Comparison of Fruit Parameters and Elemental Composition of Commercial Varieties of Blackberries

: Blackberries are a valuable crop that has a positive effect on human health due to its fruits’ antioxidant and antihyperglycemic properties. The main goal of the research was to compare the fruit parameters of modern blackberry varieties. The experiment involved six varieties of blackberries: ‘Natchez’, ‘Loch Tay’, ‘Brzezina’, ‘Black Gem’, ‘Heaven Can Wait’, and ‘Ouachita’. The data were collected in 2021–2022 in the Rostov region of Russia. On one hectare, 3000 plants with trellises were planted. To prevent winter damage, the plants were covered for the winter period with a non-woven covering material with a density of 60 g/m 2 . To assess the quality of the fruits, harvesting was carried out from seven to nine in the morning once every 5–6 days. The results showed that the most productive varieties are the ‘Loch Tay’ (4.8 kg/bush), ‘Black Gem’ (4.2 kg/bush), ‘Heaven Can Wait’ (3.9 kg/bush), and ‘Ouachita’ (3.8 kg/bush) varieties. The heaviest fruits are as follows: ‘Natchez’ (13.3 g), ‘Black Gem’ (11.2 g), and ‘Ouachita’ (10.3 g). The varieties with the highest amount of sugar are the following: ‘Black Gem’ (14.7 Brix), ‘Ouachita’ (13.4 Brix), ‘Loch Tay’ (12.9 Brix), and ‘Heaven Can Wait’ (11.6 Brix). In terms of the combination of the parameters, the most promising varieties for industrial production in this region are the ‘Ouachita’, ‘Black Gem’, ‘Loch Tay’, and ‘Heaven Can Wait’ varieties. Medium and strong relationships were established between the parameters of the fruits and the elemental composition of the leaves. During the study, we also developed systems of equations for predicting the parameters of a berry based on the content of one or another macro and microelement of a leaf; these systems are suitable for both the manual calculations in nurseries and the correcting of programs for the automated determination of fruit quality and the calculation of productivity in large industrial farms. The obtained data will make it possible to increase the blackberry production area in Russia from 4.34% to 22.06% in various growing regions.


Introduction
Due to the unfavorable environmental situation and the irrational nutritional structure of the country's population majority, expressed in a deficiency of biologically active substances, more and more attention is being paid to the use of not only the nutritional, but also the therapeutic and prophylactic properties of fruit and berry plants [1].The main advantage of blackberry culture is the unique taste and useful properties of the fruits, which depend on the amount of sugars and organic acids in the berries, and are more related to their genotype [2].In the studies of Makarkinoy M.A., the genotypes of 'Black Satin', ' Čačanska Bestrna', 'Chester', 'Natchez', 'Triple Crown', ELS LN-14, OS LN-1, and OS LN-7 were chosen as the blackberries with a high content of bioactive substances in the fruits, namely ascorbic acids and phenolic compounds [3][4][5].
Blackberry fruits are rich in anthocyanins, flavonoids, ellagic acid, tannins, and other antioxidants, and also have an optimal concentration of selenium, which helps to prevent many diseases [6].
However, blackberries have not only an antioxidant activity, but also an anti-cholinesterase activity, which allows their extract to be used to treat neurodegenerative diseases by increasing brain activity.The fruits also have strong anti-aging and anti-cancer properties [7][8][9].
The genus Rubus contains over 740 species and 12 subgenera around the world [10].Blackberries (Rubus L. subgenus Rubus, Watson.) began to be grown in Europe to create protective plantings around houses; then, the crop began to be used for medicinal and food purposes [11].Wild blackberries are still cultivated all over the world for their berries: for example, 3600 ha of Rubus glaucus are cultivated in Ecuador; 2400 ha of Rubus armeniacus and Rubus laciniatus are cultivated in Romania; 2000 ha of Rubus ulnifolius are cultivated in Chile; about 100 ha of Rubus coriifolius are cultivated in Mexico; and 100 ha of planted Rubus glaucus plants are present in Venezuela [12].
The leading countries in the cultivation of varietal blackberries are the United States and Serbia.At the same time, in 2021, the United States of America imported 58,967 tons of fresh blackberries and 11,000 tons of frozen ones.Indeed, Mexico provided nearly all of the US' fresh blackberry imports, accounting for a four-year average market share of 96.8% between 2014 and 2017.Instead, Chile leads the US' imports of frozen blackberries, accounting for 61.4% of the market on an average calculated over four years, between 2014 and 2017 [13].
The total area of blackberry cultivation in Russia in 2022 was less than 100 hectares.This crop is less popular than raspberries, currants, and strawberries, but it is present on the shelves of chain stores all year round.The demand for blackberries in Russia today is over 1.5 thousand tons, while the production of Russian raw material does not exceed 500 tons.The price of blackberries varies depending on the sales period.For example, the lowest price for blackberries is registered in July and August, when the cost per kilogram is $17.61, while, in the winter period, the price increases to $36.47 [14].For the annual expansion of planting areas, it is necessary to select varieties that are suitable for both the climatic conditions and the requirements of Russian farmers.In total, there are about 400 varieties of blackberries in the world; in 2016, only one variety, 'Agatovaya', was bred in Russia [15], but it has not been widely used both in industrial production and in amateur gardening.
Blackberry cultivation in Russia is mostly concentrated in the southern regions, which occupy 4.34% of the total area of our country.In the central strip and in the far north, the plants have a relatively low frost resistance in the above-ground part.It is possible to overcome the low frost resistance of blackberries by using modern cultivation technologies, such as container technology, vertical trellis coverings for the winter, and the use of various fertilizers [16][17][18].
The high demand and market prices for blackberries are of interest to many berry producers.The supply on the market is not very large due to complex agricultural practices, which include formative pruning, sheltering blackberries for the winter in the more northern regions of Russia, and shading berries with a net to protect them against burns in the southern ones.However, this crop is ideal for family farms, where the planting area can be small, eliminating the need for machinery and reducing the initial cost of establishing and maintaining a plantation.
When laying a plantation, it is important to consider varietal characteristics, the type of blackberry shoots, and nutrients needs.Studies carried out by scientists Strik and Vance show that the varietal characteristics and blackberry shoots type have a significant impact on the concentration of nutrients in the leaves [19].
As far as is known, no studies have been conducted on the content of nutrients in leaves and their effect on the parameters of blackberry fruits.Blackberry plants are highly adaptable and have relatively low nutrient requirements compared to other berry crops [20,21], so there is little research on blackberry cultivation.Selection of varieties and understanding of nutritional elements influence fruit parameters are necessary for drawing up technological charts in blackberry cultivation.
The purpose of our study is to identify varieties suitable for both industrial cultivation and use in garden plots, as well as to trace the correlation between fruit parameters and the content of elements in blackberry leaves to adjust the nutrition system.

