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Article

Ecklonia maxima and Glycine–Betaine-Based Biostimulants Improve Blueberry Yield and Quality

by
Tiago Lopes
1,2,3,4,
Ana Paula Silva
1,2,5,
Carlos Ribeiro
1,2,5,
Rosa Carvalho
5,
Alfredo Aires
1,2,5,
António A. Vicente
3,4 and
Berta Gonçalves
1,2,6,*
1
Centre for the Research and Technology of Agro-Environmental and Biological Sciences (CITAB), University of Trás-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal
2
Institute for Innovation, Capacity Building and Sustainability of Agri-Food Production (Inov4Agro), University of Trás-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal
3
Centre of Biological Engineering (CEB), University of Minho (UM), Campus de Gualtar, 4710-057 Braga, Portugal
4
LABBELS—Associate Laboratory, 4710-057 Braga, Portugal
5
Department of Agronomy, University of Trás-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal
6
Department of Biology and Environment, University of Trás-os-Montes e Alto Douro (UTAD), 5000-801 Vila Real, Portugal
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(9), 920; https://doi.org/10.3390/horticulturae10090920
Submission received: 19 July 2024 / Revised: 26 August 2024 / Accepted: 26 August 2024 / Published: 29 August 2024
(This article belongs to the Section Fruit Production Systems)
Browse Figures
Versions Notes

Abstract

:
The consumption of blueberries has increased in recent years due to their excellent flavor and high antioxidant activity, which promote human well-being and health. Several sustainable cultural practices, such as biostimulants, have been applied to increase crop performance. The pre-harvest foliar application of two doses of a biostimulant based on the macroalgae Ecklonia maxima (EM), two doses of a glycine–betaine (GB) biostimulant, and two doses of the combination of the biostimulants in ‘Duke’ and ‘Draper’ blueberry cultivars in 2022 and 2023 were studied. The application of 4 L ha−1 EM significantly increased the yield of ‘Draper’ blueberries, while the same occurred in ‘Duke’ fruits treated with 4 L ha−1 EM + 4 kg ha−1 GB. The blueberries sprayed with both doses of EM + GB were heavier and larger. ‘Duke’ fruits treated with EM were firmer and, following 4 L ha−1 EM + 4 kg ha−1 GB treatment, presented a lower concentration of organic acids, determined by HPLC, greater sensorial sweetness, and lower acidity. Therefore, these biostimulants are recommended for a more environmentally friendly production perspective, as they may increase blueberry yield and improve fruit quality.

1. Introduction

The production and commercialization of blueberries (Vaccinium corymbosum L.) have increased over the last few years, which can be explained by their attractive taste, color, and nutritional content [1,2]. In fact, blueberries are known for their high antioxidant activity due to their composition of phenolic compounds, vitamins, and organic acids that have several bioactive properties [3]. These bioactive compounds are attributed to several health benefits, such as anti-inflammatory, antioxidation, and immunomodulatory effects, neuroprotection, anticancer effects, vision improvement, and the prevention of skin disorders [3,4,5,6]. In addition to health benefits, consumers also prioritize blueberries with a good appearance, firmness, and specific sensory properties, like sweet and intense flavor [7,8]. Considering climate change, such as the rising temperatures, changed levels of precipitation, and irregular weather conditions, new strategies must be adopted to improve blueberries’ quality and maintain competitiveness, for example, by the pre-harvest foliar application of biostimulants. A plant biostimulant is defined as a “product stimulating plant nutrition processes independently of the product’s nutrient content with the sole aim of improving one or more of the following characteristics of the plant or the plant rhizosphere: nutrient use efficiency; tolerance to abiotic stress; quality traits; and availability of confined nutrients in soil or rhizosphere” [9]. Because of their minimal impact on the environment, as well as their potential to reduce the utilization of pesticides and chemical fertilizers, these products could be an appropriate substitute for conventional agronomic practices [10,11,12].
Since ancient times, seaweeds have been used as biostimulants for improving agricultural soils [13,14]. Their extracts are widely used, cost-effective biostimulants [15] that are sources of nutrients [14,16], vitamins [16,17], amino acids [16,17], polysaccharides [18], peptides [17], omega-3 fatty acids [17], betaine compounds [19], photosynthetic pigments [20], phenolic compounds [14,17], and phytohormones such as auxins, cytokinins, abscisic acid, gibberellins, ethylene, or brassinosteroids [14]. Seaweed-based biostimulants can enhance plants’ natural defenses against biotic and abiotic stresses and promote plant growth under such conditions [21,22], as well as improve nutrient absorption and utilization by plants, enhance product quality, and increase root growth [23,24]. The use of seaweeds has been shown to enhance the size, weight, firmness, total soluble solids (TSS), and bioactive compounds of grapes, pears, watermelons, strawberries, sweet cherries, apples, and tomatoes, increasing profits and minimizing postharvest losses [23,25,26,27,28,29,30,31,32,33,34,35], in addition to increasing blueberry yield, weight, size, firmness, TSS, and total sugar content, and decreasing its total acidity [36,37,38,39]. Specifically, it was verified that brown macroalgae Ecklonia maxima (EM) application increased the yields of sweet cherries, strawberries, tomatoes, chicory plants, and common beans [40,41,42,43,44].
Glycine betaine (GB), also known as N,N,N-trimethylglycine, is a quaternary ammonium compound and exists as a dipolar molecule that is electrically neutral under physiological pH conditions. It is found in many living organisms, including plants, and is synthesized either by the N-methylation of glycine or by choline oxidation [45,46,47]. GB has several antioxidant effects and plays an important role in the protection of cell membranes, the photosystem II (PSII) complex, and proteins such as ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) against salt stress [48]. This osmolyte is also responsible for increasing crop resistance to different stresses, like drought or freeze damage, due to its involvement in osmotic adjustment. Additionally, it is essential for improving physiological properties and the activity of antioxidant enzymes in plants [49,50]. As far as we know, no studies exist on GB’s role in blueberry yield and quality. However, after the pre-harvest application of GB, other fruits have demonstrated several benefits. Applying this compound to grapes improved berry quality and increased the concentration of bioactive compounds [51]. It also enhanced tomato-fruit yield in heat-stressed conditions and promoted the photosynthetic activity of apples under drought and heat stress [52,53]. Additionally, the exogenous application of GB increased the water-use efficiency, chlorophyll content, and antioxidant activity of cherry leaves, as well as fruit weight, firmness, anthocyanins, and vitamin C contents [34,54,55,56].
The objective of this study was to analyze the impact of pre-harvest foliar application of EM and GB-based biostimulants on the yield, quality, and sensory properties of ‘Duke’ and ‘Draper’ blueberry cultivars. Analyses of the yield per plant, fruit size, weight, color, texture, pH, TSS, titratable acidity, organic acids content, and sensory attributes were performed.

