence of sunlight. / AFRIKAANSE OPSOMMING: Sonbrand op appel en peervrugte kom jaarliks voor in Suid-Afrikaanse boorde en lei tot groot afnames in vrugte wat geskik is vir die uitvoermark. Produsente beraam dat verliese a.g.v. sonbrand jaarliks 10-20% beloop. Kennis van drempelwaarde temperature vir die ontwikkeling van sonbrand sowel as die tegnologieë wat beskikbaar is om sonbrand te bekamp, is van groot belang om uitpakke te verbeter. Die effek van oorhoofse besproeïng op vrugtemperature en sonbrand van 'Cripps' Pink', 'Royal Gala' en 'Fuji' appels sowel as 'Forelle' pere is ondersoek. Oorhoofse besproeïng het vrugtemperature betekenisvol verlaag in al die proewe. Dit wil voorkom of appels onder oorhoofse besproeïng geakklimatiseer het en dié appels het hoër skil temperature geopenbaar wanneer hulle droog was as die kontrole vrugte. Moontlik is die effek te wyte aan 'n verandering in die kutikulêre waslaag. Verdere proewe om hierdie verskynsel te probeer verklaar is nodig. Die effek is nie waargeneem op die 'Forelle' pere nie. Sonbrand is betekenisvol verminder op 'Royal Gala' appels. Toediening van weerkaatsende kaolin-gebaseerde partikels (Surround'" WP) het sonbrand betenisvol verlaag op 'Braeburn' , 'Granny Smith', en 'Fuji' appels. Surround® WP toedienings het blaarhuidmondjie-geleiding en die tempo van fotosintese verlaag. Vier toedienings van Surround® WP met 'n kommersiële waaierblaser het totale oplosbare vastestowwe (TOVS) beduidend verhoog in 'Braeburn' appels. Vier toedienings met 'n waaierblaser en vyf toedienings met 'n toring spuitkar het gelei tot 'n verhoging in vrugmassa en vrugferrnheid, en 'n verlaging in persentasie styselafbraak in 'Granny Smith' appels. Surround® WP toedienings het gelei tot effens beter kleur op 'Granny Smith' appels. Verdere proewe is nodig om te bepaal of Surround® WP op 'n betroubare en ekonomiese wyse van vrugte verwyder kan word in die pakstoor, en wat die hou-vermoë is van appels wat só behandel is. Die effek van vrugoppervlaktemperature (24°C, 30°C, 33-35°C, 40-43°C en 48-49°C) vir toenemende tydsdure (twee, vier, ses en agt ure) op maksimum kwantum-opbrengs van fluoressensie is gemeet op sonkante en skadukante van geplukte 'Cripps' Pink' en 'Royal Gala' appels. Metings is geneem direk na verwydering uit die oonde sowel as 12 ure later om moontlike herstel waar te neem. Permanente skade aan Fotosisteem II (PSII) het plaasgevind tussen 48-49°C ongeag tydsduur, met permanente skade ook moontlik by 42-43°C wanneer blootstelling aan genoemde temperature ses ure oorskry het. Daar was geen betekenisvolle verskille in Fv/Fm tussen skadu- en sonkante van appels na blootstelling aan hoë temperature nie. Die tydsduur van blootstelling was belangrik om PSII effektiwiteit te verlaag in 'Cripps' Pink', maar minder so in 'Royal Gala'. Dit wil voorkom of 'Cripps' Pink' appels later in die seisoen beter daartoe in staat is om te herstel van hitte stres as vroeër in die seisoen. Ons het egter slegs die effek van hoë temperature op appel weefsels ondersoek. Verdere proewe is nodig om die reaksie van appelweefsels op hoë temperature in die teenwoordigheid van sonlig te ondersoek.

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: In order to study the dormancy of apple buds in conditions of inadequate chilling a number of trails were done during 2000 and 2001. Year-old, unbranched shoots of 'Royal Gala', 'Braeburn', 'Cripps' Pink' and 'Granny Smith' apple were harvested randomly from bearing commercial orchards in the Koue Bokkeveld [33°S, 945m, ca.1300 Utah model chili units (CU)) and Elgin (34 "S, 305m, ca.750CU) regions of the Western Cape, South Africa, respectively. Shoots were chilled at 5-rC. Two replicate bundles were removed from the cold room, prepared and forced at 25°C with continuous illumination until budburst had occurred on at least 25% of the shoots per bundle. The change in the rate of budburst over time was calculated for each orchard and to this response; either a linear or a quadratic function was fitted. Poorly correlated variables were selected that best describe these functions. Using these variables, the orchards were separated into cluster groupings that represented a dormancy pattern. The first split separated the lower chilling requirement cultivars from the higher cultivars. The second and third split separated the orchards according to area differences. The clusters representing the warmer area orchards initially entered deeper into dormancy before exiting. The clusters for the colder area immediately had an increased budburst rate. This data confirm that the chilling requirement includes a period of dormancy induction. An important genotype and environment interaction, other than cold unit accumulation, was observed that could be responsible for terminating bud dormancy. Terminal apple buds from 'Royal Gala' Braeburn', 'Cripps' Pink' and 'Granny Smith' apples were cut from orchards in the Koue Bokkeveld and Elgin regions of the Western Cape, South Africa. Buds were harvested every two weeks during the dormant period. The buds were cut in half and leaf scales removed before the water potential were measured. Fresh and dry weights of the buds were also determined. The data presented confirms the changes in availability of free water in dormant buds and that it could be measured in this way. A definite influence of temperature was illustrated. The water potential from buds in a cold production area (Koue Bokkeveld) behaved more "normally" - water is in a bound form during most of the winter and change to an available form later in winter - whereas buds from a warmer production area did not change much in water potential or content. In the trial, two-year-old proleptic-branched shoots, ca. 500mm long, were selected from a 'Royal Gala' orchard in the Koue Bokkeveld region in the Western Cape, South Africa. During the dormancy period of 2000, shoots received two cold treatments; chilling in a cold room at 5-7°C and the natural chilling received in the field. In 2001, the trail was repeated, but only with the field chilling. The shoots received five dormant pruning treatments: control (not pruned), pruning