Study Site
The studies were carried out in 2021 and 2022 on blackberry plants aged 6 and 7 years in the city of Semikarakorsk (47 • 33 55 N, 40 • 56 52 E, Rostov, Russia).USDA hardiness zone 5b (USDA Agricultural Research Service, 2014) [22].Plants are arranged in a pattern of 2.0 × 1.5 m (3000 plants/ha).The aisles are covered with a covering fabric with a density of 130 g/m (Agrojutex, Juta, Czech Republic).The bushes were watered with one line of drip tubes (MasterProf 50M length MR-U DS.060105, Krasnodar, Russia) containing emitters with a pressure compensation of 1.2 L * h −1 in-line, located every 0.3 m.All studied parameters (leaves and fruits) were collected from one plant.Available with 3 plants.
During the season was carried plants pruning, forming 3-4 fruit-bearing shoots and 3-4 replacement shoots on one bush.A trellis system has been installed on the blackberry plantation.The wires are attached to steel poles at a height of 0.6, 1.0 and 1.6 m above the ground.In erect and semi-erect blackberry varieties, shoots were pinched at a height of ≈1.0-1.5 m to stimulate lateral branching.In mid-November, blackberry plants were covered for the winter with non-woven covering material with a density of 60 g/m 2 (Russia) to preserve shoots from winter damage.
The temperature during the summer period 2021/2022 ranged from +18 • C at night to +33 • C during the day.In 2021, the air humidity during fruit ripening was average 63%, while by 2022 it was 49%.

Soil Testing
Soil samples were taken from the soil under experimental plants in early September using a Hoffer Soil Sampler-36 (0.92 m) (Sweden).Soil samples were taken at a depth of 0.3 m in the center of the row, ≈0.3 m from the crown between plants and in the emitter drip irrigation zone.Three samples were sent for analysis for the content of macro-, microelements (mobile phosphorus-P 2 O 5 ; mobile potassium-K 2 O; organic matter; ammonium nitrogen N-NH 4 ; nitrate nitrogen N-NO 3 ; calcium-CaO; magnesium-MgO; iron-Fe 2 O 3 ; nickel-Ni; chromium-Cr; lead-Pb; zinc-Zn; copper-Cu; manganese-MnO; aluminum-Al 2 O 3 ; silicon-SiO 2 ) and pH to the Testing Center for Soil and Ecological Research of the Russian State Agrarian University-Moscow Timiryazev Agricultural Academy (RSAU-MTAA), Moscow (Table 1).