2. Materials and Methods

2.1. Characteristics of the Research Area and Plant Material

The experimental trial was conducted in 2022 and 2023 in an orchard located in Vilarandelo, Valpaços municipality, in the north of Portugal (41°40′8.38″ N, 7°19′22.81″ W, 593 m asl). The climate of this region is classified as “Csa” according to the Köppen classification system, which means that it faces a temperate climate with a rainy season in winter and a hot and dry summer. Precipitation and temperature data, provided by a weather station near the experimental site, can be observed in Figure 1. In general, 2022/2023 was characterized by higher average temperatures than the previous year, with an increase of approximately 1 °C in the average annual temperature. In addition, it was a year with a higher occurrence of precipitation (almost double the accumulated precipitation of the previous year). Thus, the year 2021/2022 was drier, although with peak rainfall in September (64.9 mm) and October (81.3 mm). In the following year, the months with the highest accumulated precipitation corresponded to November (102.6 mm) and December (194.2 mm). The higher temperatures observed in the years 2022/2023, namely in March and April, may have contributed to the anticipation of bud breaking and blooming. Likewise, this year, there was greater precipitation in May and June, as well as higher temperatures in June, when the blueberry went into production.
According to soil analyses carried out in 2022, the soil has a medium texture, moderate acidity, and pH 5.6, with 4.71% organic matter, high extractable phosphorus (105 mg P2O5 kg−1), and very high extractable potassium (426 mg K2O kg−1). Blueberry ‘Duke’ and ‘Draper’ northern highbush cultivars were planted in 2012 with a north–south orientation and 3 m of spacing between rows and 1 m between shrubs. ‘Duke’ is a very early cultivar that produces firm fruits with medium size and color and a small scar, while its flavor is mild. On the other hand, ‘Draper’ is an early mid-season cultivar that produces large, light-blue, and very firm blueberries with a small scar, characterized by their excellent flavor and good shelf life [57]. The orchard has a drip irrigation system, with 2 lines per bush with auto-compensated dripper spacing of 33 cm in line and a flow rate of 1.6 L h−1. The orchard was fertilized based on soil analyses and crop recommendations. Throughout the assay, no phytosanitary treatments were applied.

2.2. Experimental Design and Sampling

Different treatments were applied involving the use of Ecklonia maxima macroalgae biostimulant (Kelpak®, Daymsa, Zaragoza, Spain), which is a liquid concentrate of 100% EM whose declared content presents 0.55% K2O (w/w), a pH of 4.4, and a conductivity of 20 mS/cm. A commercial glycine–betaine-based product (97% GB), extracted from sugar beet (Greenstim®, Massó Agro Department, Barcelona, Spain) was also applied, whose composition (w/w) included 12% of total N, 11.5% organic N, 56% organic C, and a C/N ratio of 4.9. The doses used were 4 L ha−1 (T1) and 2 L ha−1 (T2) for EM and 4 kg ha−1 (T3) and 2 kg ha−1 (T4) for GB. In addition, a combination of 4 L ha−1 EM + 4 kg ha−1 of GB (T5) and 2 L ha−1 EM + 2 kg ha−1 GB (T6) was used, while a control treatment with water (T0) was also included. The foliar treatments were applied three times during each growing season at full bloom (BBCH 65), early green fruit (BBCH 71), and fruit coloring (BBCH 81) [58]. The spraying was conducted in the morning, covering the entire canopy, when there was no expected precipitation for the next 24 h. Each treatment was applied to a row of 9 plants, and thus, each cultivar studied contained an assay of 63 plants, with 126 in total.
In 2022, the fruits of cv. ‘Duke’ and cv. ‘Draper’ were harvested on June 14 and June 27, respectively. In 2023, the harvest occurred on June 12 and June 20, respectively. At the same stage of ripeness, hundreds of blueberries with an identical average size were randomly collected per treatment and promptly transported to the laboratory for analytical determinations. To conduct different types of analyses, including fruit quality assessment, sensory analysis, and organic acids determination by HPLC, the blueberries were divided accordingly. For biochemical analysis, the fruits were immediately frozen with liquid nitrogen and stored at –80 °C. Once lyophilized, the fruits were ground into a dried powder using a commercial blender.

2.3. Yield and Fruit Quality Assessment

The yield per plant was determined before harvest by counting the number of fruits per plant without picking them and regardless of their state of ripeness. Taking into account the average blueberry weight (g) per treatment and the number of fruits per plant, the effect of the treatments on blueberry yield was analyzed. Weight (g), height (mm), width (mm), and calyx scar diameter (mm) were determined for each treatment in 50 fruits. An electronic precision scale (EW2200-2NM, Kern, Germany) was used to determine the weight of the fruits, and their size was determined using a digital caliper. Fruit color was measured in 30 fruits per treatment, utilizing a colorimeter (ModelCR-300, Minolta, Japan), according to the CIELab classification scale. Subsequently, the chroma (C*) and hue angle (h°) parameters were calculated. Measurements were taken from one side of each fruit. For the determination of the total soluble solids (TSS in °Brix), pH, titratable acidity (TA) (% citric acid), and maturity index (MI), the juice of three groups of 10 fruits per treatment was extracted with a dispersor (T 25 digital ULTRA-TURRAX®, Staufen, Germany). The TSS was determined using an electronic refractometer (ATAGO PR-101, Tokyo, Japan), and the pH measurement was performed with the aid of a pH meter. TA was determined using a Schott Easy Titroline automatic titrator from 10 mL of pulp extract obtained from each group of 10 blueberries diluted in 10 mL of distilled water and titrated with 0.1 mol L−1 sodium hydroxide (NaOH) at pH 8.2, recording at the end the amount of NaOH (0.1 mol L−1) used to balance the solution. Subsequently, taking into account the TSS content obtained and the % of citric acid, the TSS/TA ratio (MI) was calculated. To analyze the texture of blueberries, the flesh firmness (FF) and epidermis rupture force (ERF) of the blueberries were measured using a TA. XTPlus texture analyzer (Stable Micro Systems, Godalming, UK). For the analysis of FF (N mm−1), a cylindrical 7.5 cm diameter plate probe was used. A 2 mm needle probe was used to determine the ERF (N). The maximum force (N) applied was determined at 1 mm/s of speed. Each test was conducted on 10 fruits per treatment.

2.4. Determination of Organic Acids

The determination of organic acids was performed according to Phillips et al. [59]. To extract the organic acids, 1 g of DW was mixed for 5 min with 10 mL ultrapure water in a commercial sonicator (Sonorex Digitec DT 100, Bandelin, Germany). The homogenate was centrifuged for 15 min at 4000 rpm (Centrico 250, UniEquip, Munich, Germany). The supernatant was filtered through a 0.20 μm cellulose ester filter (WhatmanTM, Spartan 13/0.2 RC, Maidstone, UK) and transferred (1 mL) to amber HPLC vials. Then, the samples were stored at –20 °C until quantification by HPLC. For the quantification, an HPLC-DAD-UV/VIS system with a diode array detector and a reverse phase column (C18 Spherisorb ODS2, 250 mm × 4.6 mm) was used. The mobile phase of the isocratic gradient consisted of potassium dihydrogen phosphate, at a concentration of 6.8 g L−1, with orthophosphoric acid (85%) to achieve a pH of 2.1. The flow rate was set to 0.8 mL min−1 with an injection volume of 20 μL, and the detection was made at 210 nm. The organic acids were identified by comparing their retention times to external standards (Sigma-Aldrich, St. Louis, MO, USA). Three replicates were conducted for each treatment and cultivar. The results were expressed as mg g−1 DW.

