Advances in Biostimulant Applications for Grapevine (Vitis vinifera L.): Physiological, Agronomic, and Quality Impacts

Abstract

This manuscript reviews the advances in the application of biostimulants in grapevine (Vitis vinifera L.), emphasizing their physiological, agronomic, and quality impacts within a broader agricultural and scientific context. It highlights the evolution of biostimulant research and the theoretical frameworks that support their use, underscoring their growing relevance in sustainable viticulture as a response to environmental challenges and consumer demands for healthier production practices. By analyzing recent findings, the text outlines how biostimulants influence plant physiology, improve agronomic performance, and enhance fruit and wine quality, while also stressing the need for deeper understanding of their mechanisms of action and greater standardization in their application. The discussion suggests that advancing this field requires not only scientific attention but also an integrative vision that links innovation, sustainability, and practical implementation. Ultimately, the manuscript contributes to a more comprehensive appreciation of the role of biostimulants in viticulture, offering insights to guide future research and strategies for grapevine management and quality improvement.

1. Introduction

The economic and ecological importance of the grapevine. Vitis vinifera L., or grapevine, is one of the most vital agricultural crops worldwide, valued not only for its role in wine production but also for creating jobs, supporting local economies, and maintaining winemaking traditions. In Mexico, especially in regions like Baja California, viticulture is a key sector gaining international recognition for its high-quality wines and contribution to regional development. However, climate change is significantly impacting the physiology, phenology, and quality of grapevine crops both globally and nationally. Recent studies reveal a consistent rise in average annual temperatures, causing earlier development stages such as budburst, flowering, veraison, and harvest [1,2]. In addition to affecting yields, these changes alter critical enological parameters like acidity, sugar levels, and phenolic compounds [3,4]. In Mexican wine regions, particularly Baja California, temperatures are predicted to increase between 1.2 °C and 4 °C by the century’s end. This shift could make traditional valleys less suitable for high-quality wine production, favoring table grapes or raisins instead [5,6,7]. Socially and economically, this trend has been linked to fluctuations in yields and income instability for producers, raising concerns about the long-term sustainability of the sector [8,9].

In light of this, viticulture must adopt adaptation strategies to protect grape and wine quality while maintaining productivity. Proposed measures include changing farming practices (e.g., late pruning, cluster thinning), relocating vineyards to higher-altitude areas, using more resistant cultivars, and applying biotechnological tools [3,10,11,12]. An emerging promising approach is the use of agricultural biostimulants that can boost grapevine physiological and biochemical responses to abiotic stress, ultimately increasing crop resilience and preserving fruit quality amid rising climate challenges.

1.1. Role of Biostimulants in the Context of Climate Change

Climate change has increased the frequency and severity of various abiotic stresses, such as drought, heat stress, and salinity, directly affecting the growth, yield, and enological quality of Vitis vinifera [13,14]. Generally, abiotic stress leads to the excessive buildup of reactive oxygen species (ROS), disrupting essential metabolic processes like photosynthesis and respiration, which negatively impact berry composition, especially sugar, acid, and phenolic content [15]. The vulnerability to these stresses also varies by cultivar, with varieties like Tempranillo and Gewurztraminer being more susceptible than others such as Pinot Gris or Pinot Noir [15].

In this context, agricultural biostimulants have become a crucial strategy for improving the physiological and metabolic resilience of grapevines under difficult climatic conditions. Among the traditional groups of agricultural biostimulants, brown seaweed extracts, humic substances, chitosan, and beneficial microorganisms such as PGPR and mycorrhizae have shown positive effects on root structure, photosynthesis, foliar heat regulation, biological control, and the activation of antioxidant defenses [16,17,18,19,20]. New biostimulants of significant interest are also being studied. Protein hydrolysates, which are rich in bioactive peptides and amino acids, improve tolerance to water and heat stress, stimulate chlorophyll and phenolic compound production, and influence defense-related gene expression [21,22,23]. Furthermore, applying antioxidants like glycine betaine externally has been shown to increase levels of polyphenols, flavonoids, and anthocyanins in berries, as well as activate key genes in the phenylpropanoid pathway, helping to safeguard cellular integrity and fruit quality during stress [13,24]. Another innovative approach involves nanostructured formulations, such as cerium oxide or chitosan–salicylic acid nanoparticles, which allow controlled release and increased bioavailability of bioactive compounds improve drought and salinity tolerance by enhancing ionic balance and activating antioxidant systems [25,26,27]. Ultimately, natural growth regulators like brassinosteroids and jasmonates offer additional benefits by influencing hormonal balance and phenotypic plasticity in grapevines, supporting resilience to climate change [28]. Overall, combining traditional and innovative biostimulants presents a promising approach to mitigating climate change impacts on viticulture. However, challenges such as inconsistent formulations, application timing, efficacy standards, and limited regulatory frameworks remain significant obstacles [28]. Overcoming these issues will require long-term, comparative, field-scale research to validate their effectiveness and help integrate them into sustainable, adaptive vineyard management practices.

1.2. Objectives of the Review Article

This review aims to provide an integrative analysis of the use of agricultural biostimulants in Vitis vinifera L. under optimal cultivation conditions and abiotic stress scenarios. It evaluates their effects on grapevine physiological development and on the enological quality of fruits and wines. Additionally, it examines the molecular and physiological mechanisms involved in plant responses to these inputs, with particular focus on the most suitable phenological stages for application. Lastly, it reviews international regulatory frameworks and offers an overview of products currently available on the market, providing a critical and updated perspective that could help develop more resilient and sustainable viticultural management strategies in the face of climate change.

2. Phenology of Vitis vinifera L. and the Effects of Climate Change

2.1. Key Phenological Stages and Hormonal Regulation

Vitis vinifera L. is a perennial species with a well-defined annual phenological cycle regulated by environmental factors and hormonal signals. During autumn, when temperatures fall below 7 °C, the grapevine enters dormancy, a physiological resting state that helps conserve energy and protect meristematic tissues [29]. As spring arrives, rising temperatures and increasing day length trigger metabolic reactivation, leading to budburst followed by vegetative growth, flowering, fruit set, berry development and ripening, and ultimately senescence. The transition between these stages is controlled by phytohormones such as auxins, gibberellins, cytokinins, abscisic acid, and ethylene [30]. In the early stages of fruit development, auxin plays a key role: transcriptomic studies have shown that genes related to auxin biosynthesis and signaling are highly expressed from flowering through fruit set, regulating cell division and expansion. Blocking its activity reduces mesocarp diameter, confirming its essential role in berry formation.

2.2. Effect of Environmental Variables on Grapevine Phenology

Temperature plays a crucial role in phenological regulation. Increases of 2–4 °C accelerate budburst and flowering by 10 to 16 days, shortening the period between veraison and harvest. This reduces the time required for the accumulation of vital metabolites, resulting in lower acidity, higher sugar content, and decreased yields [31,32,33]. On a physiological level, heat stress hampers photosynthesis, affecting PSII stability (photosystem II), Rubisco activity, and water balance. Consequently, berries have lower anthocyanin levels, altered aroma profiles, and a loss of typicity [34]. Light serves not only as an energy source but also as an environmental signal. Solar radiation influences auxin production and promotes vegetative growth [35]. It also impacts the production of flavonoids and anthocyanins, which are essential for fruit and wine quality. Water deficit triggers ABA-, HSF-, and MYB-dependent signaling pathways that regulate stress tolerance genes, including those involved in producing heat-shock proteins, antioxidants, and secondary metabolites [36,37,38]. Salinity stress particularly reduces chlorophyll content and increases reactive oxygen species (ROS), requiring the activation of antioxidant defenses such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) [39,40]. These physiological changes threaten photosynthetic efficiency and, ultimately, the crop’s productivity.

2.3. Phenological Alterations and Fruit Quality Under Abiotic Stress

Phenological shifts caused by environmental factors directly affect berry composition and wine quality. Advancing stages like veraison and harvest reduce polyphenol accumulation, which alters key factors such as acidity, alcohol content, aroma intensity, and color stability. Research on cultivars like Petite Sirah and Ruby Red shows that high levels of anthocyanins and flavonoids are associated with wines that have greater antioxidant capacity and longer shelf life [41]. Enological quality also depends on the balance among free anthocyanins, condensed tannins, and stable polymeric pigments. Heat stress and water shortages can disturb these balances, impact phenolic richness (PR), and increase oxidative risk (OR), both of which influence wine stability and complexity [42,43]. While moderate stress can enhance the accumulation of secondary metabolites, improving the phenolic profile of wine [44], prolonged stress can disrupt sugar transport and impair both technological and phenolic ripening of the berries.

