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

Thesis--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (p.61-68).

Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 203-225).

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

Thesis (MSc (Horticulture))--University of Stellenbosch, 2006. / Rind breakdown of ‘Nules Clementine’ mandarin (Citrus reticulata Blanco) is a physiological rind disorder that develops during storage. The disorder appears following leakage of essential oil from oil glands in the flavedo, which then leaks into and oxidises the albedo. Oxidised tissue appears as brown spots in the rind. Occurrence of this disorder over the years has caused high financial losses to ‘Clementine’ mandarin producers and exporting companies. Therefore, research aimed at solving this problem was identified as a priority by the citrus industry. Several factors have been reported to be associated with rind breakdown of ‘Clementine’ mandarin fruit, and include environmental factors, fruit maturity at harvest, ethylene gas degreening, storage temperature and storage duration, canopy position where fruit are borne, plant growth regulators, and differences in susceptibility among selections. Practical information has been generated on rind breakdown, but the basic physiology of the disorder is still unresolved. The objective of this study was, therefore, to quantify the effects of various factors on the development of rind breakdown of ‘Nules Clementine’ mandarin fruit, as well as to establish an association between rind pigments and rind antioxidant capacity on the development of this disorder. In this study a series of five experiments was conducted, and included quantifying the differences in susceptibility to rind breakdown between ‘Nules’ and ‘Oroval Clementine’ mandarin fruit, investigating the effects of fruit canopy position, harvest date, ethylene gas degreening, storage temperature and duration on the development of rind breakdown. The effect of these factors on rind pigments and antioxidant capacity was also reported. Generally, ‘Nules’ and ‘Oroval Clementine’ mandarin fruit exhibited similar characteristics at harvest, in terms of maturity and antioxidant capacity. After storage, ‘Nules Clementine’ mandarin developed higher levels of rind breakdown than ‘Oroval Clementine’ mandarin. However, the difference in susceptibility to rind breakdown of ‘Nules’ and ‘Oroval Clementine’ mandarin fruit could not be associated with the antioxidant capacity measured at harvest...

Thesis (MSc. Agriculture (Horticulture)) -- University of Limpopo, 2018 / Newly developed mandarin selection ―M37‖ has the potential to become a future export soft citrus cultivar. However, the selection is highly susceptible to chilling injury, which normally reduces post-storage quality and marketability of citrus fruit. Silicon (Si), applied at post-harvest as potassium silicate (K2SiO3), has potential to mitigate against chilling injury. So far, the effect of Si on ―M37‖ mandarin chilling susceptibility is unknown. Therefore, the aim of the study was to investigate the effect of cold storage temperature and postharvest potassium silicate dips on the chilling susceptibility and physico-chemical properties of new mandarin selection ―M37‖ fruit. The experiment was carried out in a factorial, arranged in a completely randomised design (CRD) with three replicates. Treatment factors were: 2 x cold storage temperature (-0.6±1 and 4.5 ±1°C) and 4 x potassium silicate concentration (0, 50, 100 and 150 mL L-1 K2SiO3). Fruit were dipped in different potassium silicate solutions (0, 50, 100 and 150 mL L-1) for 30 minutes, air dried, waxed; and thereafter, stored for 28 days at -0.6 and 4.5°C with 85-90% relative humidity. After withdrawal from cold storage, fruit were held at ambient temperature (±23°C) for 7 days (shelf-life); during shelf-life fruit were evaluated for chilling injury, physical properties (weight loss and firmness loss) and biochemical properties (electrolyte leakage, total soluble acids (TSS), titratable acids (TA) and TSS: TA ratio). The results showed that fruit were highly susceptible to chilling injury after storage at 0.6°C when compared with 4.5°C. However, treating fruit with postharvest potassium silicate dips improved their chilling susceptibility, especially with 50 and 100 mL L-1 K2SiO3 concentrations. Electrolyte leakage was lower for fruit treated with K2SiO3 compared to the control across all the storage temperatures. Although, ―M37‖ fruit stored at 4.5°C showed higher weight loss, firmness loss, TSS and TSS: TA ratio when compared with -0.6°C storage. Fruit firmness increased with the increase in potassium silicate concentrations during storage at -0.6 and 4.5°C; with the highest firmness loss occurring on fruit treated with 150 mL L-1 than control. Similarly, TSS increased concomitant with K2SiO3 concentration. Although, TA decreased with increasing K2SiO3 concentrations for fruit stored at 4.5°C; resulting in higher TSS: TA ratio. In conclusion, postharvest silicon dips effectively improved the storability of ―M37‖ mandarin fruit, preserved quality and extended the cold storage period. xi Keywords: Biochemical properties; Chilling injury; Firmness loss; Potassium silicate dips; Weight loss / Agricultural Research Council (ARC-LNR) and National Research Fund (NRF)

