2019 Volume 88 Issue 2 Pages 189-201
Abscisic acid (ABA) and ethylene are well-known phytohormones that are involved in the maturation of grape berries and other fruits. However, the process of yellow-green skinned grape berry maturation is not well understood due to difficulties in determining grape maturity from changes in skin color. Skin browning during maturation is a major commercial problem in some yellow-green skinned grape cultivars including ‘Shine Muscat’. To resolve this issue, a better understanding of the mechanisms involved in grape maturation and skin-browning is needed. We treated ‘Shine Muscat’ grape clusters at the veraison stage (45–50 DAFB) with spray applications of ABA or ethephon. These treatments produced darker colors and increased the trans-resveratrol and flavonol contents of berry skins. The ABA and ethephon treatments significantly increased the severity of skin browning. Changes in the expression of genes involved in polyphenol biosynthesis and oxidation were consistent with increases in polyphenols and the severity of browning in berry skins. The expression of VvACO2 and VvYUC1 genes, which are involved in ethylene and auxin biosynthesis, respectively, were upregulated in berries with brown skins. Although ABA treatment also increased the size of the berries, the effect of ethephon treatment on berry maturation was similar to, or greater than, that of ABA treatment. In berry skins, the expression of VvACO3, which is involved in phytohormone biosynthesis, increased significantly in response to ABA treatment. Overall, the changes in gene expression produced by ABA and ethephon treatments differed. Therefore, different mechanisms may regulate the physiological responses to ABA and ethephon, although both treatments accelerate berry maturation.