3. Effect of Salinity and Related Abiotic Stress on Grapevine Physiology and Metabolism

In Vitis vinifera L., the progression of stages such as budburst and flowering under warmer spring conditions is well documented and affects water timing and the buildup of quality-related compounds [33]. This environmental trigger activates a genetic and biochemical control network that includes stress perception, signal transduction, transcriptional reprogramming, and effector responses in primary and secondary metabolism, with direct impacts on yield and fruit quality. The ability of Vitis vinifera L. to tolerate adverse conditions depends on a complex network of genes that connect environmental signals with developmental and ripening processes. Several gene families have been studied in this species, revealing mechanisms that link ion balance, antioxidant defense, hormonal and light signaling, as well as fruit quality. Table 1 provides an overview of the involved genes and their responses to different abiotic stress conditions in Vitis vinifera L. First, ion homeostasis and osmotic adjustment modules form the basis for tolerance to salinity and drought.

Genes such as SOS1, SOS2/3, NHX1, HKT1;5, and VvKCS11 are involved in sodium exclusion, vacuolar sequestration, and regulation of the Na⁺/K⁺ ratio, ensuring cellular stability and supporting photosynthesis during veraison and ripening [45,46]. Additionally, transporters like VvAAAP23 and VvAAAP46 help move amino acids and osmolytes such as proline, aiding in osmotic adjustment as well as root and berry development [47].

Antioxidant and redox defense modules preserve cellular integrity under oxidative stress. Transcription factors like VvWRKY28, NAC, MYB, WRKY, and RBOHD/F activate antioxidant enzymes (SOD, CAT, POD, APX), decrease lipid peroxidation, and slow leaf senescence. These processes are essential for maintaining metabolism stability during berry ripening when facing cold, drought, or salinity stress [36,48].

A third level involves hormonal integration, where ABA controls stomatal closure and connects water and salinity responses with floral development [49], while jasmonates (JA) and salicylic acid (SA) modulate antioxidant defenses and male fertility [38,50]. Auxins and gibberellins (GA₃) promote cell elongation, floral primordia differentiation, and ovule development, supporting reproductive continuity under tough conditions [51].

Genes related to structural development have a dual role: supporting plant growth under normal conditions and strengthening plants under stress. VvGRFs regulate the development of leaves, stems, and fruits but are mostly suppressed under abiotic stress [37]. VvLRXs (leucine-rich extensins) and VvLIMs remodel the cell wall and cytoskeleton, aiding in mechanical resistance and tissue differentiation, while VvKCS11 enhances suberin synthesis in roots, acting as an apoplastic barrier against sodium entry [46,52,53].

Light and circadian signaling form another essential axis of environmental integration. VvFRSs (FHY3/FAR1-like) and VvNRLs regulate photomorphogenesis, circadian rhythms, and phototropism, while VviGATAs are involved in photosynthesis, stomatal closure, and senescence, as well as berry ripening [38,54,55]. These pathways enable grapevines to adjust growth and reproduction based on light quality while boosting defenses against salinity, drought, and cold.

Regarding ripening and fruit quality, genes in the phenylpropanoid and anthocyanin pathways are affected by both environmental factors and transcription factors. Structural genes such as VvCHS2, VvF3H, VvDFR, VvANS, VvUFGT, and VvAOMT are transcriptionally regulated by TFs from the bHLH, MYB, NAC, WRKY, ERF, and bZIP families. Notably, VvbHLH137 directly binds to the promoters of VvDFR and VvF3H, activating their expression, while the regulatory cascade VvHY5 → VvMYB24 → VvMYBA1 links light signaling to anthocyanin biosynthesis, ultimately influencing berry coloration and fruit quality [56,57].

Additionally, proteins like VvUFD1, part of the ERAD pathway, help remove misfolded proteins under stress and regulate ripening and metabolite buildup [58]. Finally, nutrient- and amendment-related genes such as VvNIP2;1 and VvArsb promote silicon uptake and mobilization, strengthen ion balance, boost antioxidant activity, and improve tolerance to salinity [59].

Overall, evidence shows that Vitis vinifera’s response to abiotic stress relies on interconnected genetic modules, where ion transporters, transcription factors, antioxidant pathways, hormones, and light signals work together to support growth, regulate flowering, and ensure consistent berry ripening under challenging conditions.

Table 1. Genes involved in the response to abiotic stress in Vitis vinifera L.

Gene/Family	Stress Type	Type of Response	Signaling/Hormonal Mediator	Response in Grapevine	References
SOS1, SOS2, SOS3, NHX1, HKT1;5	Salinity, drought	Ion transport, Na+/K+ homeostasis	ABA, Ca2+	Na+ exclusion, maintenance of photosynthesis, salt tolerance	[45]
VvKCS11	Salinity	Suberin barrier, ion transport, osmotic adjustment	ABA	↓ Na+ entry, ↑ proline, ↓ MDA, more tolerant roots	[46]
VvWRKY28	Cold, salinity	Antioxidant, osmolytes, ABA signaling	ABA, ROS	↑ SOD, CAT, POD; ↑ proline; ↓ MDA; improved tolerance to cold and salinity	[48]
VvAAAP23, VvAAAP46	Salinity, drought	Amino acid transport, osmotic adjustment	ABA, MeJA, SA	Maintain proline and osmolyte flux, support roots and fruits	[47]
VvSNARE2, VvSNARE15, VvSNARE37/44/46	Salinity, cold	Vesicular trafficking, osmotic and antioxidant homeostasis	ABA, MeJA, SA	Cellular defense, stomatal closure, tolerance to NaCl and low temperatures	[60]
HSF3, NAC31/35, bHLH14, AP2.47, MYB154/166, LOB29, Dof5	Mild salinity	Metabolic adjustment (N, C, lignin, flavonoids)	ABA, JA	Maintain growth, balance N metabolism and antioxidants	[36]
MYB36/148, AP2.118/76/140, GRAS24, LOB25	Severe salinity	Metabolic adjustment, antioxidant, proteolysis	ABA	Growth arrest, prioritization of survival and defense	[36]
VvLRX7 (LRR-Extensin)	Salinity	Cell wall, structural	ABA, auxin	Cell wall remodeling, ↑ germination and survival under NaCl	[52]
VvLIM1–6	Cold, salinity, drought	Cytoskeleton, lignification, phenolic metabolism	ABA, auxin, MeJA, GA, SA	Bud and inflorescence differentiation; lignification under stress	[53]
VviGATA5a, 21, 24a/d	Cold, drought, salinity	Antioxidant, osmotic adjustment, photosynthesis	ABA, auxin, MeJA, SA, GA	Stomatal closure, senescence regulation, berry ripening	[55]
VvFRS6, VvFRS7, VvFRS12	Salinity, light, cold	Photomorphogenesis, antioxidant, circadian clock	ABA, MeJA, ethylene	Chlorophyll regulation, photoperiod, and light defense	[38]
VvNRL4, VvNRL6	Blue/red light	Auxin transport, phototropism	Auxin, ABA	Leaf orientation, light adaptation	[54]
VvUFD1a/VvUFD1c	Salinity, radiation, ripening	ERAD (protein degradation), antioxidant	ABA, SA	Ripening regulation, removal of misfolded proteins, defense	[58]
VvNIP2;1, VvArsb	Salinity (with Si)	Nutrient transport, antioxidant	ABA	↑ Si uptake, ↓ Na+, ↑ antioxidant enzymes, root vigor	[59]
Anthocyanin genes (CHS2, F3H, DFR, ANS, UFGT, AOMT) + TFs (VvbHLH137, VvMYB24, VvMYBA1, VvHY5)	Light stress, ripening	Metabolic adjustment (phenylpropanoids, flavonoids)	ABA, auxin, light (HY5)	↑ Anthocyanin accumulation, berry coloration, fruit quality	[56]

↓: Decrease; ↑: increase; MeJA: Methyl Jasmonate; MDA: malondialdehyde.

Table 1. Genes involved in the response to abiotic stress in Vitis vinifera L.

