Effects of temperature on skin coloration at different developmental stages of potted ‘Ruby Roman’ grape berries

The effects of temperature on the color of ‘Ruby Roman’ grape berry skin in 5-year-old potted trees were investigated. Thirty-six trees were divided into six groups: five groups received low-temperature treatment (28℃/20℃, day/night) at different developmental stages: at 54 (13 days after veraison) to 63 days after full-bloom (DAFB) (54 DAFB group); 63-72 DAFB (63 DAFB group); 72-81 DAFB (72 DAFB group); 81-90 DAFB (81 DAFB group); 54-90 DAFB (low-temperature control, 28℃/20℃); and one group received high-temperature treatment (35℃/27℃) at 54-90 DAFB (high-temperature control). Before and after treatments, the trees were kept under high-temperature conditions. After treatment, color change including the color chart value and concentration of anthocyanin in berry skin were the highest in the 63 DAFB group, followed by the 72 DAFB group. For harvested berries, the low-temperature control group had the deepest skin color, whereas the high-temperature control and 54 DAFB groups had the lightest skin colors. These results indicate that the color of ‘Ruby Roman’ berry skin is enhanced by exposure to low temperature after 63 DAFB and is the most sensitive to low temperature from 63 to 80 DAFB. Gene expression analysis showed higher expression levels of the VlMybA1-2 and VlMybA1-3 genes in the high-temperature than in the low-temperature control group. However, the expression levels of VviF3′H and VviF3′5′H2 immediately following low-temperature treatment in the 63 and 72 DAFB groups were higher than in both control groups. These findings suggest that the decrease in anthocyanin accumulation under high-temperature conditions might not be controlled by VlMybA1 transcriptional factors, and that a different mechanism may be involved in regulation of the biosynthesis of anthocyanin in ‘Ruby Roman’ grape berry skin.