Thesis (Ph. D.)--University of Wisconsin-Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Thinning of stone fruit, just as in any other deciduous fruit crop, plays an important role in producing fruit of the right size and quality. Hand thinning is highly labor intensive and time consuming, thus an alternative method of thinning is important to the industry. Chemical and mechanical thinning either alone or in combination could be the alternative. Two chemicals, 1-aminocyclopropane-1-carboxylic acid (ACC) and 6-benzyladenine (6-BA) were evaluated on Japanese plums, cling peaches and nectarines. In addition, the Darwin 300™, a mechanical string thinner, was also included in trials on early maturing ‘Alpine’ nectarine and ‘African Rose™’ plum. In all trials the objective was to reduce the required hand thinning during commercial hand thinning without compromising on yield and fruit quality. In Japanese plums we were able to reduce the hand thinning requirement significantly with both the ACC thinning and mechanical thinning strategies. Regarding ACC, cultivars differed in their sensitivity to the chemical and the recommended rate will differ for cultivars. ACC consistently reduced the required hand thinning linearly with increasing rate. The recommended rate of ACC for ‘African Rose™’ is 600 μl.L-1 and for ‘Laetitia’ 400 μl.L-1. For ‘Fortune’ a recommended rate could not be determined at this stage, thus further trials should be conducted. The Darwin 300™ reduced hand thinning significantly without reducing the yield significantly. Combining the Darwin 300™ with ACC 600 μl.L-1 in ‘African Rose™’ gave promising results with regard to hand thinning requirement and fruit size, without reducing yield efficiency significantly. No leaf drop was observed on Japanese plums, except in the pilot trial when applications were made at high temperatures, which should therefore be avoided. ACC was effective as thinning agent in cling peaches. In ‘Keisie’, the results were positive during both seasons, and ACC reduced the hand thinning requirement without reducing yield efficiency. The recommended rate of ACC for ‘Keisie’ is 600 μl.L-1. Slight leaf drop was observed. In ‘Sandvliet’, there was a significant reduction in fruit set, without reducing the required hand thinning. The reduction in fruit set led to a significant reduction in yield. Severe leaf drop was observed, indicating that cultivars differ in sensitivity to ACC. ACC would not currently be recommended for ‘Sandvliet’. In nectarines, ACC only thinned ‘Turquoise’ but not ‘Alpine’ or ‘August Red’ at the rates and phenological stage used, again indicating cultivar differences in sensitivity. In ‘Turquoise’, the highest ACC rate (500 μl.L-1) reduced fruit set per tagged shoot, as well as the hand thinning requirement, but this rate also reduced the total yield. The Darwin 300™ evaluated on ‘Alpine’ reduced fruit set significantly and the hand thinning requirement without reducing yield efficiency, indicating that mechanical thinning is a viable option in nectarines. Slight leaf drop was observed in all nectarine trials and ACC would not currently be recommended for nectarines. 