back to the fourth lateral (heading) before or after chilling; and removal of the 2nd and 3rd laterals (thinning) before or after chilling. After pruning and chilling treatments, the shoots were removed from the orchard or cold room every two weeks and forced in a growth chamber. The rate of bud burst (1/days to 50% bud burst) was calculated for the terminal buds of the lateral shoots. Laterals were categorisation according to position: the terminal extension shoot, the 4th lateral, and all other laterals were pooled. Removing distal tissue by pruning (heading more than thinning) promoted bud burst on laterals. Pruning before chilling was more effective than after chilling. The correlative phenomena that inhibit bud burst on proximal shoots within two-yearold branches were manipulated by pruning. The branching response of one-year-old unbranched shoots, 0.5m long, from 'Royal Gala' and 'Cripps' Pink' apple and 'Rosemary' pear were studied after physical manipulation treatments. Shoots for treatment a to d were re-orientated from either a horizontal or vertical position or left in the original position as control, treatment e to h involved the same re-orientation of shoots and were headed. The amount of growth (in mm) from each node was recorded as well as the position from the terminal bud. The 'Cripps' Pink' had a definite shift in the acrotonic branching pattern (for headed and unheaded), towards a more basitonic response. The reduced effect on 'Royal Gala' and 'Rosemary' suggest a difference in genotype response to the treatments as well as time of treatment. / AFRIKAANSE OPSOMMING: Ter wille van die navorsing oor die invloed van gebrekige koue op dormansie van apple knoppe en die gepaardgaande probleme is 'n reeks proewe gedoen gedurende 2000 en 2001. Jaar oue onvertakte lote van 'Royal Gala', 'Braeburn' , 'Cripps' Pink' en 'Granny Smith' appels is ewekansig geoes vanaf komersieële boorde in die Koue Bokkeveld [33°S, 945m, ca.1300 Utah koue eenhede (CU)] en Elgin (34°S, 305m, ca.750CU) omgewings van die Wes Kaap , Suid Afrika. Die lote is daarna verkoel gehou by 5- 7°C. Lote is elke twee weke vanuit die koue kamer geneem en geforseer met 25°C en deurlopend belig. Die aantal knoppe wat groenpunt bereik het is genoteer totdat 25% van die lote begin bot. Die verandering oor tyd vir elke boord is bereken en 'n liniëre of kwadratiese funksie is daarop gepas. Swak gekorreleerde waardes is gekies wat die funksies die beste beskryf. D.m.v hierdie die waardes is die boorde in groepe ingedeel wat 'n dormansie patroon verteenwoordig. Na die eerste vedeeling is die hoë en lae koue behoefte kultivars geskei. In opvolgende verdelings is die boorde verder in die twee areas geskei met elk 'n spesifieke dormansie patroon. Die groepe wat die warmer area se boorde bevat het aanvanklik dieper in dormansie in beweeg voor dit 'n styging in groei potensiaal getoon het. Die groepe vanaf die kouer produksie area het onmiddelik 'n verhooging in bot tempo getoon. Die data bevestig dat 'n koue behoefte 'n periode van dormansie induksie insluit. 'n Belangrike kultivaromgewing- interaksie, ten spyte van koue eenhede akkumulasie, is waargeneem wat verantwoordlik kan wees vir beëindiging van dormansie. Om die verandering van water status in dormante appel knoppe te bestudeer, was die volgende proef uitgevoer. Terminale apple knoppe van dieselfde vier kultivars en vanaf die selfde twee areas in die Wes Kaap as bogenoemde, is elke tweede week gedurende die winter 2001 gesny vanaf komersieële boorde. Daarna is die knoppe middel deur gesny en die skudblare verwyder voor die vars massa gemeet en daarna die waterpotensiaal bepaal is. Die data het bevestig dat daar veranderings in beskikbaarheid van vry water in dormante knoppe gedurende dormansie plaasvind. 'n Definitiewe invloed van temperatuur op waterpotensiaal is geïllustreer. Die waterpotensiaal van knoppe in die kouer produksie area toon 'n meer normale respons (gedurende die winter is die water in 'n gebonde vorm, wat later in die winter na vry water verander). Daar teenoor is daar in die knoppe van die warm produksie area nie veel verandering in waterpotensiaal of water massa getoon nie. Gedurende die winter van 2000 is twee jaar oue proleptiese vertakte 'Royal Gala' lote, ongeveer 500mm lank, gekies vanaf 'n boord in die Koue Bokkeveld. Die lote is verdeel en het twee koue behandelings ontvang. Koue kamer by 5-T'C en natuurlike koue in die boord. In 2001 is net die natuurlike koue behandeling herhaal. Daar is vyf dormante snoei behandeling op die lote gedoen; kontrole (geen), snoei terug tot die vierde lateraal voor en na die koue; verwydering van die 2de en 3de laterale voor en na koue. Na koue en snoei is die lote verwyder en in die groeikamer geforseer by 25°C en met konstante illuminasie. Die tempo waarteen die laterale gebot het is bereken (1\dae to 50% groen punt) waarna die laterale in klasse gedeel is; terminale knop, die vierde lateraal en die res van die laterale saam. Verwydering van distale weefsel d.m.V. snoei verhoog die tempo waarteen laterale knoppe groenpunt bereik. Snoei voor die koue behandeling was meer effektief as daarna. Die korrelatiewe fenomeen wat bot inhibeer van proksimale lote kan gemanipuleer word in die twee jaar apple loot. Die vertakkings gedrag van een jaar oue onvertakte 'Royal Gala', 'Cripps' Pink' apple en 'Rosemary' peer lote, 0.5m lank, is ondersoek na fisiese manipulasies gedoen is gedurende mid winter 2000. Vir die eerste vier behandelings (a,b,c,d) is die lote in 'n horisontale of vertikale possisie gelos as kontrole, of horisontale of vertikale gebuig en daar gehou d.m.v. binddraad. Behandelings e tot h het dieselfde behels maar die lote is ook nog in die helfte deur gesny (getop). Die hoeveelheid groei in mm vir elke node is aangeteken asook die posisie vanaf die terminale knop. Die 'Cripps' Pink' het 'n definitiewe veskuiwing vanaf 'n akrotoniese na 'n basitoniese vertakkingspatroon getoon. Die reaksies op die manipulasies of die gebrek daaraan ('Royal Gala' en 'Rosemary' ) kan 'n aanduiding wees dat genotipes verskillend reageer op die behandelings asook op die tyd wat dit gedoen was.

Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Research was carried out to increase the current knowledge on sunburn development and its control in apples. In addition to its chief causes, viz. high irradiance and high temperatures, water stress has long been thought to contribute to sunburn susceptibility. Certain fruit chemical and textural characteristics have also been suspected to increase sunburn, while it is not clear how factors such as crop load affect sunburn in relation to other fruit quality parameters. In red and blushed cultivars, sunburn could be underestimated due to masking by the red colour overlay. Half and total irrigation water were withheld for two weeks in ‘Cripps’ Pink’ apples while in a concomitant trial, mulching with vermicompost (plus a thin layer of woodchips), woodchips, plant compost and black geotextile were used to regulate plant water by reducing soil evaporative loss. Sunburn increased with an increase in moisture stress. Mulching had no effect on plant water status, but it generally enhanced plant photochemistry, reducing fruit surface temperature (FST) and sunburn. Chemical and textural characteristics of exposed, but non-burned ‘Cripps’ Pink’ apples were compared with that of fruit with induced and naturally occurring sunburn. Flesh firmness, total soluble solids (TSS), and titratable acidity (TA) of induced and naturally occurring sunburnt fruit did not differ from each other, but were significantly different from the non-burnt fruit. Based on this, we concluded that sunburn induces textural and compositional changes in sunburnt fruit rather than some fruit being predisposed to develop sunburn due to their texture and chemical composition. Differences in heat stress tolerance, flesh texture and chemical composition of sun exposed and shaded fruit sides seem to relate to their light exposure history. The effect of crop load on sunburn and fruit quality were assessed on a fruit cluster level in 2008-09 and on a whole tree basis in 2009-10 in ‘Cripps’ Pink’. In 2008-09, sunburn, red colour and the proportion of first grade fruit decreased with an increase in number of fruit per cluster. Crop load did not have an effect on sunburn and fruit colour in 2009-10 although the lowest thinning severity seemed to increase sunburn severity while the proportion of first grade fruit was highest for the highest thinning severity. Fruit number per cluster had no effect on fruit size, while at the whole tree level, fruit size decreased with increasing crop load. Flesh firmness, starch breakdown, TA and TSS were neither affected by the number of fruit per cluster nor the crop load of the tree as a whole. Green ‘Granny Smith’ and ‘Golden Delicious’, blushed ‘Royal Gala’, ‘Fuji’, ‘Braeburn’ and ‘Cripps’ Pink’, and full red ‘Topred’ were used to assess how red colour (anthocyanins) masks superficial sunburn browning and bleaching. The greater reduction in superficial sunburn, but not in sunburn necrosis in red and blushed compared to green cultivars with increasing red colour a month towards harvest seemed to confirm the effect of masking. / AFRIKAANSE OPSOMMING: Hierdie navorsing is verrig ter uitbreiding van die huidige kennis oor die ontwikkeling en beheer van sonbrand in appels. Addisioneel tot die hoof oorsake van sonbrand, naamlik hoë irradiasie en hoë temperatuur, word waterstres gesien as bydraend tot sonbrandsensitiwiteit. Daar word ook vermoed dat sekere chemiese en teksturele eienskappe van die vrug sonbrand kan verhoog terwyl daar nie duidelikheid is oor hoe faktore soos oeslading sonbrand relatief tot ander vrugkwaliteitparameters kan affekteer nie. Die omvang van sonbrand in rooi en bloskultivars kan dalk onderskat word vanweë maskering deur die oorliggende rooi pigmentasie. Besproeiing is vir twee weke gehalveer of gestop in ‘Cripps’ Pink’ appels. Sonbrand het toegeneem met ‘n toename in vogstres. ‘n Deklaag van vermikompos (plus ‘n dun laag houtstukkies), houtstukkies, plantkompos en ‘n swart geotekstiel is toegedien om die plant waterstatus te reguleer deur evaporasie vanuit die grond te beperk. Die deklae het geen effek op die plant waterstatus gehad nie, maar het wel die blaar fotochemie bevorder en terselftertyd die vrugoppervlaktemperatuur verlaag en sonbrand verminder. Die chemiese en tekturele eienskappe van sonligblootgestelde ‘Cripps’ Pink’ appels sonder sonbrand is vergelyk met vrugte met geïnduseerde sonbrand en vrugte met sonbrand wat natuurlik ontwikkel het. Vrugvleisfermheid, totale oplosbare vastestowwe (TOV) en titreerbare suur (TS) van vrugte met natuurlik en geïnduseerde sonbrand het nie onderling verskil nie, maar het wel betekesnisvol verskil van vrugte sonder sonbrand. Ons het gevolglik afgelei dat sonbrand teksturele en komposisionele veranderinge teweeg bring eerder as dat sekere vrugte gepredisponeer word om sonbrand te ontwikkel vanweë hul tekstuur en chemiese samestelling. Dit kom voor dat verskille in hittestres toleransie, tekstuur en chemiese samestelling tussen die sonligblootgestelde en skadu kante van appels verband hou met hul verskil in sonligblootstelling. Die effek van oeslading op sonbrand en vrugkwaliteit in ‘Cripps’ Pink’ is ge-evalueer op trosvlak in 2008-09 en op ‘n per boom basis in 2009-10. Sonbrand, rooi kleur en die proporsie eersteklas vrugte het afgeneem met ‘n toename in die aantal vrugte per tros. Op ‘n per boom basis is rooi kleur en sonbrand egter nie deur oeslading geaffekteer nie. Die laagste vlak van vruguitdunning het wel oënskynlik die graad van sonbrand verhoog terwyl die hoogste vlak van vruguitdunning