Abstract
Foliar calcium (Ca) treatment exhibits strong potential for enhancing yield and quality in some fruit crops. This study aimed to assess the impact of foliar application of Ca-organomineral (Ca-OM) suspension on total soluble solids (TSS) and Ca dynamics in leaves and berries across five red currant cultivars during the vegetation and storage. A randomized block design with two treatments: (1) Control (without Ca-OM treatment) and (2) foliar Ca-OM treatment, with three repetitions, was applied on five different red currant cultivars. Although foliar Ca-OM treatments did not impact Ca or TSS in leaves, they positively influenced Ca and TSS in fruits, displaying significant variability among cultivars. In addition, Ca-OM treatment increased berry density, reduced abscission, and inhibited the development of diseases, extending storage periods for “Lvovyanka,” “Vika,” and “Gazel” cultivars by three to seven days compared to the Ca-OM untreated control. Ca-OM treatment in the early stages of the ontogenesis of currants provided a high percentage of Ca intake in berries. At the stage of complete maturation, the Ca content in berries decreased and depended on the ripening period of the cultivars. Before harvesting, Ca-OM increased the strength of berries (Fc) and reduced the shedding of berries in the clusters (Fs). At the vegetation stage, Ca-OM increased TSS in berries, and the content of TSS depended on the genotype and weather conditions. The Ca-OM treatment and low temperatures contributed to preserving berry density, reducing the shedding of berries and PLW, and restraining the development of diseases during storage. In addition, the high content of TSS and Ca in berries against the background of a slow rate of decrease in berry density in the Ca-OM variants ensured an extension of the shelf life of “Lvovyanka,” “Vika,” and “Gazel” by three to seven days compared to the control untreated with Ca-OM. Clustering analyses identified these cultivars as similar in terms of TSS and calcium content in fruits, emphasizing their common traits. The study underscores the potential of foliar Ca treatment to enhance berry quality during growth and storage, significantly improve storage duration, and fortify resistance against adverse factors, presenting promising opportunities for elevating yield and quality in specific red currant cultivars.
1. Introduction
The global demand for cultivating and consuming berry crops has increased in recent decades [1]. This trend is connected, firstly, with the beneficial qualities of berries for human health. Red currant berries are a source of biologically active compounds with a high content of ascorbic acid, phenolic compounds, anthocyanins, and high antioxidant activity [2, 3]; secondly, due to improved agrotechnological methods for growing berry crops. New elements of cultivation technology have made it possible to expand these crops’ availability and distribution area [4]. The production of currant berries ranks second in the world after strawberries. According to Faostat 2022, the world’s average production of currant berries is 45000 tons. The primary production of currants is located in Europe (Poland, France, Estonia, the Netherlands, Belgium, Russia, and Ukraine) [5]. Berry crops have a high value, so their production and sale can significantly contribute to the economy of the regions of several countries [6]. Most berry crops are intended primarily for use in processed products, but at the same time, the priority is the sale of fresh berry products [7].
Berry products are perishable raw materials [8]. After harvesting, the berries quickly lose their commercial qualities and organoleptic acceptance (berry weight loss, berry density reduction, berry rot) [9], and this affects the marketing of these products, which leads to significant economic losses [10].
To extend the shelf life of fruit and vegetable products and preserve the nutritional value and quality characteristics of fruits, chemical preparations (pesticides, preservatives), biological compounds (plant extracts) [11, 12], and physical methods (ultrasound, ultraviolet, electric field, pressure, temperature regimes) are used [12–15]. However, there is a scientific trend in switching to environmentally friendly and safe plant compounds to reduce crop losses during storage [16].
