Difference of Coloration between ‘Aki Queen’ and ‘Ruby Roman’ Grapes Treated with Abscisic Acid-containing Fertilizer at Late Stage of Maturation

Abstract

The effects of abscisic acid (ABA)-containing fertilizer treatment at a late growing stage (from 25 to 40 days after véraison) on the color development and quality of tetraploid red grape cultivars ‘Aki Queen’ and ‘Ruby Roman’, undergoing seedless cultivation, were investigated. The treatments at the late growing stage promoted ideal coloration without negative effects such as over-coloration or a decrease in the sugar content, which indicated the beneficial effect of color improvement induced by this fertilizer treated at the late growing stage. The enhanced accumulation of total anthocyanins due to this treatment was more notable in ‘Aki Queen’ than in ‘Ruby Roman’. Time-dependent anthocyanin accumulation and the expression of genes involved in anthocyanin biosynthesis and related transcription factors, VlMybA1-2 and VlMybA1-3, and expression of the enzyme UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) revealed the difference between these cultivars: all values were higher in ‘Ruby Roman’ than in ‘Aki Queen’ at the late stage of berry development, suggesting that higher levels of anthocyanins are accumulated in ‘Ruby Roman’.