Effect of Salicylic Acid and Calcium on Growth, Yield, and Fruit Quality of Pepper (Capsicum annuum L.) Grown Hydroponically

Abstract

The aim of this study was to investigate the effects of spraying plants with 0.03% salicylic acid (SA), 0.7% calcium nitrate (Ca), and 0.03% salicylic acid together with 0.7% calcium nitrate (SA + Ca) on plant growth, yield, and fruit quality of peppers grown in a mineral wool substrate. The control plants were sprayed with water (C). Two red-fruited sweet pepper cultivars were used in the study: ‘Aifos’, and ‘Palermo’, which produce fruits characterized by different shapes. Biometric measurements of the plants showed a higher growth rate of pepper plants when SA and Ca were applied foliarly compared to the control. Plants treated simultaneously with SA and Ca were characterized by the highest steady-state fluorescence yield [Fs]. The relative chlorophyll content of pepper leaves was also higher in plants sprayed with SA, Ca, and SA + Ca than in plants in the control. The analysis of pepper yield showed in both cultivars the effect of foliar treatment of plants with SA and Ca and SA + Ca on increasing pepper resistance to the occurrence of Ca deficiency on pepper fruit (Blossom end rot). Pepper fruits harvested from plants treated with SA, Ca, and SA + Ca had more juicy flesh.

1. Introduction

The genus Capsicum includes 40 plant species [1], among which are vegetables and spice plants, including sweet pepper (Capsicum annuum L.). After the potato and tomato, peppers are the third most economically important vegetable in the Solanaceae family [2]. The cultivated varieties of pepper differ in fruit shape (block, conical, oblong fruit), fruit size and color, and pericarp wall thickness, among others. In commercial production, the most popular sweet pepper varieties are those with fleshy block-type fruit colored red. They are used primarily for fresh consumption but also in processing and for dried or frozen foods [3]. Pepper fruits have a high value in terms of health benefits. They contain bioactive compounds, including phenols, carotenoids, and antioxidants such as β-carotene, or provitamin A, and vitamin C [4,5,6]. The vitamin C content of pepper fruit depends on a number of factors, including cultivar, cultivation method, weather conditions, and fruit maturity. Its content in ripe fruit of sweet pepper varieties varies between 62 and 150 mg in 100 g of fresh weight. However, there are known varieties whose fruit contains up to 350 mg of ascorbic acid in 100 g of fresh weight [7].

Demand for fresh, good-quality pepper fruits is high throughout the year. Peppers require adequate temperature and plenty of light for proper yield [8]. Such conditions for growing peppers throughout the year can be achieved under covers. Commercial pepper production in temperate climate countries is carried out both in plastic tunnels using conventional, soil-based cultivation and also in year-round greenhouses using soilless cultivation technology, including hydroponics [9]. Soilless culture systems (SCS) are increasingly being used for vegetable cultivation in the high-tech greenhouse production industry. Soilless cultivation is often referred to as ‘hydroponics’. Soilless cultivation using different growing media (substrates), such as rockwool, perlite, and coconut, is the most commonly used SCS in the world for the production of fruit and vegetables, including peppers. This technology of greenhouse pepper production in mineral wool is very popular in the Netherlands [10,11,12,13].

The quality of fruit is influenced by a number of cultivation factors. An undesirable phenomenon is the Blossom end rot (BER) physiological disorder, the symptoms of which are located on the fruit, reducing the marketable yield of peppers [14]. The causes of BER are related, among other things, to water stress, which reduces Ca transport in the plant. Too low concentration of Ca in the fruit, particularly at the top of the fruit, results in dry, brown spots, a characteristic of BER. The symptoms of this disorder can cover up to half of the fruit surface. Most often, the onset of the spots is a darkening of the tissues at the top of the fruit resulting from cell death. The appearance of BER symptoms is the result of cell membrane rupture and irregular softening of cell walls due to enzymatic processes of pectin chain breakdown, which is caused by Ca deficiency in the fruit [15]. Calcium is an essential plant nutrient, mainly used for cell wall construction, and cell signaling response, cell membrane stability, and selectivity [16]. Ca²⁺ ions can bind strongly with organic acids (e.g., in vacuoles), limiting Ca mobility [17]. Calcium is relatively immobile in the phloem. Therefore, the contribution of phloem transport to Ca distribution may be limited [18]. Calcium uptake by the root system is transported via the xylem to various tissues and organs [19].

Among the exogenous substances that reduce the adverse effects of various abiotic and biotic stresses in plants, calcium has proven to be effective. Calcium is used not only as an essential nutrient for plant growth but also as a component actively involved in various metabolic processes and as an intracellular messenger for many signal transductions such as abscisic acid (ABA) and reactive oxygen species (ROS) et al. [20,21]. Nowadays, foliar fertilization is widely used as a treatment to complement root fertilization [22] and provide plants with nutrients with limited mobility, such as Ca or micronutrients, among others [23,24].

Salicylic acid is a natural growth regulator of vascular plants that influences plant physiological and metabolic processes, including photosynthesis, transpiration, and transport [25,26,27,28]. Foliar application of salicylic acid can reduce the negative effects of stresses and increase the yield of susceptible vegetable species [29]. The first observations on the involvement of SA in plant resistance were made by Raymond F. White in 1979 [30]. The use of acetylsalicylic acid in virus-susceptible tobacco (Nicotiana tabacum cv. Xanthinc) resulted in the development of resistance to TMV—tobacco mosaic virus [31]. In tobacco with a virus-resistance gene, an increase in endogenous SA levels was found following virus infection, and, at the same time, an accumulation of pathogenesis-related PR (Pathogenesis-Related) proteins was found [32]. SA also has functions in plant development, ranging from seed germination to fruiting, DNA repair, and a variety of abiotic stress tolerance mechanisms [33,34]. However, different vegetable species and cultivars respond very differently to exogenous salicylic acid [35].

Due to the occurrence of high temperatures under covers, especially in summer, peppers are exposed to abiotic stress. The main effect of this stress is a high proportion of non-marketable pepper fruits with BER symptoms. For many years, numerous studies have been conducted on effective ways to reduce the occurrence of calcium deficiency symptoms in peppers and other vegetable species. However, there are few reports on the effect of salicylic acid in reducing BER in peppers grown hydroponically. Hydroponic cultivation of peppers in the greenhouse in an inert substrate is increasingly used due to the high efficiency of irrigation and plant nutrition. On the other hand, problems with physiological disorders occurring in the cultivation result in reduced yield quality. The aim of this study was to evaluate the effects of both calcium nitrate and salicylic acid on the growth, yield, and quality of pepper fruit grown hydroponically.

2. Materials and Methods

2.1. Location of Research

The research was conducted at the Greenhouse Experimental Centre of the Warsaw University of Life Sciences [longitude 21° E, latitude 51°15′ N] in the cultivation chambers of the Department of Vegetable and Medicinal Plants.

2.2. Plant Material and Experimental Conditions

Two red-fruited sweet pepper cultivars were selected for the study: ‘Aifos’—with block fruit Seminis brand by Bayer, and ‘Palermo’—with elongated pointed fruit by Rijk Zwaan. The ‘Aifos’ cultivar is characterized by rapid and strong growth, with no tendency to spread. The fruit is 3–4 chambered, red, block type, resistant to cracking, with a long and strong stalk. The flesh thickness of ‘Aifos’ pepper fruit reaches 10 mm, and the average fruit weight is 220 g. Plants of the ‘Palermo’ cultivar have a strong root system and a loose habit. The ‘Palermo’ fruit is elongated, of the Dulce Italiano type, and has a high sugar content. The skin of the fruit of this cultivar is very fine, smooth, and shiny. The average weight of a ‘Palermo’ fruit is 125 g.