According to the International Federation of Organic Agriculture Movements (I.F.O.A.M.), such a production system supports the health of soils, ecosystems, and people [17–19]. Many farmers often use freezing to increase the period of consumption of berries. Still, in the process of such storage (−12°С, −18°С, −24°С), several chemical processes change: sucrose is inverted, acidity increases, and the amount of tannins decreases [20]. There is evidence of a decrease in changes in the structure of red currant berries when stored in the refrigerator for up to 7–10 days [21, 22]. Rational nutrition considers the consumption of fresh fruits and berries as a vital factor. The berries’ harvest quality is crucial and should be at the right point for improved storage. In this case, biological foliar fertilizing is becoming very important, significantly enhancing metabolic processes, yield, and fruit quality [23, 24]. The mineral composition of fruit crops affects fruits’ quality and technological indicators, including their shelf-life capacity. One of the critical problems in ensuring the high quality of products and their safety is providing the optimal calcium content in fruits and berries [25–27].
The role of calcium is crucial to ensure the excellent storage ability of fruits and berry products; the higher the calcium content in berries, the greater and longer their preservation abilities, and, consequently, the possibility of more prolonged consumption of high-quality products rich in essential trace elements and vitamins [26]. Calcium is a critical component in maintaining the hardness of fruits during storage, as it is responsible for the integrity of the cell [25, 26]. Calcium ions create compounds between the peptic molecules in the middle of the plate, which are responsible for the integrity of the cell [25–27]. For instance, it was confirmed that apple fruits with a content of Ca >5 mg/100 g f.w., with a ratio (K + Mg)/Ca <25 mg/100 g f. w. and Ca/Mg >1 mg/100 g f. w. have high resistance to diseases during storage [27, 28]. Thus, the softening of the fruit may result from the loss of calcium in the middle of the plate and/or its absence in the bonds between the peptic molecules [28]. When treated during the preharvest period, the entrance of calcium into fruits delays the fruit’s softening and ripening rate, thereby slowing down the decay of cell walls [28]. The preharvest use of calcium can slow down the aging of fruits without adversely affecting the consumer qualities of fruits [29, 30]. There are also studies of the positive effect of calcium-containing drugs on increasing the level of Brix in Rubus Eubatus Focke fruits [31]. The storage duration of berry crops, especially currants, is significantly influenced by calcium. It addresses a significant issue where red currants rapidly deteriorate within 3-4 days after the harvest, leading to logistical challenges in their distribution to major retail chains [32].
Thus, this study aimed to elucidate the effects of foliar Ca application in five red currant genotypes on (i) changes in total soluble solids (TSS) and calcium content in the biomass and fruits during the preharvest and postharvest period and (ii) the duration of the shelf life of berries under the influence of low temperatures.
2. Materials and Methods
2.1. Location, Facilities, Weather Conditions, and Agrochemical Measures
The study was conducted in 2021/2022 and 2022/2023 vegetation seasons at the site (0.2 ha) of the primary variety study of VNIISPK red currants. The experimental site was in the north-east of the central Chernozem region of Russia. The soil of the experimental site belonged to the Loamy Haplic Luvisol type (IUSS Working Group W.R.B., 2015), with a surface humus horizon of 0.55 m. During two growing seasons, the soil samples from three repetitions, in triplicates, were taken in spring (before the buds of red currant blossomed) from the rhizosphere at a depth of 0–0.2 m and 0.2–0.4 m and were subjected to chemical analyses. The exchangeable potassium content was determined using a flame photometric method with a flame spectrophotometer. The phosphorus content was determined by the spectrophotometric method using a Bio-RAD SmartSpec plus spectrophotometer (California, U.S.A.). Soil acidity (pH) was determined in a 20 g suspension with the addition of a 0.1 N KCI solution [33]. Measurements were carried out by the pH-150MI device (Moscow, Russia).
The experimental site was presented with five red currant cultivars of different ecological, geographical, and genetic origins: (“Jonkheer Van Tets” (“Faya Plodorodnaya” × “London Market”), Holland; “Vika” (“Chulkovskaya” × “Red Lake”), Russia; “Asya” (“Chulkovskaya” × “Maarses Prominent”), Russia; “Gazel” (“Chulkovskaya” × “Maarses Prominent”), Russia; Lvovyanka (“Weisse Hollandische” × “Jonkheer Van Tets”), Ukraine). The cultivars were of early, medium-early, and late ripening, planted in 2018 with a spacing of 2.8 × 0.5 m, and interrow plowing without irrigation.
