Thesis (MScAgric)--University of Stellenbosch, 2006. / Bibliography.

Thesis (MScAgric)--University of Stellenbosch, 2007. / Bibliography. Also avilable via the Internet.

Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Most South African peach and nectarine production areas lack in adequate winter chilling. To address these issues, a conventional breeding programme was started, to develop new and improved stone fruit cultivars with special emphasis on climatic adaptation and pomological attributes. This study was conducted to test the accuracy of the scientific method called the phenological method of classification, currently used by the breeding programme to classify the selections in the second phase of evaluation according to chilling requirement. During April 2000 and May 2001 and continuing until the next spring, 20 oneyear- old shoots of 30 peach and nectarine selections were harvested fortnightly from an evaluation orchard on Bien Donné Experiment Farm, Simondium, Western Cape (34° S). All selections were previously categorised as high (>800 Utah chilling units [CU]), medium (400-800 CU) or _low «400 CU) chilling requirement based on phenologic observations. According to the preliminary classification of the selections included in this study, six selections were classified as high, three as medium and 21 as low chilling requirement. Two replicate bundles of shoots of each selection were prepared and forced at 25° C with continuous illumination until no further changes in bud burst occurred for a period of five days after which the shoots were then discarded. CU in the orchard were calculated according to the Utah and Infruitec models. The hours below 12° C and 7° C were also calculated. For each selection the number of days until 20% vegetative and reproductive bud break was plotted over day of year, Utah CU, Infruitec CU, hours below 12° C, and hours below 7° C, and expressed as a parabolic function. Similarly, the inverse of the number of days until 20% bud break or the rate of bud growth was also plotted against all the above variables. The area under these parabolas was statistically analysed using the CANDISC procedure of SAS Release 8.1. The groupings of the CANDISC procedure were more or less consistent with the preliminary groupings obtained with the phenoligical classification method. On 16 May 2000 and 15 May 2001, 100 one-year-old shoots of the same peach and nectarine selections were harvested from the evaluation orchard on Bien Donné Experiment Farm, covered in wet paper towelling and black plastic bags and placed in a cold room kept at a temperature range between 4° C and 7° C. Two replicate bundles of 10 shoots of each selection were prepared fortnightly and forced at 25° C with continuous illumination until no further changes in bud burst occurred for a period of five days after which the shoots were then discarded. CU accumulated in the cold room at each transferral date was calculated according to the Utah model. For each selection the number of days until 20% vegetative bud break was plotted over Utah CU, and expressed as a parabolic function. Similarly, the inverse of the number of days until 20% bud break or the rate of bud growth was also plotted against the above variables. The area under these parabolas was statistically analysed using the CANDISC procedure of SAS Release 8.1. Once again, the groupings of the CANDISC procedure were more or less consistent with the preliminary groupings obtained with the phenoligical classification method. Due to the nature of the scientific method used in this study, there is room for a certain margin of experimental error to occur, which could account for the misclassifications by the CANDISC procedure, when performed on the 2001 season's data. It can be concluded that the phenological method of classifying the selections, as currently used in the breeding programme, is consistent with the results of the scientific method described here. Therefore, it is recommended that the phenological method be used in future to classify the selections according to chilling requirement (CR), as this method is less time consuming and less costly to perform. Finally the outcome of the analysis of one season's data was used as calibration data against which the other season's data was tested and the consistency of the results, using one set of discriminant functions, was tested. It can be concluded that a unique set of discriminant functions is necessary for each winter season to accurately classify selections according to CR with the CANDISC procedure. / AFRIKAANSE OPSOMMING: 'n Studie van dormansie