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Abstract
The southern highbush (Vaccinium corymbosum) and rabbiteye (V. virgatum) blueberries are commonly grown cultivars in the southeastern U.S. The objective of this study was to investigate mechanisms involved in ripening and factors affecting postharvest fruit quality in blueberry. The first study investigated the molecular and metabolic basis of regulating fruit development and ripening in rabbiteye blueberry, revealing continual sucrose uptake during fruit ripening, stimulated glycolysis, tri-carboxylic acid (TCA), and anthocyanin-related metabolism during ripening. Follow-up gene expression analyses revealed important genes associated with sugar, acid, and anthocyanin metabolism. The second study investigated the effect of ethylene releasing plant growth regulators (PGRs) on ripening, metabolite composition, and postharvest fruit quality attributes. Both ethephon and 1-amino cyclopropane 1-carboxylic acid (ACC) transiently stimulated sugar, acid, and anthocyanin metabolism, increasing the rate of ripening with minimal impact on fruit quality attributes. The increase in transcript abundance of VACUOLAR INVERTASE (vINV), PHOSPHOENOLPYRUVATE CARBOXYKINASE (PEPCK), and anthocyanin biosynthesis related genes, were associated with ethylene-induced ripening related changes. The third study characterized ripening related transcription factors (TFs) during fruit development and ripening, and identified four important TFs, potentially involved in fruit ripening. Among them, the transcript abundance of VvMADS7, VvNAC1, and VvNAC2 increased after the application of ethephon, suggesting that they are ethylene inducible. The transcript abundance of VvNAC8 remained unaffected by ethylene application, suggesting that the expression of this gene during ripening is independent of ethylene-mediated signaling. The fourth study used the linear and LASSO regression models to identify physical traits and metabolite markers associated with fruit firmness during postharvest storage. This study identified titratable acidity (TA), specifically quinate and citrate, exhibited positive associations with fruit firmness. Conversely, sugars and amino acids displayed negative associations with fruit firmness. In summary, our research has shed light on both the applied aspect like utilization of PGRs as a ripening aid, and basic aspects of ripening and postharvest physiology mechanisms in blueberries, which can be utilized to improve ripening characteristics, fruit quality, and postharvest shelf-life.