Apple is one of the most valuable fruit consumed worldwide due to its excellent quality features and high degree of acceptation by consumers. However, apples are susceptible to various postharvest disorders, leading to significant economic losses. To slow down food decay and provide constant fresh food to the market, postharvest strategies including decreasing the temperature can slows down the metabolism of fruits, but in parallel can also trigger the occurrence of typical chilling injury related disorders. Among all the physiological disorders, superficial scald is one of the most challenging, causing discoloration and skin browning triggering therefore consumers unacceptance. The development of superficial scald in apple fruit is a complex process influenced by various factors, including genetic background, storage conditions and preharvest management practices. Recent research partially disclosed the molecular mechanisms underlying the development of superficial scald in apple fruit. It has been shown that this disorder is associated with the accumulation of reactive oxygen species (ROS) and the oxidation of alfa-farnesene, a sesquiterpene largely considered as a major actor in the onset of this disorder. Various postharvest treatments have been used to control the development of superficial scald in apple fruit, such as including the application of the ethylene competitor 1-methylcyclopropene (1-MCP) or controlled atmosphere storage. This thesis aimed to identify and characterize the genetic factors involved in symptoms development and to disclose the regulation of this phenomenon. To this end, a comparative multidisciplinary study integrating transcriptomics and metabolomics analysis have been performed in a wide range of storage conditions and across different genetic background. The mechanism of action and effectiveness of two preventing strategies, such as the exogenous application of 1-MCP and storage at low oxygen concentration were assessed in two apple cultivars, ‘Granny Smith’ and ‘Ladina’. The metabolite and transcriptomic profiles revealed that 1-MCP treatment actively stimulated the production of unsaturated fatty acids such as oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3), thereby successfully preventing the development of superficial scald in ‘Granny Smith’. ‘Ladina’, on the other hand, was less responsive to these strategies and was characterized by a higher accumulation of very long chain fatty acids (VLCFAs), together with an increased level of fatty acid saturation. Additionally, the integration of the transcriptomic survey and VOCs assessment underlined that storage at low oxygen concentration stimulated the expression of genes involved in anaerobic respiration, such as malate, alcohol dehydrogenase, and pyruvate decarboxylase, leading to the accumulation of ethanol and acetaldehyde in both cultivars. The expression of three members of the VII subgroups of ERF genes was also observed in ‘Granny Smith’, which coordinate the acclimation process to hypoxia in plants. The effect of controlled atmosphere in the prevention of superficial scald was furthermore investigated in fruit of ‘Granny Smith’ stored for different time and employing both a static and dynamic controlled atmosphere approach. The transcriptome analysis found that the duration of storage had an important effect on the coordination of gene expression, and the expression patterns of DEGs identified a distinct networks and types of transcriptomic hubs. Samples that developed superficial scald were characterized by higher concentration of chlorogenic acid and a time-specific increase in the expression of PAL and PPO genes. Prevention of superficial scald was related to a peculiar realigning episodes that involved the accumulation of specific antioxidant metabolites, very long chain fatty acids, and the expression of genes that coordinate the hypoxia acclimation process, such as RAP2-like and PCO. A complementary research was conducted to investigate the connection between the application of 1-MCP, low oxygen, and superficial scald. The study highlighted the possible application of genes involved in key fruit ripening pathways, including ethylene-related pathways and sugar/fermentation metabolism, as potential biomarkers for molecular characterization of the major changes that occur during fruit storage. The specific expression of polyphenol oxidase, along with sorbitol-6-phosphate dehydrogenase, were also used to investigate the onset of superficial scald in apples and correlated with the accumulation of the sugar alcohol sorbitol, which plays a protective role against chilling injuries. Assessing the transcriptional signature of these biomarkers can contribute to the development of new tools for a more informed understanding of the physiological progression of postharvest ripening in apples. Overall, these studies provide insights into the genetic and metabolic mechanisms underlying the development and prevention of superficial scald in apple cultivars during storage. The results obtained here paved the way for the identification of a core set of genes to be used as functional marker suitable to better comprehend this phenomenon and to select new accession characterized by a superior fruit quality and postharvest performance.