The scientific institutions of Russia, Ukraine, and Europe provided the cultivars under the program «A unique scientific set, a collection of living plants of the open field—bioresource collection of VNIISPK».
Ammonium nitrate (NH4NO3) was applied in an amount of 60 g. per plant, every vegetation season is in spring, the first decade of April. To protect against Sphaerotheca mors-uvae, the experimental plants were treated with a bio-phytoncides complex of botanical extracts on an organo-mineral basis. The preparation of systemic and contact action (pH = 7.5–8.0) has the form of a suspension of minerals of natural origin containing Quassia amara, Cinnamomum zeylanicum, and Azadirachta indica (the drug was obtained from AgroPlus, Russia). The treatments were performed before bud blossoming, during green berry formation, the initial ripening, and full ripeness, using a 5.0% solution.
The summary of weather conditions during the 2021-2022 and 2022-2023 vegetation seasons is presented in Table 1 and was obtained using a meteorological station iMetes 3.3. (Weiz, Austria) at the experimental site.
2.2. Experiment Design
2.2.1. Vegetation Period
To examine the impact of a foliar Ca application on red currant cultivars, a Ca-organomineral (Ca-OM) suspension derived from the oceanic bio flora containing Ca (1.31%), CaO (0.4%), SiO2 (5.6%), Fe2O3 (0.4%), Al2O3 (0.16%), and MgO (0.4%) was applied. To determine the calcium content in the suspension, a solution of 10 ml was taken and subjected to burning in a muffle furnace at a temperature of +450°C. Burning was gradually carried out, raising the oven temperature by 50°C every 30 minutes. The total mineralization time was 8 hours. The resulting ash was dissolved, and a suspension was obtained. The complexometric method determined the calcium content in the test preparation suspension [34].
A randomized block design with two treatments: (1) Control (without Ca-OM treatment) and (2) foliar Ca-OM treatment, with three repetitions, was applied on five different red currant cultivars. There were five plants per treatment, with two plants between each treatment.
Foliar treatments were applied by the RT-16LI knapsack sprayer (Patriot, China), with a 1% Ca-OM solution and a consumption of 0.18 m3/h. Treatments were carried out following the phases of ontogenesis of red currant plants (Table 2).
The TSS (Brix %) in leaves and fruits was determined using a refractometer (ATAGO, pocket PAL-1. Kyoto, Japan). The selection of plant material was carried out according to the experimental scheme (Table 2). The leaves and berries were selected five days after the treatments. To determine the soluble solids content in the leaves, a sample of 0.7 g was used. To determine the soluble solids content in the berries, a sample of 12 g was used. The sample was a mixture of leaves or berries from five plants of one repetition from the same cultivar.
Determination of the calcium content in the leaf tissue was performed by the complexometric method for organic substances at the beginning stages of the ripening of berries and the full ripening of berries [34, 35]. Dry ash was used for plant samples. Dry samples were burned in a muffle furnace at a temperature of +450°C, and the ash was obtained from a plant sample (Figure 1).
The resulting ash was dissolved and titrated with a 0.01 N. solution of complex III. The calcium content (X) in mmol/100 g of soluble solids was determined in the following formula: is the volume of complexon III for titration, sm3; n –0.01 N solution of complexon III, is the ratio of the solution amount for dissolving ash to the amount of ash. In this experiment, (100 : 5 = 20), m is the weight of the sample, g.
2.2.2. Storage
The berries of tested red currant cultivars were harvested during biological ripening when >90% of the berries from the bush were mature. Berry ripening was accessed visually. To assess the extent of berry maturation, we determined the physico-mechanical parameters of the berries, specifically focusing on separation force and crushing force by the Dina-2 device (Siberian Institute of Physics and Technology of Agrarian Problems, Russia) [36]. The crushing force was determined using the Plodtest-1 device (Siberian Institute of Physics and Technology of Agrarian Problems, Russia). Mature berries were randomly selected from the experimental plants. The number of berries in the cluster varied from 8 to 16 pieces, depending on the genotype. Red currant berries can be stored at room temperature for no more than 20 hours before the appearance of the berries begins to deteriorate [37, 38].