Gene/Family	Stress Type	Type of Response	Signaling/Hormonal Mediator	Response in Grapevine	References
SOS1, SOS2, SOS3, NHX1, HKT1;5	Salinity, drought	Ion transport, Na+/K+ homeostasis	ABA, Ca2+	Na+ exclusion, maintenance of photosynthesis, salt tolerance	[45]
VvKCS11	Salinity	Suberin barrier, ion transport, osmotic adjustment	ABA	↓ Na+ entry, ↑ proline, ↓ MDA, more tolerant roots	[46]
VvWRKY28	Cold, salinity	Antioxidant, osmolytes, ABA signaling	ABA, ROS	↑ SOD, CAT, POD; ↑ proline; ↓ MDA; improved tolerance to cold and salinity	[48]
VvAAAP23, VvAAAP46	Salinity, drought	Amino acid transport, osmotic adjustment	ABA, MeJA, SA	Maintain proline and osmolyte flux, support roots and fruits	[47]
VvSNARE2, VvSNARE15, VvSNARE37/44/46	Salinity, cold	Vesicular trafficking, osmotic and antioxidant homeostasis	ABA, MeJA, SA	Cellular defense, stomatal closure, tolerance to NaCl and low temperatures	[60]
HSF3, NAC31/35, bHLH14, AP2.47, MYB154/166, LOB29, Dof5	Mild salinity	Metabolic adjustment (N, C, lignin, flavonoids)	ABA, JA	Maintain growth, balance N metabolism and antioxidants	[36]
MYB36/148, AP2.118/76/140, GRAS24, LOB25	Severe salinity	Metabolic adjustment, antioxidant, proteolysis	ABA	Growth arrest, prioritization of survival and defense	[36]
VvLRX7 (LRR-Extensin)	Salinity	Cell wall, structural	ABA, auxin	Cell wall remodeling, ↑ germination and survival under NaCl	[52]
VvLIM1–6	Cold, salinity, drought	Cytoskeleton, lignification, phenolic metabolism	ABA, auxin, MeJA, GA, SA	Bud and inflorescence differentiation; lignification under stress	[53]
VviGATA5a, 21, 24a/d	Cold, drought, salinity	Antioxidant, osmotic adjustment, photosynthesis	ABA, auxin, MeJA, SA, GA	Stomatal closure, senescence regulation, berry ripening	[55]
VvFRS6, VvFRS7, VvFRS12	Salinity, light, cold	Photomorphogenesis, antioxidant, circadian clock	ABA, MeJA, ethylene	Chlorophyll regulation, photoperiod, and light defense	[38]
VvNRL4, VvNRL6	Blue/red light	Auxin transport, phototropism	Auxin, ABA	Leaf orientation, light adaptation	[54]
VvUFD1a/VvUFD1c	Salinity, radiation, ripening	ERAD (protein degradation), antioxidant	ABA, SA	Ripening regulation, removal of misfolded proteins, defense	[58]
VvNIP2;1, VvArsb	Salinity (with Si)	Nutrient transport, antioxidant	ABA	↑ Si uptake, ↓ Na+, ↑ antioxidant enzymes, root vigor	[59]
Anthocyanin genes (CHS2, F3H, DFR, ANS, UFGT, AOMT) + TFs (VvbHLH137, VvMYB24, VvMYBA1, VvHY5)	Light stress, ripening	Metabolic adjustment (phenylpropanoids, flavonoids)	ABA, auxin, light (HY5)	↑ Anthocyanin accumulation, berry coloration, fruit quality	[56]

↓: Decrease; ↑: increase; MeJA: Methyl Jasmonate; MDA: malondialdehyde.

4. Effect of Abiotic Stress on Berry and Wine Quality

The impact of abiotic stress on grape, must, and wine quality has been thoroughly documented under various experimental conditions. Moderate water stress (water potential between −0.4 and −0.6 MPa), applied from flowering to ripening in Vitis vinifera cv. Marselan, accelerated veraison, increased total soluble solids, and improved the antioxidant profile of the fruit by elevating tannins, anthocyanins, and proanthocyanidins. However, this was accompanied by reduced titratable acidity in the berries and diminished plant vigor and photosynthesis [61]. Similar findings were observed in Syrah, where water restriction from fruit set to maturity caused physiological limitations but promoted anthocyanin accumulation in the berry, mediated by the activation of key genes in the flavonoid pathway: CHS2, CHI1, FLS1, DFR, ANR, LAR1, UFGT, MybA1 [62]. Studies on Merlot also show that post-veraison water deficit lowers yield and titratable acidity, with berry pH reaching 4.3, while sugars, anthocyanins, and phenols increase [63].

In Tocai Friulano, extended drought promoted the accumulation of antioxidant and aromatic compounds (phenylpropanoids, flavonoids, zeaxanthin, tocopherols, and monoterpenes), although it resulted in smaller berries and lower yields [64]. Similarly, the review by Mirás-Ávalos (2017) [65] concluded that water deficit decreases acidity and malic acid but can increase soluble solids, anthocyanins, and phenols up to a certain level. However, under extreme conditions, limitations in photosynthesis hinder the production of sugars and secondary metabolites [49]. Salinity stress in Pinot Noir negatively impacted acidity, reducing malic and tartaric acids while increasing lactic and gluconic acids, which signaled microbial decomposition of berries. Sugar levels in the berries rose, but nitrogen compounds declined [66].

The review by Mirás-Ávalos (2017) [65] also pointed out that salinity promotes the buildup of Na⁺ and Cl⁻, increases pH, and degrades the sensory quality of wine. Heat stress is one of the biggest risks to berry composition; in Cabernet Sauvignon and Riesling, higher temperatures decreased organic acids, polyphenols, flavonoids, and anthocyanins, while increasing pH and reducing acidity [67,68]. Heat also lowers sugar concentration, whereas cold stress mainly delays ripening, preserves acidity, and promotes phenolic synthesis [68]. Additionally, high solar radiation boosts the production of flavonols and resveratrol, while free flavanols decline during ripening, which impacts antioxidant capacity and wine quality in varieties like Chardonnay [69].

To address these issues, various treatments have proven effective: CaCO₃ application increased wine color and phenolic content in Shiraz [70], while brassinosteroids enhanced photosynthesis, firmness, and berry quality under stress [71,72].

Overall, studies indicate that water, salinity, and heat stress decrease acidity and damage enological quality, but when controlled or with biostimulants, they can encourage the production of secondary metabolites essential for wine color, stability, and antioxidant capacity.

5. Agricultural Biostimulation in Grapevine

A plant biostimulant is defined as “a product that stimulates plant nutrition processes independently of the product’s nutrient content, with the sole aim of improving one or more of the following plant or rhizosphere characteristics: nutrient use efficiency, tolerance to abiotic stress, quality traits, or availability of confined nutrients in the soil or rhizosphere.” This functional definition, adopted by the European Biostimulants Industry Council (EBIC) [73], emphasizes product function rather than composition (according to: https://biostimulants.eu/plant-biostimulants/ (accessed on 10 September 2025)).

In his review, du Jardin (2015) [74] proposed a unified definition for agricultural biostimulants: “any substance or microorganism applied to plants with the aim of enhancing nutrient efficiency, abiotic stress tolerance, and/or crop quality.” He also created a widely accepted classification that includes humic substances, seaweed extracts, protein hydrolysates, osmoprotectants (such as glycine betaine), and plant growth-promoting rhizobacteria (PGPR). Subsequent reviews [75] have highlighted consistent effects on flowering, fruit set, growth, productivity, nutrient use efficiency, and resilience against drought, salinity, and extreme temperatures. In the European Union, Regulation (EU) 2019/1009 officially recognizes biostimulants as PFC 6 (plant biostimulant) and defines their function, differentiating between microbial [PFC 6(A)] and non-microbial [PFC 6(B)] products. The regulation sets labeling requirements, proof of claimed effects, and limits on contaminants (heavy metals, pathogens, etc.), thereby standardizing market access through conformity assessment procedures.

In the United States, there is still no single federal legal definition for “agricultural biostimulants.” The U.S. Environmental Protection Agency (EPA) has published and revised the Draft Guidance for Plant Regulator Claims, including biostimulants, which clarifies when certain ingredients or claims classify a product as a “plant growth regulator” (and therefore subject to FIFRA as a pesticide). In practice, classification and labeling are mostly determined at the state level. Recent literature highlights this fragmented framework and the terminological ambiguity with “biofertilizers” [76].

In Mexico, although there is no specific regulatory category for “biostimulants” like in the US, obligations do exist for plant nutrition inputs. The NOM-077-FITO-2000 [77] sets the requirements and specifications for biological efficacy studies (protocols, evaluation criteria, and compliance) applicable to organic fertilizers, soil conditioners, inoculants/PGPR, and growth regulators, a framework into which products with biostimulant action typically fall.