The studies were conducted in two years—2019 (term 1) and 2020 (term 2). In term 1 and equally in term 2, pepper seedlings were planted on 13 May, and cultivation was completed on 15 October. On both dates, the peppers were grown hydroponically in a mineral wool substrate. To prepare the pepper seedlings, seeds of both cultivars were sown into mineral wool plugs on 1 March and 7 March 2019, and 2 March and 6 March 2020. The mineral wool plugs used for sowing seeds were soaked in a nutrient solution before sowing. The plugs were pre-soaked in a nutrient solution with an EC (electrical conductivity) of approximately 1.4 dS·m⁻¹ and pH 5.5. The seedling nutrient solution contained the following components in mg·dm⁻³: N-NO₃-195, P-57, K-273, Mg-47, Ca-187, Fe-2, Mn-0.6, B-0.3, Cu-0.15, Zn-0.3, Mo-0.05. After sowing, the seeds were covered with vermiculite and placed in an air-conditioning chamber (Sharma Scientific Co., Delhi, India) at 28 °C day/night (D/N) until the seeds germinated 7 days after sowing (DAS). The pepper seedling plugs (14 DAS) were then placed in Grodan Delta mineral wool cubes by Grodan (measuring 10 cm × 10 cm × 6.5 cm), soaked in nutrient solution with EC 2.8 dS·m⁻¹ and pH 5.5. The ready pepper seedlings were planted into mineral wool growing mats on 28 DAS. Grotop Master cultivation mats by Grodan were used in the experiment (measuring 100 cm × 20 cm × 10 cm). There were 8 beds in the cultivation chamber, each bed about 9 m long and about 1 m wide. There were 9 cultivation mats of mineral wool and 3 pepper plants per mat (Figure S4). Each plant was cut into two shoots. The plant density in the chamber was 2.5 plants per 1 m² of growing area. The nutrient solution was dosed to each plant with a single capillary. The nutrient solution was dosed by computer in amounts based on the light conditions and the age of the plants. The nutrient solution concentrated 100 times in tanks A and B was prepared from single fertilizers. The composition of the basic nutrient solution for pepper cultivation was in mg·dm⁻³: N-NO₃-230, P-57, K-330, Mg-55, Ca-180, Fe-2.5, Mn-0.8, B-0.33, Cu-0.15, Zn-0.33, Mo-0.05. The parameters of the capillary nutrient solution averaged over the growing period were EC from 2.9 to 3.2 dS·m⁻¹ and pH 5.5–5.8.

Microclimate parameters were controlled with the Hortimax system. In the cultivation chamber, the average day temperature in term 1 was 25.5 °C and 20.9 °C at night, and in term 2, it was 25.8 °C and 20.8 °C, respectively. Very often, during the vegetation period of the plants in each of the cultivation dates studied, the average day temperature was close to 30 °C, and the night temperature was 25 °C. The reason for such high temperatures in the greenhouse was high solar radiation. The radiation sum in term 1 during the growing season of the plants was 192.11 kJ/cm², while in term 2 it was 209.41 kJ/cm². The daily radiation totals averaged 1231 J/cm² in term 1 and 1342 J/cm² in term 2 (Figures S1–S3).

The pepper plants were cut into two shoots, removing the side shoots during the treatment. In the main branching of the pepper plants, the first fruit bud was removed. The two strongest shoots were then brought out, and each was wrapped with polypropylene string tied to two wires stretched in parallel at a height of about 3 m above the cultivation bed. Each pepper shoot was tied with string to a different wire, forming a ‘V’ plant guidance system. Plants were cut, and excess vegetative parts (e.g., leaves, side shoots) and generative parts (flowers, fruit set) were removed in such a way that one node contained 1 leaf, 1 set, and a side shoot with 1 leaf (1 fruit and 2 leaves). Pruning of the peppers started on 18 DAP (the day after planting) and was carried out every two weeks, depending on the growth of the plants.

Yellow sticky traps from Horiver and Swirski-Mite Plus sachets from Koppert containing the predatory mite species Amblyseius swirskii were used for plant protection and pest monitoring.

2.3. Experiential Factors

The research investigated the effect of foliar treatments on plants of two pepper cultivars with individual treatment of salicylic acid (SA), individual treatment of calcium nitrate (Ca), and simultaneous treatment of salicylic acid in combination with calcium nitrate (SA + Ca). The control consisted of plants sprayed with water (C). The experiment was designed using the randomized block method. There were four replicates for each combination, with six plants in each combination.

Plants were sprayed once a week between 7 DAP and 151 DAP. In the (SA) combination, plants were sprayed with individual treatment of salicylic acid at a concentration of 0.03% [34,35,36]; in the (Ca) combination, plants were sprayed with individual treatment of calcium nitrate at a concentration of 0.7% [37], and in the (SA + Ca) combination plants were sprayed with salicylic acid together with calcium nitrate at a concentration of 0.03% and 0.7%, respectively. Control plants were sprayed with water (C).

2.4. Evaluated Parameters

2.4.1. Biometric Measurements of Plants

In each combination, six representative test plants were selected and measured once a week between 7 DAP and 158 DAP to determine the plant height and the number of fully developed leaves per pepper plant. Plant height was measured with a tape measure from the root neck to the top of the plant. The number of leaves per plant was reported as the sum of the fully developed leaves located on the two shoots of the plant.

2.4.2. Photosynthetic Activity of Pepper Plants

Twice during the cultivation period, on 31 DAP and 102 DAP, modulated chlorophyll a fluorescence of pepper leaves was measured on pepper test plants using an FMS-2 fluorimeter (Hansatech Instruments Ltd., King’s Lynn, Norfolk, England). Active, fully mature leaves that were at two developmental stages were selected for measurement: a younger, fully developed 5th leaf, counting from the top of the plant, and an older 10th leaf, counting from the top of the plant. Steady-state fluorescence yield [Fs], light-adapted fluorescence maximum [Fm’] and photosystem II quantum yield [ΦPSII] were measured on these leaves. At the same locations on the leaf, after the leaf had been adapted to darkness for 30 min using special clips, the maximum quantum yield of PSII [Fv/Fm] and the PSII lifetime index [PI] were measured using a Handy PEA fluorometer (Hansatech Instruments Ltd., King’s Lynn, Norfolk, England). The relative chlorophyll content of the leaves was then measured at these locations. The measurement was made with a Minolta SPAD-502 Plus chlorophyll meter, and the result was given as an SPAD index. The result was the average of 5 unit measurements taken on one leaf, each at several millimeters apart, avoiding the locations of the conductive bundles in the leaf.

2.4.3. Pepper Fruit Yield

Pepper fruits were harvested at harvest maturity as discolored fruits and fully colored fruits. Harvesting started at 56 DAP, and fruits were harvested as they matured every 10 days or so, up to 158 DAP, both in term 1 and term 2. Harvested fruits were weighed and counted. The weight and number of fruits of total yield (TY), marketable yield (MY), and fruit with BER symptoms were determined.

2.4.4. Dry Matter Content and Color Measurement of the Fruit

Five fruits from each combination were randomly selected for analysis at two time points (84 DAP and 140 DAP). The fruits, without seeds and seed sepals, were cut into small cubes of approximately 4 mm × 4 mm, and representative samples for analysis were taken in triplicate from the fruit samples cut and mixed. The dry matter content of the pepper fruits was determined using the dry-weight method at 105 °C (SUP-65W laboratory dryer, Wamed, Warsaw, Poland). Fruit skin color at each date was measured on three randomly selected fruits from each combination using a MiniScan XE PLUS D/8-S portable color spectrophotometer on the CIE L*a*b* system scale, where L*—lightness [from 0 to 100 units], a*—intensity of red [a* > 0] or green [a* < 0], b*—intensity of yellow [b* > 0] or blue [b* < 0].

2.4.5. Sensory Evaluation of Pepper Fruit Quality

Sensory quality testing of pepper fruits was performed in the Sensory Analysis Laboratory of the Department of Vegetable and Medicinal Plants, which complies with the standards PN-EN ISO 8589:2010/A1:2014-07 [38]. The quantitative descriptive analysis method QDA (Quantitative Description Analysis) was used for the evaluation according to the procedure included in the PN-ISO standard [39,40,41]. The evaluation was carried out immediately after harvesting the fully colored fruits on two dates: 84 DAP and 140 DAP, both in term 1 and term 2. On each measurement date, 5 fruits from each combination were randomly selected for analysis. Each sample consisted of 3 elongated sticks of pepper fruit pericarp (approximately 80 mm × 40 mm in size). The evaluation team consisted of 18 trained individuals.

The qualitative characteristics of odor, texture, and flavor of pepper fruits harvested from plants from all tested combinations were evaluated. The overall impression relating to sensory quality was also assessed as a separate differentiator. The consumer evaluation concerned general desirability and taste desirability. It was carried out by the same team of 18 people as the profile sensory evaluation, marking on a linear scale of 0 to 10 contractual units [c.u.], with boundary markings: scale minimum—very undesirable; maximum—very desirable. The sensory quality attributes of the pepper fruits were evaluated, and their definitions are presented in

Table 1. Pepper fruits sensory descriptors and definitions.

Quality Descriptor		Definition	Anchoring Points
Odor	Odor of fresh pepper fruit	Odor characteristic of fresh pepper fruit	None—very intensive
Texture	Skin hardness	Degree of force needed to bite the skin	Soft—very hard
	Flesh fibrousness	Mouthfeel of flesh homogeneity	Smooth—very fibrous
	Flesh firmness	Degree of force needed for chewing the flesh	Soft—companies
	Flesh juiciness	Amount of liquid released when the sample is chewed	Not very juicy
Flavor and taste descriptors	Typical pepper flavor	Flavor characteristic of fresh sweet pepper fruit	None—very intensive
	Sour taste	Basic taste	Not very intensive
	Sweet taste	Basic taste	Not very intensive
	Bitter taste	Basic taste	Not very intensive
	Pungent flavour	Flavor which gives an impression of burning on the tongue	None—very intensive
	Off-flavor	Untypical flavor of pepper fruit	None—very intensive
Overall quality	Overall quality	General sensory quality impression	Low-quality—high-quality fruit
	Overall desirability and overall taste desirability	Overall consumer quality	Highly undesirable—highly desirable

.