6-BA was included to combat ACC-induced leaf drop and was partially successful. The reason for the differences observed in response to ACC between cling peaches and plums on the one hand, and nectarines on the other, cannot currently be explained. / AFRIKAANSE OPSOMMING: Uitdun van steenvrugte, net soos vir enige ander sagtevrugte soort, speel 'n belangrike rol in die produksie van vrugte met die regte grootte en gehalte. Uitdun van steenvrugte is hoogs arbeidsintensief en tydrowend, dus is dit belangrik om ʼn alternatief te vind vir die bedryf. Chemiese of meganiese uitdunning alleen of in kombinasie kan die alternatiewe wees. Twee middels, 1-aminosiklopropaan-1-karboksielsuur (ACC) en 6-bensieladenien (6-BA) is geëvalueer op Japanese pruime, taaipitperskes en nektariens. Daarby is die Darwin 300™, ʼn meganiese uitdunmasjien, ingesluit vir twee vroeë kultivars, nl. Alpine nektarien en African Rose™ pruim. Die doel van die proewe was om handuitdunning tydens kommersiële handuitdun te verminder, sonder om die opbrengs en vrugkwaliteit negatief te beïnvloed. Vir Japanese pruime kon ons die nodige handuitdunning beduidend verminder met beide die ACC en meganiese uitdun strategieë. Daar was wel ʼn verskil tussen die kultivars se sensitiwiteit teenoor ACC en die aanbevole konsentrasie sal verskil tussen kultivars. ACC het die benodigde handuitdunning vir al drie kultivars lineêr verminder met ʼn toename in konsentrasie. Die aanbevole konsentrasie van ACC vir ‘African Rose ™’ is 600 μl.L-1 en vir ‘Laetitia’ 400 μl.L-1. Vir ‘Fortune’ kan daar nog nie op hierdie stadium 'n konsentrasie aanbeveling gemaak word nie. Die Darwin 300™ behandeling het die benodigde handuitdunning beduidend verminder sonder om die opbrengs te beïnvloed. Die kombinasie van die Darwin 300 ™ met ACC 600 μl.L-1 het ook goeie resultate opgelewer wat handuitdunning en vruggrootte aanbetref sonder om die opbrengsdoeltreffendheid te verlaag. Geen blaarval was opgemerk by die pruime nie, behalwe in ʼn voorlopige proef toe die ACC toegedien is by hoë temperature, wat dus vermy moet word. Die effektiwiteit van ACC as uitdunmiddel van taaipitperskes was belowend. Vir ‘Keisie’ was die resultate positief vir beide seisoene, en ACC het handuitdunning verminder sonder om die opbrengs te beïnvloed. Die aanbevole ACC konsentrasie vir ‘Keisie’ is 600 μl.L-1. Effense blaarval is wel waargeneem. Vir ‘Sandvliet’ was daar 'n beduidende vermindering in vrugset, sonder dat handuitdunning verminder is. Daar was ook 'n beduidende afname in opbrengs en erge blaarval in die proef waargeneem. ACC sal tans nie aanbeveel word vir 'Sandvliet’ nie. Met nektariens het ACC net ‘n uitduneffek op ‘Turquoise’ getoon, maar nie teen die aangewende dosisse en ontwikkelingstadium op ‘Alpine’ of ‘Augustus Red’ nie. Dit dui daarop dat ACC kultivarspesifiek mag wees. In ‘Turquoise’ het die hoogste konsentrasie (500 μl.L-1) vrugset van gemerkte lote en die handuitdunning verminder, maar ook die totale opbrengs. Die Darwin 300 ™ het die vrugset van ‘Alpine’ asook die benodigde handuitdunning aansienlik verminder sonder om die opbrengs te verlaag. Effense blaarval was opgemerk in alle nektarien proewe. ACC sal nie aanbeveel word as uitdunmiddel vir nektariens nie. 6-BA was in die studie ingesluit om ACC-geïnduseerde blaarval teen te werk en was slegs gedeeltelik suksesvol. Die rede vir die verskille in respons tot ACC tussen pruime, perskes en nektariens kan nie tans verklaar word nie.

Thesis (Ph.D.) -- University of Western Sydney, Hawkesbury, 1998. / Thesis submitted for the degree of doctor of philosophy. Reprints of related publications by N. Abdi, P. Holford and W.B. McGlasson included in back. Includes bibliographical references (leaves 129-152).