2.5. Sensory Analysis

The sensory analysis involved eleven trained food sensory evaluation tasters who evaluated the samples of blueberries that were randomly distributed to obtain a sensory profile of each sample by conducting a descriptive and quantitative analysis. Both organoleptic analyses take place in a room with a controlled environment (20 ± 2 °C; 60 ± 20% RH) [60]. To reach a temperature of around 18 °C, the samples were kept at room temperature for 2 h. A list of fifteen blueberry attributes was evaluated according to Vilela et al. [61]. The panelists were presented with coded white plates containing three blueberries per treatment and the cultivar and were provided with a tasting form to record the organoleptic characteristics of the fruits. The analysis included parameters related to visual perception, olfactory perception, gustatory perception, taste perception (retro-nasal), and texture. Each attribute of each sample was evaluated on a scale of 1 (lowest intensity) to 5 (highest intensity) points [62]. The panelists were advised to cleanse their palates with low-salt crackers, drink room-temperature water, and wait briefly before every test.

2.6. Statistical Analysis

All data were subjected to analysis of variance (ANOVA) with a post hoc Tukey’s HSD test at 5% significance for comparison between the means, using version 27.0 of SPSS software (SPSS-IBM, Orchard Road, Armonk, New York, USA). It was performed using a one-way, two-way, and three-way ANOVA to verify the effect of the treatments and the cultivars for each year and the year effect. For the analysis of sensory data, a one-way ANOVA was performed, followed by a post hoc Tukey’s HSD test at a 5% significance level.

3. Results

3.1. Fruit Yield

In both years, the yield per plant (Figure 2) was affected by treatment and cultivar (p < 0.001), and significant differences were found between their interaction (p < 0.01) in 2023. Thus, the ‘Duke’ cultivar had lower yields (p < 0.001) than the ‘Draper’. This parameter was also affected by year (p < 0.001) (Table A1 in Appendix A), as the fruit yield was higher in 2023. The ‘Draper’ and ‘Duke’ blueberry bushes sprayed with 4 L ha−1 EM (T1) and with the combination of 4 L ha−1 EM + 4 kg ha−1 GB (T5), respectively, exhibited significantly higher (p < 0.001) production per plant in both years (78% increase for T1 and 84% for T5, on average). Moreover, in 2022, the foliar application of 2 L ha−1 EM (T2) also improved (p < 0.001) the yield of the ‘Duke’ (90%) and ‘Draper’ (64%) blueberries. The same occurrence was observed after spraying the ‘Duke’ fruits with T1, T4, and T5 (p < 0.001) and the cultivar ‘Draper’ with T3 (p < 0.001). In 2023, the combination of 2 L ha−1 EM + 2 kg ha−1 GB (T6) increased (p < 0.001) by 118% of the yield per plant of the ‘Duke’ blueberries.

3.2. Fruit Weight and Size

The weights and sizes of the treated fruits can be seen in Table 1. In both years, the weight, height, and width of the blueberries were affected by preharvest foliar treatment (p < 0.001), cultivar (p < 0.001), and the interaction between them (p < 0.05). Furthermore, the calyx scar diameter was influenced by treatments (p < 0.05) and cultivar (p < 0.001) in both years and by their interaction (p < 0.05) in 2023. The width-height ratio varied significantly among treatments and cultivars (p < 0.001) in both years. In addition, it was observed that, in 2022, this parameter was affected by the interaction between treatment and cultivar (p < 0.001). All the biometric parameters were influenced by year (p < 0.001), and the width was affected by the interaction between treatment, cultivar, and year (p < 0.05) (Table A1 in Appendix A). In both years and cultivars, the foliar application of both doses of the mixture of the two biostimulants (T5 and T6) significantly increased (p < 0.001) the blueberries’ weight (on average, 13% for T5 and 15% for T6) and width (on average, increases of 5% for both treatments). Additionally, the high dose of EM (T1) improved (p < 0.001) the fruit width of both cultivars in the two years of the assay. In 2022, T1 and T4 sprays were demonstrated to increase (p < 0.001) the weight of ‘Duke’ blueberries, while the application of T2 and T3 contributed to the increase (p < 0.001) in their width. In 2023, in both cultivars, the treatment with the high dose of EM (T1) increased the fruit weight (p < 0.001), and the application of both doses of T5 and T6 contributed to the increase of the fruit height (p < 0.001). Meanwhile, the high dose of GB (T3) enhanced blueberry width (p < 0.001). This year, the ‘Duke’ fruits sprayed with 2 L ha−1 EM (T2) and 2 kg ha−1 GB (T4) presented higher (p < 0.001) weight, height, and width. In addition, the ‘Duke’ blueberries treated with 4 kg ha−1 GB (T3) had a higher weight (p < 0.001), whereas the blueberries treated with 4 L ha−1 EM (T1) presented a higher (p < 0.001) height and a larger calyx scar diameter. Regarding the width-weight ratio, in 2022, the exogenous application of T5 significantly increased (p < 0.001) the ratio in both cultivars. This year, the same effect was observed (p < 0.001) after spraying T6 in the ‘Duke’ blueberries and T1 in the ‘Draper’ blueberries. In addition, the ’Duke’ fruits treated with T2 and T3 showed a higher (p < 0.05) ratio in both years.

3.3. Fruit Color

The chromatic parameters of the treated fruits are shown in Figure 3. In 2022, the luminosity (L*) was affected by the treatment (p < 0.001) and by the interaction between the treatment and the cultivar (p < 0.001). The parameter C* was affected by the treatment (p < 0.01), cultivar (p < 0.001), and their interaction (p < 0.001). The parameter h° was affected by the interaction between treatment and cultivar (p < 0.05). In 2023, the L* parameter varied significantly among treatments (p < 0.001), cultivars (p < 0.05), and their interaction (p < 0.001). The parameter C* was affected by the treatment (p < 0.001), cultivar (p < 0.05), and their interaction (p < 0.01). The parameter h° was affected by the treatment (p < 0.001) and by the interaction between treatment and cultivar (p < 0.05). All the chromatic parameters were influenced by year (p < 0.001), and the L* parameter was affected by the interaction between treatment, cultivar, and year (p < 0.01). The ‘Duke’ blueberries treated with T1 and T5 in 2022 had decreased (p < 0.001) L* and C* parameters. Additionally, this year, the ‘Draper’ blueberries sprayed with T5 showed lower (p < 0.001) L* values. In 2023, all treatments contributed to the decrease (p < 0.001) in the L* and C* parameters of the ‘Draper’ blueberries. For the cultivar ‘Duke’, the blueberries from T1, T3, T4, and T6 presented lower (p < 0.001) L* and C* values. In addition, T1 contributed to the increase (p < 0.001) of the h° parameter.