2.5. Statistical Analysis

Statistical analysis was performed using one-factor, two-factor, and three-factor analysis of variance, ANOVA (Statistica, version 13, Warsaw, Poland). A detailed comparison of means was performed using the Tukey test at a significance level of α = 0.05.

When developing the results of the sensory quality evaluation of the peppers, the ANALSENS ver. 6 program was used to prepare the tests, record individual evaluations, and statistically process the results.

3. Results

3.1. Biometric Measurements of Plants

The results of the biometric measurements showed the effect of the treatment of peppers with individual treatments of SA and Ca on plant growth and the number of leaves in peppers. Weekly pepper shoot length growth depended on plant treatment and cultivar. Spraying peppers with individual treatment of calcium nitrate influenced higher weekly shoot growth of peppers compared to control plants sprayed with water (

Table 2. Effect of salicylic acid and calcium treatment of pepper plants on weekly growth of the stem, height of the plant, and number of leaves depending on cultivar [±SE].

Parameter	Cultivar	Term of Growing	Treatment
			SA	Ca	SA + Ca	Control
Weekly growth of stem [cm]	‘Aifos’	term 1	19.7 ± 1.99 ns	20.3 ± 1.77 ns	19.2 ± 1.77 ns	16.8 ± 1.69 ns *
		term 2	19.7 ± 1.99 ns	20.5 ± 1.76 ns	18.2 ± 1.77 ns	16.8 ± 1.69 ns
	Average		19.8 ± 1.42 NS	20.4 ± 1.25 NS	18.2 ± 1.25 NS	16.8 ± 1.20 NS
	‘Palermo’	term 1	22.5 ± 2.05 ns	25.3 ± 2.17 ns	23.1 ± 1.89 ns	20.7 ± 1.55 ns
		term 2	24.6 ± 2.37 ns	25.3 ± 2.17 ns	23.1 ± 1.89 ns	20.7 ± 1.55 ns
	Average		23.5 ± 1.57 NS	25.3 ± 1.53 NS	23.1 ± 1.34 NS	20.8 ± 1.10 NS
Average			21.7 ± 2.12 AB	22.8 ± 1.99 A	20.6 ± 1.85 AB	18.8 ± 1.64 B
Height of plant [cm]	‘Aifos’	term 1	142.9 ± 6.21 ns	139.9 ± 6.00 ns	135.6 ± 5.24 ns	133.5 ± 5.15 ns
		term 2	142.4 ± 6.39 ns	139.1 ± 6.13 ns	134.0 ± 5.27 ns	131.7 ± 5.15 ns
	Average		142.7 ± 4.46 NS	139.5 ± 4.29 NS	134.8 ± 3.72 NS	132.6 ± 3.65 NS
	‘Palermo’	term 1	172.8 ± 6.24 ns	170.5 ± 6.37 ns	170.8 ± 5.87 ns	159.2 ± 6.12 ns
		term 2	171.5 ± 6.28 ns	167.5 ± 6.37 ns	169.7 ± 5.95 ns	158.1 ± 6.18 ns
	Average		172.1 ± 4.43 NS	169.0 ± 4.51 NS	170.2 ± 4.19 NS	158.6 ± 4.36 NS
Average			157.4 ± 0.25 A	154.3 ± 3.19 AB	152.5 ± 2.97 AB	145.6 ± 2.93 B
No. of leaves [No./plant]	‘Aifos’	term 1	30.8 ± 1.02 a	30.7 ± 0.97 a	27.3 ± 0.82 ab	27.4 ± 0.79 ab
		term 2	28.3 ± 1.07 ab	27.9 ± 0.97 ab	24.4 ± 0.82 b	24.5 ± 0.78 b
	Average		29.5 ± 0.75 A	29.25 ± 0.69 A	25.8 ± 0.59 B	25.9 ± 0.57 B
	‘Palermo’	term 1	39.0 ± 1.25 a	37.9 ± 1.02 a	35.3 ± 1.25 ab	32.7 ± 1.03 bc
		term 2	36.0 ± 1.23 ab	34.9 ± 1.03 ab	32.4 ± 0.92 bc	29.8 ± 1.02 c
	Average		37.5 ± 0.89 A	36.4 ± 0.74 AB	33.9 ± 0.66 BC	31.3 ± 0.74 C
Average			33.5 ± 0.62 A	32.8 ± 0.54 A	29.9 ± 0.49 B	28.6 ± 0.49 B

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to the combination term × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

).

The ‘Palermo’ plants had longer weekly shoot growth than the ‘Aifos’ plants. Plants sprayed with individual treatment of SA were more than 11 cm higher on 158 DAP than plants in the control. Spraying peppers with salicylic acid and SA + Ca influenced higher weekly shoot growth of peppers compared to control plants. Plants treated with foliar individual treatment of SA, individual treatment of Ca, and SA + Ca were higher than control plants. Peppers treated with both individual treatments of SA and Ca had more leaves than plants in the control (Table 2). Plants of the ‘Palermo’ cultivar were higher than those of the ‘Aifos’ cultivar, reaching an average height of about 172 cm by 158 DAP, while plants of the ‘Aifos’ cultivar reached about 143 cm (Table 2). Plants treated with individual treatment of SA and individual treatment of Ca had a higher number of leaves per plant than the control and plants treated simultaneously with SA and Ca (SA + Ca). The parameters of plant height and number of leaves reached higher values for the cultivar ‘Palermo’ than for ‘Aifos’ (Table 2; Figure S5).

3.2. Photosynthetic Activity of Peppers

The highest steady-state fluorescence yield was found in plants treated simultaneously with SA and Ca—SA + Ca combination (

Table 3. Effect of salicylic acid and calcium treatment of pepper plants on selected chlorophyll a fluorescence parameters and chlorophyll index of leaves depending on cultivar [mean of two terms ± SE].