Nectarines suffer low temperature disorders (LTD)when stored for more than 2 - 3 weeks at temperatures below 8 degrees C. LTD take the form of flesh bleeding and browning, loss of juiciness, development of mealiness and failure to ripen normally.It has been shown previously that adding about 15% CO2 to the storage atmosphere at 0 degrees C can delay the development of LTD in some cvv. of peaches and nectarines. The initial aim of this research was to explore the genetic basis of the differences among cultivars in the responses to high CO2.After much investigation, it was shown that both genetic and seasonal factors are involved in the development of LTD in nectarines. The development of LTD is a form of chilling injury since they only occur at temperatures below 8 degrees C. but there was no evidence of of a direct role for ethylene in either causing or delaying LTD. It was proposed that storage at low temperatures causes a metabolic imbalance resulting from changes in the amounts or activities of proteins associated with normal ripening. Proposals were presented to further examine protein expression using storage conditions that affect the rate of development of LTD. / Doctor of Philosophy (PhD)

Thesis (Ph.D.)--University of Western Sydney, 2003. / "A thesis presented in fullfillment of requirement for the degree of Doctor of Philosophy."--t.p. "June 2003" Includes bibliographic references.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Producing fruit of the appropriate size and high quality is of the upmost importance to realize a profit in the fruit industry. This can be achieved through bloom or fruitlet thinning to reduce the number of fruit left on the tree. The cost of production is rising and labour cost forms a large part of the total production cost. Thinning of stone fruit is labour intensive and expensive, so an alternative to hand thinning needs to be found. Two alternatives are chemical and mechanical thinning. Chemical thinners are not routinely used in stone fruit as it is in pome fruit production and gibberellins were evaluated in this study. The Darwin 300TM was evaluated as a mechanical alternative to hand thinning. It thins flowers during bloom, before fruitlet thinning by hand is performed. In our trials on nectarines and Japanese plums the objective of reducing the time required for hand thinning was achieved, with the Darwin 300TM reducing the time required by up to 50%. When the time required to thin was reduced too much it also reduced the yield, but this could be overcome by lowering the rotor speed or using different strategies during supplementary hand thinning at the fruitlet stage. The bloom thinning and reduction in yield led to an increase in the fruit size. Care should be taken when using the Darwin 300TM as the earlier thinning could increase pit splitting and/or fruit cracking, especially in cultivars that are sensitive to these defects. The optimal rate of thinning needs to be determined for each cultivar individually. The application of gibberellic acid (GA3) and gibberellin A4+7 (GA4+7) at the pit hardening stage in the previous season could decrease the number of flowers for the following growing season. There was no effect on the yield at harvest or fruit size in the season of GA3 and GA4+7 applications, but the fruit firmness was increased. This effect was more pronounced for the GA4+7 applications. Our objective of reducing the time required for thinning was achieved in some but not all cultivars. The yield was not significantly reduced, with the fruit maturity only delayed in ‘African Rose’ plum. Again no increase in fruit size was found, but the fruit firmness was again increased. The GA-applications therefore were not satisfactory in their reduction of the time required for hand thinning. A positive effect is the increase in fruit firmness, which could possibly increase the storage potential of the fruit without having negative effects on the other aspects of fruit quality but this needs further evaluation. / AFRIKAANSE OPSOMMING: Produksie van vrugte met die verlangde vruggrootte en hoë vrug kwaliteit is baie belangrik vir die realisering van ‘n wins in die vrugte-industrie. Met