Evaluation of Fruit Quality Immediately after Harvest
Fruits harvesting was carried out in the full ripeness phase.Randomly formed samples of 30 fruits of each variety, the description was carried out on 180 fruits.Fruit weight was measured on an electronic balance brand Aqua-Lab.RF, YA501 (Russia) with an accuracy of 0.1 g.The length and width of the fruit were determined using an electronic caliper Ada Mechanic 150 (Russia) with an accuracy of 0.01 mm.To determine sugars was used a refractometer AQ-REF-BRIX4 (Russia) with an accuracy of 1 • Bx by squeezing juice onto the instrument's measuring panel.The density of the berry was determined using a digital penetrometer Megeon 03004 (Russia) in grams, then the grams were transferred in point, where 1 point corresponds to low density, and 10 points to high density.
The fruit shape, external and tasting evaluations were determined in accordance with the "Program and methodology for the study of fruit, berry and nut crops varieties" [30].The external assessment was considered based on the fruits' uniformity in points from 1 to 10, where 1 point-the fruits are deformed and ugly, and 10 points-the fruits are completely homogeneous.Five people participated in the fruit tasting.The points of this assessment were from 1 (sour, not pronounced taste) to 10 points (rich blackberry sweet taste) [31].

Evaluation of Fruit Quality Immediately after Storage
Fruit picking was carried out in the morning hours from 7.00 A.M. to 9.00 A.M. Collected blackberries in the amount of 30 pieces of each variety were placed in correxes with a napkin at the bottom, in a refrigerator with a constant temperature of 4 • C.After 7 days, the quality of commercial fruits was assessed.Fruits were considered marketable without violating the integrity of the berries and without mold damage.Rejected fruits were removed and the percentage of preserved ones was calculated.Further, the remaining fruits in correx were transferred to a room with a temperature of 20 • C, where they were stored for another 48 h, then non-commercial of them were rejected and the percentage of suitable fruits was counted.This method for assessing the quality of fruits will allow us to calculate varieties suitable for storage [32].

Evaluation of the Productivity of Varieties
The collection of blackberry fruits was carried out once every 5-6 days.The fruits were harvested in the morning from 7.00 to 9.00.During each collection, the average weight of one fruit was determined, the quantity of fruits per collection ranged from 40 to 100 pieces, depending on the variety.At the end of the productivity accounting, the quantity of fruits collections was summed up and recalculated per bush.

Leaf Sampling
Leaf samples for tissue analysis were taken during the period when the concentration of nutrients is most stable.For floricane-fruiting blackberry, the optimal time to collect leaves from annual shoots (primocanes) is after fruit ripening.The amount of nutrients in the leaves varies depending on the variety [33], so samples were taken from a plant of each variety.The selection was carried out from well-developed 5-8 shoots, 50 leaves were selected along with leaf petiole, then they were put into paper bags and sent to the laboratory.Leaves were not washed before tissue analysis [34].Leaf Nitrogen (N) was determined using a combustion analyzer with an induction furnace and a thermal conductivity detector [35].Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Aluminum (Al), Boron (B), Copper (Cu), Manganese (Mn), Iron (Fe) and Zinc (Zn) were determined using an inductively coupled plasma (ICP) spectrophotometer after wet ashing the samples in nitric acid [35].Floricane, primocanes nutrients in the leaves.

Statistical Data Analysis
Statistical calculations were performed using the SPSS Statistics 25 software.Confidence intervals for the mean values of the features are indicated as the arithmetic mean ± standard deviation (p = 0.05).The division into groups according to significant differences between varieties was obtained based on the Duncan criteria in a two-way analysis of variance (p = 0.05).The correlation coefficients were determined by the Spearman method.Cluster analysis was built with Gower distances, bootstrap 100 was applied, preliminary z-standardization of quantitative data was carried out.To establish the traits that contribute to the similarity of varieties, the method of principal components was used.

