Changes in sucrose and the VcADR gene induced sugar accumulation in blueberries during ripening and after chitosan treatment

BACKGROUND: The sweetness of highbush blueberries (Vaccinium corymbosum L.) is related to changes in sucrose and other primary sugar metabolites. OBJECTIVE: This study compared the fruit quality and sugar metabolism in the blueberry cultivars Brigitta and Elizabeth at three ripening stages and with a postharvest chitosan treatment to determine which factors are important in sugar metabolism in the two cultivars. METHODS: Blueberries were harvested at three ripening stages. Fully ripe fruit was treated with chitosan and kept at room temperature for 5 and 10 days. GC-MS was used to measure organic acids, individual sugars, and sugar derivatives. Gene expression was analysed using qPCR. RESULTS: Elizabeth fruit was less firm than Brigitta fruit, but contained more soluble solids. The sweeter taste of Elizabeth versus Brigitta was due to down-regulated VcINV, VcSPS, and VcADR transcription and increased sucrose concentration. Chitosan inhibited VcADR and VcINV transcription in Elizabeth, but activated these genes in Brigitta after 5 days of storage. CONCLUSIONS: Aldose reductase might be an essential enzyme in blueberry sugar metabolism. These findings support research on the mechanism of sugar accumulation in fruit during maturation and after postharvest treatments in blueberries.