3.4. Texture Attributes

The ERF (N) and the FF (N mm−1) can be seen in Figure 4. In both years, the treatment (p < 0.01), cultivar (p < 0.001), and effect of their interaction in ERF (p < 0.05) were significant. In 2023, the foliar application of 4 L ha−1 EM (T1) significantly decreased (p < 0.001) the ERF of the ‘Duke’ blueberries compared to the untreated control. The treatment and cultivar affected the FF in both years (p < 0.001). In both years, the application of EM-based biostimulants (T1 and T2) contributed to the increase (p < 0.01) in the FF of ‘Duke’ blueberries (on average, 41% and 33%, respectively). In addition, the foliar spraying of 4 L ha−1 EM (T1) increased (p < 0.05) this parameter by 24% in the ‘Draper’ blueberries in 2022, and the application of T6 also increased by 31% (p < 0.01) in the FF of the ‘Duke’ cultivar. In 2023, the exogenous application of 4 kg ha−1 GB (T3) and the high dose of the combination of the two biostimulants (T5) enhanced (p < 0.001) the FF of both cultivars. Furthermore, ‘Duke’ blueberries treated with T4 and ‘Draper’ fruits treated with T6 presented, respectively, higher (p < 0.001) FFs. Both parameters were affected by year (p < 0.001) (Table A1 in Appendix A).

3.5. pH, Total Soluble Solids, Titratable Acidity, and Maturation Index

The pH, TSS, TA, and MI values of the treated blueberries are presented in Table 2. The pH was affected (p < 0.001) by treatment and cultivar in both years, and the interaction between these variables was significant (p < 0.05) in 2022. The application of the high dose of GB (T3) and the low dose of the combination of both biostimulants (T6) significantly increased (p < 0.05) the pH of the ‘Draper’ blueberries in 2023. Significant differences between treatments (p < 0.01) and cultivars (p < 0.001) in TSS content were found in both years. This parameter was also affected by the interaction between treatments and cultivars in 2022 (p < 0.001) and 2023 (p < 0.05). The application of both doses of GB (T3 and T4) and the low dose of both biostimulants (T6) improved (p < 0.001) the TSS of the ‘Duke’ fruits in 2022 and the ‘Draper’ blueberries in 2023. Additionally, the ‘Draper’ blueberries sprayed with 4 L ha−1 EM + 4 kg ha−1 GB (T5) showed higher (p < 0.001) values of TSS in 2023 compared to T0. TA was influenced by treatment (p < 0.01) in the year 2023. In both years, significant differences (p < 0.001) were observed among cultivars. In 2023, the treatment with 4 kg ha−1 GB (T3) caused a decrease (p < 0.05) in the TA of ‘Duke’ blueberries, and the same occurred after the application of T6 in ‘Draper’ fruits. Regarding MI, significant differences were found between treatments (p < 0.01) and cultivars (p < 0.001) in 2023. This year, the application of T6 improved (p < 0.05) the MI of ‘Draper’ blueberries. The pH (p < 0.001), TSS (p < 0.01), and TA (p < 0.05) were affected by year. In addition, the interaction between treatment, cultivar, and year was significant for pH (p < 0.01) and TSS (p < 0.001) (Table A1 in Appendix A).

3.6. Organic Acids

The organic acids content can be seen in Figure 5. Citric, malic, and quinic acids were the most abundant organic acids found in the blueberries studied, as verified by Correia et al. [63] and Aires et al. [64]. Citric acid was the predominant organic acid in both cultivars, as confirmed by several authors on blueberries [63,64,65,66]. The composition of these organic acids and the total organic acids content varied significantly among treatments, cultivars, and their interaction (p < 0.001). This parameter was influenced by year (p < 0.001) and by the interaction between treatment, cultivar, and year (p < 0.001) (Table A1 in Appendix A). In 2022, ‘Duke’ blueberries treated with T4 presented lower (p < 0.001) total organic acids, while the spraying of T2, T3, T5, and T6 decreased (p < 0.001) their content in 2023. Additionally, T6 increased (p < 0.001) this content in 2022, which was verified with T1 in 2023. In both years, the ‘Draper’ fruits sprayed with 4 kg ha−1 GB (T3) and with the combination of both biostimulants (T5 and T6) had lower (p < 0.001) concentrations of organic acids. In addition, T1 in 2022 and T4 in 2023 significantly decreased (p < 0.001) the organic acids content of this cultivar compared to the control. In 2023, both doses of EM (T1 and T2) significantly increased (p < 0.001) the organic acids content of ‘Draper’ blueberries.

3.7. Sensorial Analysis

The sensory profile of the treated blueberries is shown in Figure 6. There were no significant differences (p > 0.05) between treatments in both cultivars in 2022. However, in 2023, significant differences (p < 0.05) were observed for the ‘Duke’ cultivar. The improvement in fruit sweetness was significant when 4 kg ha−1 GB was sprayed, and the combination of both products was used at a high dose (T5) when compared with the untreated control in 2023. Furthermore, the T5 application decreased (p < 0.001) the acidic taste of the blueberries.

4. Discussion

4.1. Can Biostimulants Impact Blueberry Yield

The fruit yield per plant was higher in the 2023 harvest compared to 2022. Although annual cultural practices such as pruning can influence fruit production, the increased rainfall between July 2022 and June 2023, especially during May and June, may have contributed to the improved yields in this last year. Our data suggest that applying EM- and GB-based biostimulants and combining both products can be an effective method for increasing blueberry yield per plant. However, the results may vary depending on the cultivar and year. The foliar spraying of EM at the highest rate (4 L ha −1) improved by 78% the yield of the ‘Draper’ cultivar, while the ‘Duke’ fruits sprayed with 4 L ha−1 EM + 4 kg ha−1 GB showed a 84% higher yield compared to the control in both years. The timing of biostimulant applications, which coincided with both the rapid cell division and the cell-expansion phases in blueberries, may have potentially contributed to the increased productivity. For example, spraying EM, especially during the full bloom stage, probably allowed the pollen tube to become longer and the pollen to germinate better, which led to more fruit set and yield [41]. Polyamines in EM-based biostimulants are crucial for several development processes, namely flowering, pollen maturation, and germination. They also contain several bioactive substances, such as phytohormones, polysaccharides, and polyphenols, including phlorotannins, that can enhance crop growth performance and nutrient absorption [14,67]. According to Mousavi et al. [68], the increase in fruit yield after the foliar application of seaweeds may be linked to the improvement of water relations, higher mineral concentration, increased levels of phenols and antioxidant enzymes, the inhibition of chlorophyll decomposition, and the enhancement of plant growth. Previous studies showed that the foliar application of seaweed-based biostimulants enhanced by 39% the yield of ‘Duke’ blueberries [39] and positively impacted other crops, such as strawberries [43,69,70], grapes [25,71], tomatoes [30,40,72], peppers [73], apples [68], and sweet cherries [33,41]. The role of GB in protecting the photosynthetic apparatus may be responsible for the observed increase in yield following its foliar application [74]. Indeed, it has been demonstrated that GB can contribute to an increase in chlorophyll concentration, which, in turn, leads to the production of a greater amount of photoassimilates through an enhanced photosynthetic rate, thus promoting fruit development [75]. Other studies have also reported that foliar spraying of GB increased the yields of tomatoes [52,76], strawberries [77], and olive trees [78].