tot ‘n toename in die proporsie eersteklas vrugte gelei het. Die aantal vrugte per tros het geen effek op vruggrootte gehad nie terwyl vruggrootte afgeneem het met oeslading op ‘n heelboombasis. Vrugvleisfermheid, styselafbraak, TOV en TS is nie deur aantal vrugte per tros of die oeslading per boom geaffekteer nie. Groen ‘Granny Smith’ en ‘Golden Delicious’, rooiblos ‘Royal Gala’, ‘Fuji’, ‘Braeburn’ en ‘Cripps’ Pink’, en volrooi ‘Topred’ is gebruik om die maskering van oppervlakkige sonbrandverbruining en –verbleiking deur rooi antosianien te bestudeer. Oppervlakkige sonbrand het minder toegeneem in die maand voor oes in die rooi- en bloskultivars as in die groen kultivars terwyl vrugkleur skynbaar nie die aanwesigheid van die meer sigbare sonbrandnekrose geaffekteer het nie. Maskering speel dus ‘n rol in die aanwesigheid van sigbare sonbrand.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2007. / The production of high quality fruit that meet international standards is of vital importance to the South African fruit industry. Detrimental climatic conditions are forcing producers to examine alternate production methods. In this study the effect of protective netting on apple tree (Malus domestica) physiology, microclimate and fruit quality was investigated to determine the potential of apple production under netting in the Western Cape Province of South Africa. The influence of 20% black shade netting on the photosynthetically photon flux density, leaf and fruit surface as well as air temperature was measured on four blush apple cultivars over a two year period in the Koue Bokkeveld area, in the Western Cape, South Africa. Measurements were also taken on leaf gas exchange, including net CO2 assimilation rate under ambient and saturating CO2 conditions, stomatal conductance, and transpiration rate. A decrease in light conditions of 22 - 31% was measured under black netting thus reducing the amount of light available to the plant significantly. Leaves under the netting were cooler by 1.7 – 3.9°C on a milder day (11 January 2005) and by 4.3 – 6.2°C on a hot day (28 February 2005) than control leaves. Fruit surface temperature under the netting was cooler by 0.7 - 2.9°C on milder days, and by 4.0 - 5.3°C on a hot day (28 February 2005) than control fruit. Significant increases in CO2 assimilation, stomatal conductance and transpiration were found under the netting. Netted treatments also showed a lower leaf vapour pressure deficit and tended to be less water stressed having higher leaf water potential than the control treatments. Differences in leaf nitrogen were not significant between treatments except for ‘Cripps’ Pink’ where non netted treatments had higher leaf nitrogen levels than the netted treatments during the 2004 season. Heat tolerance and the ability to recover after exposure to different temperatures for different lengths of time, was evaluated for the same four blush apple cultivars grown under protective netting. The results showed that fruit taken from the netted treatments had a higher incidence of injury based on chlorophyll fluorescence measurements, and did not recover well at temperatures higher than 45°C. The higher tolerance of the non-netted fruit at 45°C could be due to better acclimation to high light and heat levels than the fruit from the netted treatment. Fruit quality of ‘Royal Gala’, ‘Fuji’, Cripps’ Pink’ and ‘Braeburn’ was evaluated for netted and non-netted treatments as well as between five different crop loads as sun-treatments. It was found that cultivars reacted differently to the altered microclimate under the netting. Significant interaction between net and crop load treatments was found for fruit mass of ‘Royal Gala’ and ‘Fuji’. Fruit mass declined more rapidly with increased crop load under nets than in the open. The net treatment reduced sunburn significantly in all the cultivars except ‘Cripps’ Pink’. Ground colour was found to be positively influenced by netting on ‘Braeburn’ and during 2005 on ‘Royal Gala’. Blush colour was reduced under the netting for ‘Braeburn’ and ‘Fuji’ and unaffected for ‘Royal Gala’ and ‘Cripps’ Pink’. Fruit firmness, total soluble solids and titratable acidity, were reduced under nets for most of the cultivars. Netting thus seems to have a positive effect in reducing sunburn damage but a varying effect on other fruit quality parameters, which seem to be cultivar specific. The influence of black protective netting on vegetative growth was determined by measuring total prunings and trunk circumference. Reproductive bud development analysis was also done. An increase was found in summer prunings for ‘Fuji’ and ‘Cripps’ Pink’ which was most likely due to the topping of the trees to prevent them from growing into the netting. Seasonal trunk growth was affected significantly for ‘Braeburn’ with a higher percentage recorded under the netting. Reproductive bud development was higher for the netted treatments and on trees with lower crop loads. Photosynthetic photon flux density was reduced significantly in a ‘Granny Smith’ orchard at harvest by black, blue and grey type netting. Sunburn was significantly reduced under the black and blue netting. Fruit mass was higher under the netted treatments during the second season of measurements. Firmness and total soluble solids were lower under the netting. Blush colour was found to be significantly lower under the black netting. Seed viability, ground colour, titratable acidity, starch breakdown, stem end russet and the occurrence of Fusicladium pyrorum damage was unaffected by the netting.

