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Quality Responses of Sweet Pepper Varieties Under Irrigation and Fertilization Regimes

A peer-reviewed version of this preprint was published in:
Horticulturae 2025, 11(2), 128. https://doi.org/10.3390/horticulturae11020128

Submitted:

26 November 2024

Posted:

27 November 2024

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Abstract

Sweet peppers are economically important since they are widely farmed and consumed worldwide. As a high‐value crop, it has a significant impact on the horticulture economy. This study aimed to improve the quality of sweet pepper fruits (total polyphenols; A and B chlorophyll; lycopene; and B‐carotene, tannins ABTS, DPPH) under effects of various fertilization methods (chemical, organic, biologic), irrigation regimes (5200 and 7800 m3∙ha‐1, respectively) and three hybrids: Kornelya, Kaptur and Napoca. The results revealed substantial similarities between organic and conventional management practices. From a technological point of view, the local cultivar Kornelya reacted well with most compounds with antioxidant effects. This study revealed that peppers react positively when subjected to hydric and nutrient stress, with the fruits having the highest values for total polyphenols; chlorophyll A and B; lycopene; and ABTS, DPPH. Following the interactions between factors, Kornelya reacted positively to control fertilization when irrigated with 5200 m3∙ha‐1.

Keywords: 
sweet pepper varieties
;  
organic and conventional farming
;  
irrigation regime
;  
antioxidant activity
;  
polyphenols
;  
lycopene and b‐carotene
;  
tannins
Subject: 
Biology and Life Sciences  -   Horticulture