hierdie mikpunt in gedagte, is blom- en vruguitdunning baie belangrik om die aantal vrugte per boom te verminder. Die kostes geassosieer met vrugte produksie is besig om te styg en arbeidskoste vorm ‘n groot deel van die totale produksiekostes. Uitdunning van steenvrugte is arbeidsintensief en baie duur, dus moet ‘n alternatief vir handuitdunning gevind word. Daar is twee alternatiewe naamlik chemiese en meganiese uitdunning. Chemiese uitdunmiddels word algemeen in kernvrugproduksie gebruik, maar daar is tans geen chemiese middels vir steenvrugte nie. In hierdie studie was gibberelliene ge-evalueer as potensiële uitdunmiddel. Die Darwin 300TM is ge-evalueer gedurende blomtyd as ‘n meganiese alternatief vir handuitdunning. Die masjien verwyder blomme en verminder so die vruguitdunning benodig. In ons eksperimente op nektarien- en Japanese pruimkultivars het ons gevind dat die tyd benodig vir handuitdunning met tot 50% verminder is deur die Darwin 300TM. Dit het ook daartoe gelei dat die totale oes per boom verlaag is. Hierdie effek kan vermy word deur die rotor spoed te verminder of die strategie vir aanvullende handuitdunning aan te pas. Die feit dat die grootste deel van die uitdunproses in blomtyd uitgevoer is en ook die feit dat die totale oes per boom verlaag is, het daartoe gelei dat die vrugte groter was. Die vroeër uitdunning met die Darwin 300TM kan egter lei tot ‘n verhoging in vrugkrake en gesplete pitte. Dit moet veral in gedagte gehou word by kultivars wat geneig is tot hierdie afwykings/defekte. Die optimum tempo van uitdunning moet vir elke kultivar individueel bepaal word. Wanneer gibberelliensuur (GA3) of gibberelien A4+7 (GA4+7) by pitverharding toegedien word in die vorige groeiseisoen, kan dit lei tot die vermindering van die hoeveelheid vrugte in die volgende seisoen. Daar was geen effek op die totale oes per boom en die vruggrootte tydens oes in die seisoen van aanwending nie, maar die vrugfermheid is verhoog. Die effek was hoër na die GA4+7 as na die GA3 aanwending. Die mikpunt om die tyd benodig vir handuitdunning te verminder, is in sommige kultivars bereik. Die oes per boom in die opvolgseisoen is weer eens nie verlaag nie, maar die vrug rypheid van ‘African Rose’ pruime is vertraag. Geen effek is op die vruggrootte opgemerk nie, maar die vrugfermheid was weer eens verhoog. Die GA-toedienings het dus nie bevredigend die tyd benodig vir handuitdunning verminder nie. ‘n Positiewe effek is die verhoging van die vrugfermheid, wat moontlik kan lei tot die verhoging van die opbergingspotensiaal van die vrugte sonder enige ander negatiewe effekte, maar hierdie aspek benodig verdere navorsing.

Thesis (MComm)—Stellenbosch University, 2015. / ENGLISH ABSTRACT: The purpose of this study was to undertake an inquiry on the competitive performance of the South African stone fruit industry since the early 1960s, with an emphasis on the more recent years since the mid-1990s, when the industry was deregulated. A comprehensive approach was applied in reaching conclusion in this study by employing a five-step analytical framework, built on well-established approaches by Balassa (revealed comparative advantage, RCA), Vollrath (relative trade advantage, RTA) and the Porter Diamond Model, adapted to accommodate innovative statistical methods to reflect differences in opinions and views more accurately. Competitiveness in this study is defined to give effect to the global trade orientation of the industry as the sustained ability of the South African stone fruit industry to attract investment by trading its produce competitively within the global marketplace, whilst continuously striving to earn returns greater that the opportunity cost of scarce resources engaged. Five phases were identified in the competitive performance of the South African stone fruit industry since 1961, showing the fluctuating nature of the performance of this industry:  Phase I (1961-1982): Increasingly regulated competitiveness  Phase II (1983-1990): Politically constrained competitiveness  Phase III (1991-1999): Economic deregulation and internal rivalry  Phase IV (1999-2007): Towards international competitiveness  Phase V (2007 – present): Increasingly