Thesis (MScAgric)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Sunburn is a major problem in the apple industry worldwide. A kaolin product, M-97- 009 (100% kaolin), originally developed for insect control, was evaluated for its efficacy in controlling sunburn on pome fruit. Trials were conducted over two seasons in two different areas of the Western Cape, South Africa. During the first season, 'Royal Gala', 'Fuji' and 'Granny Smith' apples were evaluated in the Koue Bokkeveld. The kaolin was mixed with water and applied to the trees by means of a hand-gun regularly throughout the season. In addition to the effect on sunburn, effects on yield, colour development, snout beetle damage and other defects were determined. Sunburn was reduced on all the cultivars tested, although not significantly on 'Granny Smith'. Inconsistent effects on yield parameters were observed. The applications significantly reduced red colour on 'Fuji', but this problem was rectified by an improved application technique the following season. During the second season, additional apple cultivars and 'Rosemarie' pears were included in the trials. The apple trials were conducted in the Elgin area, and the 'Rosemarie' trial in the Koue Bokkeveld. Surround™ (95% kaolin) was applied to the trees by means of a commercial "blower". The effects on sunburn, yield, colour development and fruit maturity were determined. In contrast to the previous season, sunburn was not reduced on any of the cultivars examined. Yield parameters were not affected except in the case of 'Royal Gala' where the number of fruit was increased, and 'Cripps' Pink' where the number of fruit was reduced. Fruit colour was not affected in the apple cultivars, but chroma of 'Rosemarie' pears was reduced, indicating a less intense colour. The kaolin applications had a variable effect on fruit maturity. The effect of the foliar applications on photosynthetic photon flux density (PPFD), photosynthetic rate, stomatal conductance and transpiration rate was determined. In addition to these spot measurements, photosynthetic light response curves were determined. Measurements were taken on both the inner and outer canopies The applications significantly reduced photosynthetic rates in the inner canopy and reduced the apparent quantum efficiency of leaves on the outer canopy. No significant effect on PPFD was found. It appears that the white coating reflects light and allows less light to penetrate the leaf, thus reducing photosynthesis. Surround™ treatments could not counteract the damaging effects of the high temperatures experienced in the Western Cape during this season and was not effective as a control measure for sunburn. This does not appear to be a commercially viable solution for the sunburn problem and it would be worthwhile to investigate the use of alternative options, such as evaporative cooling. / AFRIKAANSE OPSOMMING: Sonbrand is een van die grootste probleme wat wêreldwyd in die appelbedryf ondervind word. 'n Nuwe produk, M-97-009 (100% kaolien), is oorspronklik ontwikkel vir insekbeheer in geïntegreerde plaagbeheer, maar daar is beweer dat dit moontlik sonbrand op kemvrugte kan verminder. Proewe is oor twee seisoene uitgevoer in die Koue Bokkeveld en ook in die Grabouw-omgewing in die Wes-Kaap. Tydens die eerste seisoen is die effek van M-97-009 op 'Royal Gala', 'Fuji' en 'Granny Smith' appels beoordeel. Die kaolien is met water gemeng en deur die loop van die seisoen met 'n handspuit op die bome gespuit. Die effek van die produk op sonbrand, oesgrootte, vruggrootte, kleurontwikkeling, kalanderskade en ander defekte is bepaal. Sonbrand is op alle kultivars verminder, alhoewel nie betekenisvolop 'Granny Smith' nie. Die effek van kaolien op oesparameters was rue konsekwent nie. kleurontwikkeling op 'Fuji' benadeel, heel moontlik Die toedienings het as gevolg van die toedieningstegniek. Met verbeterde toedieningsmetodes die volgende seisoen, is kleurontwikkeling van 'Fuji' nie benadeel nie. Tydens die tweede seisoen is die effek van kaolien op nog appelkultivars en 'Rosemarie' pere ge-evalueer. Die appelproewe is in Elgin uitgevoer, terwyl die 'Rosemarie'-proefin die Koue Bokkeveld uitgelê is. Surround™ (95% kaolien) is met kommersiële spuitpompe toegedien. Weereens is die effek van die produk op sonbrand, oesgrootte, vruggrootte, kleurontwikkeling en vrugrypheid bepaal. Sonbrand is nie verminder nie. Vruglading tydens oes is nie betekenisvol beïnvloed nie, behalwe in die geval van 'Royal Gala' waar die vruglading verhoog is, en 'Cripps' Pink' waar daar minder vrugte op die gespuite bome was. Die Surround™ toedienings het geen uitwerking op kleur van appels gehad nie, maar het die chromawaarde van 'Rosemarie' pere verlaag, d.w.s die vrugkleur was minder intens. Die kaolienspuite het 'n uiteenlopende effek op vrugrypheid gehad. Fotosintetiese foton vloeddigtheid (FFV), fotosintesetempo, huidmondjieweerstand en transpirasietempo is gemeet en ligreponskurwes van beide die buitenste en binneste blaardak is bepaal. Die Surround™ toedienings het fotosintese van blare ill die binneste gedeelte van die blaardak verminder en die kwantumdoeltreffendheid van blare op die buitenste deel van die blaardak verminder. Geen betekenisvolle effek is op FFV gekry nie. Dit wil voorkom asof die wit laag kaolien op die bome lig weerkaats en veroorsaak dat minder lig na die blaar deurdring. Dit verminder dan die fotsintesetempo. Met die baie warm weer wat in die Wes-Kaap gedurende die tweede seisoen ervaar is, kon die SUITound™behandelings nie sonbrand verhoed nie. Dit wil voorkom asof Surround™ nie 'n baie doeltreffende oplossing in kommersiële boorde sal wees nie. Alternatiewe oplossings, soos byvoorbeeld evaporatiewe verkoeling, saloorweeg moet word.