1. Introduction

Sweet pepper is a popular vegetable around of the world for nutritional compounds [1]. The species (Capsicum annuum L. ssp. annuum) is a Capsicum genus from the Solanaceae family, a largest vegetable crops, used for fresh or dried, culinary arts, and processing. [2,3]. Peppers have high nutritional value because of their antioxidant properties, as well as other excellent traits, such as flavour, colour, and texture [4,5,6]. In the main case, secondary metabolites from pepper fruits are influenced by biotic and abiotic conditions [7,8]. This is why several vegetable fruits are highly valued not only for their nutritional value but also for their health benefits. The World Health Organization recommended as daily consumption at the least of 400 g od vegetable and fruits [9]. Current agricultural practices prioritize yield over ecosystem sustainability and food production. [10]. These include rising consumer demand for healthier products and existing policies on sustainable food production, which prioritize organic farming approaches over chemical-intensive conventional cultivation [11].
China is the world’s largest producer of pepper, accounting for 38 million tonnes [12]. In recent years, Romania has consistently produced more than 135,000 tonnes each year. This constancy implies that Romania’s pepper-growing business is resilient, most likely due to factors such as favourable climatic conditions, technological advancements, and market demand. These characteristics support Romania’s position as a major player at the European market, with promising prospects for growth and sustainability [1,12], which require less maintenance and are less prone to disease and pests than other crops from Solanaceae family [13].
Constantly, horticultural research, understanding the impact of irrigation regimes and growing techniques on the quality attributes of Solanaceum varieties has involved management and production practices, with the goal of identifying critical parameters of fruits quality [14]. The quality of sweet pepper fruits is given by flavonoids, total polyphenol, lycopene, β-carotene, ascorbic acid, tocopherols and antioxidant activity, nutrient content that differs according by variety, nutrients, irrigation etc [15,16,17,18]. Pepper fruits compounds are good for human health, against cardiovascular disease, cancer, diabetes, neurological illnesses, and cataracts [7,19]. Phytochemicals are a class of physiologically active, non-nutritive substances found in pepper fruits that have antioxidant activity and other health advantages [20]. Many studies have reported strong associations between the consumption of carotenoids and lycopene and a lower risk of cancer and coronary and cardiovascular disease. The positive effects of carotenoids are assumed to be due to their activity as antioxidants [21]. Tannins represent a wide group of compounds that can be found in fruits and vegetables. Tannins are also known as pro-anthocyanins that possess beneficial properties, such as antioxidant, antiaging, anticancer, anti-inflammatory, and anti-atherosclerotic effects, and protect the heart and blood vessels [22]. Given the rising demand from consumers for healthy products and existing policies promoting sustainable farming systems, organic cultivation is a viable alternative to traditional farming practices [23,24]. The consumption of these compounds has health benefits because of their antioxidant properties, high protection of cells from oxidative damage [25].
The effect of technological factors is directly reflected in the quality of the sweet pepper harvest. Pepper variety differ in many morphological characteristics and the content of biologically active substances [1,26]. This direct link between diet and health has piqued the interest of plant breeders, who are focusing their research on genotypes with high antioxidant levels [27]. As a result, it is critical to investigate the changes in different genotypes during maturity in various geographical areas to identify the optimum genotypes and techniques for achieving health advantages [1,27].
The fertilizers play an important role in improving the soil, environment, fruit quality, physiological growth, and photosynthesis of plants; the nutritional quality of fruits; and the contents of chlorophyll and total flavonoids [10]. Many researches from the literature highlight the special influence of fertilizing elements on the quality of pepper fruits. The application of biological fertilizers, but especially with organic fertilizers, has determined a good percentage of antioxidant activity (ABTS, DPPH, total polyphenols [28], a type of phenolic compound; ascorbic acid; capsaicinoids; and carotenoids are among the chemicals that help against oxidative stress. In general, using an organic farming system is considered beneficial to the soil, the environment and humans as a result of not using pesticides that are harmful to humans and the environment and thus obtaining safer fruits [29]. Fertilization is a vital aspect of agricultural productivity and can be classified into three types: chemical, biological, and organic. Chemical fertilizers are widely utilized in agriculture; however, their use is highly yield [28]. Alternatives, such as organic and biological fertilizers, are gaining popularity among producers and consumers because of their environmental friendliness. In this context, organic fertilizers include manure, algae, and biological fertilizers include microorganisms improved the quantity and quality of production.[30]. In the last decade, much research has focused on the beneficial effect of biological fertilizers on the quality, especially of the harvest. These fertilizers are thought to be more environmentally friendly than chemical fertilizers, which are overused and detrimental to the environment. [31]. In the context of climate change, drought and salinization, irrigation systems focus on creating techniques that minimize water consumption or efficient use of water, increasing global water shortages and irrigation costs. The development of drip irrigation for greenhouses has significantly decreased the amount of water used for irrigation of horticultural crops [32]. Vegetable crops have shown variations in the composition of specific nutritional components as irrigation regimes change in response to water availability [33]. Recent studies have shown that the correct application of irrigation determines the qualitative improvement of Solanaceae fruits in correlation with genotypes, ripening stage, edible parts, growth conditions and nutrition fertilizers [34].
While previous studies, our current experiment focuses on the effects of different modern agricultural practices involving irrigation regimes and three types of fertilization (organic, biological and chemical) to improve the quality of long pepper fruits (ABTS, DPPH, total polyphenols; A and B chlorophyll; lycopene; and β-carotene, tannins, 15 N and protein).

