Anthocyanin Accumulation and Its Corresponding Gene Expression, Total Phenol, Antioxidant Capacity, and Fruit Quality of 'Crimson Seedless' Grapevine (Vitis vinifera L.) in Response to Grafting and Pre-Harvest Applications

The color of grapevine berries is one of the most important quality parameters that define the appearance, attracts the consumer, and determines the price, especially in red grape cultivars. Some grape varieties show less color development due to many factors such as temperature, light intensity, and agricultural management. The present study aimed to evaluate diverse phytohormones coupled with grafting on quality and fruit coloration of 'Crimson Seedless' grapes. Pre-harvest foliar treatments of abscisic acid (ABA) at 400 mg L-1, methyl jasmonate (MeJ) at 1 mM L-1, ethephon (Eth) at 480 mg L-1, and melatonin (Mel) at 100 mu mol were applied after 7 days and repeated after 21 days of 'Veraison' (beginning of the coloring phase). The results exposed that the ABA application provided the best anthocyanin accumulation with grafted grapevines whereas Eth displayed the maximum anthocyanin accumulation with ungrafted grapevines. Moreover, the expression of anthocyanin biosynthesis genes (chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), and flavanol 3-O-glucosyl transferase (UFGT)) was consistent with the anthocyanin concentration in berry peel. Moreover, Eth treatment revealed the highest total phenols and antioxidant capacity for both grafted and ungrafted grapevines. MeJ phytohormone exhibited the largest total yield, whereas the treatment of Eth increased the weight of 50 berries and the bunch. Furthermore, ABA induced the uppermost firmness and removal force. Regarding the chemical attributes, the Mel treatment revealed the minimum value of titratable acidity (TA) and the highest polyphenol oxidase (PPO) activity, while the MeJ treatment recorded the superior soluble solids content (SSC), in addition to phenylalanine ammonia-lyase (PAL) and catalase (CAT) enzymes activities. Eth treatment produced the highest activity of the peroxidase (POD) enzyme. Finally, the grafting treatment improved most of the studied fruit attributes.