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The objectives of this work was to estimate the potential of flesh browning development in Gala , Royal Gala , Fuji e Braeburn apples after controlled atmosphere storage (CA). This study was realized through correlation of predictive methods and fruit quality and ripening parameters with the flesh browning occurrence after CA storage. Experiments were carried out with fruits from different orchards and years. In 2004, a first experiment was carried out with Fuji apples from three orchards. In 2005, Gala , Royal Gala , Fuji and Braeburn apples were evaluated from 11 orchards using two picking dates. Theses experiments were carried out at the Núcleo de Pesquisa em Pós-colheita of Federal University of Santa Maria, Santa Maria, Brazil with fruits from Vacaria, RS, Brazil. In 2006 to 2007 experiments were carried out in Germany using Braeburn apples from seven orchards. These methods the disorder occurrence after six months CA storage was correlated with the predictive methods, and with quality and ripening parameters. The predictive methods evaluated were: Mg infiltration, maturity acceleration with ethephon, and stress induction with high CO2. It was also evaluated the capacity of chlorophyll-fluorescence to detect possible stress occurrence on fruits exposed to high CO2 concentrations. Results show that in Fuji fruit juice percentage were able to predict flesh browning, but only in high CO2 (2.0 kPa) CA condition, while TSS level has been able to predict the occurrence of this disorder in fruits stored in low CO2 (<0.5 kPa). The chlorophyll fluorescence was capable of detect stress in fruits caused by exposure to high CO2 at harvest, and with this method it could be predicted the occurrence of physiological disorders in early harvested and with delay CA storage. By nutritional analysis of fruits, the level of K show high correlation with the occurrence of flesh browning after the CA storage of Braeburn apple. Some predictive methods and quality parameters evaluated at harvest were able to predict flesh browning occurrence in apple stored, in certain storage conditions, but in other storage conditions there wasn t significant correlation between flesh browning and this predictive methods and quality parameters. These predictive methods and quality parameters do not show high correlation with flesh browning in all situations. / O objetivo deste trabalho foi correlacionar à degenerescência da polpa das maçãs Gala , Royal Gala , Fuji e Braeburn após o armazenamento em atmosfera controlada (AC). O estudo foi realizado através da correlação com métodos preditivos e com atributos de qualidade e maturação dos frutos com a incidência real de degenerescência da polpa após o armazenamento em AC. Foram realizados experimentos com frutos de diferentes pomares, sendo executado em 2004 o primeiro experimento com a cultivar Fuji. Em 2005, os experimentos foram realizados com as cvs. Gala, Royal Gala, Fuji e Braeburn, avaliando frutos de 11 pomares em duas épocas de colheita. Os experimentos destes dois primeiros anos foram realizados no Núcleo de Pesquisa em Pós-colheitas da UFSM com frutos provenientes de pomares de Vacaria, RS. No período de 2006 e 2007 foram desenvolvidos experimentos em Ravensburg, na Alemanha, com a cv. Braeburn de sete pomares. Para isso, foram correlacionados a ocorrência de degenerescência da polpa após o armazenamento de seis meses em AC, com os testes preditivos e com atributos físico-químicos dos frutos analisados em duas épocas de colheita. Os testes preditivos avaliados foram: infiltração de Mg, aceleração da maturação com Ethephon e indução de estresse pelo alto CO2. Avaliou-se no experimento de 2006/2007 a possibilidade de detectar o estresse no fruto causado por diferentes concentrações de CO2 através da fluorescência de clorofila. Conforme os resultados, no ano de 2004 com a cv. Fuji, a percentagem de suco dos frutos foi capaz de prever a degenerescência da polpa, porém somente na condição de armazenamento de 2,0kPa CO2, enquanto que os SST previu a ocorrência dessa desordem somente em frutos armazenados com baixo CO2 (<0,5kPa). A fluorescência de clorofila foi capaz de detectar após colheita o estresse causado por pressões parciais de CO2 nos frutos armazenados. Com essa metodologia foi possível prever a ocorrência de degenerescência, somente quando se realizou a colheita precocemente e com atraso na instalação da AC. A análise nutricional dos frutos, destacando o nível de K, foi o atributo que melhor previu a ocorrência de degenerescência da polpa durante o armazenamento em AC na cv. Braeburn. Alguns métodos preditivos e atributos avaliados na colheita foram capazes de prever a incidência de degenerescência da polpa nos frutos armazenados numa determinada condição de AC, porém em outra condição de armazenamento não se confirmou essa correlação. Isso significa que estes testes e atributos de qualidade não apresentam alta correlação com a ocorrência da degenerescência em maçãs armazenadas em qualquer situação.