4.2. EM and GB Improve Blueberry Biometric Properties

The foliar application of EM and GB increased the fruit’s weight and size. However, blueberries treated with both doses of the combination of biostimulants (T5 and T6) showed the most promising results in both years and cultivars, enhancing fruit weight by 13% and 15%, respectively, and improving blueberry width by 5% compared to the control. The increase in fruit biometric properties following EM application may be attributed to the increased concentration of phytohormones, such as auxins, cytokinins, abscisic acid, and gibberellins, by the activation of different biosynthetic pathways, and through network interactions, modulating hormone pathways [14,67]. Additionally, polysaccharides can also be responsible for seaweed’s growth-promoting properties [79]. Previous studies reported that the application of biostimulants based on marine algae extracts significantly improved by 12% the weight of ‘Bluecrop’ blueberries and by 43% the weight of ‘Duke’ [38,39]. Similarly, these biostimulants enhanced the biometric properties of other fruits [25,27,28,29,68,70,71,80]. Furthermore, as observed in our study, foliar spraying of GB enhanced the weight and size of several fruit species [51,54,76]. The increase in fruit weight after GB application can be related to improved plant performance, specifically through better water-use efficiency and its role in osmotic regulation [81]. It has been demonstrated that this compound can increase the activities of enzymes that promote sucrose synthesis, modulate the source-sink metabolism, and affect several phytohormones that promote cell growth and division, resulting in larger fruits. Moreover, GB could regulate cell division and expansion-related genes as well as induce the expression of other specific fruit-development genes, thereby contributing to improving fruit size [75]. Furthermore, a higher width-to-height ratio was observed in fruits treated with both biostimulants, which led to the formation of flatter blueberries. Likewise, in 2022, the fruits of both cultivars sprayed with the combination of 4 L ha−1 EM + 4 kg ha−1 GB were flatter compared to the untreated control.

4.3. Effect of Biostimulants Application on Blueberry Color

The color of blueberries can be a good indicator of their ripeness and quality [82]. The light-blue color of fresh blueberries is influenced by the concentration of anthocyanins and cuticular wax in the skin [57]. Generally, the foliar application of both EM and GB tended to decrease the L* and C* parameters of blueberries, resulting in darker fruits, which can suggest a more advanced stage of maturity. Additionally, the application of EM at the highest rate (4 L ha−1) led to higher h◦ values. Similarly, strawberries with lower L* were reported following the foliar application of a seaweed-based biostimulant [83]. Consistent with our findings, Gonçalves et al. [34] demonstrated that the foliar spraying of a seaweed-based biostimulant on sweet cherries decreased both the L* and C* parameters, whereas the application of GB also decreased the L* value of these fruits.

4.4. Blueberry Texture Is Affected by EM and GB Foliar Application

Regarding the ERF, ‘Duke’ blueberries treated in 2023 with 4 L ha−1 EM showed a lower epidermal rupture force compared to the control. On the other hand, overall, the application of EM and GB-based biostimulants may contribute to an increase in blueberry FF, with particular emphasis on the application of both doses of EM, which increased the fruit firmness of the ‘Duke’ cultivar in the two years of the trial. In addition, the application of 4 kg ha−1 GB and the combination of 4 L ha−1 EM with 4 kg ha−1 GB increased this parameter in both cultivars in the second year. Cultivars with firmer fruits and less variation in firmness across maturation stages allow for longer harvest intervals [84]. The efficiency of seaweed-based biostimulants in increasing blueberry firmness was observed for the ‘Vital’ and ‘Bluecrop’ cultivars [38,39]. Similar results were found for strawberries [43,69]. This effect can be attributed to the presence of several bioactive compounds in seaweeds, such as polysaccharides and phytohormones, and the improvement of nutrient absorption and utilization, which play a beneficial role in the structure and composition of cell walls. According to Khan et al. [85], the application of seaweed-based biostimulants can increase the number and size of parenchyma cells, which may contribute to increased fruit firmness. However, Paraschiv et al. [39] found that seaweed application decreased firmness in ‘Elliott’ blueberries. In another way, Correia et al. [54] and Li et al. [55] reported an increased firmness in GB-treated sweet cherries, as observed in this study, whose effect may be related to its role in osmotic adjustment, contributing to the maintenance of cell turgor and influencing the texture of the fruits.

4.5. The Influence of the Foliar Application of Biostimulants on pH, TSS, TA, and MI

The pH and TSS levels are greatly associated with fruit taste. Higher TSS and pH indicate a sweeter flavor, which consumers generally prefer [86]. On the other hand, TA contributes to fruit sourness, which is inversely related to overall liking [87]. In 2023, ‘Draper’ blueberries treated with 4 kg ha−1 GB and the mixture of 2 L ha−1 EM with 2 kg ha−1 GB exhibited a higher pH. The increase in pH of several fruits following the foliar application of seaweed and GB-based biostimulants has been reported in other studies [30,34]. The foliar application of both GB doses and the combination 2 L ha−1 EM + 2 kg ha−1 GB produced the highest levels of TSS for ‘Duke’ fruits in 2022. A similar effect was observed in the ‘Draper’ cultivar in 2023. Furthermore, this year, the high dose of the combined products also increased the TSS levels of ‘Draper’ blueberries. Previous studies have reported a positive relationship between the foliar application of seaweed-based biostimulants and the improvement of TSS in blueberries [36,39] and other fruits, such as sweet cherries [34], strawberries [43,69], grapes [71], tomatoes [72], and sweet peppers [73]. Moreover, our data suggest that the application of 4 kg ha−1 GB can decrease the TA of ‘Duke’ blueberries, and the application of 2 L ha−1 EM + 2 kg ha−1 GB can decrease the TA and increase the MI of ‘Draper’ fruits, indicating that this treatment may contribute to accelerating the ripening process and advancing the harvest, as verified by Mannino et al. [88] in tomatoes after a seaweed-based biostimulant application. According to Gilbert et al. [87], the ratio of TSS to TA is commonly used as an indicator of fruit quality. The stage of ripeness of blueberries affects their quality, since more mature fruits have greater taste, aroma, and nutrients [86]. Previous research has reported a decrease in TA after GB foliar spraying in cherries [55], after a seaweed-based treatment in grapes [71], and following seaweed and GB-based biostimulant application in grapes [51].