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Delayed foliation is commonly observed in apple and pear producing countries with warm and/or short winter climates, resulting in less synchronised budburst, of fewer buds and reduced yield. Applications of rest-breaking agents minimise the symptoms of delayed foliation. According to chilling models used in fruit producing areas of the world, the climate of South Africa is not suitable for deciduous fruit production, however fruit has been successfully produced here for a long time. This study aimed to quantify the effects of freezing temperatures, different chilling temperatures and the period of chilling, to obtain a better knowledge of bud dormancy release on apple and pear shoots. The chilling period was the most important factor influencing the progression of dormancy. While in some cases the chilling temperature and the freeze treatment effects were significant, the contribution to differences in the progression of dormancy was negligible. Our findings indicate that currently used chilling models should emphasise the time of exposure to low temperatures more than the difference in temperatures between I to ro-c. The South African apple and pear industry made good progress in moving towards high density plantings, but large variation in soil types, non-optimum growing conditions, replant situations and a lack experience with dwarfing rootstocks limited further development. However, there is sti II an urgency to obtain higher early yields of good quality fruit applying the most efficient production practices. We aimed to quantify the field performance of locally available apple and pear rootstocks, in particular from data outside of previously reported local trials, as well as early production of newly planted trials. Information obtained form the industry indicates that BPI and BP3 are the preferred pear rootstocks. From production records of 'Packham's Triumph' pears, it appeared that BP3 and OHxF97 produced the best yields compared to the other rootstocks. Production of 'Doyenne du Cornice' was the best on QA and BP3. In newly planted 'Rosemarie', 'Flamingo', and 'Forelle' trials, different rootstocks were evaluated. 'Rosemarie' showed indications 01 incompatibility with QA and QC5 I, but on BPI and QA with a 'Beurre Hardy' interstock produced good initial yields although BPI induced slightly larger trees. 'Flamingo' on QA and QC51 produced the best yields. 'Forelle' on BPI, BP3, and QA produced similar yields up to the 4th leaf. For apples M793 seems to be the preferred rootstock in the South African industry. From production records of 'Golden Delicious' and 'Granny Smith' apples, it appeared that M793 and MM 106 produced the best yields when compared to Seedling rootstock. In a 'Cripps' Pink' trial, MMI09, M793 and M25 were more vigorous than M7, MMlll and MMI06. MMI06 was cumulatively, over four years from planting, the most yield efficient, although no consistent trend regarding fruit quality was observed between the rootstocks evaluated. / AFRIKAANSE OPSOMMING: Vertraagde bot word algemeen opgemerk in appel en peer produserende lande met n' warm enlof kort winter klimaat, wat veroorsaak dat bot van minder knoppe, meer ongelyk plaasvind en gevolglik lei tot swakker opbrengste. Toediening van rus-breek middels beperk die simptome van vertraagde bot. Volgens koue modelle wat in vrugte produserende areas in die wereld gebruik word, is Suid Afrika se klimaat nie geskik vir die verbouing van sagtevrugte nie alhoewel sagtevrugte al vir n lang tyd met groot sukses hier verbou word. Hierdie studie is daarop gemik om die effek van vries temperature, verskillende koue temperature en die periode van koue op die vrystelling van dormansie op knoppe van appel en peer lote te kwantifiseer. Die peri ode van koue was die mees belangrikste faktor wat die ontwikkeling van dormansie beinvloed het. In sommige gevalle was die effek van die koue temperature betekenisvol, maar die bydrae tot die verskille in die ontwikkeling van dormansie was weglaatbaar klein. Ons bevindinge dui aan dat die huidige koue modelle wat gebruik word, meer klem moet le op die periode van blootstelling aan koue as aan die effek van verski llende temperature tussen 1 en 10°e. Die Suid Afrikaanse appel en peer bedryf het goeie vordering in die beweging na hoe digtheid aanplantings gemaak, maar groot verskille in grond tipes, sub-optimale groei toestande, herplant probleme en n' tekort aan ondervinding met dwergende onderstamme het verdere ontwikkeling beperk. Ten spyte hiervan is daar steeds n' dringendheid om hcer produksies, van goeie kwaliteit vrugte so vroeg as moontlik te kry deur die toepassing van die mees effektiewe produksie praktyke. Ons het gepoog om die prestasie van plaaslik beskikbare appel en peer onderstamme te kwantifiseer, in besonder deur data wat nog nie van tevore oor verslag gedoen is nie en ook deur te meld van vroee produksies op nuut aangeplante proewe. lnformasie uit die bedryf het aangedui dat BP 1 en BP3 die voorkeur peer onderstamme is. Deur na die produksie geskiedenis van 'Packham's Truimph' pere te kyk kom dit voor of BP3 en OHxF97 die beste produksies in vergelyking met die ander onderstamme gelewer het. Die produksie van 'Doyenne du Com ice' was die beste op QA en BP3. In nuut geplante 'Rosemarie', 'Flamingo', en 'Forelle' pro ev e was verskillende onderstammc gecvalueer. 'Rosemarie' het tekens van onverenigbaarheid getoon met QA en Q 51, maar op BP 1 en QA met n 'Beurre Hardy' tussenstam het 'Rosemarie' goeie aanvanklike opbrengste gel ewer, al was bome op BP 1 effens grater. 'Flamingo' op QA en QCS 1 het die beste opbrengste gelewer. 