Therefore, according to the experiment’s design, the hand-picked berries of the varieties were placed in plastic disposable fruit containers with a volume of 0.8 liters. Within 1 hour, they were transported to the laboratory and stored in the refrigerator Polair CM105-Gm (Switzerland) at +2.8 to +4.0°C (the relative humidity of the air was 95%). The berries were stored for 27 days. The repetition of the experience was threefold. Before laying currant berries for storage, their weight was determined.
The measurements of TSS, the density of the berry skin, and Physiological Loss in Weight (PLW) were carried out at intervals of 3-4 days. Five currant clusters (60 berries) were selected from each container to determine TSS and the density of the berry skin. The TSS (Brix %) examination using a PAL-3 digital refractometer (ATAGO, Japan). The density of the berry skin was determined by the MEGEON 03004 penetrometer (Russia).
The Physiological Loss in Weight (PLW) was defined as the difference between the initial weight of the berries (M1) and the subsequent weight of the berries (Mi) in each container. It was determined by the following formula [39]:
The berries were weighed on the Scout Pro SP 202 laboratory scale (OHAUS, Parsippany, NJ, USA).
The values of TSS, the density of the berry skin, PLW, and the visual evaluation of spoiled berries determined the storage period. The maximum shelf life of the berries was the period during which the berries retained the optimal specified qualities, and the PLW did not exceed 10% [40].
The calcium content in berries during the postharvest period was determined by the previously specified method (Section 2.2.1) at three key stages: (a) initial, (b) midpoint, and (c) final phase of storage.
2.3. Statistical Analysis
The raw data were statistically summarized and graphically presented in Microsoft Excel. Then, an independent samples t-test (at a 5% significance level) was performed using SPSS version 22.0 to determine whether the control and applied treatments had a statistically different effect on the measured parameters. To compute and visualize the principal component analysis (PCA), the function of res.pca < -prcomp(df, scale = TRUE) from the factoextra R package was used, and to compute and visualize cluster analysis, the function of res.hcpc < -HCPC (res) from the FactoMineR R package was used.
3. Results and Discussion
3.1. Vegetation Period
Foliar treatments in intensive technologies are essential elements in managing growth and production processes in the plant, as well as an important factor in the rapid impact on the processes that determine the yield and quality at the vegetation stage and the storage of fruits [41]. At the same time, Ca has a unique role in the nutrition of plants [28]. Calcium is an element that is not reutilized in the plant body, but young and growing organs and tissues constantly need this element [42]. For many fruit and berry crops, removing calcium per unit of yield is comparable to removing nitrogen [43–45]. The summary of agrochemical soil characteristics at the experimental site is presented in Table 3, confirming the acid soil conditions with a high content of available phosphorus and potassium [46].
The weather conditions guided foliar treatment with the Ca-OM during the growing seasons. In 2022, the beginning of red currant vegetation lagged the average annual values for the test crop by 10–15 days (Table 1). This difference affected the subsequent dates of Ca-OM treatments and physiological processes in the plant (Table 3). In 2023, the weather conditions at the experimental site conformed to the region’s average, long-term climatic patterns, with no deviations observed in the progression of the ontogenetic stages of red currant development.
3.1.1. Effect of Foliar Calcium Treatments on Vegetative Mass
Monitoring the phases of ontogenetic development allows for specific adjustments in the implementation of the production process and the yield quality due to agrochemical measures [47]. The stages of fruit formation and quality management are of the most significant interest [48]. The Ca content in currant leaves depends on the cultivar and the vegetation stage. The studies of Hogue et al. [49] in apples, it was reported that the accumulation of Ca in the leaves is a complex process that depends on exogenous factors (weather conditions, abiotic and biotic stress) and endogenous factors (genotype, ontogenetic stages of development). The Ca content in the leaves of fruit crops [50–52] is lower than in berry crops [53]. The leaves of red currants are rich in calcium, potassium, and magnesium, and the content of these elements depends on the date of leaf collection [54–58]. A low seasonal variability of the Ca content in currant leaves is shown in Figure 2. Insignificant dynamics of the Ca content in the apple leaves were found during the growing season [59].
