Effects of S-abscisic acid treatment on fruit color and quality in ‘Kyoho’ grape

High temperature affects color and quality of grape fruits, especially at the maturing stage. In this study, (S)-2-cis-abscisic acid (S-ABA)-containing fertilizer was applied to 'Kyoho' grapes in order to improve their fruits quality. In 2012, 0, 20, 100 or 400 mg L-1 S-ABA-containing liquid fertilizer was sprayed on fruits at 6, 16 and 24 days after veraison (DAV). Anthocyanin level was increased and titratable acidity (TA) was declined by the S-ABA treatments. The treatment of 400 mg L-1 S-ABA at 24 DAV significantly increased fruits weight and total soluble solids (TSS). In 2014, 100 or 400 mg L-1 S-ABA and racemic RS-ABA were applied to 'Kyoho' grape fruits at 7, 14 and 21 DAV. The application of S-ABA resulted in the increments of anthocyanin by 100 and 400 mg L-1 at 14 and 21 DAV. Fruit weight and TSS were not influenced by the treatments, while TA was decreased by the treatments at 14 and 21 DAV. RS-ABA was less effective than S-ABA, probably because concentration of active (S)-2-cis-ABA form in the commercially available synthetic RS-ABA was lower than that of S-ABA containing-fertilizer. (S)-2-cis- and (R)-2-cis-ABA were isomerized into isomers such as (S)-2-trans-ABA and (R)-2-trans-ABA after UV exposure for 3 days. Effects of S- and RS-ABA on fruit quality were discussed.