Orientadores: José Camilo Novello, Ione Salgado / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-17T05:39:26Z (GMT). No. of bitstreams: 1 Fontanesi_KarinaKleinfelder_M.pdf: 2853236 bytes, checksum: 30ce9c486d1739927e3bd38f96e22015 (MD5) Previous issue date: 2009 / Resumo: O sistema citrícola no Brasil representa um setor de grande importância econômica. O Estado de São Paulo é o principal produtor de citros, fazendo do país o maior exportador de suco de laranja concentrado congelado. Apesar do Brasil ocupar uma posição de destaque no cenário mundial de citricultura, o país não consegue aumentar a sua produtividade devido à ocorrência simultânea de pragas e doenças, sendo que a clorose variegada dos citros (CVC) se mostra como uma das mais limitantes sobre esta produção. Ela é causada pela bactéria Xylella fastidiosa, que é capaz de infectar todas as variedades de laranja doce (Citrus sinensis L. Osbeck), embora a tangerina Poncan (Citrus reticulata Blanco) seja considerada tolerante à sua infecção. Apesar de muitos estudos já tenham sidos realizados a fim de se compreender melhor os mecanismos da sua patogenicidade, questões ainda permanecem em aberto acerca dos mecanismos que controlam o seu processo de infecção e o desenvolvimento da doença. Desse modo, foi realizado um estudo comparativo do proteoma das folhas de laranja Pêra e de tangerina Poncan após 30 dias da inoculação com a X. fastidiosa e o dos obtidos de folhas não infectadas, empregando a técnica de eletroforese bidimensional (2DE) e espectrometria de massas (MS). Foram confeccionados mapas 2DE com o intuito de se verificar proteínas diferencialmente expressas que por ventura poderiam estar relacionadas aos mecanismos de defesa e resistência da planta. Entre as proteínas (spots) de laranja Pêra, separadas por eletroforese bidimensional, 60 spots foram considerados como estatisticamente relevantes, apresentando alteração de intensidade. Entre as proteínas de tangerina Poncan analisadas na mesma condição, 38 foram consideradas como estatisticamente relevantes. Confeccionou-se para a planta tangerina Poncan géis de poliacrilamida utilizando IPG com gradiente de pH linear de 4-7, visto que houve um grande número de proteína diferencialmente expressas nesta faixa. Como resultado, foram obtidos 45 spots com diferença de expressão. A identificação dessas proteínas foi feita por meio do seqüenciamento por espectrometria de massas através do sistema LC ESI-MS/MS ou MALDI-Q-TOF. O seqüenciamento por MS possibilitou a aquisição da seqüência de aminoácidos de 49,7% dos spots. Dentre eles, 76% dos spots foram identificados, enquanto que 24% não apresentaram homologia com nenhuma base de dados. Entre as proteínas identificadas quatro foram representadas por mais de um spot, podendo indicar a ocorrência de eventos provenientes do splicing alternativo, modificações pós-traducionais, variações alélicas de uma mesma proteína ou degradação da amostra. As proteínas identificadas foram relacionadas com a produção de energia, com o metabolismo primário, com mecanismo de defesa, proteínas de microrganismos e proteínas desconhecidas. Laranja Pêra apresentou uma diminuição da expressão de proteínas relacionadas à fotossíntese, o que coincide com os primeiros efeitos sentidos pelas plantas colonizadas pela bactéria. Em contrapartida, tangerina Poncan apresentou um aumento de expressão de proteínas relacionadas à resposta de defesa contra esse patógeno. / Abstract: The citrus system in Brazil represents one of the most important economic sectors. The State of São Paulo is the main producer of citrus, settling the country as the biggest exporter of concentrated freezing orange juice. Besides holding the outstanding position in the worldwide citrus culture scene, the country cannot raise its productivity due to simultaneous occurrence of plagues and diseases, being the citrus variegated chlorosis (CVC) one of the most limiting diseases affecting the citrus production. This disease is caused by bacterium Xylella fastidiosa, that which is able to infect all sweet orange (Citrus sinensis L. Osbeck) varieties, however ponkan (Citrus reticulate Blanco) was considered resistant to it. Although, many studies have already been done in order to understand, in a better way, the mechanism of its pathogenicity, there are still queries about the mechanisms which control the process of its infection and the development of the disease. In this manner, we did a comparative proteomics study of leaves from sweet orange and ponkan after 30 days of the inoculation with X. fastidiosa versus leaves not infected with this bacterium (healthy plants), using two-dimensional gel electrophoresis (2DE) and mass spectrometry techniques. Comparative 2DE maps were done with the aim to verify differentially expressed proteins related with defense mechanism and the plant resistance. Among the proteins (spots) extracted from sweet orange, separated by two-dimensional gel electrophoresis, 60 spots were considered with statistical significance, showing intensity alteration. On the other hand, among the proteins (spots) extracted from ponkan and analyzed in the same condition, 38 spots were considered with statistical significance. Gels using linear pH gradient ranging from 4 to 7 were prepared for ponkan gels using, because there were a larger number of differentially expressed proteins in this area. As a result, we obtained 45 spots with difference in its expression. The identification of these proteins was done by sequencing using mass spectrometry like LC ESI-MS/MS or MALDI-Q-TOF. 143 spots were analyzed by mass spectrometry and were obtained amino acid sequence from 71 (49,7%) of the spots. Between them, 54 (76%) were identified, while 17 (24%) presented no homology in the database used. Overall, 4 proteins appeared as multiple spots and accounted for most of the protein found in the group. This observation may reflect post-translation modification, alternative splicing events, isozyme variation, allelic variation of the same protein, but also protein degradation. The identified proteins play a role in energy, primary metabolism, defense mechanism, unknown proteins and microorganism proteins. The sweet orange presented a decrease in expression of photosynthesis related protein, indicating a possible lower photosynthetic activity resulting from early effects of the bacterial colonization in affected plants. On the other hand, ponkan showed an increase in defense-related proteins response against this pathogen. / Mestrado / Bioquimica / Mestre em Biologia Funcional e Molecular