Foliar treatment with Ca-OM did not affect the Ca content in currant leaves. Similar results were obtained using different concentrations of calcium-containing preparations on strawberry, raspberry, BlackBerry, and blueberry cultivars [49, 59]. Lobos et al. [47] suggested that the elemental composition of the leaf is relatively stable and is little influenced by agrochemical techniques and weather conditions. The Ca content in the leaves increased with their ontogenetic development (Figure 2). The reports of Nour et al. [56] also showed that by the time the berries ripened, the calcium, magnesium, and iron content in currant leaves was the highest. An increase in Ca with leaf age was also revealed in apple cultivars and was explained by the immobility of Ca in leaf tissues and the absence of its redistribution to other plant organs [51]. At the stage of berry ripening, significant differences in the content of Ca in the leaves were in the red current cultivars “Vika,” “Asya,” “Lvovyanka,” and “Jonkheer Van Tets” (Figure 2).
The TSS content in red currant leaves did not exceed 4% (Table 4). In the studies in apples [60] and in Cydonia oblonga, Chaenomeles japonica, Ribes nigrum, Aronia melanocarpa, Vaccinium macrocarpon, and Vaccinium myrtillus [61], the TSS content in the leaves also did not exceed 10%. Foliar treatments with Ca-OM at different stages of currant development did not significantly impact the TSS content in the leaves (Table 4). However, the reliability of the data is difficult to assess since no information has been found in the literature on the effect of foliar treatments with Ca on the TSS content in the leaves of fruit plants.
A decrease in TSS in leaves during the adverse weather of 2022 is shown (Table 4). A positive correlation was found between TSS in currant leaves and temperature (r = +0.80–+0.92). The positive effect of temperature on TSS in leaves is shown in grapes [62].
At the berry ripening stage, the TSS content in the leaves decreased (Table 4). In “Jonkheer Van Tets” and “Lvovyanka” the decrease occurred when 20% of the berries on the bushes acquired a characteristic color; for other cultivars, this pattern occurred later, when a larger percentage of berries acquired a red color. Similar results were obtained in Persica davidiana Carr. [63]. The decrease in TSS content in the summer period may be explained by the intensification of hydrolytic processes in the leaves and the outflow of hydrolysis products from the leaves to the ripening fruits [63].
3.1.2. The Effect of Foliar Calcium Treatments on Berries
The mechanism of intake and distribution of Ca is complicated and is determined not only by the anatomy of the fruit but also by the genotype and stage of plant development [64].
The intake of Ca into the fruits occurs through the stomata on the surface of the fruits. Not only is the conductivity of stomata essential, but so is their number and distribution on the surface of the fruit [65]. A decrease in the number of stomata and a decrease in their conductivity reduce the intake and accumulation of Ca in fruits [47]. The Ca content in immature red currant berries is higher than in leaves (Figures 2 and 3). This is probably due to the functional activity of the stomata of the fruits.
The intake and distribution of Ca in fruits depends on the stage of plant ontogenesis [66, 67]. A high percentage of the Ca accumulation was at the initial stage of the development of currant berries. The Ca accumulation slowed and decreased when the berries were fully ripe (Figure 3). Thus, treating Ca-OM in the early stages of the ontogenesis of red currants provides a high percentage of the Ca intake in berries and ensures the high strength of berries. This again shows Ca’s role in the development of fruits and determines their quality. In the early stages of the growth and development of fruits or berries, Ca is involved in cell division and metabolism. Ca is mainly involved in the intercellular junction in the later stages of fruit or berry development [42]. It is known that the movement of Ca through the plant depends on the xylem fluid. When the fruits are fully ripe, the movement of water switches from the xylem to the phloem, so the movement of Ca to other parts of the plant is limited [68]. Calcium accumulation in fruits decreases when the xylem losses function [67, 69]. The effect of dilution of the Ca content is observed as the fruit grows [70, 71].
