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Abstract
Blueberry (Vaccinium spp.) is an important crop for the United States, and the consumption of this fruit has been increasing due to its popularity as a nutraceutical. In spite of the increase in blueberry production, there exists a gap in knowledge regarding factors that regulate ripening and postharvest fruit quality. Blueberry ripening is non-uniform during the growing season, and requires multiple harvests resulting in higher production costs. Besides, the postharvest shelf-life of blueberry is only between 1-6 weeks after harvest. In order to 1) synchronize and manipulate blueberry ripening and 2) generate information for maintaining postharvest fruit quality, we would like to investigate the mechanisms involved in ripening and postharvest fruit quality in the four studies below. The first study investigated the respiration and ethylene production patterns during fruit ripening and the response of ethephon (ethylene releasing agent) application on ethylene biosynthesis in southern highbush and rabbiteye blueberry. Our data has shown that southern highbush and rabbiteye blueberry display an increase in the rate of respiration and ethylene evolution characteristic of climacteric behavior. However, blueberry fruit did not display auto-catalytic ethylene regulation during ripening. The second study explored the effect of three plant growth regulators, ethephon, abscisic acid (ABA), and methyl jasmonate (MeJA), on rabbiteye blueberry ripening and postharvest fruit quality. The results indicate that ethephon but not ABA or MeJA promotes fruit ripening by increasing the proportion of blue (ripe) fruit with limited effect on postharvest fruit quality. The third study further investigated the mechanism of ethylene-induced ripening in blueberry by RNA-seq, a technique that reveals global changes in gene expression. The results show that ethylene initiates ripening mainly by downregulating photosynthesis-related genes and regulating hormone and cell wall modification genes. In the last study, to understand the mechanism that controls postharvest fruit quality in blueberry, RNA-seq was conducted using southern highbush cultivars with superior and inferior postharvest fruit quality during storage. The data reveal several processes that may play essential roles during postharvest storage, such as cytoskeletal and cell wall changes, accumulation of important amino acids, and water loss. In sum, the research has generated information that can be applied to the blueberry industry immediately and expanded the basic knowledge in blueberry ripening and postharvest fruit quality.