4.6. Do the Foliar Treatments Affect Blueberry Acidity

The foliar application of 2 kg ha−1 of GB decreased the total organic acids content in 2022. Meanwhile, 2 L ha−1 EM, 4 kg ha−1 GB, and both doses of the mixture of both biostimulants decreased the content, in 2023, of ‘Duke’ blueberries. Furthermore, the ‘Draper’ fruits sprayed with a high dose of GB and both doses of the combination of biostimulants presented lower contents of total organic acids over the two years compared to the untreated control. This content was reduced in 2022 by the spraying of 4 L ha−1 EM, and in 2023, the application of 2 kg ha−1 GB showed the same tendency. The higher chlorophyll content and photosynthetic efficiency of the plants treated with GB may lead to an improved use of resources, reducing metabolic alterations caused by stress, such as the accumulation of organic acids [89]. According to Zhang et al. [65], the sum of organic acids positively correlates with the content of citric acid. Our data suggests that both the ‘Duke’ fruits treated with 4 kg ha−1 GB and the ‘Draper’ blueberries sprayed with 2 L ha−1 EM + 2 kg ha−1 GB exhibit lower TA and a lower content of citric acid than the control. However, the foliar application of 2 L ha−1 EM + 2 kg ha−1 GB increased the total organic acid content of the ‘Duke’ fruits in 2022, while the spraying of 4 L ha−1 EM enhanced this content in 2023. Furthermore, in 2023, both doses of EM (T1 and T2) significantly increased the total organic acids content of ‘Draper’ blueberries. Paraschiv et al. [39] reported that several blueberry cultivars increased the sum of organic acids after the foliar application of a seaweed-based biostimulant. Alterations in physiological processes, particularly in nitrogen and carbon metabolism, may cause the variation and accumulation of organic acids after the application of seaweed-based biostimulants [90]. Furthermore, it was found that the application of seaweed and GB-based biostimulants to sweet cherries enhanced their total organic acid content [54].

4.7. The Role of Spray Treatments on Sensorial Attributes

Consumers’ perceptions of fruit quality are influenced by their appearance, texture, aroma, and taste [8]. In 2023, it was found that the foliar spraying of a 4 L ha−1 EM and 4 kg ha−1 GB mixture enhanced sweetness and reduced the acidity taste of ‘Duke’ blueberries. Furthermore, fruits treated with a higher dose of GB exhibited greater sweetness compared to the control group. The increased perceived sweetness of ‘Duke’ fruits treated with 4 kg ha−1 GB can be attributed to their lower TA and total organic acid levels. Similarly, the higher sweetness and lower acidity of T5-treated blueberries noted by the panel may be related to their lower concentration of total organic acids. As a result, it can be concluded that treatments T3 and T5 may improve consumer perceptions of the quality of the blueberries of this cultivar, leading to a possible increase in market demand. However, increasing productivity and improving fruit quality without compromising its sensory profile can also be seen as advantages. Correia et al. [33] demonstrated that the foliar application of seaweed and GB-based biostimulants does not affect the flavor and taste profile of cherries, as verified in our study for ‘Draper’ blueberries.

5. Conclusions

Our findings demonstrate that the pre-harvest foliar application of Ecklonia maxima (EM) and glycine–betaine (GB), either individually or in combination, has the potential to enhance blueberry yield and quality. Variations between years were observed and were probably related to the different climatic conditions. An average of 78% increase in yield for the ‘Draper’ cultivar and of 84% for the ‘Duke’ cultivar were observed for blueberries treated with 4 L ha−1 EM and the combination of 4 L ha−1 EM + 4 kg ha−1 GB, respectively. The higher dose of EM was the most effective for increasing the weight and dimensions of ‘Duke’ blueberries over two years, while the combination of EM and GB was most efficient for ‘Draper’. Despite only experiencing this effect for one year, blueberries from this cultivar treated with both biostimulants (T6) exhibited higher TSS and MI, as well as lower TA and total organic acids. ‘Duke’ blueberries treated with both doses of EM were firmer (41% for T1 and 33% for T2), although the higher dose decreased the fruit’s epidermis rupture force in the second year. For both cultivars, the higher dose of GB and the combination of biostimulants (T5) improved blueberry firmness in the second year of the trial. In 2023, EM (T1) increased the total organic acid content in both cultivars, whereas GB (T3) and the combination of the two biostimulants (T5) were the most effective at reducing organic acids. Additionally, the mixture of biostimulants (T5) enhanced the perceived sweetness and decreased the acidity of ‘Duke’ blueberries from the consumer’s perspective. Thus, cultivar and application year may affect treatment efficacy. Future studies should focus on how these treatments perform in different environmental and soil conditions, consider using other cultivars, explore different timings and methods of application, and evaluate their effects on prolonging the shelf life of blueberries.

Author Contributions

Conceptualization, T.L., A.P.S., A.A.V., and B.G.; methodology, T.L., A.P.S., A.A.V., and B.G.; investigation, T.L., C.R., R.C., and A.A.; writing—original draft preparation, T.L.; writing—review and editing, T.L., A.P.S., C.R., A.A., A.A.V., and B.G.; supervision, A.P.S., A.A.V., and B.G.; All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by National Funds from FCT—Portuguese Foundation for Science and Technology, MCTES, and FSE, grant number 2021.07171.BD, and under the projects UIDB/04033/2020 (https://doi.org/10.54499/UIDB/04033/2020) (CITAB), LA/P/0126/2020 (Inov4Agro), UIDB/04469/2020 (CEB) and LA/P/0029/2020 (LABBELS—Associate Laboratory in Biotechnology, Bioengineering, and Microelectromechanical Systems).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The author Tiago Lopes is grateful to FCT, MCTES, and FSE for the PhD Fellowship (2021.07171.BD). The authors also thank Helena Ferreira, Maria Ferreira, Sandra Pereira, and Vânia Silva for their support in the laboratory; João Santos and André Fonseca for providing the climate data; and the eleven trained food sensory evaluation tasters of ECVA/DeBA (UTAD) who participated in the sensorial analysis.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Appendix A