The genetic characteristics of currants determined the date of the decrease in the content of Ca in fruits. In early-ripening cultivars “Lvovyanka,” “Asya,” “Vika,” and “Jonkheer Van Tets,” the decrease in Ca occurred 5-6 days earlier than in the late-ripening cultivar “Gazel.” Similar results were obtained in blueberry [65], kiwi [67], and grape cultivars [69].
Varietal differences in the content of Ca in currant berries were revealed. “Asya” and “Gazel” had a significantly high content of it. By the time the berries ripened, Ca-OM minimized the decrease in Ca in the berries, and its content was 20% higher than in the control. Similar results on the content and distribution of Ca during the growing season were obtained in blueberry cultivars. Calcium accumulated rapidly at the initial stage of berry ripening; at the beginning of berry coloring, its accumulation slowed down and stopped when the berries were fully ripe [65].
The physical and mechanical parameters of currant berries (the crushing force of berries ((Fc) and the separation force of berries in the cluster (Fs)) were indicators of the period of biological maturity of the berries [36]. The data on the physical and mechanical qualities of the berries corresponded to the indicators of the Ca content in the fruits (Figure 3). Ca-OM increased the strength of berries (Fc) in currant cultivars and also reduced the shedding of berries in the cluster (Fs) compared to the control (Table 5). This is confirmed by the role of Ca in regulating fruit ripening and its quality. Foliar treatment with Ca stabilizes the cell wall of plants, maintains the elasticity of tissues, and preserves the hardness of fruits [42]. Pectin acid can combine with Ca and form calcium pectate, which is the structural basis of the cell wall, increasing its strength and preventing the gel layer’s disintegration in the cell [72]. In the studies by Wójcik et al. [73] in cherries, Madani et al. [74] in papaya, Siddiqui et al. [75] in apples, Bonomelli et al. [76] and Martins et al. [77] in table grapes, Lobos et al. [47] in blueberry, and Souza et al. [78] in Ficus carica L. it is shown that the use of Ca before harvest increased the hardness of fruits.
The TSS increased in immature berries during the growing season (Table 6). By the time the berries ripened, the TSS in all cultivars exceeded 10%. In “Vika” and “Lvovyanka,” a sharp increase in TSS (45–70% of the initial level) corresponded to the stage of TSS decline in the leaves (Table 4). A rise in TSS by the fruit ripening period was noted in grapes. It was explained by the high consumption of sugars at the early stages of berry growth and development. Subsequently, metabolic changes occurred during berry ripening that contributed to the accumulation of sugars in fruits [62, 79]. At the same time, Ca-OM essentially increased TSS in berries. Similar results were observed under foliar treatments of strawberries [80] and apples [81, 82] with Ca at different stages of ontogenesis. The variation coefficient (CV) of this trait in control and experimental variants exceeded 20% over the years of the studies. A sufficiently large spread and minimal alignment of values for the studied characteristics are once again confirmed by the dependence of the trait on climatic conditions and genetic origin. The significant influence of the genotype, stage of plant development, and climate conditions on the TSS content in berries is shown in the blueberry studies of Yang et al. [65].
3.2. Storage Period
In storing berry products, there are several problems: a decrease in the hardness of berries, a color change (darkening), and the abscission of berries in the bunches, and the development of diseases [83].
The TSS of level and the density of berries are essential in assessing the quality of berries and extending their shelf life [83].
In red currant varieties, the TSS content increased slightly during storage until a certain period (Tables 7 and 8). This is due to the loss of moisture in the berries and the hydrolysis of carbohydrates to soluble sugars [84].
