# Effect of Seawater Irrigation on the Sugars, Organic Acids, and Volatiles in 'Reliance' Grape
## 4 Discussion  
In this experiment, 10% seawater treatment did not alter the average berry weight of the berries, which concurs with the trends of a 4-year seawater irrigation experiment performed by our team [2]. Contrarily, another study showed spraying NaCl (100 mM or 150 mM) on grape leaves increased the fresh weight of the berries. The authors attributed the increment to a rise in relative water content (RWC), mediated by the osmotic regulation of Na\({}^{+}\) and Cl\({}^{-}\) ions in the berries [7]. The discrepancy between the two results could be because the concentration of NaCl in 10% seawater was so low that osmotic regulation was negligible. Besides, as an essential index for turgor evaluation, the decline in skin hardness and frangibility of the S1 groups at EL 35 indicates that berry softening was promoted, which is a sign of fruit-ripening. Moreover, berries in the S1 group had greater firmness and hardness when compared with the control group berries in the last period, EL 38, suggesting the fruits from the S1 group could have better storage and transport attributes. Sugar and organic acids are basic indexes of grape-ripening. They also determine the organoleptic quality and flavor of table grapes [7]. It is postulated that salt-treated cherry tomatoes have higher titratable acid concentrations and reduced sugars than the controls [6]. It is also postulated that water with high electrical conductivity (EC) can enhance the TA and TSS content of tomato [23]. Herein, the concentration of TSS, glucose, and fructose in treated grape berries was increased at the EL 35 stage. However, malic and tartaric acid content had a decreasing trend compared to the control. The trends of titratable acidity and TSS levels were consistent with those of a 4-year seawater treatment for grapevines [2]. Based on the disparities of these results, the influence of salt treatment on grape quality could have been affected by the various salt concentrations used. The significant changes in glucose and fructose levels due to seawater treatment indicate that environmental changes easily affect sugar concentrations and maintain osmotic pressure. As an essential determinant of grape quality, volatiles exist as free or bound glycosides. Among them, the free forms could be more vital ingredients that determine the flavor, although odorless bound glycosylated forms could be hydrolyzed to odor-active free forms during fermentation [24]. C6 esters and terpen are the main contributors to the abundant fruits and negligible flower scent in 'Reliance' grape. The aroma in different pathways first reduced and then increased (Figure 4). The turning point was during the fruit expansion period because the concentration of volatiles in the fruit may be diluted, which concurs with previous results [25]. Furthermore, since C6 volatiles (also called GLVs) were more sensitive to environmental changes [26], the change in the concentration of its volatiles occurred earlier than the volatiles of the other two pathways. Previous studies in strawberry [27] and Nero d'Avola wine [28] found that moderate and low salinity levels increased ester concentrations consistent with the trend observed in this experiment. In this experiment, aroma content related to the isoprene pathway at EL 31 reached 23.22 \(\mu\)g kg\({}^{-1}\) (Table S4). It was mainly eucalypt (63.43%), with a \"eucalypt\" and \"medicinal\" flavor, that was found in 'Reliance', 'Riseling', and Australian 'Cabernet Sauvignon' grapes but not in the Shine Muscat grape [29]. In contrast, [PERSON] reported that isoprene pathway volatiles, especially terpen, are the main contributors of the flower scent, and their concentrations were substantially low before veraison [25]. The divergence between our findings and that of [PERSON] et al. (2020) can be attributed to differences in the aroma features of various grape cultivars.