2. Materials and Methods

2.1. Experimental Site

The experiment was carried out in a greenhouse via a split-plot design at the “V. Adamachi” Farm of Iasi University of Life Sciences (47019’25” N, 27054’99” E, 150 m altitude) from 2021-2022.
The soil is characterized as a loam-clay chernozem with a pH of 7.20; an electrical conductivity (EC) of 482 µS·cm-1, CaCO3 of 0.42%, organic matter (OM) of 2.83%, C/N of 5.87, N total of 2.8 g·kg-1, and P of 34 mg·kg-1 were used for the experiment [35].
A total of 24 versions were collected from experimental plots representing three sweet varieties of peppers (Kornelia F1, Kaptur F1 and Napoca F1), including chemical, organic, and biological fertilization under two different irrigation regims. Some photos from experimental greenhouse are presented in Figure S1.
Two distinct irrigation regimes (IR) were implemented. Drip irrigation was used at a rate of 5200 m3·ha-1 (IR1) and 7800 m3·ha-1 (IR2), respectively.
Moreover, three different fertilization methods were used: organic, chemical and biological compare with control. Fertilizers were applied to the soil at a dose of 800 kg ha−1 for the chemical treatment and 2500 kg ha−1 for the organic treatment. Both fertilizers were applied three times as follows: 50% of the total applied during soil preparation; 25% when the first fruit reached a 1 cm and the last dose (25%) when the fruit from third level reached 1 cm. For chemical fertilizer was used a complex fertilizer N:P:K -20:20:20,400 kg·ha-1, which was applied during the soil preparation, and Nutrispore®, N:P:K -8:24:24, kg·ha-1, which was applied the same time like organic application. Biological fertilization with Micoseed MB®, 60 kg·ha-1, was applied to the soil; and during the vegetation period, Nutryaction®, 1.5 l·ha-1, was applied three times. Biological fertilizer is based on microorganisms and contains the following arbuscular mycorrhizal fungal spores: Claroideoglomus etunicatum, Funneliformis mosseae, Glomus aggregatum, and Rhizophagus intraradices. In addition, the product is complexed with fungi and bacteria belonging to the genera Trichoderma, Streptomyces, Bacillus, and Pseudomonas. All the experimental factors were compared with a version unfertilized.

2.2. Materials and Sample Preparation

Each group of pepper fruits was collected when they reached physiological maturity (809 BBSH scale). The samples were chopped into small 1 cm pieces, homogenized, and freeze-dried via an ECO EVO freeze-dryer (Tred Technology S.R.L., Ripalimosani, Italy). The dried samples were powdered and stored at -80°C until analysis [36]. Each statistic represents the mean of three replicates. The flowchart of sweet pepper analysed is presented in Figure S2.

2.3. Chemicals and Materials Used in the Experiment

HPLC-grade methanol, formic acid, hydrochloric acid, acetone, hexane and water were acquired from Panreac (Barcelona, Spain). Sodium carbonate, Folin-Ciocalteu reagent, gallic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6 sulfonic acid) diammonium salt (ABTS), potassium persulfate, (+)-catechin and vanillin were obtained from Sigma‒Aldrich (Steinheim, Germany).

2.4. Hydrophilic Extraction

Hydrophilic extraction was performed with a solution of deionized water and methanol (20:80, v/v) containing 1% formic acid. A total of 0.2 g of freeze-dried material was extracted with 1 ml of extraction solvent after being sonicated in an ultrasonic bath for 10 minutes and centrifuged at 15,000 rpm for 15 minutes. The supernatant was collected, and the pellet was extracted again via the same technique. The samples were transferred to vials and kept at -80°C until analysis. This extraction was tested for antioxidant activity, total phenolic compounds, and total condensed tannins. The total polyphenol content (TPC) was assessed via the Folin‒Ciocalteu reagent in accordance with Slinkard and Singleton’s method. First, 10 μl of hydrophilic extract was combined with 175 μl of distilled water, followed by 12 μl of Folin‒Ciocalteu reagent. After 3 min, 30 μl of 20% aqueous sodium carbonate solution was added. The samples were allowed to rest for 1 hour before being read at 765 nm with a spectrophotometer and compared to a range of known quantities of similarly produced gallic acid standards. The results are presented as milligrams of gallic acid equivalents per 100 grams of fresh weight (mg GAE·100 g-1 f.w.) [37].

2.5. Antioxidant Activity

The antioxidant activity was determined via two distinct tests, ABTS and DPPH, with a Synergy HTX multimode microplate reader (Biotek Instruments, Winooski, VT, USA). The ABTS free radical scavenging activity of the phenolic extract was tested via the previously disclosed procedures of Biotek Instruments [36]. The antioxidant activity data are presented as mmol Trolox equivalents per 100 g dry weight (mmol TE 100 g-1 d.w.). The DPPH method was adapted to a microplate reader [36]. Antioxidant activity was measured as mmol of Trolox equivalents per 100 g dry weight (mmol TE 100 g-1 d.w.).