Evaluation of Fruits Immediately after Collection
Blackberry fruits weight varies significantly from one variety to another (Figure 1).Based on a two-way analysis of variance by Duncan's criteria all varieties were divided under average weight values for two years into 5 groups.The first group is characterized by low average weight and includes varieties 'Loch Tay' (6.78 ± 1.27 g) and 'Heaven Can Wait' (6.83 ± 1.34 g).The variety 'Brzezina' also has a low weight (7.61 ± 1.19 g), however, it significantly differs from the first two varieties.Varieties 'Ouachita' (10.37 ± 2.95) and 'Black Gem' (11.45 ± 2.14) differ significantly from each other and have an average weight of fruits, while 'Natchez' (13.32 ± 3.05) has a large weight.The conditions of the year and the combination of cultivar*year factors significantly affect the weight variability.Thus, the conditions in 2022 contributed to a fruit weight decrease for 'Natchez' (by 19% compared to 2021), for 'Brzezina' (by 12%), but were significantly favorable for 'Heaven Can Wait' (average weight increased by 32%) and 'Ouachita' (by 64%).The varieties 'Loch Tay' and 'Black Gem' proved to be resistant to the conditions of the year and practically did not change weight (in 2022 it was only 3% higher).Considering the variability of fruits within a variety, it should be noted that in 2021 the fruits of all varieties were more even, and their coefficient of variation did not exceed 10%, and in 2022 from 15 ('Ouachita', 'Heaven Can Wait', 'Brzezina') to 25% ('Black Gem', 'Loch Tay', 'Natchez') fruits differed from the average sample.This section may be divided by subheadings.It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn.According to the length of the berry, four groups of varieties can be distinguished (Figure 1): the first one is with small-fruited varieties in the sample -'Heaven Can Wait' (27.25±2.72 mm), 'Loch Tay' (29.00±2.52 mm) and 'Ouachita' (29 .57±3.08 mm); the second According to the length of the berry, four groups of varieties can be distinguished (Figure 1): the first one is with small-fruited varieties in the sample-'Heaven Can Wait' (27.25 ± 2.72 mm), 'Loch Tay' (29.00 ± 2.52 mm) and 'Ouachita' (29.57± 3.08 mm); the second with fruits of medium length-'Brzezina' (31.53 ± 4.21 mm); third-'Black Gem' (43.04 ± 9.38 mm); fourth-'Natchez' (44.23 ± 10.26 mm).Such factors as variety, the conditions during the year, and the combination of these factors make a significant contribution to fruit variation.So, 2021 was favorable for 'Natchez' (fruits are 34% longer on average than in 2022), 'Black Gem' (by 32%), 'Brzezina' (by 17%), 'Loch Tay' (by 11%).However, 2022 was a better year for 'Heaven Can Wait' and 'Ouachita', with fruit lengths up 10% and 18% respectively.The fruit length variation coefficients in 2021 vary between 4-7%, and in 2022-10-15%.

Productivity of Varieties
The productivity of varieties in 2022 was higher than in 2021 by about 25%, except for the variety-'Ouachita', because.The difference over the years is only 2% (Table 2).

Evaluation of Tasting Qualities
'Natchez' (10.63 ± 1.81 brix) and 'Brzezina' (10.88 ± 1.38) are statistically similar in terms of sugar content, since the group of varieties 'Ouachita' (13.17 ± 3.06) and 'Loch Tay' (13.13 ± 1.62).A high sugar content of 14.5 brix was noted in the 'Black Gem' variety (Figure 3).The conditions of 2021 were favorable for the accumulation of sugars in the 'Natchez' variety (by 30% more than in 2022), 'Brzezina' (by 12%), 'Heaven Can Wait' (by 11%), and in 2022 'Ouachita' (by 37% more than in 2021), 'Loch Tay' (up 15%) and 'Black Gem' (up 7%).The variability of the trait relative to the average values was lower in 2021 and varied within 1-7% for all varieties, in 2022 it was in the range of 10-14%.The productivity of varieties in 2022 was higher than in 2021 by about 25%, except for the variety-'Ouachita', because.The difference over the years is only 2% (Table 2).

Evaluation of Tasting Qualities
'Natchez' (10.63 ± 1.81 brix) and 'Brzezina' (10.88 ± 1.38) are statistically similar in terms of sugar content, since the group of varieties 'Ouachita' (13.17 ± 3.06) and 'Loch Tay' (13.13 ± 1.62).A high sugar content of 14.5 brix was noted in the 'Black Gem' variety (Figure 3).The conditions of 2021 were favorable for the accumulation of sugars in the 'Natchez' variety (by 30% more than in 2022), 'Brzezina' (by 12%), 'Heaven Can Wait' (by 11%), and in 2022 'Ouachita' (by 37% more than in 2021), 'Loch Tay' (up 15%) and 'Black Gem' (up 7%).The variability of the trait relative to the average values was lower in 2021 and varied within 1-7% for all varieties, in 2022 it was in the range of 10-14%.Parameter estimates on a 10-point scale are shown in Figure 3.All fruits of 'Heaven Can Wait' and 'Ouachita' for two years have the highest score-10 points, for 'Natchez' and 'Loch Tay' the average score is at the level of 9.3-9.4 points, for 'Black Gem' is stable 9 points.A low level of density was noted in the 'Brzezina' variety-7 points in 2021 and 5.1 in 2022.The external score for 'Natchez', 'Black Gem' and 'Heaven Can Wait' is consistently at a high level of 10 points.Varieties 'Loch Tay' and 'Ouachita' in 2021 were 9 points on this trait, and 10 points in 2022.The 'Brzezina' variety annually received 9 points according to external evaluation.A taste score of 10 points is typical for 'Black Gem' and 'Heaven Can Wait'.Conditions in 2022 were more favorable for 'Natchez' and 'Ouachita' than 2021 (10 points versus 9 points), and vice versa for 'Brzezina' (10 points in 2021 and 8 points in 2022), while 'Loch Tay' received 9 points in both years.