en koue behoefte van perskes en nektariens Gebrekkige winterkoue is 'n gegewe in die meeste Suid-Afrikaanse perske en nektarien-produksie-streke. Om die gevolge hiervan aan te spreek, is 'n konvensionele teelprogram tot stand gebring om verbeterde steenvrug cultivars te ontwikkel met voortreflike pomologiese eienskappe en wat aangepas is by die plaaslike klimaatstoestande. Hierdie studie is geloods om die akkuraatheid van die wetenskaplike metode, genoem die fenologiese klassifikasie metode, soos tans deur die teelprogram gebruik, waarvolgens seleksies volgens kouebehoefte geklassifiseer word, te toets. Vanaf April 2000 en Mei 2001 tot en met die daaropvolgende lente, is 20 eenjaar-oue lote van 30 perske en nektatrien seleksies twee weekliks in 'n fase 2 evaluasie boord op Bien Donné Proefplaas, te Simondium in die Wes- Kaap (34° S) versamel. AI die seleksies was vooraf op grond van fenologiese waarnemings geklassifiseer in kategorieë van hoog (>800 Utah koue-eenhede [CU]), medium (400-800 CU) of laag «400CU) ten op sigte van kouebehoefte. Hiervolgens val ses van die seleksies wat in die studie ingesluit is in die hoë-, drie in die medium- en 21 in die lae kategorie. Lote van elke seleksie is voorberei en in twee herhalings gebondel, waarna dit geforseer is teen 25° C met deurlopende beligting totdat geen verdere knopbreek vir 'n periode van vyf dae voorgekom het nie, waarna die lote verwyder is. CU in die boord is volgens die Utah en Infruitec modelle bereken. Die aantal uur onder 12° C en onder 7° C is ook bereken. Die aantal dae wat dit elke seleksie geneem het om 20% vegetatiewe en 20% reproduktiewe knopbreek te bereik is bereken en geplot teenoor die dag van die jaar, Utah CU, Infruitec CU, aantal uur onder 12° C en aantal uur onder 7° C en uitgedruk as 'n paraboliese funksie. Die inverse van die aantal dae tot 20% knopbreek, of die tempo van knopbreek, is op soortgelyke wyse geplot teenoor al bogenoemde veranderlikes. Die oppervlakte onder die parabole is statisties ontleed met behulp van die CANDISC prosedure van die SAS program (Vrystelling 8.1). Die groeperings wat met die CANDISC prosedure verkry is het grootliks ooreengestem met die groeperings volgens die fenologiese klassifikasie metode. Op 16 Mei 2000 en 15 Mei 2001, is 100 eenjaar-oue lote van dieselfde perske en nektarien seleksies in die evaluasie boord op Bien Donné versamel, toegedraai in klam handdoekpapier, in swart plastiek sakke geplaas en in 'n koelkamer geplaas waarvan die temperatuur konstant gehou is tussen die grense van 4° C en T" C. Twee herhalings van 10 lote elk, van elke seleksie, is twee weekliks voorberei en geforseer by 25° C met deurlopende beligting totdat geen verdere knopbreek vir 'n periode van vyf dae plaasgevind het nie, waarna die lote verwyder is. Op elke oordragdatum is die aantal CU, wat in die koelkamer geakkumuleer het, volgens die Utah model bereken. Die aantal dae wat dit elke seleksie geneem het om 20% vegetatiewe knopbreek te bereik is bereken en geplot teenoor die Utah CU en uitgedruk as 'n paraboliese funksie. Die inverse van die aantal dae tot 20% knopbreek , dus die tempo van groei, is op soortgelyke wyse bererken en geplot teenoor bogenoemde veranderlikes. Die oppervlak onder die paraboliese funksies is statisties ontleed met behulp van die CANDISC procedure. Die groeperings van die CANDISC prosedure het weereens grootliks ooreengestem met die groeperings wat met die fenologiese metode van klassifikasie verkry is. Weens die aard van die wetenskaplike metode wat tydens hierdie studie gebruik is, kom daar 'n sekere mate van eksperimentele fout voor, wat moontlik die misklassifikasies van die CANDISC prosedure kan verklaar, wanneer dit op die 2001 seisoen se data uitgevoer word. Die gevolgtrekking kan gemaak word dat die resultate van die fenologiese metode, soos dit tans deur die teelprogram gebruik word, ooreenstem met die resultate wat deur die wetenskaplike metode, wat hier beskryf word, verkry is. Dus word daar aanbeveel dat die fenologiese metode in die toekoms gebruik word om die seleksies te klassifiseer volgens koue behoefte (CR), aangesien hierdie metode minder tyd in beslag neem en goedkoper is om uit te voer. Laastens is die resultaat van die analise van een seisoen se data gebruik as kalibrasiedata waarteen die data van die ander seisoen getoets is om so ooreenstemmendheid van die resultate te toets as slegs een stel diskriminant funksies gebruik word. Die slotsom was dat 'n unieke stel diskriminantfunksies nodig is vir elke winter seisoen om die seleksies akkuraat met behulp van die CANDISC prosedure volgens koue-behoefte te klassifiseer.