Table A1. Statistical effect of treatment (T), cultivar (Cv), year (Y), and their interactions on the analyzed blueberry parameters.
Table A1. Statistical effect of treatment (T), cultivar (Cv), year (Y), and their interactions on the analyzed blueberry parameters.
Parametersp (T)p (Cv)p (Y)p (T × Cv)p (T × Y)p (C × Y)p (T × Cv × Y)
Yield<0.001<0.001<0.001<0.01<0.001>0.05>0.05
Weight<0.001<0.001<0.001<0.001>0.05<0.001>0.05
Height<0.001<0.001<0.001<0.001<0.01<0.001>0.05
Width<0.001<0.001<0.001<0.001>0.05<0.001<0.05
Calyx scar<0.001<0.001<0.001>0.05>0.05<0.05>0.05
Width/Height<0.001<0.001<0.001<0.001<0.01>0.05>0.05
L*<0.001<0.001<0.001<0.001<0.001>0.05<0.01
C*<0.001<0.001<0.001<0.001<0.001>0.05>0.05
h°<0.001<0.001<0.001<0.001<0.05>0.05>0.05
ERF<0.001<0.001<0.001<0.001<0.001>0.05>0.05
FF<0.001<0.001<0.001>0.05<0.05<0.001>0.05
pH<0.001<0.001<0.001>0.05>0.05<0.001<0.01
TSS<0.001<0.001<0.01<0.05<0.05>0.05<0.001
TA<0.001<0.05<0.05>0.05>0.05<0.001>0.05
MI<0.001<0.001>0.05>0.05>0.05<0.001>0.05
Quinic Acid<0.001<0.001<0.001<0.001<0.001<0.001<0.001
Malic Acid<0.001<0.001<0.001<0.001<0.001<0.001<0.001
Citric Acid<0.001>0.05<0.001<0.001<0.001<0.001<0.001
Total Organic Acids<0.001<0.001<0.001<0.001<0.001<0.001<0.001