Evaluation of Fruits after Storage
According to the results of two years observations, the best varieties for storage are 'Brzezina' and 'Heaven Can Wait', after 7 days of storage at 4 • C, the rejection of berries is kept at the level of 11-12%, and after 48 h of warm storage-at the level of 22-30% (Figure 4).A high result of storage in the refrigerator was also shown by 'Black Gem' (90% of marketable berries) and 'Loch Tay' (89%).However, after additional storage in warm conditions, only half of the marketable berries remain.
Parameter estimates on a 10-point scale are shown in Figure 3.All fruits of 'Heaven Can Wait' and 'Ouachita' for two years have the highest score -10 points, for 'Natchez' and 'Loch Tay' the average score is at the level of 9.3-9.4 points, for 'Black Gem' is stable 9 points.A low level of density was noted in the 'Brzezina' variety -7 points in 2021 and 5.1 in 2022.The external score for 'Natchez', 'Black Gem' and 'Heaven Can Wait' is consistently at a high level of 10 points.Varieties 'Loch Tay' and 'Ouachita' in 2021 were 9 points on this trait, and 10 points in 2022.The 'Brzezina' variety annually received 9 points according to external evaluation.A taste score of 10 points is typical for 'Black Gem' and 'Heaven Can Wait'.Conditions in 2022 were more favorable for 'Natchez' and 'Ouachita' than 2021 (10 points versus 9 points), and vice versa for 'Brzezina' (10 points in 2021 and 8 points in 2022), while 'Loch Tay' received 9 points in both years.

Evaluation of Fruits after Storage
According to the results of two years observations, the best varieties for storage are 'Brzezina' and 'Heaven Can Wait', after 7 days of storage at 4 °C, the rejection of berries is kept at the level of 11-12%, and after 48 h of warm storage-at the level of 22-30% (Figure 4).A high result of storage in the refrigerator was also shown by 'Black Gem' (90% of marketable berries) and 'Loch Tay' (89%).However, after additional storage in warm conditions, only half of the marketable berries remain.'Heaven Can Wait', 'Loch Tay' and 'Black Gem' reacted quite strongly to the conditions of the year, so for the first two varieties 2022 turned out to be more favorable-100% yield of marketable berries after seven days of storage and rejection after 48 h only 20 and 40%, respectively.And for the variety 'Black Gem', on the contrary, the conditions of 2021 were more suitable-100% yield of marketable berries versus 80% in 2022, and the rejection was kept at the level of 20-25%.Varieties that did not respond to the conditions of the year are 'Ouachita' (20% rejection after the first storage period and 40% after the second) and 'Natchez' (20% rejection after the first storage period and 50-55% after the second).'Heaven Can Wait', 'Loch Tay' and 'Black Gem' reacted quite strongly to the conditions of the year, so for the first two varieties 2022 turned out to be more favorable-100% yield of marketable berries after seven days of storage and rejection after 48 h only 20 and 40%, respectively.And for the variety 'Black Gem', on the contrary, the conditions of 2021 were more suitable-100% yield of marketable berries versus 80% in 2022, and the rejection was kept at the level of 20-25%.Varieties that did not respond to the conditions of the year are 'Ouachita' (20% rejection after the first storage period and 40% after the second) and 'Natchez' (20% rejection after the first storage period and 50-55% after the second).

Relationship between Berry Parameters and Analysis of Leaf Diagnostics of Macro and Microelements
Spearman's correlation analysis confirmed the relationship with the content of leaf diagnostic elements (Figure 5).