sustained competitiveness The RTA calculations, including both exports and imports, showed that the industry is highly competitive, both internationally – in the Southern Hemisphere where this industry is only out-performed by Chile and locally – compared to other South African (SA) horticultural crops, with plums consistently claiming the top position when individual stone fruit types in the SA deciduous fruit category are analysed. Through the Stone Fruit Executive Survey (SFES), views and opinions of prominent industry role-players were critically employed to interrogate the topic under discussion. A total of 84 factors affecting the competitiveness of the industry were identified, and these were rated on a five-point Likert scale (where 5 were most enhancing and 1 was most constraining). This study expanded the analytical framework used in recent agri-competitiveness studies to verify and cross-check the results and findings through statistical procedures, such as cluster analyses, principle component analyses and Cronbach’s alpha. This broadened the scope of analysis by accommodating the variance in opinion statements from the respondents. As different cluster groupings based on functional value chain positions were analysed, it became clear that there were significant differences between the respondents involved in the primary production and packing/processing of stone fruit and the respondents involved in activities lower down the value chain, such as in pack houses/processors and exporters/marketers. Further down the value chain the respondents expressed more optimistic views and positive statements on competitiveness than those exposed to primary production risks and uncertainties. This confirms the importance to expand competitive analysis to different points in the value chain The rated factors were grouped into Porter’s six determinants and the general scored ratings yielded the two most enhancing determinants, being business strategy, structure and rivalry (3.55 out of 5) and related and supporting industries (3.14 out of 5). Production factor conditions (2.81 out of 5) and demand/market factors (2.76 out of 5) were identified as being less enhancing determinants. Chance factors (2.66 out of 5) and government support and policy (2.35 out of 5) were identified as the two most constraining determinants. The current approach is that the framework of Esterhuizen (2006) is applied to agriculture-related competitiveness studies. This study, however, investigated the extension of the conventional model by adapting the Porter diamond model within the frameworks of the Institute for Management Development’s World Competitiveness Yearbook (WCY) and the World Economic Forum’s Global Competitiveness Report (GCR), which generally focus on the macro-economic situation. It was confirmed that the stone fruit industry is integrated into and forms part of the ‘broader economic picture’. The results and findings of this study were discussed in a number of focus sessions with industry role players. A strategic planning framework was drafted, which consisted out of eleven industry level strategic proposals. Some of the most important strategic improvements to enhance competitive performance argued for in this study are improved industry-based lobby discussions, i.e. to build and strengthen the necessary communication between industry role players and government agencies through an improved strategic intelligence database, by focusing on aspects such as trade agreements, international market development and policy development. / AFRIKAANSE OPSOMMING: Die doelwit van hierdie studie was om ’n ondersoek van die mededingende prestasie van die Suid-Afrikaanse steenvrugbedryf sedert die vroeë 1960’s te onderneem, met die klem op die meer onlangse tydperk sedert die middel-1990’s, toe die bedryf gedereguleer is. ’n Omvattende benadering is ingespan deur gebruik te maak van ’n vyfstap- analitiese raamwerk wat geskoei is op die goed gevestigde benaderings van Balassa (onthulde vergelykende voordeel – revealed comparative advantage - RCA), Vollrath (relatiewe handelsvoordeel – relative trade advantage - RTA) en die Porter-diamantmodel, wat