Parameter	Cultivar	Leaf Stage	Treatment
			SA	Ca	SA + Ca	Control
Fs	‘Aifos’	5th	512.8 ± 18.4 bc	582.2 ± 24.8 abc	627.9 ± 35.4 ab	523.8 ± 25.7 bc *
		10th	478.6 ± 24.6 c	495.7 ± 33.3 bc	664.9 ± 52.6 a	549.9 ± 27.8 abc
	Average		495.7 ± 13.9 B	538.9 ± 21.5 B	646.4 ± 31.8 A	536.9 ± 19.0 B
	‘Palermo’	5th	606.6 ± 24.1 ns	568.8 ± 27.7 ns	755.6 ± 32.2 ns	534.9 ± 28.6 ns
		10th	582.5 ± 35.1 ns	571.2 ± 36.9 ns	574.6 ± 32.0 ns	553.3 ± 34.3 ns
	Average		594.5 ± 21.3 NS	569.9 ± 23.1 NS	665.1 ± 20.0 NS	544.1 ± 20.9 NS
Average			545.2 ± 13.4 B	554.5 ± 15.8 B	655.7 ± 16.7 A	540.5 ± 14.1 B
Fm	‘Aifos’	5th	2026.0 ± 63.3 ns	2902.0 ± 110.1 ns	2147.0 ± 76.0 ns	2031.4 ± 86.0 ns
		10th	2044.5 ± 100.0 ns	2166.4 ± 121.6 ns	2303.6 ± 81.1 ns	2131.4 ± 90.9 ns
	Average		2035.3 ± 50.9 NS	2534.2 ± 60.1 NS	2225.3 ± 56.4 NS	2081.4 ± 62.9 NS
	‘Palermo’	5th	2318.8 ± 80.5 ns	2188.0 ± 94.0 ns	2438.1 ± 140.0 ns	2090.9 ± 104.3 ns
		10th	2251.7 ± 86.6 ns	2287.9 ± 112.1 ns	2162.2 ± 99.5 ns	2122.2 ± 103.0 ns
	Average		2285.2 ± 59.3 NS	2237.9 ± 73.4 NS	2300.1 ± 55.9 NS	2106.6 ± 66.3 NS
Average			2160.2 ± 40.6 NS	2386.1 ± 44.2 NS	2262.7 ± 43.0 NS	2094.0 ± 45.7 NS
ΦPSII	‘Aifos’	5th	0.74 ± 0.00 abc	0.73 ± 0.02 abc	0.69 ± 0.02 c	0.74 ± 0.01 abc
		10th	0.76 ± 0.02 ab	0.76 ± 0.01 a	0.70 ± 0.02 bc	0.74 ± 0.01 abc
	Average		0.75 ± 0.00 A	0.75 ± 0.01 A	0.70 ± 0.02 B	0.74 ± 0.01 A
	‘Palermo’	5th	0.73 ± 0.01 ns	0.73 ± 0.01 ns	0.71 ± 0.01 ns	0.75 ± 0.00 ns
		10th	0.74 ± 0.01 ns	0.74 ± 0.01 ns	0.73 ± 0.02 ns	0.75 ± 0.02 ns
	Average		0.73 ± 0.01 NS	0.74 ± 0.01 NS	0.72 ± 0.01 NS	0.75 ± 0.00 NS
Average			0.74 ± 0.001 A	0.75 ± 0.003 A	0.71 ± 0.01 B	0.75 ± 0.001 A
Fv/Fm	‘Aifos’	5th	0.81 ± 0.008 abc	0.82 ± 0.007 ab	0.80 ± 0.006 c	0.81 ± 0.002 bc
		10th	0.81 ± 0.003 abc	0.82 ± 0.003 a	0.81 ± 0.008 abc	0.81 ± 0.008 bc
	Average		0.81 ± 0.001 B	0.82 ± 0.008 A	0.81 ± 0.003 B	0.81 ± 0.005 B
	‘Palermo’	5th	0.80 ± 0.009 ns	0.81 ± 0.002 ns	0.80 ± 0.001 ns	0.80 ± 0.006 ns
		10th	0.80 ± 0.001 ns	0.81 ± 0.007 ns	0.80 ± 0.005 ns	0.80 ± 0.04 ns
	Average		0.80 ± 0.002 AB	0.81 ± 0.002 A	0.80 ± 0.005 B	0.80 ± 0.002 B
Average			0.81 ± 0.006 B	0.82 ± 0.001 A	0.80 ± 0.003 B	0.80 ± 0.004 B
PI	‘Aifos’	5th	7.7 ± 0.33 a	7.6 ± 0.36 ab	7.3 ± 0.40 ab	7.0 ± 0.30 ab
		10th	6.9 ± 0.41 ab	7.3 ± 0.35 ab	6.8 ± 0.26 ab	6.2 ± 0.33 b
	Average		7.3 ± 0.25 AB	7.4 ± 0.25 A	7.1 ± 0.24 AB	6.6 ± 0.23 B
	‘Palermo’	5th	6.7 ± 0.24 ns	6.7 ± 0.28 ns	6.2 ± 0.28 ns	6.4 ± 0.29 ns
		10th	6.2 ± 0.25 ns	6.5 ± 0.33 ns	5.8 ± 0.21 ns	6.2 ± 0.37 ns
	Average		6.4 ± 0.17 A	6.6 ± 0.22 A	6.0 ± 0.18 A	6.3 ± 0.22 A
Average			6.9 ± 0.15 AB	7.0 ± 0.17 A	6.5 ± 0.15 AB	6.4 ± 0.16 B
SPAD	‘Aifos’	5th	65.4 ± 1.10 c	64.3 ± 0.91 c	65.7 ± 1.01 c	64.0 ± 1.39 c
		10th	72.2 ± 2.29 a	71.4 ± 0.75 a	70.8 ± 2.30 ab	66.7 ± 0.93 bc
	Average		68.8 ± 0.78 NS	67.8 ± 0.74 NS	66.8 ± 0.90 NS	68.2 ± 0.72 NS
	‘Palermo’	5th	63.2 ± 0.98 cd	64.0 ± 1.01 cd	66.1 ± 1.21 bc	60.2 ± 1.13 d
		10th	70.9 ± 0.93 a	70.7 ± 0.98 a	69.8 ± 0.80 ab	66.0 ± 2.25 bc
	Average		67.0 ± 0.84 NS	67.3 ± 0.82 NS	65.6 ± 0.73 NS	67.9 ± 0.81 NS
Average			67.9 ± 0.57 A	67.6 ± 0.55 A	68.1 ± 0.75 A	64.2 ± 0.58 B

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to combination leaf stage × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

). The highest value of the Fs parameter of chlorophyll a fluorescence was found in younger 5th leaves, counting from the top of the plant in the cultivar ‘Palermo’, and the lowest in older 10th leaves, counting from the top of the pepper shoot in the cultivar ‘Aifos’. It was found that plants sprayed simultaneously with SA and Ca had a lower quantum yield of photosystem II than plants from the other combinations. The highest maximum PSII quantum yield was found in plants treated with individual treatment of Ca compared to the control and plants treated with individual treatment of SA. The PSII viability index was also higher in plants treated with individual treatment of Ca than in control plants. Young 5th leaves had the highest PI in the ‘Aifos’ cultivar in the combination sprayed with individual treatment of SA. Older 10th leaves, counting from the top of the pepper shoot, had the lowest PI in ‘Palermo’ plants in the combination where Ca was applied together with SA (SA + Ca) (Table 3). The relative chlorophyll content of pepper leaves was significantly higher in plants sprayed with individual treatment of SA, individual treatment of Ca, and SA + Ca than in the control. The results indicate that the SPAD index values were higher in the 10th leaves than in the 5th leaves (Table 3). In the ‘Aifos’ plants treated with individual treatment of SA in the 10th leaves, counting from the shoot apex, the relative chlorophyll content was the highest. However, in the cultivar ‘Palermo’, in plants sprayed together with SA and Ca, the 5th leaves, counting from the shoot apex, obtained a higher SPAD index than the 5th leaves in the control (Table 3). No differences were found between cultivars for the parameters Fm, ΦPSII, Fv/Fm, and SPAD (Figure S6).

3.3. Pepper Yields

Total pepper fruit yield and marketable yield did not differ significantly between plants treated with individual treatment of SA and individual treatment of Ca or SA + Ca treatment compared to the control, although in term 1, the marketable yield in the ‘Aifos’ cultivar treated with individual treatment of SA was significantly higher than in the control. In term 2, there was also such a trend, but the difference was not statistically significant (

Table 4. Effect of salicylic acid and calcium treatment of pepper plants on total and marketable yield, fruit with BER, and average weight of fruit depending on cultivar [±SE].

Parameter	Cultivar	Term of Growing	Treatment
			SA	Ca	Ca + SA	Control
Total yield [kg/plant]	‘Aifos’	Term 1	3.0 ± 1.15 ns	2.5 ± 1.49 ns	2.5 ± 1.56 ns	2.5 ± 0.83 ns *
		Term 2	3.0 ± 0.34 ns	2.9 ± 2.03 ns	3.2 ± 0.36 ns	3.1 ± 0.81 ns
	Average		3.0 ± 1.13 NS	2.7 ± 1.77 NS	2.8 ± 1.90 NS	2.8 ± 1.46 NS
	‘Palermo’	Term 1	2.8 ± 1.28 ab	2.7 ± 0.95 ab	2.3 ± 0.30 b	2.1 ± 1.01 b
		Term 2	3.1 ± 2.14 ab	2.6 ± 5.41 ab	3.8 ± 2.21 ab	4.2 ± 1.39 a
	Average		2.9 ± 2.07 NS	2.7 ± 3.36 NS	3.0 ± 3.01 NS	3.2 ± 3.92 NS
Average			3.0 ± 1.11 NS	2.7 ± 1.79 NS	2.9 ± 1.69 NS	3.0 ± 2.02 NS
Marketable yield [kg/plant]	‘Aifos’	Term 1	2.3 ± 1.10 ab	2.0 ± 1.71 ab	1.7 ± 1.49 ab	1.4 ± 1.06 b
		Term 2	2.5 ± 0.72 a	2.4 ± 1.75 ab	2.4 ± 1.65 ab	2.3 ± 0.59 ab
	Average		2.4 ± 1.10 NS	2.2 ± 1.96 NS	2.0 ± 2.11 NS	1.8 ± 1.72 NS
	‘Palermo’	Term 1	1.0 ± 0.76 abc	1.0 ± 0.36 abc	0.7 ± 0.72 bc	0.3 ± 0.43 c
		Term 2	1.5 ± 1.72 ab	1.3 ± 2.58 abc	2.1 ± 1.23 a	2.1 ± 1.00 a
	Average		1.3 ± 1.64 NS	1.1 ± 2.00 NS	1.4 ± 2.69 NS	1.2 ± 3.21 NS
Average			1.8 ± 1.63 NS	1.7 ± 1.79 NS	1.7 ± 1.79 NS	1.5 ± 1.87 NS
Fruit with BER [kg/plant]	‘Aifos’	Term 1	0.8 ± 0.52 ab	0.5 ± 0.77 b	0.8 ± 0.23 ab	1.1 ± 0.56 a
		Term 2	0.5 ± 0.71 b	0.6 ± 0.36 b	0.8 ± 0.75 ab	0.9 ± 0.38 ab
	Average		0.6 ± 0.86 B	0.6 ± 0.64 B	0.8 ± 1.06 AB	1.0 ± 0.61 A
	‘Palermo’	Term 1	1.8 ± 0.57 ns	1.7 ± 0.88 ns	1.6 ± 0.54 ns	1.8 ± 0.78 ns
		Term 2	1.6 ± 0.71 ns	1.4 ± 1.81 ns	1.7 ± 0.82 ns	2.2 ± 0.63 ns
	Average		1.7 ± 0.78 NS	1.5 ± 1.60 NS	1.6 ± 0.76 NS	2.0 ± 0.94 NS
Average			1.2 ± 1.39 NS	1.1 ± 1.43 NS	1.2 ± 1.08 NS	1.5 ± 1.28 NS
Weight of marketable fruit [g]	‘Aifos’	Term 1	233.0 ± 2.44 ns	237.4 ± 6.06 ns	223.1 ± 6.59 ns	178.7 ± 11.47 ns
		Term 2	226.7 ± 10.49 ns	234.8 ± 10.30 ns	218.4 ± 5.67 ns	178.1 ± 3.94 ns
	Average		229.9 ± 10.00 NS	236.1 ± 9.96 NS	220.7 ± 14.72 NS	178.5 ± 15.20 NS
	‘Palermo’	Term 1	144.6 ± 7.18 ns	144.9 ± 7.08 ns	131.5 ± 2.98 ns	92.6 ± 12.04 ns
		Term 2	148.8 ± 3.58 ns	140.3 ± 10.44 ns	132.4 ± 9.23 ns	93.1 ± 2.62 ns
	Average		146.7 ± 4.82 A	142.6 ± 4.52 A	131.9 ± 12.94 AB	92.8 ± 7.56 B
Average			188.3 ± 13.75 NS	189.4 ± 14.53 NS	176.3 ± 12.66 NS	135.7 ± 13.45 NS