Relationship between Berry Parameters and Analysis of Leaf Diagnostics of Macro and Microelements
Spearman's correlation analysis confirmed the relationship with the content of leaf diagnostic elements (Figure 5).It has been established that there are significant correlations between the yield of marketable berries after the first stage of storage and after the second.Thus, the % yield of marketable berries after 7 days of storage at low temperatures is significantly positively related to the weight of the berry, length, number of drupes, and inversely related to the density of the berry.High scores, according to taste, lead to a high yield of marketable berries after additional storage in warm conditions.
Nutrients in leaf tissues are strongly related to the parameters of the berry (Figure 5).So, magnesium (Mg) is associated with the density of the berry, manganese (Mn) and boron (B)-with the productivity of the bush, calcium (Ca) is associated with the external assessment of the fetus, zinc (Zn)-with taste, phosphorus (P 2 O 5 ) is associated with sugar content, potassium (K 2 O)-with the weight of the fruit and the percentage of marketable berries after 7 days of storage at 4 • C, iron (Fe) is associated with the weight of the fruit.Based on the above, we propose a regression equation for predicting the parameters of the fruit, as well as productivity from the bush.(Table 3) Table 3. Prediction of changes in the quantitative parameters of the berry depending on the content of macro-and microelements based on regression equations.

Independent Variable in Equation (x) Regression Equation Equation Quality (Determination Coefficient)
Yield per bush, kg

Fruits Evaluation Immediately after Harvest
In 2022, there was a decrease in fruit weight in 'Natchez', 'Brzezina', but was significantly favorable for 'Heaven Can Wait' and 'Ouachita'.Presumably, this is due to the climatic conditions of the year and the ripening period of the varieties.Varieties 'Natchez' and 'Brzezina' are among the earliest.In 2022, they began to ripen at the end of June, when a significant temperature difference was observed during the day and night, which could contribute to a decrease in the development of drupes.However, varieties 'Loch Tay' and 'Black Gem' proved to be resistant to the conditions of the year and practically did not change their weight, which indicates their stability.In the studies conducted by Evdokimenko S.N. and Kalugina V.L. in the Bryansk region (Russia), a stable fruit weight of the 'Loch Tay' variety was noted for three years, where the fruit weight was 6.2 g, while in our studies the average fruit weight is 6.9 g [36].
Large fruits are not always the main factor when choosing a variety, since for confectionery, for example, a weight of 6-7 g and a high fruit density are required.There is an appropriate caliber for berries that are supplied to restaurants and chain supermarkets.For sales on the fresh market, large-fruitedness, external evaluation and palatability are important.

Varieties Productivity
One of the factors affecting the productivity of blackberries and raspberries is soil pH and irrigation [37].In our studies, soil pH varied from 5.3 to 6.5, which is acceptable when growing these crops [38].The decrease in productivity in 2021 could be due to one drip line irrigation in a row and low rainfall in the summer.According to Prive et al., adequate irrigation is a key component influencing raspberry yield [39].Even though blackberries have a deeper root system compared to raspberries, varieties with upright and semi-upright shoots are quite demanding on irrigation.Blackberry with creeping shoots is more drought-resistant due to a powerful root system, which can go into the soil to a depth of 2 m.That is why some farmers grow creeping blackberries without additional irrigation.In their study, Dixon et al. did not find a decrease in productivity in the next year without the use of additional irrigation [40].
Blackberry has the distinctive ability to recover quickly from damage [16,41], which allows the gradual expansion of production areas in most parts of the country.Additional application of various preparations at the end of the growing season to increase the frost resistance of plants, increases the possibility of selecting varieties for plantations [42].For example, without winter cover and without the use of various fertilizers in the North-West, Central, Central Black Earth regions, it is possible to grow only one variety of blackberry-'Agawam'.More modern varieties 'Ouachita', 'Natchez', 'Black Gem' and others require strict observance of agrotechnical elements.In our research, the varieties with the highest productivity are 'Loch Tay'-4.8kg / bush, 'Black Gem'-4.1 kg / bush.Under the conditions of Rostov region, it is possible to get a higher yield, but it may reduce the frost resistance of plants and lead to minimum productivity next year, because presumably at high load the nutrients are distributed in fruits, and there may not be enough substances for differentiation of generative buds and maturation of shoots.Therefore, productivity of 3 to 5 kg per bush is optimal for cultivation in this region.

Evaluation of Tasting Qualities
Studying blackberry varieties in the Russian Research Institute of Fruit Crop Breeding in 2021, the sugar content of the variety 'Brzezina' was 14.2 Brix, 'Loch Tay'-12.7 Brix, 'Natchez'-10.8Brix, 'Ouachita'-11.7 Brix.In our studies-'Brzezina'-10.9Brix, 'Loch Tay'-13.1 Brix, 'Natchez'-10.6Brix, 'Ouachita'-13.1 Brix.The number of sugars in fruits depends on factors such as weather conditions, nutrition system and varietal characteristics.On average, the data of Margarita Makarkina et al. [43] on sugar content are like ours, which indicates their stability and the possibility of using both in breeding work and in production.