aangepas is om innoverende statistiese metodes te akkommodeer om verskille in gesigspunte beter te weergee. Mededingendheid in hierdie studie word gedefinieer om effek te gee aan die globale handelsoriëntasie van die bedryf as die volhoubare vermoë van die Suid-Afrikaanse steenvrugbedryf om belegging te lok deur sy produkte mededingend in die globale mark te verhandel, terwyl daar voortdurend gestreef word om opbrengste te verdien wat groter is as die geleentheidskoste van die skaars hulpbronne gebruik. Vyf fases in die mededingendheid van die Suid-Afrikaanse steenvrugbedryf is sedert 1961 geïdentifiseer en toon die wisselende aard van die prestasie in hierdie bedryf:  Fase I (1961-1982): Toenemend gereguleerde mededingendheid  Fase II (1983-1990): Polities beperkte mededingendheid  Fase III (1991-1999): Ekonomiese deregulering en interne mededinging  Fase IV (1999-2007): Op weg na internasionale mededingendheid  Fase V (2007 – vandag): Toenemend volhoubare mededingendheid Die RTA-berekenings, wat uitvoere en invoere insluit, het aangetoon dat die bedryf hoogs mededingend is, beide internasionaal – waar die industrie slegs die Chili oortref word en plaaslik – in vergelyking met ander Suid-Afrikaanse (SA) hortologiese gewasse, met pruime wat voorop staan wanneer individuele steenvrugsoorte in die SA sagtevrugtebedryf geanaliseer is. Deur die Steenvrug Uitvoerende Opname (Stone Fruit Executive Survey (SFES)) is die sienings en opinies van vooraanstaande rolspelers krities gebruik om die onderwerp te ondervra. ’n Totaal van 84 faktore wat die mededingendheid van die bedryf beïnvloed, is geïdentifiseer, en hierdie is op ’n vyfpunt-Likertskaal geëvalueer (met 5 as die mees versterkend en 1 as die mees stremmend). Hierdie studie het die analitiese raamwerk wat in onlangse agri-mededingendheidstudies gebruik is, uitgebrei om die resultate deur middel van statistiese prosedures te verifieer en te kruiskontroleer, naamlik deur bondelanalises, hoofkomponent-ontledings (principle component analyses) en Cronbach se alfa. Dít het die strekking van die analise verbreed deur die verskillende opinies van die respondente te akkommodeer. Soos verskillende bondels op grond van funksionele posisies in die waardeketting geanaliseer is, het dit duidelik geword dat daar noemenswaardige verskille was tussen die respondente in die primêre produksie en verpakking/verwerking van steenvrugte en die respondente betrokke in aktiwiteite laer af in die waardeketting, soos in pakhuise/verwerkers en uitvoerders/bemarkers. Verder af in die waardeketting het die respondente meer optimistiese opinies en positiewe stellings oor mededingendheid uitgespreek as dié wat aan primêre produksierisiko’s en onsekerhede blootgestel was. Dit bevestig die belangrikheid daarvan om mededingende analise na verskillende punte in die waardeketting uit te brei. Die gemete faktore is in Porter se ses determinante verdeel en die algemeen aangetekende skattings het die twee mees versterkende determinante opgelewer, naamlik sakestrategie, struktuur en mededinging (3.55 uit 5) en verwante en ondersteunende bedrywe (3.14 uit 5). Produksiefaktortoestande (2.81 uit 5) en vraag/markfaktore (2.76 uit 5) is geïdentifiseer as minder versterkende determinante. Toevallige faktore (2.66 uit 5) en regeringsondersteuning en -beleid (2.35 uit 5) is geïdentifiseer as die twee mees stremmende determinante. Die huidige benadering is dat Esterhuizen (2006) se raamwerk op landbou-verwante mededingendheidstudies toegepas word. Hierdie studie het egter die uitbreiding van die konvensionele model ondersoek deur die Porter-diamantmodel binne die raamwerke van die Institute for Management Development se World Competitiveness Yearbook (WCY) en die World Economic Forum se Global Competitiveness Report (GCR) aan te pas. Hierdie dokumente fokus oor die algemeen op die makro-ekonomiese situasie. Daar is bevestig dat die steenvrugbedryf in die ‘breër ekonomiese situasie’ geïntegreer is en daarvan deel is. Die resultate en bevindings van hierdie studie is in ’n aantal fokussessies met bedryfsrolspelers bespreek. ʼn Strategiese beplanningsraamwerk was opgestel wat bestaan uit elf industrie-vlak strategiese voorstelle. Van die belangrikste strategiese verbeterings om mededingende prestasie te verhoog, waarvoor daar in hierdie studie geargumenteer is, is verbeterde “drukgroepgesprekke”, m.a.w. om die nodige kommunikasie tussen bedryfsrolspelers en die regering te bou en te verstrek deur ’n verbeterde strategiese intelligensie- databasis wat o.a. fokus op aspekte soos handelsooreenkomste, internasionale markontwikkeling en beleidsontwikkeling.