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to the combination term × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

). Plants in the control showed a higher fruit weight affected by BER than plants in which both individual treatment of SA and individual treatment of Ca were applied weekly and in combination where plants were sprayed simultaneously with SA + Ca. The average weight of marketable pepper fruit was higher in plants sprayed with individual treatment of SA and individual treatment of Ca than in the control (Table 4). The marketable yield of the cultivar ‘Palermo’ was lower than that of the cultivar ‘Aifos’, especially in term 1. A higher fruit weight with BER was found in this cultivar compared to the cultivar ‘Aifos’ (Table 4). The number of fruits in total yield was higher in control plants than in plants treated with individual treatment of SA or individual treatment of Ca. In marketable yield, there were no significant differences in fruit number between combinations. The number of fruits in total yield in the cultivar ‘Aifos’ was lower than in the cultivar ‘Palermo’ (

Table 5. Effect of salicylic acid and calcium treatment of pepper plants on number of fruit in total and marketable yield and fruit with BER depending on cultivar [±SE].

Parameter	Cultivar	Term of Growing	Treatment
			SA	Ca	SA + Ca	Control
Total yield [No./plant]	‘Aifos’	Term 1	19.5 ± 0.62 ab	16.4 ± 0.86 ab	17.0 ± 1.07 ab	21.2 ± 0.28 a *
		Term 2	15.9 ± 0.34 ab	12.5 ± 2.03 b	19.6 ± 0.36 ab	19.5 ± 0.81 ab
	Average		17.7 ± 0.82 AB	14.4 ± 1.79 B	18.3 ± 0.97 AB	20.4 ± 1.94 A
	‘Palermo’	Term 1	41.9 ± 3.78 ab	39.6 ± 1.76 ab	42.0 ± 0.41 ab	51.3 ± 2.00 ab
		Term 2	40.1 ± 2.14 ab	35.0 ± 5.41 b	49.2 ± 2.21 ab	61.2 ± 1.39 a
	Average		41.0 ± 2.10 B	37.3 ± 4.33 B	45.6 ± 2.10 AB	56.2 ± 3.27 A
Average			29.3 ± 3.17 NS	25.9 ± 3.48 NS	32.00 ± 3.39 NS	38.3 ± 4.40 NS
Marketable yield [No./plant]	‘Aifos’	Term 1	12.1 ± 0.50 ns	11.2 ± 0.81 ns	10.2 ± 0.91 ns	9.8 ± 0.47 ns
		Term 2	12.5 ± 0.21 ns	9.8 ± 1.52 ns	13.1 ± 0.84 ns	12.3 ± 0.46 ns
	Average		12.3 ± 0.42 NS	9.7 ± 1.33 NS	11.6 ± 1.07 NS	11.0 ± 0.66 NS
	‘Palermo’	Term 1	12.3 ± 1.14 ab	12.1 ± 0.47 ab	11.0 ± 0.82 ab	4.7 ± 0.27 b
		Term 2	16.6 ± 1.61 ab	14.7 ± 3.13 ab	20.9 ± 1.85 a	22.5 ± 2.59 a
	Average		14.4 ± 1.79 NS	13.4 ± 2.41 NS	15.9 ± 2.32 NS	13.6 ± 3.71 NS
Average			13.4 ± 0.90 NS	11.6 ± 1.34 NS	13.8 ± 1.29 NS	12.3 ± 1.80 NS
Fruit with BER [No./plant].	‘Aifos’	Term 1	7.3 ± 0.73 ab	5.2 ± 0.87 b	6.8 ± 0.27 b	11.5 ± 0.61 a
		Term 2	3.3 ± 0.53 b	4.2 ± 0.27 b	6.5 ± 0.57 b	7.2 ± 0.39 ab
	Average		5.3 ± 0.98 B	4.7 ± 0.71 B	6.7 ± 0.47 AB	9.3 ± 0.93 A
	‘Palermo’	Term 1	29.6 ± 2.49 bc	27.5 ± 1.35 bc	31.1 ± 1.09 bc	46.6 ± 2.07 a
		Term 2	23.5 ± 0.61 c	20.4 ± 2.53 c	28.3 ± 0.77 bc	38.7 ± 2.03 ab
	Average		26.6 ± 2.20 B	23.9 ± 2.48 B	29.7 ± 1.11 B	42.6 ± 2.58 A
Average			16.0 ± 2.75 NS	14.3 ± 2.57 NS	18.2 ± 2.77 NS	26.0 ± 4.13 NS

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to the combination term × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

). In term 1, the cultivar ‘Aifos’ in total yield, on average of the combinations tested, produced about 18.5 fruits per plant during the growing season, and in term 2, it produced, on average, 16.9 fruits per plant. The cultivar ‘Palermo’, on the other hand, produced 43.7 and 46.4 fruits per plant, respectively (Table 5). For marketable yield in term 1, the cultivar ‘Palermo’ had more marketable fruit in combination with individual treatment of SA and individual treatment of Ca than in the control (Table 5). For fruit with BER occurrence, plants sprayed with individual treatment of SA and individual treatment of Ca, and in the SA + Ca combination, had less fruit with BER than the control. The cultivar ‘Palermo’ had more fruit with BER symptoms than the cultivar ‘Aifos’ (Table 5). Total yield did not differ significantly between cultivars, while for the average weight of fruit and marketable yield parameter, lower values were found for the ‘Palermo’ cultivar compared to ‘Aifos’. The cultivar ‘Palermo’ had higher values for the following parameters: number of fruits TY, number of fruits MY, number of fruits with BER, and weight of fruits with BER (Figure S7).

3.4. Dry Matter Content and Color Evaluation of the Fruit

There was no effect of spraying plants with individual treatment of SA and individual treatment of Ca on the dry matter content of pepper fruits (

Table 6. Effect of salicylic acid and calcium treatment of pepper plants on dry weight content and CIE Lab color of fruit depending on cultivar [±SE].