'Forelle' op BP 1, BP3, en QA het ongeveer ewe veel tot die 4dc blad geproduseer. By appels is M793 die voorkeur onderstam van die Suid-Afrikaanse appel bedryf. M793 en MM 106 gee beter opbrengste as Saailing onderstam wanner die produksie geskiedenis van 'Golden Delicious' en 'Granny Smith' appels evalueer word. In n' 'Cripps' Pink' proefwas MMI09, M793 en M2S meer groeikragtig as M7, MMlil en MMI06. MM I 06 het kumulatief meer geproduseer en was ook meer produsie doeltreffend tot en met die 4de blad na plant. Daar was egter geen konstante neiging rakende vrug kwaliteit tussen die verskillende onderstamme wat getoets is nie.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Peel colour is an important quality factor in the production of bi-coloured apple fruit. Most markets set minimum requirements for red colour coverage. Fruit that do not meet these requirements are downgraded and has a major impact on the profitability of apple production in South Africa. South African apple production areas are amongst the warmest in the world. Since anthocyanin accumulation requires induction at low temperature and synthesis require mild temperatures, experiments were conducted to investigate optimum day and night temperatures for red colour development throughout fruit development for red and bi-coloured apple cultivars grown in South Africa. We found that redder strains of bi-coloured apple cultivars did not appear to owe their enhanced pigmentation to higher temperature optima for anthocyanin synthesis. The optimum day temperatures for red colour development in the different cultivars seemed to differ between seasons, but not between production areas. In general, red colour in the cultivars evaluated developed maximally between 17 ºC and 25 ºC. The optimum day temperature for red colour development remained constant throughout fruit development for most cultivars, but increased roughly from 14 ºC to 22 ºC in ‘Cripps’ Pink’ between January and April. The extent of red colour development increased during fruit development in all the cultivars assessed. We were unable to determine optimum induction temperatures for red colour development. ‘Royal Gala’ from Ceres seemed to benefit from induction at 4 ºC while red colour in ‘Fuji’ decreased with decreasing temperature. To explain the presence of anthocyanins in immature apple fruit, we tested the hypothesis that anthocyanins protect the peel from photoinhibition and photooxidative damage during conditions of increased light stress. First we established that the rate of colour change in response to a passing cold front appears to be sufficient to provide photoprotection during a cold snap. Also in agreement with the hypothesis, ‘Cripps Pink’ peel incurred significantly more photoinhibition at low temperature (16 ºC) compared to mild (24 and 32 ºC) and high (40 ºC) temperature under high irradiance with visible light. Recovery rate was temperaturedependent, being the slowest at low temperature and increasing with temperature. The photoapparatus in ‘Cripps Pink’ peel appears to be particularly sensitive to light stress at low temperature throughout the season, with significant photoinhibition occurring even at moderate temperature (24 ºC). The sensitivity of the apple peel to photoinhibition increased throughout the season at lower irradiance levels, but remained the same at higher irradiance. In our final experiment, fruit were exposed to high irradiance at low and mild temperature before exposure to high temperature in combination with high irradiance. This was done to test the hypothesis that photoinhibition incurred during cold snaps predisposes peel to photothermal damage when temperature increases again after the cold snap. Unfortunately, due to the severity of the stress incurred in response to high temperature treatment, the results were inconclusive. / AFRIKAANSE OPSOMMING: Vrugkleur is ‘n belangrike kwaliteitsfaktor in die produksie van tweekleurappels. Die meeste markte stel minimum vereistes vir rooi kleurbedekking. Vrugte wat nie aan hierdie vereistes voldoen nie, word afgegradeer. Suid-Afrika se appel produksie areas word beskou as van die warmste ter wêreld. Antosianien akkumulasie benodig induksie by lae temperature gevolg deur sintese in lig by matige temperature. Gevolglik het swak rooi kleurontwikkeling onder plaaslike toestande ‘n groot impak op die winsgewendheid van appelproduksie in Suid-Afrika. Eksperimente is uitgevoer om die optimum dag- en nagtemperature vir rooi kleurontwikkeling tydens vrugontwikkeling vir die rooi en tweekleur appel kultivars wat in Suid-Afrika geproduseer word te bepaal. Ons het gevind dat die verhoogde pigmentasie van rooier seleksies van tweekleurappel kultivars nie aan ‘n hoër temperatuur optimum vir antosianiensintese toegeskryf kan word nie. Die optimum dag temperature vir rooi kleurontwikkeling vir die onderskeie kultivars verskil klaarblyklik tussen seisoene, maar nie tussen produksie areas nie. Oor die algemeen het kleurontwikkeling maksimaal plaasgevind tussen 17 ºC en 25 ºC. Die optimum dagtemperatuur vir rooi kleurontwikkeling het konstant gebly tydens vrugontwikkeling, buiten vir ‘Cripps’ Pink’ waar dit toegeneem het van ongeveer 14 ºC tot 22 ºC vanaf Januarie tot April. Die mate van rooi kleurontwikkeling het in al die kultivars toegeneem deur die loop van vrugontwikkeling . Ons kon nie daarin slaag om optimum induksie temperature vir rooi kleurontwikkeling vas te stel nie. Rooi kleurontwikkeling van ‘Royal Gala’ uit Ceres is moontlik bevorder deur induksie by 4 ºC, terwyl ‘Fuji’ se rooi kleur afgeneem het met ‘n verlaging in induksie temperatuur. Ten einde die teenwoordigheid van antosianien in onvolwasse appelvruggies te