# Effect of Seawater Irrigation on the Sugars, Organic Acids, and Volatiles in 'Reliance' Grape
## 1 Introduction  
Grapes are a popular fruit consumed worldwide and products from grape processing, such as raisins and wine, also have high economic value. Although grapevines have substantial drought tolerance [1], the shortage of water resources due to global warming, increasing water tax, pollution, and other problems restrict the full exploitation of the grapevine. In this case, the utilization of diluted seawater for vineyard irrigation is a water-saving strategy worth exploring. Seawater is approximately 3.5% saline, and the significant elements are sodium, magnesium, calcium, and potassium, inducing salinity stress in plants and negative effects on the soil [2]. Research on the effects of diluted seawater treatments and salt stress on plants has made significant progress in various crops, including watermelon, apple [3], and grape [4]. Previous studies demonstrated that irrigation with diluted seawater resulted in the accumulation of soluble sugars, polyphenols, carotenoids, and fatty acids in leafy vegetable crops [5]. For instance, tomato plants irrigated with diluted seawater produced berries characterized by high amounts of vitamin C, vitamin E, and dihydropic acid [6]. Another study evaluated the effects of long-term NaCl-treatment on grapes and found that moderate salinity (20 and 60 mM) enhanced the overall berry quality but decreased the aroma. However, high salinity (100 and 150 mM) decreased berry quality [7]. Our previous work demonstrated that field irrigation with seawater improves fruit quality, and more than four consecutive years of seawater irrigation didnot induce secondary soil salinization. These findings prove that seawater irrigation could provide a feasible and beneficial irrigation strategy in viticulture [2]. At present, the effect of diluted seawater on grape volatiles is obscure. As one of the well-known fruits globally, grapes have hundreds of volatiles [8; 9], and their concentrations, properties, and balances between each other determine the features of different grape cultivars and wines [10; 11]. Grape volatiles can be divided into terpenoids, norisoprenoids, aromatic compounds, aliphatic volatile compounds, methoxypyrazines, and organo-sulfur compounds [12]. These biomolecules can be further classified into three categories according to the types of precursors and the synthetic routes: isoprene pathway, fatty acid pathway, and amino acid pathway volatiles. Straight-chain fatty acid derivatives are also called green leaf volatiles (GLVs); they include C6 aldehydes, C6 alcohols, and C6 esters, all of which are generated through the lipoxygenase pathway from C\({}_{18}\)-polyunsaturated fatty acids (\(\alpha\)-linolenic acid and linoleic acid). Various genes, including _VvLOX_ (lipoxygenase), _VvHPL_ (hydroperoxides lyase), _VvADH_ (alcohol dehydrogenase), and _VvAAT_ (alcohol acyltransferases), are key in this fatty acid metabolism [12; 13; 14]. Generally, the fruity and floral scent of these GLVs, especially C6 esters, is the primary source of the fruity and floral scent of aroma in both grapes and wine [15; 16]. Moreover, these volatiles have also been shown to serve as essential signal molecules for the pollination and/or prevention of pathogen intrusion [17; 18; 19]. Furthermore, as a product in the isoprene pathway, terpen are considered primary compounds of Muscat cultivars, such as Shine Muscat and Thermal Spring [20]. Amino acid pathway volatiles also contribute to the aromatic characteristics of grapes; benzene acetaldehyde has a hyacinth-like smell, and methoxy pyrazines (MPs), found in immature Cabernet Sauvignon grapes, has a vegetal aroma. Therefore, this study aimed to determine the effect of 10% seawater irrigation starting at different grapevine phenological stages on grape volatiles. The 'Reliance' grape (Ontario \(\times\) Suffolk Red), which is abundant in fruity but little floral scent, was selected, and its volatiles were analyzed according to the three synthetic routes.