6. Application of Agricultural Biostimulants in Grapevine Under Different Abiotic Stress Conditions

6.1. Water Stress

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR): In V. vinifera cv. Malvasia di Candia Aromatica, annual applications over three years of AMF-based products showed different functional improvements: MycoUp^® (Biogard; Rhizophagus iranicus [labeled as Glomus iranicum] var. tenuihypharum) increased photosynthetic efficiency compared with the control, while Tricoveg^® (Chemia S.p.a., Turin, Italy; Rhizophagus spp., labeled as Glomus spp.) enhanced anthocyanins, phenolic acids, and stilbenes in fruit [78]. In cv. Ecolly (Chardonnay × Riesling × Chenin blanc), MycoApply^® (a consortium of Funneliformis mosseae, Glomus aggregatum, Claroideoglomus etunicatum Mycorrhizal Applications, Grants Pass, OR, USA) applied to the substrate in early stages mitigated drought through osmolyte accumulation (proline, sucrose), lower ROS and lipid peroxidation, increased activity of antioxidant enzymes SOD/POD, higher glutathione in leaves, and induction of genes VvNCED, VvP5CS, VvBG, VvCYP, and aquaporins (VvSIP, VvPIP1;2, VvTIP2;1) [79].

In cv. Debina, soil application of Bacillus amyloliquefaciens QST713 (SERENADE^® ASO, (SERENADE^® ASO, Bayer CropScience, St. Louis, MO, USA)) or Sinorhizobium meliloti B2352 (HYDROMAAT^®, Futureco Bioscience, Barcelona, Spain) under deficit irrigation at 57% of available water improved vegetative growth (total length, leaf area, roots, shoots, leaf dry biomass) and physiology (total chlorophyll, RWC, total phenols, and proline). In both cases, the response nearly compensated for the water deficit [80]. In table grape cv. Sweet Celebration, a combined program with Accudo^® (Bacillus paralicheniformis; Bayer CropScience, St. Louis, MO, USA, fertigation) + Seamac Rhizo^® (Ascophyllum nodosum extract, 15% + amino acids and nutrients, foliar; Seamac^®, Dublin, Ireland), applied at budburst, flowering, and fruit set, under −10% irrigation, advanced harvest, increased mycorrhization, and improved water productivity without yield penalties [81].

Seaweed extracts: In cv. Pinot Noir grown in greenhouse conditions, the commercial extract Acadian Marine Plant Extract Powder (Ascophyllum nodosum, Acadian Seaplants Limited, Dartmouth, Nova Scotia, Canada) increased leaf soluble sugars and enhanced photosynthetic rate under normal irrigation. During progressive drought and rewatering, the treatment improved gas exchange and water-use efficiency (WUE, +35%), maintained Fv/Fm (+0.19), and increased leaf dry matter (+8%) and soluble sugars (+27.3 mg g⁻¹ dry weight) [82]. When combined with PGPR (Seamac Rhizo^® + Accudo^®), early ripening and water-use efficiency were also observed in cv. Sweet Celebration under −10% irrigation [81].

Protein hydrolysates: The thermal hydrolysate APR^® (collagen; fertigation) applied at flower separation in cv. Sauvignon Blanc supported the growth of young organs under drought conditions and increased berry diameter by the end of treatment under both deficit (+9.5%) and non-deficit (+3.4%) conditions [23]. In cv. Barbera under natural drought, the biostimulant LalVigne ProHydro™ (LPH)—derived from Saccharomyces cerevisiae, rich in proline, produced with Corynebacterium glutamicum—applied five times per season from “pea size” to full veraison improved leaf water potential (Ψh), net assimilation (A), stomatal conductance (gs), PSII efficiency, chlorophylls, carotenoids, and proline; in fruit, it reduced sunburn and berry dehydration, increased yield, decreased °Brix, and enhanced anthocyanins and total polyphenols [83].

Osmoprotectants and humic substances: In cv. Khoshnaw, foliar proline (200 mg L⁻¹) combined with Botminn Plus^® (humic and fulvic acids, OM, and N), applied two weeks before flowering and two weeks after fruit set, enhanced drought tolerance by increasing leaf area, chlorophyll, and nitrogen in leaves [84].

Growth regulators: In cv. Tempranillo under rainfed vineyards, foliar β-aminobutyric acid (BABA, 0.1 mM) applied before and after flowering increased berry diameter and yield in the less dry year and improved plant survival in the driest year; it also raised malic acid in berries and increased sugar content in grapes and must [85]. In cv. Cabernet Sauvignon, foliar 24-epibrassinolide (early vegetative stage) enhanced drought tolerance by protecting photosynthesis, improving carbohydrate and nitrogen metabolism, reducing ROS, and increasing proline [86].

6.2. Salt Stress

Silicon (Si): In cv. Cabernet Sauvignon, fertigation with K₂SiO₃·9H₂O (2 mM) at budburst reduced stress from 100 mM NaCl by increasing chlorophyll, photosynthetic rate, and photochemical efficiency, as well as sugars and starch, while lowering Na⁺ in leaves, leading to better growth [87]. In hydroponic culture with a halotolerant genotype (H6: V. vinifera cv. GharaUzum × V. riparia Kober 5BB) and a sensitive one (GhezelUzum), applying Na₂SiO₃ (3 mM) under 100 mM NaCl improved biomass recovery, photosynthetic efficiency, lowered Na⁺/Cl⁻ in leaves and roots, and increased osmolytes in leaves (proline, glycine betaine, sugars). In H6, the expression of VvNIP2;1 (Si channel) and VvArsb (ArsB-type transporter) was induced, which is linked to Si transport and Na⁺ exclusion [59]. In grapevine varieties known as salt-tolerant (described as Prunus dulcis × P. persica), early fertigation with SiO₂ reduced biomass loss and leaf water loss, decreased MDA/H₂O₂/electrolyte leakage, boosted SOD/CAT activity, and increased osmolyte levels (glycine betaine, water-soluble proteins), along with better photosynthesis and conductance. Moreover, expression of HKT1, AVP1, NHX1, and SOS genes related to ion homeostasis was stimulated [88].

Phenolic antioxidants (quercetin, shikonin): In cv. Pinot Noir, foliar application of quercetin at a low dose (0.01 g L⁻¹) during early developmental stages under saline stress (200 mM NaCl) enhanced SOD/POD enzymatic activity, reduced ROS, increased ascorbic acid (AsA), and elevated reduced glutathione (GSH), while decreasing leaf necrosis [89]. In cv. Öküzgözü, foliar shikonin applied at veraison and post-veraison improved berry quality, increased levels of phenolic compounds such as gallic acid and quercetin, raised sugars and malvidin-3-O-glucoside, and mitigated stress from 150 mM NaCl by enhancing antioxidant capacity and phenolic content [90].

Polyamines (spermidine): In one-year-old seedlings of Bidaneh-Sefid and Siah-Sardasht exposed to 100 mM NaCl, three foliar sprays of spermidine (applied every 15 days) reduced the decrease in root and shoot growth caused by osmotic stress. It also increased the uptake of Ca²⁺, Mg²⁺, K⁺, P, Fe, and Zn, and limited Na⁺/Cl⁻ accumulation. Additionally, it improved CAT/GPX enzymatic activity and lowered electrolyte leakage and MDA levels, indicating enhanced membrane stability [91].

Nanostructured formulations: In cv. Sultana, a nanoformulation of chitosan and putrescine (applied foliar at the early vegetative stage) protected against stress caused by metals (CdCl₂, 10 mg kg⁻¹ in soil), with increased PSII efficiency, reduced MDA/H₂O₂/electrolyte leakage, higher activity of SOD, CAT, APX, and GPX, greater anthocyanin and phenolic content, and lower Cd levels in leaves and roots [92]. Similarly, in Sultana (early vegetative stage), foliar application of proline-functionalized graphene oxide (three treatments every five days) under saline stress (100 mM NaCl) increased chlorophyll and carotenoids, improved water retention, decreased oxidative damage (less electrolyte leakage, MDA, and H₂O₂), raised proline and soluble protein levels, and boosted antioxidant enzymes (APX/SOD) compared to the control [93]. In Early Sweet seedlings (early vegetative and rooting stages under abiotic stress), foliar spraying with chitosan and salicylic acid until runoff improved survival, growth, nutritional status, and physiology: increased chlorophylls and proline, decreased Na⁺/Cl⁻ in leaves, and enhanced foliar N, P, K, and Ca [94]. Likewise, in Sultana (one year old, early vegetative stage), nanoparticles of chitosan combined with salicylic acid (70–100 nm), applied two weeks before and after saline stress, reversed the effects of 100 mM NaCl (severe oxidative damage, pigment loss, reduced photochemical efficiency, ionic imbalance), resulting in higher osmolyte levels, antioxidant enzyme activity, and restored ion homeostasis [95].

6.3. Thermal Stress

Thermal elevation degrades key enological attributes by accelerating fruit’s organic and oxidative metabolism, lowering malic acid, reducing anthocyanin accumulation, and decreasing amino acids essential for wine quality (valine, asparagine, methionine, glycine, and phenylalanine) [15]. This context justifies using biostimulant interventions aimed at preserving grapevine water-photosynthetic status and modulating antioxidant and osmotic responses to heat, drought, and salinity.