verduidelik, het ons die hipotese getoets dat antosianien die vrugskil beskerm teen fotoinhibisie en fotooksidatiewe beskadiging gedurende tydperke van verhoogde ligstres. Eerstens het ons bevestig dat die tempo van kleurontwikkeling in reaksie op ‘n koue front waarskynlik vinnig genoeg is om fotobeskerming te verleen. Vervolgens is gevind dat ‘Cripps’ Pink’ vrugskil aansienlik meer fotoinhibisie ervaar het by lae temperatuur (16 ºC) in vergelyking met matige (24 ºC en 32 ºC) en hoë (40 ºC) temperatuur onder hoë irradiasie met sigbare lig. Die hersteltempo was temperatuur-afhanklik; dit was die stadigste by lae temperatuur en het toegeneem met ‘n toename in temperatuur. Die foto-apparaat in ‘Cripps’ Pink’ vrugskil blyk besonder sensitief te wees vir ligstres by lae temperatuur regdeur die groeiseisoen met aansienlike fotoinhibisie by selfs matige temperatuur (24 ºC). Die sensitiwiteit van die vrugskil vir fotoinhibisie het toegeneem deur die groeiseisoen by laer ligvlakke, maar het dieselfde gebly by hoër vlakke van irradiasie. Laastens is vrugte blootgestel aan hoë irradiasie by lae en matige temperatuur voordat dit vervolgens blootgestel is aan hoë temperatuur in kombinasie met hoë irradiasie. Dit was om die hipotese te toets dat fotoinhibisie wat opgedoen word gedurende ‘n onverwagte koue periode, die skil meer vatbaar maak vir fototermiese skade sodra die temperatuur weer styg na die koue periode verby is. Ongelukkig het die hoë temperatuur stres al die behandelings tot so ‘n mate geaffekteer dat dit onmoontlik was om enige gevolgtrekkings vanuit ons resultate te maak.

Thesis (MSc (Horticulture))--University of Stellenbosch, 2006. / A growing number of fruit producers in warm areas are adopting the use of overtree evaporative cooling (EC) as a technique to reduce sunburn and enhance colour development of red or blushed fruit. Because fruit do not have efficient mechanisms of utilising and/or dissipating solar radiation, fruit surface temperature may rise 10 – 15oC higher than the ambient air temperature, making them very susceptible to sunburn. Sunburn negatively affects the appearance of the fruit, and they cannot be sold for fresh market consumption, which receives the highest prices. Evaporative cooling uses a sprinkler system to cool the trees from above. Energy needed to evaporate the water is extracted from the fruit skin, cooling the fruit down. The air around the trees is cooled, and a more favorable microclimate is created in the orchard. Producers have also found that the use of EC just prior to sundown and sometimes around sunrise has improved colour development on red apples (especially early varieties) before harvest. In this study, two apple (‘Cripps’ Pink’ and ‘Royal Gala’) and two pear (‘Rosemarie’ and ‘Forelle’) cultivars under EC were compared with control fruit in terms of maturity, colour, sunburn and concentrations of polyphenolics in the skin. Two EC treatments were given; early application starting from the second week in December, and late application starting two to four weeks before harvest. Photosynthetic responses were measured, as well as fruit and leaf temperatures. Underlying physiological responses of trees and fruit to EC were investigated, particularly the phenomenon of acclimation and the potential for colour development and heat stress. Fruit surface temperature of fruit under EC was found to be significantly lower than control fruit. In both apple cultivars a significant increase in fruit skin anthocyanin concentration and a decrease in phenolic content was found as the season progressed. In both pear cultivars there was a significant decrease in both anthocyanin and phenolic. No significant differences were found in anthocyanin content between treatments in either the apple or pear cultivars. In both apple cultivars a higher phenolic content was found in the peel of the EC treatments. A decrease of up to four percent in leaf and fruit surface temperature was found under EC. No significant difference in trunk circumference was found in any of the cultivars. The late EC treatment in ‘Cripps’ Pink’ had a significantly faster rate of budbreak than the control and early EC treatments. Significantly higher transpiration was observed in leaves under EC. ‘Royal Gala’ fruit under EC had less sunburn than control fruit. Unfortunately the system broke down on a hot day, causing more sunburn on ‘Cripps’ Pink’ fruit under EC. Heat tolerance of apple fruit grown under EC was evaluated in ‘Cripps’ Pink’ and ‘Royal Gala’ by determining the maximum quantum yield of chlorophyll fluorescence (Fv/Fm). Measurements were also made 12 hours after the heat treatments to determine recovery. ‘Cripps’ Pink’ fruit from both EC treatments, but particularly the early EC treatment, were less resistant to heat stress than control (non-EC) fruit at the “threshold” air temperature of 45°C. Apples were able to recover from heat treatments in the range of 32-38oC fruit surface temperature, and generally also recovered fully after 43-45°C fruit surface temperature when exposure did not exceed four hours. This knowledge could be helpful in the management of sunburn, for example when determining the threshold temperature for the activation of evaporative cooling treatments. Knowledge about the various effects evaporative cooling and the subsequent lowering of ambient temperatures has on fruit trees and fruit could contribute greatly to producers’ ability to grow high quality fruit. EC can be used successfully for controlling sunburn and increasing fruit colour, but the system needs to be controlled very carefully and care should be taken that it does not fail on a hot day, as it did during this study.