Parameter	Cultivar	Term of Growing	Treatment
			SA	Ca	SA + Ca	Control
Dry weight [%]	‘Aifos’	Term 1	7.8 ± 0.17 b	8.7 ± 0.24 ab	9.6 ± 0.08 ab	8.4 ± 0.09 ab *
		Term 2	8.1 ± 0.13 ab	7.9 ± 0.25 b	8.9 ± 0.09 a	8.0 ± 0.03 b
	Average		8.0 ± 0.13 B	8.3 ± 0.23 AB	8.8 ± 0.08 A	8.2 ± 0.01 B
	‘Palermo’	Term 1	13.2 ± 1.63 a	10.1 ± 0.05 ab	8.1 ± 1.36 b	9.5 ± 0.03 ab
		Term 2	9.8 ± 0.05 ab	8.1 ± 0.14 b	11.4 ± 0.28 ab	11.2 ± 0.03 ab
	Average		11.5 ± 1.06 NS	9.1 ± 0.40 NS	9.8 ± 0.97 NS	10.3 ± 0.36 NS
Average			9.8 ± 0.74 NS	8.7 ± 0.27 NS	9.3 ± 0.51 NS	9.3 ± 0.36 NS
L* [lightness]	‘Aifos’	Term 1	34.4 ± 1.23 ab	32.0 ± 0.97 ab	32.0 ± 1.10 ab	32.3 ± 0.63 ab
		Term 2	31.8 ± 0.93 a	28.2 ± 1.94 b	34.4 ± 1.13 a	30.9 ± 1.12 ab
	Average		32.95 ± 0.87 AB	29.91 ± 1.32 B	33.88 ± 0.82 A	31.51 ± 0.72 AB
	‘Palermo’	Term 1	32.5 ± 1.31 ns	43.3 ± 4.92 ns	43.3 ± 1.21 ns	26.8 ± 1.39 ns
		Term 2	29.3 ± 1.18 ns	24.6 ± 2.88 ns	28.3 ± 2.62 ns	35.4 ± 2.67 ns
	Average		30.71 ± 1.03 NS	32.88 ± 4.11 NS	28.48 ± 1.55 NS	31.57 ± 2.15 NS
Average			31.8 ± 0.72 NS	31.4 ± 2.18 NS	31.2 ± 1.08 NS	31.5 ± 1.13 NS
a* [intensity of red]	‘Aifos’	Term 1	31.5 ± 0.87 cd	30.4 ± 1.64 abc	33.8 ± 0.85 ab	30.4 ± 0.55 bcd
		Term 2	29.4 ± 1.04 abc	28.4 ± 1.28 d	34.2 ± 1.17 a	29.7 ± 0.60 abcd
	Average		30.3 ± 0.78 B	29.1 ± 1.07 B	33.9 ± 0.76 A	30.0 ± 0.43 B
	‘Palermo’	Term 1	31.7 ± 2.06 ns	21.7 ± 6.81 ns	29.4 ± 3.03 ns	25.8 ± 1.69 ns
		Term 2	26.4 ± 3.62 ns	27.2 ± 1.16 ns	27.2 ± 2.61 ns	30.0 ± 2.75 ns
	Average		28.7 ± 2.38 NS	24.7 ± 3.22 NS	28.2 ± 2.01 NS	28.1 ± 1.83 NS
Average			29.5 ± 1.26 NS	27.0 ± 1.78 NS	31.1 ± 1.27 NS	29.1 ± 0.96 NS
b* [intensity of yellow]	‘Aifos’	Term 1	19.4 ± 1.05 ab	18.6 ± 1.73 ab	18.2 ± 1.02 ab	15.9 ± 0.71 ab
		Term 2	15.8 ± 0.81 ab	16.2 ± 0.84 b	20.9 ± 1.03 a	17.1 ± 1.46 ab
	Average		17.4 ± 0.88 NS	17.3 ± 0.97 NS	19.7 ± 0.85 NS	16.6 ± 0.9 NS
	‘Palermo’	Term 1	20.5 ± 1.64 ab	10.7 ± 3.90 b	15.4 ± 0.90 ab	13.6 ± 1.26 ab
		Term 2	13.2 ± 1.97 b	16.3 ± 1.04 ab	16.1 ± 1.74 ab	22.5 ± 1.91 a
	Average		16.4 ± 1.78 NS	13.9 ± 2.05 NS	15.8 ± 1.05 NS	18.5 ± 1.09 NS
Average			16.9 ± 0.99 NS	15.6 ± 1.20 NS	17.8 ± 0.82 NS	17.6 ± 1.07 NS

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to the combination term × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

). ‘Aifos’ fruit, on average from the combinations and cultivation dates tested, contained 8.4% dry matter, and ‘Palermo’ fruit contained 10.2% dry matter, respectively. CIE Lab color parameters such as L*—lightness and a* intensity of red for pepper fruits did not depend on the applied plant sprays of individual treatment of SA and individual treatment of Ca. However, the parameter b*, characterizing the intensity of yellow [b* > 0], showed lower values in fruit from the individual treatment of Ca-sprayed plants compared to the control and individual treatment of SA and Ca + SA combinations (Table 6). The parameters of fruit length, diameter of fruit, and thickness of pericarp of pepper fruits did not depend on the treatment applied. Significant differences occurred between cultivars (Table S1). No differences were found between cultivars for the parameter L*, while the values of the parameters a* and b* for ‘Palermo’ were lower than for ‘Aifos’ (Figure S6). The dry matter content of the pepper fruits differed between cultivars. Fruits of the ‘Palermo’ cultivar had a higher dry matter content than those of the ‘Aifos’ cultivar (Figure S7).

3.5. Sensory Analysis of the Fruit

The results of the sensory analysis showed that pepper fruits of both individual treatment of SA and individual treatment of Ca and untreated cultivars did not differ significantly with respect to most of the tested attributes of fruit odor, texture, and taste in term 1 and term 2. The off-flavor parameter was scored 0 by the evaluators (

Table 7. Effect of salicylic acid and calcium treatment of pepper plants on the result of sensory analysis on the attributes of odor, texture, and taste of fruits depending on the cultivar [±SE].