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)

No description available.

Thesis (MScAgric (Horticulture))--University of Stellenbosch, 2007. / Most nectarine orchards in South Africa are currently planted at a distance of 4 x 1.5 m (2 500 trees/ha). These trees are mainly sylleptically trained to a central leader, although many producers also use the proleptic route. The former produces relatively high yields early in the lifetime of the orchard. A problem with nectarine production in South Africa is the lack of efficient rootstocks in terms of aspects such as size-control and the use of nematode-resistant rootstocks. The aim of this study is to evaluate different training systems for nectarine production and to investigate the role of three rootstocks that play a dominant role in the peach industry in South Africa. ‘Alpine’ nectarines were planted in the winter of 2002 at Lushof near Ceres, Western Cape, South Africa (33º18’S, 19º20’E). The trees were trained according to four different training systems: a four-leader system (5 x 3 m; 667 trees/ha), a two-leader system (5 x 1.5 m; 1 333 trees/ha), a proleptically trained central leader (5 x 1 m; 2 000 trees/ha), and a sylleptically trained central leader (5 x 1 m; 2 000 trees/ha). The trees were planted on three different rootstocks: GF 667; SAPO 778; Kakamas seedling. The time spent per tree on pruning, thinning and picking was recorded. During harvest, the number of fruit and fruit mass per tree were recorded. Light measurements were recorded annually after summer pruning. The measurements were taken at different heights and at different depths in the canopy. To compare the training systems on an economic basis, the data from the trial together with projected data gathered from farmers and advisors were used to calculate the net present value (NPV) and internal rate of return (IRR) for each training system. The results showed that rootstock only played a significant role when it came to fruit mass (fruit size). Fruit from trees on SAPO 778 were heavier, indicating bigger fruit, than fruit from trees on Kakamas seedling rootstocks and this can play a role in packout percentage and income. In terms of the training system, the four-leader system took the most time to manage per tree. However, this system took the least time to manage per hectare during the initial years. No differences were found between the two central leaders. They both took the longest time to manage per hectare. The four-leader system produced significantly less fruit than any of the other systems during the first two years of production. In the third year of production, there was no significant difference found between the systems. Light penetration seemed to be the poorest at the middle and bottom of the canopy for trees trained to a central leader. Because of the open centre of the four-leader system, light penetration into the middle of these trees was good, but poor light penetration occurred in the upper and outer parts of the canopy underneath the scaffold branches. Poor light penetration occurred in the parts lower than 1.5 m from the ground for all the systems. This was the area that was measured in this study. The result of an economic comparison showed that according to the IRR rating, the fourleader system should be preferred. The final decision should however be made according to the NPV rating. Results obtained from NPV calculations did not lead to the same conclusions as could be made from the IRR calculations. According to the rating of the NPV at five percent discounting rate, the two-leader should be the preferred system, while the proleptically trained central leader system should be preferred at a ten percent discounting rate. This implies that when the opportunity cost is low, the two-leader system should be preferred, and when the opportunity cost is high, the proleptically trained central leader system should be preferred.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2006. / Fruit quality, and especially eating quality, of nectarines has become very important to markets and consumers in recent years. Pre- and post harvest factors that influence the eating quality of nectarines were studied to optimise fruit quality at harvest and to maintain this quality during export. This will ensure good returns for a producer and will maximise his profit. The influence of the variables canopy position, initial fruit size and bearing position was studied to determine the variation in fruit quality within a nectarine tree. ‘Red Jewel’ and ‘Ruby Diamond’ fruit from the upper part of the tree canopy had significantly higher total soluble solids (TSS). Fruit position on the shoot does not seem to play a significant role in fruit quality for ‘Red Jewel’ nectarines, which will allow producers to leave more than one fruit per bearer if necessary. Fruit thinning is an important means to improve fruit size and quality in ‘Red Jewel’, but poor thinning can cause extreme variability in size and quality. Fruit that were small at thinning remained significantly smaller, weighed less, had lower sugars and higher acids at harvest. If it is possible to reduce the variation in size at thinning, fruit will be much more homogenous at harvest. The effect of pre-conditioning (PC) prior to storage and controlled atmosphere (CA) storage was evaluated on ‘Red Jewel’ and ‘Spring Bright’ nectarines. Free juice percentage was determined at the end of a simulated export protocol. The severity of woolliness differed between the two seasons for both nectarine cultivars. PC, to a firmness of 6 kg, followed by regular atmosphere (RA) storage increased percentage free juice significantly in ‘Spring Bright’ and ‘Red Jewel’ nectarines. However, a PC protocol for each cultivar and each producer must be determined beforehand to ensure fruit quality. CA storage is another technique that can be used to prevent the development of chilling injury (CI) symptoms. Both ‘Spring Bright’ and ‘Red Jewel’ showed an increase in percentage free juice with the use of CA storage during both seasons.The eating quality of nectarines depends on the composition of the individual sugars and organic acids and the ratio between them. Sucrose, fructose, glucose and sorbitol were found to be the major sugars in all evaluated nectarine cultivars. Sucrose was the dominant sugar in all cultivars at optimum maturity. The three main organic acids in nectarine cultivars were malic, citric and quinic acid, with malic acid being dominant at optimum maturity. Small amounts of shikimic, fumaric and succinic acid were also observed. It was evident that cultivars differ in the composition of sugar and organic acids at optimum maturity, especially the standard acid cultivars and the new low-acid cultivars. Individual sugars and organic acids in cultivars also differ in how they react during storage.