The introduction of Ca-OM increased the total TSS content in berries, and the decrease in TSS in the cultivars “Lvovyanka,” “Vika,” and “Gazel” was slower than in control . This is explained by the role of calcium cations in slowing down metabolic processes and cell respiration. Slowing down metabolic processes and respiration leads to a decrease in the rate of fruit ripening during storage [85]. Respiration slowdown reduces the synthesis and utilization of metabolites and decreases fruit TSS. Our results are consistent with those obtained in tomatoes [86] and strawberries [87]. Studies have reported that the amount of free sugars gradually increased during storage, and calcium cations noticeably slowed this increase.
The content of TSS is related to the strength of the fruit. A positive correlation between these indicators was noted in apples during storage [88, 89].
In this experiment, the density of berries gradually decreased, but the rate of decrease in berry density was slower in the variants with Ca-OM (Tables 9 and 10).
“Lvovyanka,” “Vika,” and “Gazel” in the Ca-OM variant maintained a high berry density compared to the control over a long storage period. The results of the study are consistent with data from Gupta et al. [90] and Rombaldi et al. [91] in peach, Changhoo et al. [92] in kiwi, and Ciccarese et al. [93] in grapes. Studies have reported that the addition increases the strength of fruits and prolongs the storage period of fruit products.
Gao et al. [30] and Vicente et al. [90] have shown that the use of Ca increases the density of the intercellular layer of the cell wall, prevents the penetration of hydrolase and the disintegration of the jelly-like layer, and also affects changes in the pectin component of the cell wall, thereby maintaining the stability of the cell wall and the hardness of fruits. Calcium, which is part of the structure of the cell wall of fruits, can reduce the availability of enzymes that destroy the cell wall and help preserve the postharvest qualities of fruits [95, 96]. Also, Ca, together with abscisic acid (A.B.A.), participates in the transmission of ethylene signals, which regulates the processes of softening, aging, and ripening of fruits [42, 90]. It has been proven that calcium is involved in transmitting the ethylene signal, where the SR1 gene encodes several calcium sensors (CaM, CML, and C.D.P.K.) responsible for fruit maturation. [97].
Studies of current cultivars have revealed genotypic differences in the calcium content of berries during storage. Foliar Ca-OM treatments increased the calcium content in berries (Figures 4 and 5).
There was a significant calcium increase compared with the control in “Lvovyanka,” “Vika,” and “Gazel.” Similar results were obtained by Tromp [70] in apples and by Fuentes et al. [25, 98] in grapes.
Changes in the calcium content in fruits are explained by the different viability of the cells of the genotypes of fruit crops to retain moisture for a specific time, thereby minimizing the percentage of calcium loss by fruits [42, 99].
In this experiment, an increase in the calcium content during storage was observed.
According to the research of White and Broadley [64], this result is explained, firstly, by the physiological loss of fruit weight and, secondly, by the peculiarity of calcium not being reutilized in the plant. In this experiment, physiological weight loss averaged 2–4% every three days.
Physiological Weight Loss (PLW) increased during the storage period (Table 11).
These results are similar to those of Dhillon et al. in mango [100], Gupta et al. in peach [90], Gangwar et al. in aonla [101], and Mahajan et al. in guava [102].
It is reported that calcium is adequate for maintaining the integrity of cell membranes, and it reduces the loss of phospholipids, proteins, and ions, which may be the reasons for reducing weight loss during storage [103].
The influence of the cultivar and the use of Ca-OM on the duration of storage and preservation of the quality of currant berries have been revealed. Ca-OM extended the shelf life of “Lvovyanka,” “Vika,” and “Gazel” berries by an average of 3–7 days compared to the control (Tables 7–11). These data are consistent with the results of Blažek et al. [104], Pissard et al. [105], and Tokala et al. [106] for apples. The shelf life is reported depending on the cultivar and cultivation technology and storage technology.