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Bacterial canker of stone fruit, caused by Pseudomonas syringae pv. syringae, is one of the most destructive crop diseases in South Africa. Chemical control has failed completely and effective long-term management strategies will have to rely on the breeding of resistant host trees. To assist in such breeding programmes, investigations into the molecular basis of the interaction between P. s. pv. syringae and stone fruit trees have been undertaken in collaboration with the ARC-Fruit, Wine and Vine Research Institute in Stellenbosch. The aim of this dissertation was to clone and identify genes that are involved in interaction between the bacterial canker pathogen and stone fruit trees. In the first part of the study, the harpin encoding gene of a local strain of the pathogen, P. s. pv. syringae NV, was amplified in a polymerase chain reaction (PCR) strategy with primers based on the hrpAZB sequences of the bean pathogen, P. s. pv. syringae 61. Sequencing of this hrpZpssNvgene revealed a high degree of homology (96%) between the harpin encoding genes and harpin proteins of the two strains. The hrpZpssNvgene was subsequently cloned into the pMAL-c2 expression vector and expressed in Escherichia co/i. This system was used for the production of purified, biologically active, recombinant HrpZpSSNV protein. In the second part of the study, differential display (DD) technology was used to identify genes that are induced in stone fruit trees in response to P. s. pv. syringae and/or its harpin elicitor. For this purpose, actively growing shoots of two Prunus sa/icina cultivars, the moderately resistant cv. 'Laetitia' and the highly susceptible cv. 'Songold' were treated with recombinant harpinpssNvprotein or live P. s. pv. syringae NV bacteria. An untreated control and wounding control was included in the experiment. Total RNA was isolated for comparative mRNA analysis 24 hours after treatment. DD profiles were generated with fifteen primer combinations. Eight candidate bands were re-amplified, cloned and sequenced. Reverse transcription PCR was employed to verify the expression patterns of the cloned bands in the original RNA sample set. Two bands, DDc and DD4 were shown to be differentially expressed between treatments and/or cultivars, while no differences in the expression levels of the remaining six bands (DDa, DDe, DD3, DD5, DD6 and DD7) were observed. BLAST similarity searches yielded significant matches for DDe, DD4 and DD7 with plant defense-related genes. / AFRIKAANSE OPSOMMING: Bakteriese kanker van steenvrugte, wat deur Pseudomonas syringae pv. syringae veroorsaak word, is een van die mees verwoestende siektes van landbougewasse in Suid-Afrika. Chemiese beheermaatreëls het geheel en al misluk en effektiewe langtermyn beheerstrategieë sal op die teling van weerstandbiedende gasheerbome moet staatmaak. Ondersoeke na die molekulêre basis van die interaksie tussen P. s. pv. syringae en steenvrugbome is in samewerking met die LNR-Vrugte-, Wyn- en Wingerdnavorsingsinstituut in Stellenbosch van stapel gestuur om tot sulke telingsprogramme by te dra. Die doelwit van hierdie proefskrif was om gene wat betrokke is in die interaksie tussen die bakteriese kanker patogeen en steenvrugbome te kloneer en te identifiseer. In die eerste gedeelte van die studie is die harpien-koderende geen van 'n plaaslike ras van die patogeen, P. s. pv. syringae NV, geamplifiseer in 'n polimerase kettingreaksie (PKR)-strategie met peilers wat op die hrpAZB-geenopeenvolgings van die boontjiepatogeen, P. s. pv. syringae 61, gebaseer is. Volgordebepaling van hierdie hrpZpssNv-geen het 'n hoë vlak van homologie (96%) tussen die harpien-koderende gene en harpien proteïene van die twee rasse getoon. Die hrpZpssNv-geen is vervolgens in die uitdrukkingsvektor pMAL-c2 gekloneer en uitgedruk in Escherichia coli. Hierdie sisteem is vir die produksie van suiwer, biologies-aktiewe, rekombinante HrpZpssNv-proteingebruik. In die tweede gedeelte van die studie is die differensiaalvertoon (DD) tegniek gebruik om gene te identifiseer wat deur P. s. pv. syringae en/of sy harpien elisitar in steenvrugbome geïnduseer word. Vir hierdie doel is aktief-groeiende lote van twee Prunus sa/icina kultivars, die matig weerstandbiedende kv. 