Attributes of Odor, Texture, and Taste	Cultivar	Term of Growing	Treatment
			SA	Ca	SA + Ca	Control
Odor of fresh pepper	‘Aifos’	Term 1	5.6 ± 0.47 ns	4.4 ± 0.44 ns	4.7 ± 0.47 ns	4.6 ± 0.53 ns *
		Term 2	5.9 ± 0.38 ns	4.7 ± 0.44 ns	5.2 ± 0.49 ns	4.3 ± 0.53 ns
	Average		6.0 ± 0.31 A	4.6 ± 0.31 B	4.9 ± 0.34 AB	4.5 ± 0.38 B
	‘Palermo’	Term 1	4.6 ± 0.52 ns	4.2 ± 0.68 ns	4.7 ± 0.68 ns	5.5 ± 0.48 ns
		Term 2	3.9 ± 0.50 ns	4.5 ± 0.68 ns	5.7 ± 0.60 ns	5.2 ± 0.54 ns
	Average		4.0 ± 0.36 NS	4.4 ± 0.48 NS	5.1 ± 0.46 NS	5.4 ± 0.36 NS
Average			4.9 ± 0.25 NS	4.5 ± 0.29 NS	5.0 ± 0.28 NS	4.9 ± 0.26 NS
Skin hardness	‘Aifos’	Term 1	5.8 ± 0.54 ns	6.0 ± 0.45 ns	5.8 ± 0.61 ns	5.6 ± 0.33 ns
		Term 2	6.0 ± 0.55 ns	6.3 ± 0.45 ns	6.2 ± 0.68 ns	5.3 ± 0.32 ns
	Average		6.1 ± 0.38 NS	6.2 ± 0.32 NS	6.0 ± 0.45 NS	5.5 ± 0.23 NS
	‘Palermo’	Term 1	5.8 ± 0.57 ns	4.5 ± 0.49 ns	4.5 ± 0.76 ns	4.9 ± 0.68 ns
		Term 2	5.2 ± 0.56 ns	4.8 ± 0.49 ns	5.6 ± 0.72 ns	5.0 ± 0.70 ns
	Average		5.4 ± 0.40 NS	4.7 ± 0.35 NS	5.0 ± 0.53 NS	5.0 ± 0.49 NS
Average			5.7 ± 0.27 NS	5.4 ± 0.25 NS	5.4 ± 0.36 NS	5.2 ± 0.26 NS
Flesh fibrousness	‘Aifos’	Term 1	5.9 ± 0.44 ns	5.7 ± 0.45 ns	6.8 ± 0.54 ns	6.2 ± 0.39 ns
		Term 2	6.0 ± 0.48 ns	6.0 ± 0.45 ns	6.3 ± 0.49 ns	5.9 ± 0.39 ns
	Average		6.0 ± 0.32 NS	5.9 ± 0.31 NS	6.6 ± 0.37 NS	6.1 ± 0.27 NS
	‘Palermo’	Term 1	5.6 ± 0.25 ns	5.5 ± 0.47 ns	4.3 ± 0.45 ns	5.3 ± 0.52 ns
		Term 2	5.4 ± 0.27 ns	5.8 ± 047 ns	5.1 ± 0.43 ns	4.6 ± 0.55 ns
	Average		5.6 ± 0.18 NS	5.7 ± 0.33 NS	4.7 ± 0.32 NS	5.0 ± 0.38 NS
Average			5.7 ± 0.19 NS	5.7 ± 0.23 NS	5.6 ± 0.28 NS	5.5 ± 0.24 NS
Flesh juiciness	‘Aifos’	Term 1	5.6 ± 0.46 ns	6.0 ± 0.45 ns	6.8 ± 0.56 ns	6.0 ± 0.35 ns
		Term 2	6.0 ± 0.45 ns	6.3 ± 0.45 ns	6.6 ± 0.58 ns	5.7 ± 0.35 ns
	Average		5.9 ± 0.34 NS	6.2 ± 0.34 NS	6.7 ± 0.40 NS	5.9 ± 0.25 NS
	‘Palermo’	Term 1	5.9 ± 0.45 ns	5.6 ± 0.54 ns	3.6 ± 0.37 ns	3.9 ± 0.44 ns
		Term 2	5.5 ± 0.47 ns	5.9 ± 0.54 ns	4.3 ± 0.38 ns	4.0 ± 0.47 ns
	Average		5.7 ± 0.33 A	5.8 ± 0.39 A	3.9 ± 0.27 B	4.0 ± 0.32 B
Average			5.7 ± 0.23 AB	5.9 ± 0.25 A	5.3 ± 0.30 AB	5.0 ± 0.23 B
Flesh firmness	‘Aifos’	Term 1	6.5 ± 0.52 ns	6.6 ± 0.49 ns	6.9 ± 0.56 ns	7.2 ± 0.44 ns
		Term 2	7.2 ± 0.45 ns	6.9 ± 0.49 ns	6.4 ± 0.50 ns	6.9 ± 0.44 ns
	Average		6.8 ± 0.35 NS	6.8 ± 0.34 NS	6.7 ± 0.38 NS	7.1 ± 0.31 NS
	‘Palermo’	Term 1	3.6 ± 0.37 ab	3.5 ± 0.30 ab	2.2 ± 0.23 b	2.5 ± 0.33 b
		Term 2	3.3 ± 0.38 ab	3.8 ± 0.30 a	2.7 ± 0.24 ab	2.4 ± 0.34 ab
	Average		3.5 ± 0.27 A	3.7 ± 0.21 A	2.5 ± 0.17 B	2.5 ± 0.22 B
Average			5.0 ± 0.30 NS	5.2 ± 0.28 NS	4.5 ± 0.33 NS	4.9 ± 0.35 NS
Typical pepper taste	‘Aifos’	Term 1	6.7 ± 0.36 ns	6.3 ± 0.34 ns	6.0 ± 0.18 ns	6.2 ± 0.33 ns
		Term 2	7.0 ± 0.37 ns	6.6 ± 0.34 ns	6.3 ± 0.20 ns	5.9 ± 0.30 ns
	Average		7.0 ± 0.26 A	6.5 ± 0.24 AB	6.2 ± 0.14 AB	6.1 ± 0.21 B
	‘Palermo’	Term 1	6.7 ± 0.47 ns	6.0 ± 0.36 ns	6.7 ± 0.37 ns	6.9 ± 0.30 ns
		Term 2	6.2 ± 0.44 ns	6.3 ± 0.36 ns	7.5 ± 0.36 ns	6.7 ± 0.36 ns
	Average		6.4 ± 0.33 NS	6.2 ± 0.26 NS	7.2 ± 0.27 NS	6.9 ± 0.24 NS
Average			6.6 ± 0.21 NS	6.3 ± 0.18 NS	6.6 ± 0.16 NS	4.4 ± 0.17 NS
Sour taste	‘Aifos’	Term 1	3.5 ± 0.45 ns	3.5 ± 0.52 ns	4.2 ± 0.56 ns	3.4 ± 0.49 ns
		Term 2	4.1 ± 0.45 ns	3.8 ± 0.52 ns	4.6 ± 0.61 ns	3.3 ± 0.48 ns
	Average		3.8 ± 0.32 NS	3.7 ± 0.37 NS	4.4 ± 0.41 NS	3.3 ± 0.35 NS
	‘Palermo’	Term 1	1.7 ± 0.25 ns	1.6 ± 0.33 ns	2.2 ± 0.44 ns	3.0 ± 0.57 ns
		Term 2	1.6 ± 0.26 ns	1.9 ± 0.33 ns	2.8 ± 0.44 ns	2.6 ± 0.45 ns
	Average		1.7 ± 0.18 NS	1.8 ± 0.24 NS	2.5 ± 0.32 NS	2.8 ± 0.37 NS
Average			2.6 ± 0.23 NS	2.7 ± 0.25 NS	3.4 ± 0.29 NS	3.0 ± 0.26 NS
Sweet taste	‘Aifos’	Term 1	3.9 ± 0.51 ns	3.6 ± 0.53 ns	3.6 ± 0.57 ns	4.3 ± 0.50 ns
		Term 2	3.5 ± 0.46 ns	3.9 ± 0.53 ns	3.8 ± 0.56 ns	4.0 ± 0.50 ns
	Average		3.7 ± 0.35 NS	3.8 ± 0.38 NS	3.8 ± 0.40 NS	4.2 ± 0.36 NS
	‘Palermo’	Term 1	6.7 ± 0.50 ns	6.5 ± 0.57 ns	5.9 ± 0.44 ns	5.8 ± 0.54 ns
		Term 2	6.6 ± 0.47 ns	6.8 ± 0.57 ns	6.4 ± 0.49 ns	5.8 ± 0.62 ns
	Average		6.7 ± 0.35 NS	6.7 ± 0.40 NS	6.1 ± 0.33 NS	5.9 ± 0.41 NS
Average			5.3 ± 0.31 NS	5.2 ± 0.33 NS	4.9 ± 0.30 NS	4.9 ± 0.28 NS
Bitter taste	‘Aifos’	Term 1	0.5 ± 0.28 ns	0.7 ± 0.28 ns	0.1 ± 0.07 ns	0.8 ± 0.28 ns
		Term 2	0.3 ± 0.10 ns	0.7 ± 0.28 ns	0.2 ± 0.08 ns	0.8 ± 0.28 ns
	Average		0.3 ± 0.16 B	0.7 ± 0.20 AB	0.2 ± 0.06 B	0.9 ± 0.20 A
	‘Palermo’	Term 1	0.3 ± 0.31 ns	0.5 ± 0.32 ns	0.0 ± 0.05 ns	0.1 ± 0.07 ns
		Term 2	0.6 ± 0.41 ns	0.5 ± 0.32 ns	0.1 ± 0.05 ns	0.1 ± 0.07 ns
	Average		0.7 ± 0.26 NS	0.5 ± 0.22 NS	0.1 ± 0.04 NS	0.2 ± 0.05 NS
Average			0.4 ± 0.16 AB	0.6 ± 0.15 A	0.1 ± 0.04 B	0.5 ± 0.12 AB
Pungent flavor	‘Aifos’	Term 1	1.1 ± 0.39 ns	0.9 ± 0.25 ns	0.9 ± 0.35 ns	0.5 ± 0.17 ns
		Term 2	1.4 ± 0.44 ns	0.9 ± 0.25 ns	1.1 ± 0.39 ns	0.5 ± 0.16 ns
	Average		1.3 ± 0.30 NS	0.9 ± 0.18 NS	1.1 ± 0.26 NS	0.6 ± 0.12 NS
	‘Palermo’	Term 1	0.4 ± 0.17 ns	0.5 ± 0.19 ns	0.8 ± 0.27 ns	0.8 ± 0.30 ns
		Term 2	0.5 ± 0.16 ns	1.0 ± 0.19 ns	1.0 ± 0.29 ns	1.0 ± 0.32 ns
	Average		0.5 ± 0.12 NS	0.6 ± 0.13 NS	1.0 ± 0.19 NS	1.0 ± 0.22 NS
Average			0.8 ± 0.16 NS	0.7 ± 0.11 NS	1.0 ± 0.16 NS	0.7 ± 0.12 NS
Overall quality	‘Aifos’	Term 1	6.9 ± 0.19 ns	6.9 ± 0.28 ns	7.3 ± 0.24 ns	7.2 ± 0.23 ns
		Term 2	7.2 ± 0.18 ns	7.2 ± 0.28 ns	7.4 ± 0.26 ns	6.9 ± 0.23 ns
	Average		7.1 ± 0.13 NS	7.1 ± 0.20 NS	7.4 ± 0.18 NS	7.1 ± 0.16 NS
	‘Palermo’	Term 1	7.0 ± 0.27 ns	6.6 ± 0.25 ns	6.4 ± 0.43 ns	6.8 ± 0.34 ns
		Term 2	6.5 ± 0.26 ns	6.9 ± 0.24 ns	7.2 ± 0.24 ns	6.4 ± 0.33 ns
	Average		6.7 ± 0.19 NS	6.8 ± 0.18 NS	6.8 ± 0.26 NS	6.7 ± 0.24 NS
Average			6.9 ± 0.16 NS	6.9 ± 0.14 NS	7.0 ± 0.12 NS	6.9 ± 0.12 NS

* Means with different letters indicate a statistically significant difference according to the Tukey HSD test at α = 0.05. Abbreviations: ns, not significant; NS, not significant. Small letters refer to the combination term × treatment, and capital letters relate to treatment (for each cultivar—two-factor analysis of variance, and for the averages of the cultivars—three-factor analysis of variance).

). Pepper fruits harvested from plants treated with the individual treatment of SA, individual treatment of Ca, and SA + Ca-treated plants had more juicy flesh compared to the control, while the least bitter flavor was found in fruits from the SA + Ca combination. No significant differences were observed in the overall preference of the fruits tested according to treatment and cultivation date (Figure 1). Fruits of the ‘Palermo’ cultivar were rated significantly higher for sweet taste and overall quality than those of the ‘Aifos’ cultivar. For the other evaluated parameters, the ‘Aifos’ fruit achieved higher values compared to the ‘Palermo’ fruit (Figure 2).