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Figure 1. Mean temperature (°C) and monthly precipitation (mm) for Vilarandelo in the period from July 2021 to June 2023.
Figure 1. Mean temperature (°C) and monthly precipitation (mm) for Vilarandelo in the period from July 2021 to June 2023.
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Figure 2. Fruit yield per plant of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv), depending on the treatments (T) used, in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 9) ± SD.
Figure 2. Fruit yield per plant of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv), depending on the treatments (T) used, in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 9) ± SD.
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Figure 3. Color parameters of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 30) ± SD.
Figure 3. Color parameters of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 30) ± SD.
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Figure 4. Fruit texture attributes of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 10) ± SD.
Figure 4. Fruit texture attributes of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 10) ± SD.
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Figure 5. Variation in organic acids content of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 3) ± SD.
Figure 5. Variation in organic acids content of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023. Lowercase letters indicate significant differences (p < 0.05) between the ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between the ‘Draper’ treatments by Tukey’s test; means (n = 3) ± SD.
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Figure 6. Sensory profile graph of ‘Duke’ and ‘Draper’ blueberry fruits depending on the treatments used in the years 2022 and 2023. Each attribute was evaluated on a scale of 1 (lowest intensity) to 5 (highest intensity) points. Significant differences in the effect of treatments are identified as * for p < 0.05 by Tukey’s test.
Figure 6. Sensory profile graph of ‘Duke’ and ‘Draper’ blueberry fruits depending on the treatments used in the years 2022 and 2023. Each attribute was evaluated on a scale of 1 (lowest intensity) to 5 (highest intensity) points. Significant differences in the effect of treatments are identified as * for p < 0.05 by Tukey’s test.
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Table 1. Fruit weight, height, width, calyx scar diameter, and width–height ratio of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023.
Table 1. Fruit weight, height, width, calyx scar diameter, and width–height ratio of ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023.
TreatmentsYearsWeight (g)Height (mm)Width (mm)Ø Calyx Scar (mm)Width/Height Ratio
DukeDraperDukeDraperDukeDraperDukeDraperDukeDraper
T020222.13 ± 0.27 a3.36 ± 0.47 A12.36 ± 0.48 ab13.72 ± 0.76 ABC17.54 ± 0.84 a20.65 ± 1.17 A6.38 ± 0.88 a6.59 ± 0.76 A1.42 ± 0.08 a1.51 ± 0.06 A
20232.18 ± 0.26 a2.99 ± 0.41 A12.82 ± 0.49 a13.57 ± 0.78 A17.55 ± 0.92 a19.34 ± 0.99 A6.94 ± 0.57 a6.49 ± 0.69 A1.37 ± 0.06 a1.43 ± 0.07 A
T120222.38 ± 0.42 b3.64 ± 0.54 AB12.59 ± 0.57 b13.67 ± 0.56 AB18.26 ± 1.21 b21.33 ± 1.02 BCD7.91 ± 1.09 a6.98 ± 1.02 A1.45 ± 0.08 ab1.56 ± 0.07 B
20232.71 ± 0.32 d3.34 ± 0.46 BC13.58 ± 0.41 d13.75 ± 0.81 ABC18.98 ± 0.77 d20.05 ± 0.97 BC7.50 ± 0.71 b6.54 ± 0.87 A1.40 ± 0.06 ab1.46 ± 0.07 A
T220222.33 ± 0.31 ab3.40 ± 0.51 A12.19 ± 0.57 a13.64 ± 0.59 AB18.35 ± 0.90 b20.79 ± 1.08 AB7.64 ± 1.01 a6.98 ± 0.83 A1.51 ± 0.09 c1.52 ± 0.07 AB
20232.51 ± 0.32 bcd3.11 ± 0.57 AB13.18 ± 0.73 bc13.58 ± 0.77 A18.59 ± 0.81 bcd19.53 ± 0.98 AB7.26 ± 0.62 ab6.83 ± 1.01 A1.41 ± 0.06 b1.44 ± 0.06 A
T320222.33 ± 0.30 ab3.34 ± 0.52 A12.39 ± 0.44 ab13.57 ± 0.51 A18.19 ± 0.82 b20.68 ± 1.12 AB7.49 ± 0.96 a6.52 ± 1.01 A1.47 ± 0.06 bc1.52 ± 0.06 AB
20232.47 ± 0.39 bc3.22 ± 0.59 ABC12.86 ± 0.66 ab13.63 ± 0.64 AB18.15 ± 1.06 b19.94 ± 1.18 BC7.29 ± 0.77 ab6.82 ± 1.03 A1.41 ± 0.06 b1.46 ± 0.07 A
T420222.40 ± 0.41 b3.55 ± 0.60 AB12.44 ± 0.53 ab13.93 ± 0.58 ABC18.01 ± 1.08 ab20.98 ± 1.30 ABC7.50 ± 0.91 a6.80 ± 0.89 A1.45 ± 0.07 ab1.51 ± 0.08 A
20232.44 ± 0.31 b3.28 ± 0.42 ABC13.18 ± 0.53 bc13.86 ± 0.65 ABC18.25 ± 0.79 bc19.82 ± 0.94 ABC7.01 ± 0.68 a6.65 ± 0.78 A1.39 ± 0.06 ab1.43 ± 0.05 A
T520222.39 ± 0.37 b3.82 ± 0.47 B12.45 ± 0.57 ab14.03 ± 0.56 C18.46 ± 0.98 b21.77 ± 0.88 D7.40 ± 1.47 a6.94 ± 1.03 A1.48 ± 0.07 bc1.55 ± 0.07 B
20232.44 ± 0.39 b3.43 ± 0.55 C13.24 ± 0.76 cd14.05 ± 0.67 C18.20 ± 0.84 bc20.28 ± 0.97 C7.05 ± 0.68 a6.77 ± 0.80 A1.38 ± 0.07 ab1.45 ± 0.07 A
T620222.44 ± 0.36 b3.76 ± 0.55 B12.39 ± 0.57 ab13.72 ± 0.76 BC18.22 ± 0.86 b21.53 ± 1.11 CD7.34 ± 0.72 a6.81 ± 0.96 A1.47 ± 0.07 bc1.54 ± 0.07 AB
20232.65 ± 0.35 cd3.37 ± 0.60 BC13.54 ± 0.59 cd14.02 ± 0.51 BC18.71 ± 0.85 cd20.27 ± 1.07 C7.30 ± 0.59 ab6.54 ± 0.85 A1.38 ± 0.05 ab1.45 ± 0.06 A
p(T)2022<0.001<0.001<0.001<0.01<0.001
2023<0.001<0.001<0.001<0.05<0.001
p(Cv)2022<0.001<0.001<0.001<0.001<0.001
2023<0.001<0.001<0.001<0.001<0.001
p(T × Cv)2022<0.05<0.01<0.01>0.05<0.001
2023<0.05<0.01<0.001<0.05>0.05
Values are means ± SD (n = 50). Lowercase letters indicate significant differences (p < 0.05) between ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between ‘Draper’ treatments by Tukey’s test.
Table 2. pH, total soluble solids (TSS), titratable acidity (TA), and maturation index of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023.
Table 2. pH, total soluble solids (TSS), titratable acidity (TA), and maturation index of fruits from ‘Duke’ and ‘Draper’ blueberry cultivars (Cv) depending on the treatments (T) used in the years 2022 and 2023.
Treatments YearspHTSS (°Brix)TA (% citric acid)Maturation Index
DukeDraperDukeDraperDukeDraperDukeDraper
T020222.92 ± 0.13 a3.46 ± 0.03 AB12.13 ± 0.15 a14.60 ± 0.20 AB0.85 ± 0.08 a0.52 ± 0.06 A14.37 ± 1.31 a28.57 ± 2.53 A
20233.08 ± 0.19 a2.78 ± 0.05 A12.93 ± 0.45 a13.13 ± 0.21 A0.56 ± 0.09 b0.89 ± 0.13 B23.37 ± 4.05 a15.02 ± 2.59 A
T120223.05 ± 0.06 a3.38 ± 0.27 AB12.63 ± 0.12 ab15.07 ± 0.06 B0.78 ± 0.08 a0.43 ± 0.05 A16.29 ± 1.54 a35.12 ± 4.10 A
20233.15 ± 0.05 a2.89 ± 0.05 AB12.37 ± 1.15 a13.27 ± 0.06 A0.46 ± 0.01 ab0.71 ± 0.09 AB26.95 ± 1.75 a19.00 ± 2.70 AB
T220223.00 ± 0.09 a3.20 ± 0.13 A12.33 ± 0.12 a14.73 ± 0.59 AB0.75 ± 0.13 a0.44 ± 0.06 A16.70 ± 2.85 a33.78 ± 5.07 A
20233.05 ± 0.08 a3.07 ± 0.13 AB12.27 ± 0.21 a14.40 ± 0.92 AB0.54 ± 0.02 ab0.63 ± 0.15 AB22.94 ± 1.41 a23.75 ± 6.52 AB
T320223.13 ± 0.15 a3.52 ± 0.07 AB13.50 ± 0.36 c14.47 ± 0.06 AB0.68 ± 0.04 a0.44 ± 0.06 A19.86 ± 0.67 a33.29 ± 4.25 A
20233.28 ± 0.16 a3.09 ± 0.05 B13.30 ± 0.17 a14.90 ± 0.30 B0.41 ± 0.10 a0.62 ± 0.06 AB33.89 ± 7.98 a24.33 ± 2.85 AB
T420223.05 ± 0.01 a3.47 ± 0.09 AB13.07 ± 0.35 bc13.77 ± 0.47 A0.86 ± 0.17 a0.54 ± 0.09 A15.56 ± 2.98 a26.04 ± 4.01 A
20233.29 ± 0.13 a3.06 ± 0.08 AB12.57 ± 0.70 a14.93 ± 0.23 B0.42 ± 0.03 ab0.72 ± 0.05 AB29.82 ± 3.11 a20.82 ± 1.65 AB
T520223.15 ± 0.06 a3.73 ± 0.08 B12.77 ± 0.25 ab15.13 ± 0.21 B0.75 ± 0.07 a0.42 ± 0.08 A17.04 ± 1.58 a36.52 ± 6.11 A
20233.32 ± 0.07 a3.06 ± 0.17 AB12.40 ± 0.46 a14.63 ± 0.64 B0.41 ± 0.05 ab0.69 ± 0.13 AB30.46 ± 4.65 a21.69 ± 4.50 AB
T620223.16 ± 0.03 a3.41 ± 0.09 AB13.27 ± 0.25 bc14.70 ± 0.50 AB0.80 ± 0.09 a0.51 ± 0.14 A16.70 ± 1.70 a30.13 ± 7.83 A
20233.30 ± 0.05 a3.14 ± 0.16 B12.77 ± 0.23 a14.70 ± 0.26 B0.46 ± 0.03 ab0.58 ± 0.06 A28.08 ± 1.78 a25.63 ± 2.79 B
p(T)2022<0.001<0.01>0.05>0.05
2023<0.001<0.01<0.01<0.01
p(Cv)2022<0.001<0.001<0.001<0.001
2023<0.001<0.001<0.001<0.001
p(T × Cv)2022<0.05<0.001>0.05>0.05
2023>0.05<0.05>0.05>0.05
Values are means ± SD (n = 3). Lowercase letters indicate significant differences (p < 0.05) between ‘Duke’ treatments and uppercase letters indicate significant differences (p < 0.05) between ‘Draper’ treatments by Tukey’s test.
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MDPI and ACS Style

Lopes, T.; Silva, A.P.; Ribeiro, C.; Carvalho, R.; Aires, A.; Vicente, A.A.; Gonçalves, B. Ecklonia maxima and Glycine–Betaine-Based Biostimulants Improve Blueberry Yield and Quality. Horticulturae 2024, 10, 920. https://doi.org/10.3390/horticulturae10090920

AMA Style

Lopes T, Silva AP, Ribeiro C, Carvalho R, Aires A, Vicente AA, Gonçalves B. Ecklonia maxima and Glycine–Betaine-Based Biostimulants Improve Blueberry Yield and Quality. Horticulturae. 2024; 10(9):920. https://doi.org/10.3390/horticulturae10090920

Chicago/Turabian Style

Lopes, Tiago, Ana Paula Silva, Carlos Ribeiro, Rosa Carvalho, Alfredo Aires, António A. Vicente, and Berta Gonçalves. 2024. "Ecklonia maxima and Glycine–Betaine-Based Biostimulants Improve Blueberry Yield and Quality" Horticulturae 10, no. 9: 920. https://doi.org/10.3390/horticulturae10090920

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