# Effect of Seawater Irrigation on the Sugars, Organic Acids, and Volatiles in 'Reliance' Grape
## 4 Discussion
Compared with the control berries, more terpen, such as citronello, \(\beta\)-myrcene, \(\alpha\)-terpineol, and trans-rose oxide, were detected in the S1 berries (Table 3); these low threshold volatiles can provide floral and rose scents to the 'Reliance' grape. However, 10% seawater treatment did not alter the aroma of the amino acid pathway volatiles, suggesting the grape cultivars characterized by the aroma from the amino pathway may not benefit from 10% seawater irrigation. The developmental period-specific evolution of grape volatiles during ripening has been reported widely. In 'Cabernet Sauvignon' grapes, C6 volatiles were mainly accumulated in the form of C6 aldehydes, C6 alcohols, and C6 esters during the veraison period, post-veraison period, and maturity period [30]. In the Muscat grape 'Shine Muscat' (Vitislabrusca \(\times\) V. vinifera), C6 aldehydes were synthesized in large quantities at the veraison stage, C6 alcohols at the post-veraison stage, and C6 esters and terpen during early maturity [31]. Though irrigation with 10% seawater significantly affects some key volatiles (Table 3), the accumulation of volatiles mainly follows the berry development patterns. The expression levels of the four structural genes in the LOX-HPL pathway were closely related to the C6 volatile generation. _VvLOXA_ was the gene responsible for changes in 'Reliance' grape volatiles under 10% seawater treatment. Previous studies postulate that plants release C6 volatiles in response to biotic stresses [17]. The remarkable upregulation is evident in many LOX genes under salt stress in tomato (_Solanum Lycopersicum_ L.) [32]. Herein, _VvLOXA_ showed two consecutive transcript abundance peaks at EL 33 and EL 35 as the first rate-limiting gene in the LOX-HPL pathway (Figure 6a). This finding was attributed to _VvLOXA_ activation, which consequently oxidized fatty acids and provided substrates for the synthesis of volatiles in response to 10% seawater irrigation, especially in the S1 treatment. The highest peak of _VvHPL_ expression and content of C6 aldehydes appeared at EL 33 and EL 36, respectively, revealing a delay between changes in the genes and volatiles under seawater treatment. In addition, water deficits also increased the transcription level of _VvLOX_ and _VvHPL_ in 'Cabernet Sauvignon' grapes, thus, enhancing the metabolism of C6 volatiles [33; 34]. Notably, the expression levels of _VvADH_ and _VvAAT_ in S2 and S3 were higher than those of the S1 berries at EL 38, with the concentrations of C6 esters showing an opposite trend. This result was attributed to the high transcript levels of _VvLOXA_ and _VvHPL_ in the S1 berries, which resulted in more abundant C6 aldehydes for the synthesis of esters. Based on the relative expression gene profiles of these volatiles, we concluded that _VvLOXA_ is the key gene that alters GLVs composition in grapes. This result was consistent with that of a previous study in which an increasing pattern of the _VvLOXA_ transcript at the pre-veraison stage was observed in four grape varieties for two vintages [14]. Seawater irrigation has a long history; in Israel in 1966, [PERSON] creatively mixed freshwater and seawater on the sand to irrigate crops [35]. Irrigating crops with undiluted seawater could cause soil salinization, nutrient loss, and damage to the soil's physical structure, which are not conducive to plant growth, but in this experiment, the soluble soil salt content under the S1 and S2 treatments did not reach 1 g kg\({}^{-1}\) and was, thus, far from causing soil salinization. This low salinity could be due to the heavy seasonal rainfalls and moderate salinity of 10% seawater. On the other hand, large-scale soil acidification due to fertilizer overdose is a current challenge in China. The application of seawater irrigation could, therefore, alleviate this soil acidification gradually. In summary, the 10% seawater irrigation of grapevines during the whole growing period is a sustainable and feasible strategy and does not cause soil salinization.