Seaweed extracts: In Vitis vinifera cv. Chardonnay, five foliar applications per season (from pre-flowering to pre-veraison) of Ascophyllum nodosum extracts (Acadian Plant Health, Canada) and Ecklonia maxima (COMPO EXPERT GmbH, Germany) demonstrated climate-dependent functional plasticity: A. nodosum enhanced photosynthesis, leaf area, and berry size in cooler climates, while E. maxima improved resistance to extreme heat (peaks > 36 °C) during the application season [96].

Protein hydrolysates: In four-month-old Cabernet Sauvignon seedlings at an early stage, foliar application of whey protein hydrolysates reduced the combined effects of heat stress (40 °C) and water shortage, leading to faster recovery of photosynthesis after rehydration, maintenance of Fv/Fm, and higher leaf water potential. At the molecular level, the expression of HSFA2, HSP101, TIP2;1, and NCED1 was increased, linking thermal proteostasis, aquaporins, and ABA signaling to tolerance [21].

Mineral salts: In Ugni Blanc cuttings, sprays with K₂SO₄ and CaCl₂ enhanced winter cold resistance and promoted growth, increasing proline levels and decreasing MDA in shoots, which indicates osmotic adjustment and reduced lipid peroxidation as protective mechanisms [97].

Antioxidants and regulators: During intense cold pulses in Giziluzum (–3 °C, 3 h), foliar application of putrescine, salicylic acid, and especially ascorbic acid enhanced the antioxidant system, boosted photosynthetic pigments, and decreased ROS and lipid peroxidation. Ascorbic acid was the most effective treatment for improving frost tolerance [95].

Selection of resistant varieties: In regenerated seedlings, cold tolerance was attributed to specific physiological traits: the Askari genotype exhibited higher accumulation of proline and soluble proteins, aiding in osmotic adjustment and protein stabilization; Siah showed lower electrolyte leakage and increased soluble sugar levels, which is consistent with maintenance of membrane integrity and osmoregulation. Rish-baba observed higher figures for maximal photosynthetic quantum efficiency (Fv/Fm). By contrast, Gavi observed reduced levels of proline and soluble proteins, suggesting greater sensitivity to cold stress compared with the other genotypes. In general, increases in osmolytes (such as proline, sugars, and soluble proteins) and in the Fv/Fm ratio are commonly associated with enhanced cold tolerance [98].

Table 2. Reported effects of agricultural biostimulants on grapevine cultivars under abiotic stress conditions.

Grapevine Cultivar	Stress Type	Treatment and Application Method	Phenological Stage	Applications (n/Interval)	Response in Grapevine	References
Malvasia di Candia Aromatica	Water	Arbuscular mycorrhizae (Tricoveg®; soil, annual for 3 years)	Full production cycles	3/yr	↑ Anthocyanins, phenolic acids, and stilbenes in fruit	[78]
Malvasia di Candia Aromatica	Water	Arbuscular mycorrhizae (MycoUp®; soil)	Full production cycles	NR	↑ Photosynthetic efficiency	[78]
Ecolly (Chardonnay × Riesling × Chenin blanc)	Water	MycoApply® (AMF consortium; substrate)	Early stages	NR	↑ Osmolytes (proline, sucrose), ↓ ROS and lipid peroxidation, ↑ antioxidant enzymes (SOD, POD, GSH); gene induction (VvNCED, VvP5CS, VvSIP, VvPIP1;2, VvTIP2;1)	[79]
Debina	Water	Bacillus amyloliquefaciens QST713 (SERENADE®) + Sinorhizobium meliloti B2352 (HYDROMAAT®); soil	Early stages	NR	↑ Vegetative and root growth, ↑ dry biomass and physiology (chlorophyll, RWC, phenols, proline); compensation of water deficit	[80]
Sweet Celebration (table grape)	Water	Accudo® (Bacillus paralicheniformis; fertigation) + Seamac Rhizo® (Ascophyllum nodosum + amino acids; foliar)	Budburst, flowering, fruit set	3/season	↑ Mycorrhization, ↑ water-use efficiency, earlier harvest, no yield reduction	[81]
Pinot Noir	Water	Ascophyllum nodosum extract (Acadian®; foliar)	Budburst	NR	↑ Foliar sugars, ↑ photosynthesis; under progressive deficit: ↑ WUE (+35%), stable Fv/Fm, ↑ soluble sugars and dry matter	[82]
Sauvignon Blanc	Water	APR® (thermal collagen hydrolysate; fertigation)	Flower separation	NR	Maintained young organ growth under drought; ↑ berry diameter under deficit (+9.5%) and control (+3.4%)	[23]
Barbera	Water	LalVigne ProHydro™ (proline-rich yeast hydrolysate; foliar)	Pea size to veraison	5/wk	↑ Leaf Ψh, photosynthesis, gs, PSII, pigments, and proline; in fruit: ↓ sunburn and berry dehydration, ↑ yield, ↑ anthocyanins and phenols, ↓ °Brix	[83]
Khoshnaw	Water	Foliar proline (200 mg/L) + Botminn Plus® (humic + fulvic acids; foliar)	Pre-flowering and post-fruit set	2/15 d	↑ Leaf area, ↑ chlorophyll and nitrogen in leaves, improved drought tolerance	[84]
Tempranillo	Water	β-aminobutyric acid (BABA, 0.1 mM; foliar)	Before and after flowering	2/15 d	↑ Berry diameter, ↑ yield in less dry years, ↑ malic acid and sugars in berries and must, ↑ survival in drier years	[85]
Cabernet Sauvignon	Water	24-epibrassinolide (foliar)	Early vegetative	1/—	↑ Photosynthesis, ↑ carbohydrate and N metabolism, ↓ ROS, ↑ proline	[86]
Cabernet Sauvignon	Salinity	K2SiO3·9H2O (2 mM; fertigation)	Budburst	NR	Under 100 mM NaCl: ↑ Chlorophyll, photosynthesis, sugars, and starch; ↓ Na+ in leaves; improved growth	[87]
GharaUzum × V. riparia Kober 5BB (tolerant) and GhezelUzum (sensitive)	Salinity	Na2SiO3 (3 mM; hydroponic fertigation)	Under 100 mM NaCl	NR	↑ Biomass, photosynthesis, osmolytes; ↓ Na+/Cl− in leaves/roots; induction of VvNIP2;1 and VvArsb in tolerant genotype	[59]
Pinot Noir	Salinity	Quercetin (0.01 g/L; foliar)	Early development	NR	↑ SOD/POD, ↑ AsA and GSH, ↓ ROS and leaf necrosis	[89]
Öküzgözü	Salinity	Shikonin (foliar)	Veraison and post-veraison	2/15 d	↑ Phenolics (gallic acid, quercetin), ↑ sugars, ↑ malvidin-3-O-glucoside; improved quality under 150 mM NaCl	[90]
Bidaneh-Sefid and Siah-Sardasht (seedlings)	Salinity	Spermidine (foliar)	Early vegetative	3/15 d	↑ Ca, Mg, K, P, Fe, Zn uptake; ↓ Na+/Cl−; ↑ CAT/GPX enzymes, ↓ MDA and electrolyte leakage	[91]
Sultana	Salinity/metals	Nanochitosan + putrescine (foliar)	Early vegetative	2/14 d	↑ PSII, ↑ SOD/CAT/APX, ↑ anthocyanins and phenols, ↓ Cd in tissues	[92]
Chardonnay	Thermal	Ascophyllum nodosum and Ecklonia maxima extracts (foliar)	Pre-flowering to pre-veraison	5/season	A. nodosum: ↑ Photosynthesis and berry size in cool climate; E. maxima: ↑ Resistance to heat peaks >36 °C	[96]
Cabernet Sauvignon (seedlings)	Thermal + water	Whey protein hydrolysates (foliar)	Early vegetative	NR	Under 40 °C + water deficit: ↑ Photosynthetic recovery after rehydration, stable Fv/Fm; induction of HSFA2, HSP101, TIP2;1, NCED1	[21]
Ugni Blanc (cuttings)	Thermal (cold)	Sprays with K2SO4 and CaCl2 (foliar)	Winterbud	NR	↑ Proline, ↓ MDA; improved cold resistance and growth	[97]
Giziluzum	Thermal (cold)	Putrescine, salicylic acid, and ascorbic acid (foliar)	Early vegetative	3/10 d	↑ Antioxidants, ↑ photosynthetic pigments, ↓ ROS and lipid peroxidation; ascorbic acid most effective	[95]

Note: Application number (n) and interval are shown when reported (d = days, wk = week, yr = year). NR = not reported. RWC: Relative Water Content; GPX: glutathione peroxidase; APX: Ascorbate Peroxidase. ↓: Decrease; ↑: increase.

provides a summary overview of the effects of the application of biostimulants on grape crops subjected to stress conditions.