Evaluation of Fruits after Storage
According to Brian Lawrence and Juan Carlos Melgar, for varieties 'Ouachita' and 'Natchez', the optimal shelf life is 1 week, with longer storage, the fluidity of berries increases [43].These findings are consistent with our studies.
The fruits of 'Brzezina' and 'Heaven Can Wait' are best preserved, presumably due to their genetic features [44].'Loch Tay' and 'Black Gem' also showed a high preservation of fruits, which allows them to be used for the purpose of industrial production for delivery to chain stores.
The genotype largely affects the quality of the fruit and the storage period.The hardness of blackberries depends on the species and variety, the stage of ripeness and the duration of storage [45].In their research, Amanda J. Vance et al. established the relationship between the variety and the number of storage days, which made it possible to predict the storage period of the studied varieties [46].

Relations between Berry Parameters and Analysis of Leaf Diagnostics of Macro and Microelements
Adjustments of macro-and micronutrient content are based on periodic analysis of nutrients in the soil, observations of plant growth and annual analysis of leaf tissues [33,39,47].
Signs of nutrient deficiency or overabundance may appear on both young and old leaves, depending on the mobility of the element in the plant.Nutrients in the plant move through the xylem and phloem.Elements that move through the xylem are immobile within the plant as they move with water to the leaves, these include sulfur, iron, manganese, calcium, zinc, copper and boron.Nutrients moving through the phloem are mobile within the plant, they are nitrogen, phosphorus, potassium, magnesium and chlorine [20,48].
The most important elements for blackberry are potassium, calcium and boron.Potassium deficiency causes marginal scalds.Potassium fertilization increases plant resistance to low negative temperatures.Boron deficiency leads to small fruit, fruit deformation, reduced productivity and shoot desiccation.Boron application affects flower buds and fruit setting in blackberry.Calcium deficiency is usually observed in stalked varieties with fast-growing shoots 3-4 m long.[48].
Regular Leaf tissue analysis can help to detect low elemental concentrations before symptoms appear on the plant.Sometimes, even when the nutrient content of the soil is optimal, plants are not able to assimilate the required nutrients [49].
In general, blackberry plants have low nitrogen and phosphorus requirements compared to other horticultural crops [50,51].The most important elements for the growth and development of blackberries are K, Ca and B. Unlike other berry crops, blackberries are less demanding for P and N. Potassium is very important for the development of the root system, frost resistance of plants and marketable quality of fruits.Tissue analysis is the best indicator of potassium requirement after harvest.In our research, the relationship between potassium content in leaves, fruit weight and the percentage of marketable berries after 7 days of storage at 4 • C was found.It was also reliably proved that potassium fertilizer combined with fungicide application reduced the incidence of Botrytis cinerea on blackberry fruit [52].In the study of Shaimaa Hassan Abd Elrahman et al., the effect of potassium fertilizers on marketable qualities of garden strawberry fruits was established [53].
Calcium is a fixed element, therefore, if there is sufficient calcium in the soil, calcium deficiency is likely to occur in leaves and fruits.Calcium deficiency may occur in varieties with fast-growing shoots, when nutrients are distributed between the above-ground part and fruit formation.In our studies, we found a relationship between calcium content in leaf tissues and external fruit grade, suggesting the effect of calcium on knuckle development and fruit uniformity.According to Rajbir Singh et al. foliar treatment with calcium fertilizer reduces the incidence of fruit rot and increases fruit density [54].
Boron deficiency can lead to fruit deformation, delayed plant development and shoot die-off.However, before feeding with boron fertilizers, it is necessary to analyze the tissue to prevent overabundance of this element, which is very toxic to plants in large doses.Boron foliar fertilization in the fall or spring, just before flowering, is effective [33].In the studies of M. S. Rahman et al., the positive effect of boron fertilization on tomato productivity [55].According to our data, boron content in blackberry leaves is related to the productivity of the shrub, which confirms the effect of boron on increasing crop yields.
To prevent the manifestation of deficiency or overabundance of nutritional elements, which can lead to a decrease in yield, it is recommended to regularly conduct tissue analysis.With soil analysis it is not always possible to determine the need for a particular element.
However, using the results of tissue diagnosis to predict fertilizer requirements for the current season does not work for perennial crops such as blackberry.This is partly due to the minimal short-term impact of fertilizer on yield.Changes in tissue nutrient concentrations may not be observed for 1-2 years after fertilizer application.In other words, tissue analysis is correct to use for the purpose of developing a nutritional system for sustained growth and productivity.

