Boosting Grapevine Resilience: The Impact of Seaweed Extracts on Vitis Vinifera Cv. Merlot under Water Stress

Water stress can significantly impact grapevine growth, physiology, and fruit quality, making it crucial to explore strategies that enhance the resilience of these plants (1). Biostimulants, including natural products such as seaweed extracts, have gained attention for their ability to improve plant tolerance to abiotic stress. Specifically, seaweed extracts are rich in bioactive compounds such as alginic acids, mannitol, and oligosaccharides, known to activate stress-related metabolic pathways and improve plant performance under drought conditions. Additionally, these extracts have been found to influence grape maturation, contributing to technological and phenolic improvements in the final product (2). The objective of this study was to evaluate the effectiveness of newly product, on the process of development, based on seaweed-based extract (ILSA S.p.a. group), on Vitis vinifera cv. Merlot under water stress conditions. Specifically, the research aimed to assess the impact of these treatments on key physiological parameters such as net photosynthesis, stomatal conductance, transpiration rate, and water-use efficiency. Additionally, the study sought to investigate the molecular mechanisms behind the grapevines' stress response by analysing the expression of genes associated with drought resistance, including AREB1, ABF1, CBF1, and PIP1. A further goal was to monitor the effects of these treatments on grape maturation, focusing on sugar content, acidity, pH, and phenolic maturity, to understand their potential influence on grape quality. The study aimed to identify sustainable practices that can enhance grapevine resilience and productivity in water-limited environments. The study was conducted on 40 grapevines of Merlot, grafted on Kober5BB, and divided into two treatments, NT (not treated) and T2 (seaweed treated) with 20 plants per treatment (4 replicates/treatment) using a randomized block design. Treatments were applied at a dose of 2 L/ha every 14 days for a total of six applications. Physiological measurements, including net photosynthesis (A), stomatal conductance (gs), transpiration rate (E), and water-use efficiency (WUE), were conducted on two central leaves of the three central plants for each treatment at three different phenological stages: flowering, 'pea-size' berries, and 50% veraison. In addition, gene expression analysis was performed on selected genes (AREB1, ABF1, CBF1, and PIP1) to understand the molecular mechanisms activated by these treatments under water stress (3; 4). The leaf samples were collected 24 hours after the treatments, and gene expression was quantified using quantitative real-time PCR. Meanwhile, by using a portable photosynthetically device (LiCOR), the eco physiological parameters were recorded. Statistical analyses were performed: one-way analysis of variance (ANOVA) was applied to assess the effects of the treatments on various physiological, genetic, and production parameters. Post hoc comparisons were conducted using Tukey’s Honest Significant Difference (HSD) test to identify significant differences among treatment means. The photosynthetic analysis showed that the T2 treatment significantly increased the net photosynthesis rate (A) and intercellular CO₂ concentration (Ci) compared to NT, suggesting a higher photosynthetic efficiency in T2 (5). Although transpiration (E) slightly increased in T2, it was not statistically significant, indicating that the plants managed to maintain their water balance effectively. WUE was improved in T2, PÓSTERS – VITICULTURA 286 reflecting a more efficient assimilation of CO₂ without a proportional increase in water loss. Stomatal conductance (gs) also showed a slight but not statistically significant increase in T2. Gene expression analysis revealed a significant upregulation of all four genes in T2 treatment compared to NT (6). The technological analysis of grape maturation showed that grapes treated with T2 had a significantly higher °Brix, indicating better sugar accumulation, and a more advanced phenolic maturity, which is essential for high-quality wine production (7). Furthermore, T2 treatment resulted in an increase in grape production per vine without significantly altering the average cluster weight. The T2 treatment was the most effective in improving the physiological performance, grape quality, and productivity of grapevines under water stress conditions compared to the non-treated control. It enhanced photosynthetic efficiency, water-use management, and induced stress-related gene expression, offering a promising strategy for sustainable viticulture practices.