2.6. Total Phenolic Content

The Folin‒Ciocalteu reagent was used to measure the total phenolic content in accordance with Slinkard and Singleton’s methodology. The findings are presented as milligrams of Gallic acid equivalents (mg GAE 100 g-1 f.w.) [37].

2.7. Analysis of Condensed Tannins

The evaluation of condensed tannins was performed via the method described by Deepa et al., 2007 [34] with minor changes. Briefly, hydrophilic extracts were mixed with a methanol vanillin solution (4% w/v) and concentrated hydrochloric acid for 20 min in the dark at room temperature. The absorbance was measured at 500 nm. The results are presented as milligrams of catching equivalents per 100 grams of dry weight (mg TE·100 g-1 d.w.).

2.8. Pigment Extraction and Analysis

We isolated lipophilic pigments following the protocol outlined by Yamashita and Nagata. In summary, 1 ml of a solvent mixture including hexane and acetone (4:6, v:v) was used to extract 0.2 g of freeze-dried material in the dark. The sample was then centrifuged for 15 minutes at 15000 rpm. Using the same procedure, the pellet was again removed from the supernatant. Prior to analysis, the samples were placed in vials and stored at -80°C [38].
The absorbance of the pigment extract was determined at 453, 505, 645, and 663 nm via a Synergy HTX multimode microplate reader (Biotek Instruments, Winooski, VT, USA). Nagata and Yamashita provided formulae for estimating chlorophyll A, chlorophyll B, β-carotene, and lycopene concentrations [38].

2.9. Protein Content Analysis

Protein content was determined by elemental analysis following the protocol performed by Muñoz-Redondo et al., 2023[39]. About 6500 µg of dried carob pulp were weighed into tin capsules (3.3 × 5 mm, IVA Analysentechnik e. K., Dusseldorf, Germany). The determination of % N values.was performed using a Flash EA elemental analyzer with TCD detector. A nitrogen to protein conversion factor of 6.25 was used to determine protein for each gram of material.

2.10. Determination of δ15N via EA-IRMS

All the peppers were sampled at the mature stage and homogenized by grinding and milling before analysis. The powdered materials were transferred into 2 mL Eppendorf tubes and kept at -18°C until analysis. A total of 4 mg of freeze-dried sweet pepper were weighed into tin capsules (3.3 × 5 mm, IVA Analysentechnik e. K., Dusseldorf, Germany) to determine the δ15N values. ISODAT software (version 3.0 from Thermo Scientific, Bremen, Germany) was used to acquire and process the signals collected by the IRMS devices. The nitrogen isotope ratios are represented relative to the international standard ratio and marked in delta notation, but milliurity (mUr) can also be used to comply with the International System of Units (SI), according to the formula published in Brand [39]. The instrument was calibrated with the following international reference standards: IAEA N1 (ammonium sulfate, δ15N = 0.43‰), IAEA NO3 (potassium nitrate, δ15N value of −4.70‰), and IAEA N2 (potassium nitrate, δ15N value of 20.30‰). To control and assure the quality of the results, working standards were inserted into each sequence, which was evaluated every ten samples. The analytical uncertainty was 0.3‰.

2.10. Statistical Analysis

Univariate statistical analyses were carried out to identify differences between samples via Statistix v. 9.0 software. The data were subjected to analysis of variance (ANOVA), followed by a comparison of means via Tukey’s post hoc tests.

3. Results

This study sought to investigate the effects of irrigation and fertilization methods, on the quality characteristics of three sweet pepper varieties (Kornelya, Kaptur, and Napoca).

3.1. Influence of Variety on Sweet Pepper Quality

ABTS and DPPH tests revealed differences in antioxidant activity among sweet pepper types (p ≤ 0.05). Kornelya F1 has the highest values for ABTS and DPPH, followed by Napoca F1 and Kaptur F1. Even if there are differences in antioxidant capacity between varieties, ABTS does not show any significance in terms of the results obtained. Kornelya F1 presented higher total polyphenol, chlorophyll A and B levels of lycopene and β-carotene than the other varieties. In terms of 15N content, the differences between cultivars are not significant. The protein content was also greater in the case of the Kornelya hybrid, with 27% difference to Napoca F1. The data in Table 1 show that there were significant differences in tannin content among the three varieties used. Similar results were also obtained in other studies on horticultural species in protected areas [40].