This is due to the varietal reactions to foliar application of Ca and the peculiarity of Ca cations that slow down the processes of spoilage of berries. At low temperatures, the additional content of Ca-pectate can contribute to the thickening of cell walls and slowing down metabolic processes in cells [107]. Under visual observation, the shedding of berries, the development of spoilage, and the darkening of berries decreased in “Lvovyanka,” “Vika,” and “Gazel” treated with Ca-OM (Figure 6). Symptoms of a decrease in the quality of berries were observed in the treated cultivars “Lvovyanka,” “Vika,” and “Gazel” after 18 days of storage.
3.3. Cluster Analysis and Variety Similarity
The results of PCA biplot according to Ca and TSS content in leaves and fruits of five different berry cultivars during growth periods are given in Figure 7 [108]. According to the results, it can be concluded that the cultivars closest to each other (with similar characteristics) are the “Asya” and “Gazel” cultivars [109]. These two cultivars are primarily similar in terms of TSS content in the control treatment and Ca content in the fruits of the Ca-OM treatment.
The Ca content was notably higher in the fruits of the control of the “Lvovyanka” cultivar than the “Gazel” and “Asya” cultivars, highlighting a distinctive characteristic of this cultivar. Similarly, TSS fruit content increased with Ca-OM treatment, but it was not determined as a defining characteristic for any cultivar. On the other hand, the “Vika” cultivar was determined to have a defining characteristic, especially regarding calcium content in leaves. The “Jonkheer Van Tets” cultivar was determined to be superior in terms of TSS content in leaves compared to other cultivars. It can be observed from Figure 7 that the OMP application did not have a significant effect on the TSS content in the leaves.
Consistent with the results analysis, the cluster analysis (CA) results (Figure 8) revealed similar groupings among the tested cultivars. Specifically, “Gazel” and “Asya” cultivars were grouped, demonstrating comparable calcium and TSS, and this grouping was also observed with the “Vika” cultivar. The remaining cultivars exhibited similarity at the 4th level of significance, indicating a considerable distance from each other in terms of these characteristics.
4. Conclusion
The application of foliar Ca-OM treatment should be strategically timed with different periods of plant ontogenesis, considering the specific characteristics of the cultivar and the prevailing climatic conditions during cultivation. Ca-OM treatment in the early stages of the ontogenesis of red currants provides a high percentage of Ca intake in berries. It improves berries’ physical and mechanical parameters by the period of full ripening. Notably, the stability of calcium content in leaves was less influenced by agrotechnical and natural factors than by fruits, underscoring its potential as a consistent indicator. The significant reduction in calcium content during the full ripening of red currant berries was attributed to their inherent biological characteristics. Additionally, the content of TSS in both vegetative mass and berries is contingent on genotype, ontogenetic stage, and weather factors.
Furthermore, exposing red currant berries to low temperatures during storage and applying Ca-OM in the berry vegetation stage demonstrated favorable outcomes, including increased TSS and berry density, reduced berry abscission within the bunch, and an extension of the storage period for “Lvovyanka,” “Vika,” and “Gazel.”
Notably, CA identified these cultivars as similar to TSS and calcium content in fruits, emphasizing their common traits. Moreover, the elevated calcium content in berries emerged as a positive influence, enhancing consumer characteristics. Contrary to this trend, the results from PCA biplot indicated that for “Asya” and “Jonkheer Van Tets,” TSS content does not determine berry quality during the storage period.
In summary, the findings of this experiment pave the way for the development of agrochemical methods aimed at managing the quality of berry products, offering valuable insights for interventions during both the vegetation and storage stages, taking into account the cultivar characteristics of berry crops. The obtained data are relevant both for agricultural producers and researchers studying the role of calcium in the growth and development of horticulture crops [94].
Data Availability
All the data included in the study will be available from the corresponding author upon reasonable request.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Authors’ Contributions
All authors contributed to writing the conception, designing the study, analyzing the data, and discussing the findings. All authors have read and approved the final manuscript submission for publication.
Acknowledgments
This research work was funded by the Ministry of Science and Higher Education of the Russian Federation, project FGZS-2022-0007.