Effects of spraying ethephon and potassium dihydrogen phosphate on fruit coloration of Merlot grape from eastern foothills of Helan Mountain in Ningxia

To address the issue of poor coloration in Merlot (Vitis vinifera L.) fruit on the eastern foothills of Helan Mountain in Ningxia, using deionized water containing 0.01% (V/V) tween 20 as a control, the leaf back and ear were sprayed with 300 mg/L ethephon and 0.3% potassium dihydrogen phosphate at different berry veraison stages: initial veraison, final veraison, 2 weeks after final veraison, initial+final veraison, final veraison+2 weeks after final veraison, and initial+final veraison+2 weeks after final veraison, and the effects of spraying ethephon and potassium dihydrogen phosphate on phenolic compounds and monomeric anthocyanin content in the fruit were investigated. The results showed that all treatments (spraying ethephon and potassium dihydrogen phosphate) significantly increased total anthocyanin content in grape pericarp (P＜0.05). Spraying 300 mg/L ethephon during initial veraison stage had the optimal effect in increasing the total anthocyanin content (12.31 mg/g) and total tannin content (25.59 mg/g) of the grape pericarp. Total anthocyanins (9.90 mg/g), total phenols (60.33 mg/g), and total tannins (26.16 mg/g) contents were the highest in grape pericarp sprayed with 0.3% potassium dihydrogen phosphate at initial veraison+final veraison+2 weeks after final veraison stages. In conclusion, spraying 300 mg/L ethephon at initial veraison stage or spraying 0.3% potassium dihydrogen phosphate three times during berry maturation could improve coloration of Merlot grape fruit on the eastern foothills of Helan Mountain in Ningxia.