Difference Between Coloration and Endogenous Abscisic Acid Accumulation Patterns in Two Red Grape Cultivars, ‘Aki Queen’ and ‘Ruby Roman’ (Vitis labruscana Bailey) Berries

Changes in anthocyanin and endogenous abscisic acid (ABA) contents in the berry skins of Vitis labruscana × V. vinifera cultivars, ‘Aki Queen’, and ‘Ruby Roman’ were investigated during the fruit development period. Color development of ‘Aki Queen’ berries mainly occurred within 20 days post véraison, while that of the ‘Ruby Roman’ was prolonged for about 40 days. In both cultivars, the ABA level in the berry skin started to increase a few days before véraison; however, ABA accumulation ceased approximately 10 days after véraison in ‘Aki Queen’, while it continued until the late stage of maturation in ‘Ruby Roman’. In addition, higher indole-3-acetate aspartate (IAA-Asp) and lower isopentenyladenine (iP) contents were observed in ‘Ruby Roman’ than in ‘Aki Queen’ at the late development stage. The expression analysis of genes involved in ABA metabolism revealed that V. vinifera 9-cis-epoxycarotenoid dioxygenase 3 (VviNCED3), which is assumed to play a major role in ABA biosynthesis, remained relatively higher in ‘Ruby Roman’ than in ‘Aki Queen’ after véraison. Considering that ABA plays a regulatory role in grape maturation, these results may indicate that the coloration of ‘Ruby Roman’ at the later stage of maturation is partly attributable to an increased ABA pool in berry skins.