L’acide ascorbique (AsA) est un antioxydant essentiel à la fois pour l’homme et les végétaux. L’AsA provenant des plantes représente la source principale de vitamine C dans l’alimentation quotidienne. Au-delà de son impact nutritionnel, augmenter la teneur en AsA dans le fruit de tomate serait susceptible d’influencer la qualité des fruits après la récolte, en termes de conservation mais également de résistance à des pathogènes. Bien que le métabolisme de l’AsA soit bien caractérisé, les mécanismes impliqués dans sa régulation restent jusqu'à présent peu compris. Des études récentes menées sur des feuilles d’Arabisdopsis thaliana montrent que certaines protéines seraient capables de réguler la teneur en AsA, en agissant au niveau transcriptionnel ou post-transcriptionnel. A ce jour, ce type de régulation n’a pas été encore décrit chez les fruits. Dans ce but, une approche de génétique directe a été développée afin d’étudier les mécanismes impliqués dans la régulation de la teneur en AsA et ceci dans le fruit de tomate (Solanum lycopersicum). L’analyse d’une population de mutants EMS de tomate Micro-Tom a permis l’identification de lignées de mutants présentant des teneurs en AsA de 2,5 à 4 fois plus importantes que celles observées dans les fruits de tomate sauvage. La caractérisation de ces lignées a conduit à des résultats prometteurs pour l’étude de la qualité des fruits après la récolte. Une stratégie de NGS-mapping a permis l’identification des mutations causales responsables du phénotype AsA observé. Ainsi, le criblage de mutants EMS a permis la découverte de nouvelles protéines inattendues, permettant de confirmer au niveau moléculaire l’existence d’une interaction directe en la signalisation lumineuse et la régulation de la voie de biosynthèse de l’AsA. / The ascorbic acid (AsA) is an essential antioxidant in both plants and humans. Plant-derived AsA is the major source of vitamin C in the human diet. In addition to its effect on tomato nutritional value, increasing tomato AsA content would likely affect postharvest storage and resistance to pathogens of the fruit. While AsA metabolism is well characterized, the mechanisms involved in its regulation remain poorly understood. Recent studies in Arabidopsis leaves indicate that few regulatory proteins can regulate this pathway at transcriptional and post-transcriptional levels. Still nothing equivalent has been described in fruits. In that aim, a forward genetic approach has been carried out to investigate the regulation of AsA in tomato (Solanum lycopersicum) fruit. The screening of an EMS tomato mutant population in the miniature cultivar Micro-Tom for identifying mutant lines with AsA-enriched fruits was done. Among the 500 M2 mutant families screened, four mutant lines with higher AsA content ranging from 2.5 to 4 fold were selected. These mutant lines have been characterized for postharvest traits quality and showed promising results. A method based on NGS-mapping allowed the identification of the putative AsA-enriched related gene. Thus, the screening of EMS mutants led to original findings such as the discovery of new unexpected proteins regulating AsA in plants, and particularly in fruits. Our work confirms at the molecular level the direct interaction between light signaling component and the regulation of the AsA biosynthesis pathway.