Orientador: Marcos Antonio Machado / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-19T08:49:23Z (GMT). No. of bitstreams: 1 Stuart_RodrigoMakowiecky_D.pdf: 10894472 bytes, checksum: 8404d2f1c15c931acb79f33e98ddde90 (MD5) Previous issue date: 2011 / Resumo: O patótipo tangerina do fungo Alternaria alternata produz a toxina hospedeiro específica ACT que afeta tangerinas e seus híbridos e causa a doença conhecida como mancha marrom de alternaria (MMA). A toxina ACT causa necrose em plantas susceptíveis, afetando ramos, folhas novas e frutos. Os sintomas incluem pontos marrons a negros circundados por um halo amarelado. Laranjas doces eram consideradas resistentes à doença uma vez que MMA nunca havia sido descrita no campo. Foi demonstrado que uma linhagem do fungo A. alternata produtor de toxina ACT é capaz de penetrar e colonizar de forma assintomática folhas de laranja 'Pera' sem perder a capacidade de causar necrose em genótipos susceptíveis. Microscopia óptica, inoculação e isolamento de A. alternata em plantas de laranja doce seguida pela inoculação cruzada em folhas susceptíveis de tangor 'Murcott', em adição a detecção por PCR do fungo em folhas assintomáticas de laranja doce no campo confirmam que laranja 'Pera' atua como hospedeiro assintomático do patógeno. A análise de genes (RT-qPCR) e proteínas (2DE) expressas durante a infecção com o fungo demonstrou que diferentes vias de sinalização foram ativadas em plantas de citros em resposta a A. alternata. Durante a resistência plantas responderam ativando as vias de sinalização mediadas por etileno e ácido jasmônico, as quais estão tipicamente envolvidas na defesa de plantas contra microrganismos necrotróficos. Aparentemente a produção de etileno também é requerida durante a susceptibilidade. Genes envolvidos na síntese de etileno aparecem induzidos durante a infecção e desenvolvimento de sintomas. Durante a infecção assintomática as plantas cítricas ativaram genes e proteínas associadas à síntese de fenilpropanóides, indicando o possível papel destes em plantas de laranja / Abstract: The tangerine pathotype of Alternaria alternata produces the host-specific ACT-toxin that affects mandarins and their hybrids and causes the disease known as Alternaria brown spot (ABS). ACT-toxin causes necrosis in susceptible plants, and the disease affects twigs, young leaves and fruits. The symptoms include brown to black necrotic spots that are surrounded by a yellow halo. Sweet oranges were considered resistant to the disease since ABS symptoms have never been reported in the field. It was demonstrated that an ACT-toxin-producing strain of A. alternata is able to penetrate and colonize Pera sweet orange leaves asymptomatically without losing its ability to cause necrosis on susceptible genotypes. Light microscopy, inoculation and recovery of A. alternata from sweet orange leaves followed by subsequent cross-inoculation in susceptible leaves of Murcott tangor and PCR detection of the fungus in sweet orange symptomless leaves collected in the field confirmed that Pera sweet orange may act as an asymptomatic host for the pathogen. The analysis of genes (RT-qPCR) and proteins (2DE) expressed during fungal infection demonstrated that different signaling pathways were activated in citrus plants in response to A. alternata. During resistance, plants respond activating ethylene and jasmonic acid signaling pathways which are typically involved in plant defense against necrotrophic pathogens. Apparently the production of ethylene is also required during susceptibility. Genes involved in ethylene biosynthesis appear to be induced during infection and symptoms development. During asymptomatic infection, citrus plants activate genes and proteins associated to phenylpropanoids biosynthesis, indicating their possible role in sweet orange plants response to the disease / Doutorado / Genetica de Microorganismos / Doutor em Genetica e Biologia Molecular