'Laetitia' en die hoogs vatbare kv. 'Songold', met rekombinante harpienpssNvproteïen of lewende P. s. pv. syringae NV bakterieë behandel. 'n Onbehandelde- en verwondingskontrole is in die eksperiment ingesluit. Totale RNA is 24 uur na behandeling vir vergelykende mRNA-analise geïsoleer. DD-profiele is met vyftien peilerkombinasies gegenereer. Agt kandidaatbande is geheramplifiseer en gekloneer, waarna hul DNA-opeenvolgings bepaal is. Trutranskriptase-PKR is gebruik om die ekspressiepatrone van die gekloneerde bande in die oorspronklike RNA monsters na te gaan. Daar is vasgestel dat twee van die bande, DDc en DD4, differensieel tussen kultivars en/of behandelings uitgedruk is, terwyl geen verskille in die ekspressievlakke van die oorblywende ses bande (DDa, DOe, 003, DOS, 006 en DO7) waargeneem is nie. BLAST-soektogte het betekenisvolle ooreenkomste vir DDe, DD4 en DD7 met plant weerstandsgeassosieerde gene opgelewer.

Spring shock syndrome (SSS) is a condition where flowering and leaf development in peach and nectarine trees is delayed and those leaves that do develop are often small and discoloured. Trees experiencing spring shock syndrome yield poorly. To learn more about the development of this syndrome, this thesis has examined the influence of root zone temperature (RZT) and genotype on the growth of peach rootstocks and the scions grafted onto them. Other factors that influence the quality of peach seedling rootstocks were also examined. Initial trials examined the influence of Okinawa (a low chill cultivar) and Golden Queen (a high chill cultivar)rootstocks on the expression of SSS. Studies found that multiple stems could originate from either multiple seeds within a single stone or from axils originating from the base of cotyledons. The incidence of both conditions was heavily influenced by variety, thus suggesting that an active selection program based on the elimination of these traits would be beneficial to the stone fruit nursery industry. / Doctor of Philosophy (PhD)

One hundred fifty-five peach (Prunus persica) cultivars, from Asia, Brazil, Europe, and the USA, were examined using eleven Simple Sequence Repeats (SSRs) to study the genetic relationships among low chill as compared to high chill peach germplasm. Data was analyzed by NTSYSpc to form a similarity matrix using Nei and Li’s Dice similarity coefficient. This similarity matrix was then subjected to a cluster analysis and a dendrogram was constructed using the UPGMA (Unweighted Pair-Group Method, Arithmetic Mean) method. A wide range of diversity was detected, from 0.33 coefficient of similarity amongst the Thai peaches to 0.97 between two Brazilian peaches. The most distant clusters were the low chill peaches from Thailand and Taiwan and the local cultivars (both fruit and ornamental types) from China. Among the improved germplasm, there were distinct clusters for the Chinese/Japanese cultivars, three clusters for the Brazilian cultivars and one for the cultivars from the USA and Europe. The Brazilian materials clustered according to breeding programs in São Paulo and Pelotas reflecting the different sets of local cultivars used in the breeding efforts. The largest group investigated was the European/USA peaches. This group subdivided into three distinct clusters, with a general clustering of the low chill germplasm. The low chill accessions from Asia were genetically distant from the improved low chill peaches from the USA or Brazil. The low chill peaches from the Americas were more closely related to the high chill peaches developed in the USA and China/Japan due to the introgression of this germplasm into a low chill background.