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.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The most widely way used to store apples is the controlled atmosphere (CA), were the oxygen is reduced, but this is far above the lower oxygen limit (LOL) tolerated by the fruit. The use of technologies that allow the monitoring of oxygen levels at least tolerated by the fruit can help maintain quality and reduce the incidence and of physiological disorders and postharvest diseases. The dynamic controlled atmosphere (DCA) is one of these technologies, which change the O2 throughout the storage period according to the fruit metabolism. The objective of this study was to evaluate effect of DCA storage monitored by the respiratory quotient (RQ) and chlorophyll fluorescence (CF), as well as their interaction with the application of 1-methylcyclopropene (1-MCP) on the physicochemical quality and physiological disorders, especially superficial scald of 'Granny Smith' apple. The following storage conditions were evaluated: a) Conventional CA with 1.5 kPa O2 plus 1.0 kPa CO2; b) DCA-RQ 1.3; c) DCA - RQ 1.5; d) DCA - RQ 1.7; e) DCA-CF (HarvestWatchTM DCA). The CO2 partial pressure was maintained at 1.2 kPa and the temperature at 1.5 °C in all treatments. After 9 months of storage, at the fruits removal from the storage chamber, evaluations were performed for superficial scald incidence and severity, decay and healthy fruits incidence. The other evaluations were performed after a 7 days period of shelf life at 20 ° C in. Fruits stored under DCA had lower ethylene production and respiration as compared to fruits stored in conventional CA, because of the lower 1-acid-aminocyclopropane-1-carboxylic enzyme activity by apples stored in DCA-RQ 1.5 and 1.7. The storage of apples in DCA-RQ 1.5 or 1.7 resulted in low superficial scald incidence. Under these conditions the application of 1-MCP had no benefit in reducing this disorder, suggesting that their application may be needless, but it is efficient when the fruits are stored in conventional CA and DCA-CF. In fruits DCA-RQ 1.7 storage occurred most volatile production associated with fermentative metabolism, but without decline of the fruit quality. Apples stored in DCA-RQ 1.7 kept greener color as compared to fruit stored in conventional CA due to the higher concentration of total chlorophyll. The firmness of the fruit stored in DCA-RQ fruit was higher as compared to the ones stored in CA, regardless of the application of 1-MCP. Under DCA-CF, application of 1-MCP has been shown not to be beneficial for maintaining the quality of the 'Granny Smith', as it provided the highest occurrence of decay. The storage in DCA provided higher number of healthy fruits as compared to the ones stored in CA. / A forma mais utilizada para o armazenamento de maçãs é a atmosfera controlada (AC), em que é reduzido o nível de O2, mas este fica muito acima do limite mínimo tolerado pelo fruto. O uso de tecnologias que permitem o monitoramento dos níveis de oxigênio no mínimo tolerado pelos frutos pode auxiliar a manutenção da qualidade e reduzir a incidência de distúrbios fisiológicos e podridões. A atmosfera controlada dinâmica (ACD) é uma destas tecnologias de controle e variação do O2 ao longo de todo o período de armazenamento de acordo com o metabolismo dos frutos. O objetivo deste trabalho foi avaliar o efeito do armazenamento em atmosfera controlada dinâmica monitorada pelos métodos do quociente respiratório (QR) e da fluorescência de clorofila (FC), bem como a sua interação com a aplicação de 1-metilciclopropeno (1-MCP) sobre a manutenção da qualidade e redução de distúrbios fisiológicos, especialmente a escaldadura superficial na maçã Granny Smith . As condições de armazenamento avaliadas foram: a) AC convencional com 1,0 kPa O2 mais 1,5 kPa CO2; b) ACD com quociente respiratório (QR) 1,3; c) ACD-QR 1,5; d) ACD-QR 1,7; e) ACD monitorada pela fluorescência de clorofila (ACD-FC) (HarvestWatchTM DCA). A pressão parcial de CO2 foi mantida em 1,2 kPa em todos os tratamentos e a temperatura em 1,5 °C. Após nove meses de armazenamento, no momento da saída dos frutos da câmara, foram realizadas avaliações quanto à incidência e severidade de escaldadura superficial, incidência de podridões e frutos sadios. As demais avaliações foram realizadas após um período de sete dias em que os frutos permaneceram expostos à temperatura de 20 °C com o objetivo de simular o período de prateleira. Frutos armazenados sob ACD apresentaram menor produção de etileno e respiração que frutos armazenados em AC convencional, como resultado da menor atividade da enzima ACC oxidase nas maçãs armazenadas em ACD-QR 1,5 e 1,7. O armazenamento de maçãs em ACD-QR 1,5 ou 1,7 favoreceu uma menor incidência de escaldadura superficial. Nestas condições a aplicação de 1-MCP não teve nenhum benefício na redução desse distúrbio, sugerindo que sua aplicação pode ser dispensada, porém é necessária quando os frutos são armazenados em AC convencional e ACD-FC. Nos frutos armazenados em ACD com QR 1,7 ocorreu maior produção de voláteis associados ao metabolismo fermentativo, contudo, não houve prejuízo à qualidade dos frutos. Maçãs armazenadas em ACD-QR 1,7 mantiveram coloração mais verde que frutos armazenados em AC convencional devido à maior concentração de clorofilas totais. A firmeza dos frutos armazenados em ACD-QR foi maior que frutos em AC, independentemente da aplicação de 1-MCP. Sob ACD-FC a aplicação de 1-MCP demonstrou não ser benéfica para a manutenção da qualidade das maçãs Granny Smith , uma vez que forneceu a maior ocorrência de podridões. O uso de ACD proporcionou um maior número de frutos sadios quando comparado a AC convencional.