7. Application of Biostimulants and Their Effect on Grapevine Fruit Quality

7.1. Seaweed Extracts and Multicomponent Formulations

In Tempranillo, hydroalcoholic extracts of brown seaweed, including Rugulopteryx okamurae, applied to leaves of young plants in the greenhouse, induced PR10, PAL, STS48, and GST1. This effect coincided with higher levels of trans-piceid and trans-resveratrol (especially with RU2), increased jasmonic acid, and decreased salicylic acid, along with elevated SOD and CAT [99]. In Cabernet Sauvignon, the Kelpkak^® formulation (containing Ecklonia maxima, amino acids, phytohormones, macro- and micronutrients) applied before flowering, at fruit set, and at veraison increased leaf area, sugar and organic acid accumulation during ripening, and boosted phenolic compounds [100]. Also in Cabernet Sauvignon, cluster-directed applications of Ascophyllum nodosum extract (two sprays at veraison and two weeks later) increased anthocyanins and total polyphenols in berries [101]. In Merlot, AZAL5 (A. nodosum combined with auxins, ABA, and cytokinins) applied foliarly in four treatments (two at fruit set and two at veraison) increased yield, berry number, and anthocyanins [102]. In Sauvignon Blanc, the biostimulant Ferrum^® (marine algae, auxins, cytokinins, gibberellins, Fe 6%, Mn 3%) applied three times increased foliar iron, chlorophyll content, photosynthesis, and yield [103]. In table grapes, spraying orthosilicic acid combined with A. nodosum during fruit set (every 15 days) enlarged cluster size and promoted ripening [104]. In Tempranillo, applying A. nodosum (Crop Plus, Adama) at veraison and one week later enhanced fruit antioxidants such as malvidins and myricetins and also increased trans-piceid and stilbenes [105]. In Pinot Noir, Cabernet Franc, and Sangiovese, five foliar applications of A. nodosum, starting two weeks before veraison, increased anthocyanins and total polyphenols [106].

7.2. Osmoprotectants and Primary Regulators

In greenhouse-cultivated Touriga Franca, applying 0.1–0.2% glycine betaine (Greenstim^®) at three stages (pea size, cluster closure, and onset of veraison) increased diphenols and antioxidant activity in berries [107]. In Red Globe, foliar applications of phenylalanine and proline (500–1000 ppm) two weeks before and during veraison improved cluster length and weight; the “phenylalanine 1000 ppm + apical reduction” treatment was most effective, resulting in higher ripeness (°Brix, pH, maturity index), phenols, anthocyanins, and antioxidant capacity [108]. In Black Magic, hydrolyzed corn gluten protein rich in phenylalanine (GDPH; SURNAN^®), applied through fertigation at veraison and early ripening, increased cluster weight, berry diameter, and soluble solids without impacting firmness, pH, or acidity. Transcriptomic analysis showed suppression of photosynthetic genes and activation of ripening-related genes (PAL, CHS, F3H, MYB5B, MYBA2), anthocyanin transport (ABCC1, AM1, GST4), and modulation of ARF, cytokinin, GA, and ethylene responses [109].

7.3. Humic Substances, Boron, and Silicon Combinations

In Feteasca Regala and Italian Riesling, vermicompost humic acids (40–50 mL L⁻¹) applied at pre-flowering and fruit set increased yield, cluster and berry size, as well as °Brix, and slightly reduced titratable acidity [110]. In Fakhri, potassium silicate combined with humic acid (one pre-flowering and two post-flowering sprays) increased cluster fresh/dry weight, total polyphenols, and anthocyanins in berries, while in leaves it enhanced chlorophyll, antioxidant activity, and micronutrients (Zn, Mn, Fe, Cu) [111]. In Sauvignon Blanc, foliar fertilization with humic acids + boron at three stages (pre-flowering, full flowering, post-veraison) increased Ca, P, K, Mg, Zn, and B in leaves (peaks at flowering and veraison) and promoted Ca, P, K, Zn accumulation in berries. In must and wine, N, K, P, and B increased, while Ca and sugars decreased slightly; in wine, yeast assimilable nitrogen (YAN) rose to 176.24 mg L⁻¹ compared to 168.36 mg L⁻¹, with no significant change in yield per plant [112]. In Garganega, foliar applications of the biodynamic Horn Silica (501) preparation during vegetative growth increased phenols and carotenoids in fruit (epigallocatechin, violaxanthin), compounds linked to antioxidant defense [113].

7.4. Salicylic Acid and Amino Acids

In Chardonnay, foliar sprays of salicylic acid at 3 mM (during veraison and one week later) increased soluble solids, titratable acidity, amino acids in berries, benzenoid compounds (fruit and floral aromas), and terpenoids [114]. In Bidane Ghermez and Bidane Sefid, applying 0.1–1 mM salicylic acid (twice: early veraison and ripening) boosted photosynthetic pigments, sugars, proline, proteins, and SOD in leaves and berries, with stronger effects in Bidane Sefid (chlorophyll and protein) and Bidane Ghermez (proline and SOD). The best dose was 0.1 mM at veraison for pigments and sugars, and 1 mM at ripening for proline, proteins, and enzymes [115]. In Thompson Seedless, applying amino acids, benzyladenine, and nano-NPK before flowering and after fruit set increased vitamin C but decreased total phenols, with additive effects when combined [116].

7.5. Biopolymers and Alginates

In Marselan, two applications of γ-polyglutamic acid (0.35%) and alginic acid (0.45%)—administered at the onset of veraison and one week later—increased delphinidin, cyanidin, peonidin, and malvidins, and upregulated VvPAL, VvCHS, VvDFR, and VvDOX [117].

7.6. Organic-Mineral Amendments

Winter application of Zeowine (zeolite + composted winery residues, 30 t ha⁻¹) before budburst in Sangiovese enhanced leaf water potential, photosynthesis, transpiration, and photochemical efficiency; increased berry size, cluster weight, sugars, and anthocyanins; and optimized the phenolic profile [118].

7.7. Postharvest Biostimulation

In

Table 3. Reported effects of biostimulant applications on grapevine cultivars: phenological stage, plant response, and fruit quality.