Orientador: Fernanda Elizabeth Xidieh Murr / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-04T02:39:35Z (GMT). No. of bitstreams: 1 Araujo_EderAugustoFurtado_D.pdf: 3550124 bytes, checksum: 4ae4c9ab1e30f5794d31594fe6304ecd (MD5) Previous issue date: 2005 / Doutorado / Engenharia de Alimentos / Doutor em Engenharia de Alimentos

M. S.

Monilinia fructicola (Wint.) Honey, and Rhizopus nigricans Erh., the causal organisms of brown rot and Rhizopus rot, respectively, have long been recognized as the two major causes of post-harvest rots on peach and nectarine fruits. Fruit losses of as much as 50% may occur during storage, transport, and marketing from these two diseases if effective fungicide treatments are not used. Application of fungicide suspensions as post-harvest dips have been reported to reduce losses from post-harvest rots considerably, however, more effective treatments are needed. Tests were made of three fungicides: benomyl [methyl-l-(butylcarbamoyl)-2-benzimidazole carbamate], Topsin-M [dimethyl-4,4'-ophenelenebis (3-thioallophanate) , and Botran (2,6-dichloro-4-nitroanaline) against the two post-harvest rot fungi, M. fructicola and R. nigricans, on peach and nectarine fruits and in vitro. Fruits were inoculated with an equal concentration of spores of both fungi, then treated, by dipping in the different fungicide suspensions at 0, 4, 8, and 12 hour intervals after inoculation. Three concentrations of benomyl or Topsin-M (300, 450, and 600 ~g/ml) were used in combination with corresponding concentrations of Botran (600" 900, and 1200 Ug/ml). Number of decayed fruits increased with time of treatment after inoculation up to 8 hours then leveled off. Lesion progression, however, was slower with all fungicide treatments as compared to those of the untreated check fruit. Percent of decayed fruit remained lower when treatments were applied within 4 hours after inoculation. Later application times were ineffective and fruits showed approximately the same level of infection as controls. Treated nectarines appeared to be more susceptible to the post harvest rots than peaches. This may be due to lower residues of the chemicals remaining on the smooth skinned fruit. Benomyl and Topsin-M were fungitoxic to M. fructicola in vitro but neither was effective against R. nigricans. Botran alone was fungistatic to both R. nigricans and M. fructicola, but often lost effectiveness after 96 hours. Combinations of benomyl plus Botran, or Topsin-M plus Botran, were fungitoxic to M. fructicola and fungistatic to R. nigricans. Botran alone and Botran in combination with benomyl or Topsin-M inhibited germination of M. fructicola and R. nigricans spores more effectively than benomyl or Topsin-M alone. There were no major significant differences in control provided by treatments containing benomyl or Topsin-M. Treatments using Botran with benomyl or Topsin-M did not effectively control post harvest rot when applied later than 4 hours after inoculation. In vitro tests, however, indicated either a synergistic or additive effect of the fungicide combinations against R. nigricans. / Master of Science