4. Discussion

4.1. Biometric Measurements of Plants and Yielding Peppers

Peppers are an economically important vegetable that is the subject of much research, including efforts to improve cultivation efficiency and fruit quality. Hydroponic cultivation of peppers in inert substrates is not as popular as traditional soil cultivation. This method of cultivation offers the possibility of monitoring and controlling the fertilization and irrigation of plants. Mineral nutrients in the form of foliar fertilization are used to supplement standard fertilization, optimizing the growth and yield of grown plants under stress conditions. Mineral nutrients can affect plant growth and yield, causing changes in plant chemistry, morphology, and anatomy. Consequently, this can trigger or enhance the mechanisms responsible for the plant’s resistance to pests and diseases or abiotic stresses. The calcium ion is one of the essential nutrients affecting plant growth and development and higher fruit yield and quality [42]. The study found that spraying peppers with calcium nitrate affected higher weekly shoot growth and number of leaves compared to control, water-sprayed plants. Also, SA-treated plants had greater weekly shoot length increments and gained higher shoots and more leaves during the growing season than the control. Total pepper fruit yield and marketable yield were not significantly different between plants treated with the individual treatment of SA and individual treatment of Ca or SA + Ca treated plants compared to the control. However, there were significantly fewer fruits with BER in plants sprayed with both individual treatment of SA 0.03% and individual treatment of Ca 0.7% and in the combination where plants were sprayed simultaneously with SA 0.03% + Ca 0.7% compared to the control. It was also found that the treatment of plants with individual treatments of SA and Ca influenced higher marketable fruit weight in both pepper cultivars grown hydroponically. The cultivars tested differed significantly in growth rate, yield, and fruit susceptibility to BER. The cultivar ‘Palermo’ had more fruit with BER symptoms than the cultivar ‘Aifos’. ‘Palermo’ had a lower average fruit weight than ‘Aifos’.

Calcium is mainly involved in the formation of the plant cell wall and is also a signaling molecule that regulates a wide range of physiological and pathological responses [43]. Ca transport to aboveground plant organs depends on several factors, such as Ca²⁺ concentration in xylem sap, balanced mineral nutrition, water uptake and water potential of the plant, transpiration, and growth rate [44]. Excessive Ca accumulation can occur in organs with a high transpiration rate (i.e., leaves) [17], while organs with a low transpiration rate (e.g., fruits) can respond to local Ca deficiencies [16,44]. Studies by El-Tohama et al. [45] and Buczkowska et al. [35] showed positive effects of Ca nutrition on pepper fruit yield.

Salicylic acid, on the other hand, is a natural phenolic acid, an endogenous growth regulator, and has many regulatory functions in plant metabolism [46]. The role of SA in plant growth has been the subject of much less research than has been the case of other plant hormones. Most publications on the subject do not consider SA, or its role is partially described [47,48,49]. Salicylic acid controls plant performance, including advanced growth, nutrient uptake, protein synthesis, and cell division and differentiation, which is associated with increased yield [50,51]. The effect of exogenous SA on growth depends on the plant species, developmental stage, and SA concentration. Growth-stimulating effects of SA have been reported for soybean [52], wheat [53], maize [54], and chamomile [55]. The results indicate that exogenous SA concentrations >1 mM SA are too high for most plants, but this depends on the plant species. Too high a concentration of SA has a negative effect on plant development and growth [52,54,56]. In contrast, the use of optimal SA concentrations has been shown to have a positive effect on plants. Depending on the experimental conditions, SA clearly stimulated growth under both normal and different abiotic stress conditions in different plant species [57,58,59].

A study by Souri and Tohidloo [60] showed that salicylic acid applied through the roots has a beneficial effect on tomato seedling growth under saline conditions. Similar results are presented in a study by Arfan et al. [61], where SA application to the roots improved tomato and wheat growth under saline conditions.

The method of foliar spraying of plants plays a key role in improving the growth and yield of vegetable plants by increasing plant’s nutrient uptake and efficiency [23,62]. The obtained results are confirmed by studies on the growth of plants treated with foliar SA in other species of the same genus Capsicum [63,64], as well as in Lycopersicum esculentum [65], Chrysanthemum morifolium [66], Carica papaya [67], Oryza sativa [68], Triticum aestivum [69,70], and Zea mays [71]. The results of the use of salicylic acid in traditional pepper cultivation are also promising [64,72,73]. The beneficial effects of salicylic acid on plants are also confirmed by studies conducted by Elwan et al. [64], where application at low concentrations [10⁻⁶ M] resulted in an increase in fresh and dry leaf weight, number of fruits, average fruit weight, and fruit yield of pepper.

4.2. Photosynthetic Activity of Peppers

The leaf is the most important organ of the plant, i.e., the so-called main source of food for the plant in which photosynthesis takes place. The foliar application of Ca closes the stomata and protects the leaves from unfavorable weather conditions [74,75]. In contrast, the application of salicylic acid affects a wide variety of plant processes, including stomatal closure, ion uptake and transport [76], membrane permeability, and the rate of photosynthesis and growth [77].

The study found that the highest steady-state fluorescence yields [Fs] were obtained by pepper plants treated simultaneously with SA [0.03%] and individual treatment of Ca [0.7%]. Plants treated with individual treatment of Ca had the highest maximum PSII quantum yield [Fv/Fm] and the highest PSII viability index [PI] compared to the control and plants treated with individual treatment of SA. The relative chlorophyll content of pepper leaves was significantly higher in plants treated with individual treatment of SA, individual treatment of Ca, and SA + Ca-treated plants than in the control.

Salicylic acid regulates ionic balance, photosynthetic activity, and ROS detoxification, which ensure normal physiological and biochemical behavior [78,79,80]. Similar SA properties have been observed in winter wheat [81], green pepper [82], bamboo shoots [83], and cucumber [84], confirming the results obtained in the study. Exogenous application of SA increased the photosynthetic rate in various crops such as thyme [85], radish [86], and maize [87]. Graham and McDonald [88] observed a decrease in Fv/Fm under high temperatures. A decrease in this parameter may indicate active protection of the plant from the sun [89]. Baker and Rosenqvist [90] concluded in their study that a decrease in Fv/Fm may inhibit the rate of photosynthesis and also affect plant growth and development. In contrast, the PI vitality index PSII shows the ability of plants to adapt to stress conditions [91]. SA is involved in improving the rate of photosynthesis through K+ uptake [92] and the ability to increase rubisco activity [93], increasing ATP content and maintaining an optimal K⁺/Na⁺ ratio in plants [94]. Thus, the application of exogenous SA can enhance photosynthesis, which is a major factor controlling plant growth and yield [95]. The application of SA affects the decomposition and removal of ROS, while antioxidant enzymes reduce the destructive effects of ROS on cell membranes, photosynthetic pigments, proteins, and other macromolecules, affecting the metabolic activity of plants and improving the growth and yield of A. hirtifolium by maintaining membrane stability and photosynthetic pigments, improving photosynthetic and respiratory activity of the plant [96].

4.3. Dry Matter Content, Fruit Color Evaluation, and Sensory Analysis of Fruit

There was no effect of spraying plants with individual treatment of SA at a concentration of 0.03% and individual treatment of Ca at a concentration of 0.7% on the dry matter content of pepper fruit. The color parameters L* and a* in pepper fruits did not depend on the application of individual treatment of SA and individual treatment of Ca. In contrast, parameter b* showed lower values in fruits from Ca-sprayed plants compared to the control and plants sprayed with individual treatment of SA and SA + Ca combination. The change in the green color of peppers is linked to the exchange of chloroplast for chromoplast, during which the conversion of pigment content in sweet peppers increases with aging [97]. Confirming the results obtained, a study by Dobón-Suárez et al. [98] showed that pre-harvest SA treatments did not affect the ripening process of pepper fruits on the plant. Pepper fruits from plants sprayed with individual treatment of SA, individual treatment of Ca, and SA + Ca treatments had more juicy flesh compared to the control, while the least bitter taste was found in fruits from the SA + Ca combination. A study conducted by Javaheri et al. [99] showed that foliar application of salicylic acid significantly improved tomato fruit quality.

5. Conclusions

Foliar application of individual treatment of salicylic acid at a concentration of 0.3% and individual treatment of Ca in the form of a solution of calcium nitrate at a concentration of 0.7% has a beneficial effect on the growth and yield of peppers in hydroponic cultivation and on the quality of pepper fruit. Pepper plants treated with both SA and Ca alone and with both individual treatment of SA and individual treatment of Ca showed less BER on fruit than plants in the control. Research on the foliar application of individual treatment of SA and Ca together with SA in greenhouse peppers grown in mineral wool substrate requires further investigation with other combinations of solution concentrations and frequency of application per plant.