Grapevine Cultivar	Treatment and Application Method	Phenological Stage	Plant/Fruit Response	References
Tempranillo	Hydroalcoholic brown seaweed extracts (Rugulopteryx okamurae; foliar)	Young plants (greenhouse)	Induction of PR10, PAL, STS48, GST1; ↑ trans-piceid and trans-resveratrol; ↑ jasmonic acid, ↓ salicylic acid; ↑ SOD and CAT	[99]
Cabernet Sauvignon	Kelpak® (Ecklonia maxima + amino acids, phytohormones, nutrients; foliar, 3 times)	Before flowering, fruit set, veraison	↑ Leaf area, ↑ sugars and organic acids, ↑ phenolics during ripening	[100]
Cabernet Sauvignon	Ascophyllum nodosum extract (foliar, 2 times)	Veraison and +2 weeks	↑ Anthocyanins and total polyphenols in berries	[101]
Merlot	AZAL5 (A. nodosum + auxins, ABA, cytokinins; foliar, 4 times)	2× fruit set, 2× veraison	↑ Yield, ↑ berry number, ↑ anthocyanins	[102]
Sauvignon Blanc	Ferrum® (marine algae + auxins, cytokinins, gibberellins, Fe 6%, Mn 3%; foliar, 3 times)	Not specified	↑ Foliar Fe, ↑ chlorophyll, ↑ photosynthesis, ↑ yield	[103]
Table grape (unspecified)	Orthosilicic acid + A. nodosum (foliar, every 15 days)	Fruit set	↑ Cluster size, improved ripening	[104]
Tempranillo	A. nodosum extract (Crop Plus; foliar, 2 times)	Veraison and +1 week	↑ Malvidins and myricetins; ↑ trans-piceid and stilbenes	[105]
Pinot Noir, Cabernet Franc, Sangiovese	A. nodosum extract (foliar, 5 times)	Starting 2 weeks before veraison	↑ Anthocyanins and total polyphenols	[106]
Touriga Franca	Glycine betaine (Greenstim®, foliar, 3 times)	Pea size, cluster closure, veraison	↑ Diphenols and antioxidant activity in berries	[107]
Red Globe	Phenylalanine + proline (foliar, 500–1000 ppm; 2 times)	Pre-veraison, veraison	↑ Cluster length/weight; ↑ °Brix, pH, maturity index, phenols, anthocyanins, antioxidant capacity	[108]
Black Magic	Corn gluten hydrolysate (GDPH; fertigation, 2 times)	Veraison and early ripening	↑ Cluster weight, ↑ berry size, ↑ soluble solids; transcriptomic activation of ripening and anthocyanin transport genes	[109]
Feteasca Regala, Italian Riesling	Vermicompost humic acids (foliar, 2 times)	Pre-flowering, fruit set	↑ Yield, ↑ cluster/berry size, ↑ °Brix, ↓ acidity	[110]
Fakhri	Potassium silicate + humic acid (foliar, 3 times)	Pre-flowering, post-flowering	↑ Cluster weight, ↑ berry polyphenols/anthocyanins; ↑ leaf chlorophyll and antioxidant activity	[111]
Sauvignon Blanc	Humic acids + boron (foliar, 3 times)	Pre-flowering, full flowering, post-veraison	↑ Ca, P, K, Mg, Zn, B in leaves; ↑ N, K, P, B in must and wine; ↑ YAN	[112]
Garganega	Horn Silica (501) biodynamic preparation (foliar)	Vegetative growth	↑ Phenols and carotenoids in berries (epigallocatechin, violaxanthin)	[113]
Chardonnay	Salicylic acid (foliar, 2 times, 3 mM)	Veraison and +1 week	↑ Soluble solids, ↑ acidity, ↑ amino acids and aroma compounds in berries	[114]
Bidane Ghermez, Bidane Sefid	Salicylic acid (foliar, 2 times, 0.1–1 mM)	Veraison, ripening	↑ Photosynthetic pigments, ↑ sugars, ↑ proline/proteins, ↑ SOD; optimal doses varied by cultivar/stage	[115]
Thompson Seedless	Amino acids + benzyladenine + nano-NPK (foliar, 2 times)	Before flowering, after fruit set	↑ Vitamin C; ↓ total phenols	[116]
Marselan	γ-Polyglutamic acid (0.35%) + alginic acid (0.45%; foliar, 2 times)	Veraison and +1 week	↑ Anthocyanins (delphinidin, cyanidin, peonidin, malvidins); ↑ PAL, CHS, DFR, DOX expression	[117]
Sangiovese	Zeowine (zeolite + winery compost; soil, 30 t ha−1)	Pre-budburst	↑ Leaf water status, ↑ photosynthesis, ↑ berry size, ↑ sugars, ↑ anthocyanins, improved phenolic profile	[118]
Kyoho (table grape)	Melatonin (postharvest, 50–400 μM; storage at 4 °C, 25 days)	Postharvest	↓ Abscission/rot, ↓ MDA (−40.8%); ↑ amino acids (arginine, proline, GABA) and polyamines; ↑ VvADC, VvODC, VvSPDS, VvCuAO	[119]
Cuibao Seedless	Melatonin + salicylic acid (postharvest; storage at 4 °C)	Postharvest	↓ Browning and weight loss; ↑ antioxidant capacity; melatonin more effective than combined treatment	[120]

↓: Decrease; ↑: increase.

, in grape cv. Kyoho, postharvest melatonin (50–400 μM; optimal 200 μM) during storage at 4 °C for 25 days reduced abscission, rot, and oxidative damage (−40.8% MDA). TMT-LC/MS proteomics identified 5156 proteins (158 modulated, mainly involved in amino acid and antioxidant metabolism), with increases in arginine, proline, GABA, and polyamines (putrescine, spermidine, spermine); VvADC, VvODC, VvSPDS, and VvCuAO were overexpressed [119]. In Cuibao Seedless, postharvest melatonin and salicylic acid delayed deterioration, reduced browning and weight loss, and enhanced antioxidant capacity; melatonin alone was more effective, with no clear synergy observed in the combination [120].

7.8. Effects of Biostimulants on Yield and Vegetative Performance

Along with enhancing stress tolerance and fruit quality, numerous studies also demonstrate that biostimulants have measurable effects on grapevine growth and yield, highlighting their significance in agriculture. These effects are frequently associated with improved water-use efficiency, increased photosynthesis, and better nutrient uptake, which collectively support vegetative growth and reproductive success even under stressful conditions (

Table 4. Reported quantitative effects of biostimulants on yield and vegetative performance in grapevine.

Grapevine Cultivar	Biostimulant/Formulation	Application (Method & Stage)	Stress Condition	Main Yield/Vegetative Outcomes	Reference
Merlot	Ascophyllum nodosum extract (AZAL5®, foliar 4×)	Two sprays at fruit set and two at veraison	None (field)	+12–18% yield; ↑ berry number and anthocyanins	[102]
Cabernet Sauvignon	Ecklonia maxima extract (Kelpak®, foliar 3×)	Before flowering, fruit set, veraison	None	+15% yield; ↑ leaf area, photosynthesis	[100]
Barbera	Protein hydrolysate (LalVigne ProHydro™, foliar 5×)	From pea size to veraison	Drought (field)	+10–13% yield; ↓ sunburn, ↑ anthocyanins	[82]
Feteasca regala, Italian Riesling	Vermicompost humic acids (foliar 2×)	Pre-flowering and fruit set	None	+8–10% cluster and berry size; ↑ °Brix	[110]
Fakhri	Potassium silicate + humic acid (foliar 3×)	Pre- & post-flowering	Heat/salinity	+17% cluster weight; ↑ polyphenols	[111]
Sweet Celebration	Bacillus paralicheniformis + Ascophyllum nodosum (Accudo® + Seamac Rhizo®)	Budburst–fruit set	Deficit irrigation	Maintained yield; ↑ water productivity, earlier harvest	[81]
Malvasia di Candia Aromatica	Mycorrhizae (MycoUp®, soil)	Full production cycles	Drought	Sustained productivity; ↑ photosynthesis	[78]
Cabernet Sauvignon	24-epibrassinolide (foliar)	Early vegetative	Drought	↑ berry diameter; ↑ carbohydrate metabolism	[85]
Sultana	Chitosan + salicylic acid nanoparticles (foliar)	Early vegetative			[94]

↓: Decrease; ↑: increase.

).

In Vitis vinifera cv. Merlot, foliar applications of an Ascophyllum nodosum extract increased yield per vine by 12–18%, along with berry number and total soluble solids [102]. Similarly, Ecklonia maxima extracts in Cabernet Sauvignon improved shoot growth and leaf area, resulting in a 15% higher yield compared with untreated vines [100]. Protein hydrolysates have shown consistent effects on cluster weight and fruit number; for example, in Barbera under field drought, LalVigne ProHydro™ enhanced photosynthetic efficiency and increased yield by 10–13%, reducing berry sunburn [82].

Humic acids and silicon-based formulations have also demonstrated yield benefits linked to improved nutrient uptake. In Feteasca regala and Italian Riesling, two foliar applications of vermicompost humic acids increased cluster and berry size by 8–10%, improving °Brix and total yield [110]. Similarly, foliar sprays of potassium silicate combined with humic acid in Fakhri increased cluster weight by 17% and total polyphenols [111].

Under salinity stress, foliar spermidine and chitosan–salicylic acid nanoparticles not only mitigated ionic toxicity but also maintained vegetative biomass and fruit set comparable to non-stressed controls [25,90]. Mycorrhizal inoculation (e.g., Glomus iranicum var. tenuihypharum) provided sustained productivity gains over three seasons, confirming the long-term effectiveness of soil-applied biostimulants [78].

Overall, current evidence supports that the positive physiological effects induced by biostimulants—such as enhanced chlorophyll content, osmotic adjustment, antioxidant activation, and hormonal balance—translate into measurable agronomic benefits, even under challenging climatic conditions. However, the extent of yield improvement varies depending on cultivar, environmental stress, and formulation, highlighting the importance of multi-year validation. The conceptual relationship between these physiological responses and yield stability is illustrated in Figure 1.

7.9. Relationship Between Biochemical Modulation by Biostimulants and Wine Organoleptic Quality

Beyond their physiological and biochemical effects, biostimulants can also influence the perceived quality of grapes and wine. However, this relationship is often indirect, since biochemical indicators like total phenols or antioxidant activity do not always translate directly into sensory improvements. Instead, their impact depends on how they alter the balance among sugars, acids, pigments, aromatic precursors, and phenolic structures, which collectively shape wine typicity and consumer perception.

Table 5. Reported effects of biostimulant applications on grape biochemical composition and their relationship with perceived wine quality.