Conclusions
The relationship between fruit parameters and nutritional elements content was found during the research.Fruit weight is highly dependent on the content of iron (Fe), phosphorus (P 2 O 5 ) and potassium (K 2 O) in leaves.Fruit storage duration is related to zinc (Zn) and K 2 O content.Blackberry productivity is related to manganese (Mn) and boron (B) content.Fruit density is related to magnesium (Mg) content.Thus, by regulating the nutrition system, it is possible to control the parameters of fruiting, which will allow predicting the nutritional requirements in the following years of cultivation.
It was found that the best varieties for use in the confectionery industry are 'Ouachita', 'Loch Tay', 'Brzezina' and 'Heaven Can Wait'.Recommended varieties for the fresh market and garden plots are 'Natchez', 'Loch Tay' and 'Black Gem'.Varieties for industrial production and supply to chain stores-'Loch Tay', 'Black Gem', 'Heaven Can Wait' and 'Ouachita'.This in-formation will increase the production area of Russia from 4.34% to 22.06% by introducing blackberries to more northern regions including Central, North-West and Volga regions.
It is recommended to use biochemical analysis of fruits in further studies to establish cause-and-effect relationships between the content of bio-logically active substances and elemental composition in leaf tissues.

Figure 1 .
Figure 1.Arithmetic averages values of the parameters by years, indicating the standard deviation for fruit weight, length, width, sugar amount and quantity of drupes, where varieties that do not have significant differences according to Duncan's a posteriori ANOVA criterion are highlighted with the same color on average for a variety over 2 years (p = 0.05), and the letters indicate the groups for each year.

Figure 1 .
Figure 1.Arithmetic averages values of the parameters by years, indicating the standard deviation for fruit weight, length, width, sugar amount and quantity of drupes, where varieties that do not have significant differences according to Duncan's a posteriori ANOVA criterion are highlighted with the same color on average for a variety over 2 years (p = 0.05), and the letters indicate the groups for each year.

Figure 3 .
Figure 3. Average amount of sugars by years (scale on the left), where varieties without significant differences on average for two years (according to the Duncan criterion, p = 0.05) are highlighted in the same color, as well as an assessment of the quality of berries (scale on the right).The letters indicate the groups of varieties for each year according to Duncan's ANOVA test.

Figure 3 .
Figure 3. Average amount of sugars by years (scale on the left), where varieties without significant differences on average for two years (according to the Duncan criterion, p = 0.05) are highlighted in the same color, as well as an assessment of the quality of berries (scale on the right).The letters indicate the groups of varieties for each year according to Duncan's ANOVA test.

Figure 4 .
Figure 4.The yield of marketable berries of blackberry varieties after seven days of storage at 4 °C and additional storage for 48 h at 20 °C.
fruit after storage % of marketable fruit after 7 days storage at 4°С % of marketable fruit after an additional 48 hours storage at 20℃

Figure 4 .
Figure 4.The yield of marketable berries of blackberry varieties after seven days of storage at 4 • C and additional storage for 48 h at 20 • C.

Figure 5 .
Figure 5. Correlations between fruit parameters and macro-, microelements in leaf samples (Leaf sampling), where orange color shows strong connections more (correlation coefficient more than 0.80) and green color shows medium connections (correlation coefficient 0.71-0.79).

Figure 5 .
Figure 5. Correlations between fruit parameters and macro-, microelements in leaf samples (Leaf sampling), where orange color shows strong connections more (correlation coefficient more than 0.80) and green color shows medium connections (correlation coefficient 0.71-0.79).

Table 1 .
Soil nutrient pH, organic matter content, and nutrient levels when sampled in September 2021/2022 at Testing Center for Soil and Ecological Research RSAU-MTAA, Moscow.

(Average Data for Three Repetitions) Defined Indicators Unit of Measure Research Results Accuracy Characteristic Permissible Levels of the Controlled Parameter Compliance of Methods with the Requirements of Regulatory and Technical Documentation Test Method
Agronomy 2023, 13, x FOR PEER REVIEW 8 of 18 with fruits of medium length -'Brzezina' (31.53±4.21mm); third -'Black Gem' (43.04±9.38 mm); fourth -'Natchez' (44.23±10.26mm).Such factors as variety, the conditions during the year, and the combination of these factors make a significant contribution to fruit variation.So, 2021 was favorable for 'Natchez' (fruits are 34% longer on average than in 2022),

Table 2 .
Evaluation of the productivity (kg) of blackberry varieties by years.

Table 2 .
Evaluation of the productivity (kg) of blackberry varieties by years.