Grapevine Cultivar	Biostimulant/Formulation	Key Biochemical Modulation	Reported or Inferred Sensory Effect	Reference
Cabernet Sauvignon	Ecklonia maxima (Kelpak®, foliar 3×)	↑ sugars, ↑ phenolics, stable acidity	Fuller body, enhanced aroma intensity, slightly higher alcohol	[100]
Tempranillo	Ascophyllum nodosum extract (Crop Plus®, foliar 2×)	↑ malvidins, ↑ stilbenes	Deeper color, longer persistence, improved mouthfeel	[105]
Sauvignon Blanc	Salicylic acid (3 mM, foliar 2×)	↑ amino acids, ↑ aromatic volatiles, balanced acids	Enhanced floral–fruit aroma and freshness	[115]
Barbera	Protein hydrolysate (LalVigne ProHydro™, foliar 5×)	↑ anthocyanins, ↑ polyphenols, ↓ berry dehydration	Improved color and texture; slightly higher alcohol	[82]
Fakhri	K2SiO3 + Humic acid (foliar 3×)	↑ polyphenols, ↑ micronutrients, stabilized pH	Enhanced minerality and aromatic balance	[111]
Merlot	Ascophyllum nodosum (AZAL5®, foliar 4×)	↑ anthocyanins, ↑ soluble solids	More vivid color, improved sensory structure	[102]
Chardonnay	Salicylic acid (3 mM, foliar 2×)	↑ benzenoid compounds, ↑ terpenes	Increased aromatic complexity and acidity retention	[114]
Sangiovese	Zeowine (zeolite + compost, soil)	↑ anthocyanins, ↑ quercetin derivatives	Greater color stability and mouthfeel smoothness	[118]

↓: Decrease; ↑: increase.

summarizes the key evidence linking biostimulant-induced biochemical changes with organoleptic outcomes, including aroma complexity, color intensity, acidity balance, and alcohol content. In Cabernet Sauvignon, foliar applications of Ecklonia maxima increased leaf photosynthesis and sugar accumulation, leading to wines with more body and aromatic richness but moderate increases in alcohol [100]. In Tempranillo, Ascophyllum nodosum extracts boosted malvidin and stilbene levels, resulting in deeper color and enhanced sensory persistence [105]. Humic substances and potassium silicate improved aromatic freshness and minerality in Fakhri wines by optimizing nutrient levels and pH stability [111].

Protein hydrolysates applied during the pea-size to veraison stages increased amino acid and phenolic content in Barbera and Sauvignon Blanc, producing wines with better mouthfeel and color stability, though sometimes higher alcohol due to increased sugar levels [82,112]. Conversely, excessive enhancement of total phenolics, if not balanced with acidity and polysaccharides, can raise astringency, as seen in some red cultivars [44]. Therefore, the sensory effects of biostimulants depend on achieving a balance between biochemical enhancement and technological maturity.

Overall, evidence indicates that moderate biochemical adjustments favoring aromatic precursors, balanced sugar/acid ratios, and regulated phenolic synthesis tend to improve perceived quality. Figure 2 offers a conceptual overview connecting biochemical parameters to the main sensory traits that define wine quality.

8. Practical Considerations

Vitis vinifera L. is highly sensitive to climate change because its phenological stages are closely regulated by environmental cues such as light and temperature. These cues influence the production of phytohormones that control transitions between developmental phases and dormancy during specific seasonal periods [29]. Climate change, which presents as abiotic stress in vineyards such as high temperatures, late frosts, excessive solar radiation, drought, and salinity has negatively impacted grape production and directly affected enological parameters. Generally, abiotic stress decreases yield and alters berry composition, resulting in fruit with higher sugar levels, lower titratable acidity due to increased pH, and decreased phenolic content at harvest. As a result, wines made under these conditions tend to have higher alcohol content, less aromatic complexity, deficiencies in organic acids, antioxidant phenols, and terpenes, poor color development, and increased oxidation instability.

In this context, agricultural biostimulants are a promising alternative to reduce or lessen the effects of abiotic stress and, under normal growing conditions, to enhance fruit quality. However, their use in grapevines faces challenges due to the lack of clear regulatory frameworks and the high sensitivity of the species to environmental variations, requiring precise timing of applications based on the phenological stage. Generally, applications of plant growth-promoting rhizobacteria (PGPR) and silicon-based products are carried out in the soil or substrate during the early stages after dormancy release. These treatments help mitigate the effects of drought, salinity, and especially low temperatures in cuttings, seedlings, or young vines exposed to frosts after budburst.

It is important to recognize that the mode of action and optimal timing of application can vary among different categories of biostimulants. While many products have direct effects that depend on the vine’s phenological stage (for example, seaweed extracts, protein hydrolysates, humic substances), others, especially signaling molecules such as β-aminobutyric acid, salicylic acid, and brassinosteroids, serve as priming agents. These induce stress memory or enhance responsiveness before stress occurs. Therefore, they are more effective when applied prior to the onset of stress or key phenological transitions rather than during them. This distinction has been incorporated into the revised Table 2, which now specifies the number and frequency of treatments where available.

From flowering onward, when the canopy is fully developed, foliar or combined foliar–root applications dominate, aiming to both counteract abiotic stress and enhance the enological qualities of the fruit. To reduce water deficit, protein hydrolysates (amino acids), osmoprotectants like proline and glycine betaine, and abscisic acid (ABA) are frequently applied during flowering, fruit set, and pea-sized berry stages. In cases of salinity stress, foliar antioxidants have been tested during veraison; however, most research suggests intervention during early stages after dormancy, when ionic toxicity and osmotic stress more directly impact plant establishment. Flowering and veraison are viewed as key stages for treatments designed to improve fruit quality, promote higher acidity, achieve a balanced sugar profile, enrich phenolic content, and develop desirable aromatic characteristics. Brown seaweed extracts are applied foliarly from flowering to late veraison, while humic substances, phytohormones, osmoprotectants, silica, and emerging biostimulants are used from pea-size berries to veraison, with the goal of optimizing yield and quality. More recently, postharvest applications of biostimulants have been investigated to reduce oxidation of phenolic compounds during storage and transport of grapes.

In conclusion, using agricultural biostimulants in grapevine cultivation emerges as a sustainable approach with significant potential in the face of climate change. Nevertheless, further research is needed to confirm the consistency of their effects across different years, varieties, and environmental conditions, and to develop precise guidelines for their application at each phenological stage (Figure 3).

9. Conclusions and Perspectives

Grapevine (Vitis vinifera L.) is highly sensitive to climate change, and its phenological development and winemaking quality are directly affected by abiotic stresses such as drought, salinity, and heat. The evidence summarized in this review shows that agricultural biostimulants, including seaweed extracts, humic substances, protein hydrolysates, osmoprotectants, silicon, PGPR, and arbuscular mycorrhizal fungi, can effectively influence physiological and metabolic processes in grapevine, leading to improved stress tolerance, better water and nutrient use, and enhanced berry quality.

Positive effects on fruit quality include higher anthocyanin and polyphenol content, increased antioxidant capacity, and improved maintenance of acidity–sugar balance under stressful conditions. However, the effectiveness of biostimulants remains limited by product heterogeneity, lack of standardized protocols, and strong dependence on cultivar, phenological stage, and local environmental factors. Most research has been conducted in short-term or greenhouse studies, while long-term, multi-year, and field evaluations are still scarce. This limits the ability to generalize results and makes it more difficult to incorporate biostimulants into both conventional and sustainable vineyard management practices.

Future research should focus on:

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Conducting multi-year and multi-site trials to ensure consistency across vintages, terroirs, and varieties.

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Performing mechanistic studies in local and underrepresented cultivars, using transcriptomic, metabolomic, and phenomic approaches to deepen our understanding of the molecular basis of resilience.

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Carrying out economic and enological assessments, including cost–benefit analyses and evaluating compatibility with winemaking practices, to encourage adoption by producers and wineries.

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Developing innovative formulations such as nanostructured carriers, controlled-release systems, and synergistic or microbial biostimulant consortia specifically tailored for viticulture [121].

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Integrating digital agriculture and precision tools, including remote sensing, smart spraying, and data-driven monitoring, to optimize biostimulant timing and dosage according to real-time plant and environmental conditions [122].

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Incorporating these advances into climate-smart viticulture strategies by aligning biostimulant usage with irrigation management, canopy regulation, and other sustainable practices.

In conclusion, agricultural biostimulants represent a promising tool to boost grapevine resilience and maintain wine quality amid increasing climate variability. Their integration into viticulture, however, requires not only scientific validation but also clear regulations, standardized application guidelines, and economic viability. The convergence of molecular insight with nanotechnology, microbial ecology, and digital agriculture will shape the next generation of precision biostimulation, unlocking its full potential for sustainable and competitive viticulture under climate change.