3.2. Influence of Fertilizers on Sweet Pepper Quality

Significant differences (p ≤ 0.05) in antioxidant activity, chlorophyll levels, and other biochemical indicators were detected between the fertilization types. Compared with chemical fertilization, biological fertilization, organic fertilization, and the unfertilized version resulted in higher ABTS and DPPH levels. Similarly, compared with the other fertilization methods, the control resulted in greater levels of chlorophyll A and B. These findings indicate that control and organic fertilization improved the antioxidant capacity and chlorophyll content of sweet peppers. Similar results were also obtained with peppers or strawberries grown in greenhouses, but the values were different
This study confirmed data from previous studies [39,42], which demonstrated that vegetables grown under chemical fertilization tend to have lower δ15N values. In our case, the mean value for δ15N of the samples was lower (6.6) than the values found for the other fertilization biological, control and organic treatments (7.5, 7.5, and 7.4, respectively), where no fertilizers from chemical synthesis were used. IRMS is a powerful technique for organic vegetable traceability. The results obtained for protein content were not significant, regardless of the fertilization regime applied to the long pepper crop.

3.3. Influence of Irrigation on Sweet Pepper Quality

Irrigation regimes have a considerable effect on sweet pepper quality. Drip irrigation with 5200 and 7800 m3·ha-1 highlights changes in antioxidant activity, phytochemical composition, and pigment concentration. The rational application of irrigation led to increased antioxidant activity and chlorophyll, β-carotene, and lycopene contents in peppers, demonstrating a positive relationship between water availability and quality. The data in Table 1 show that more water favours the primary compounds resulting from photosynthesis, particularly the N compounds, whereas a lower amount favours the secondary metabolism compounds (polyphenols, chlorophyll A and B, lycopene). Similar results have been obtained for other Solanaceae species, such as tomatoes [42,43].

3.4. Interaction Effect of Variety and Fertilization on Sweet Pepper Quality

The effects of pepper and fertilization methods resulted in significant changes in the antioxidant activity, pigment level, and tannin content (Table 2). Chemical, organic, and biological fertilization caused differences in all three types (Kornelya F1, Kaptur F1, and Napoca F1). Specifically, the untreated version and biological fertilization increased the antioxidant activity and pigment richness of the Kornelya F1 variety more than the organic version did. In contrast, the Kaptur cultivar presented a lower tannin level regardless of the fertilization type. These findings imply that the interplay between variety and fertilization method has a substantial effect on the quality features of sweet peppers.
The interaction between variety and fertilization type significantly influenced the antioxidant activity and chlorophyll content of sweet peppers (p ≤ 0.05). For example, Kornelya peppers treated with organic fertilization and an irrigation regime of 5200 m3·ha-1 presented the highest antioxidant activity and chlorophyll levels compared with those of the other combinations. In contrast, Kaptur treated with chemical fertilizer presented antioxidative activity and a lower chlorophyll concentration. In the case of protein content, the values between the variants are low, and in the case of 15N, the differences obtained between cultivar and fertilization combination are insignificant. Similar results were obtained for tomatoes by other authors. [14,44].

3.5. Interaction Effect of Variety and Irrigation on Sweet Pepper Quality

Data on the influence of cultivar and irrigation on long pepper fruit quality are presented in Table 3. The antioxidant activity determined by ABTS differed among the cultivar types and irrigation regimes. Kornelya F1, under 7800 m3·ha-1, presented the highest value, at 1.10 mg TE·100 g-1 d.w. The pigment content also varied, with Kornelya F1, and the highest values recorded when the plants were irrigated with a lower amount of water, at 5200 m3·ha-1. However, the tannin concentration did not exhibit a consistent pattern among the genotypes under the different amounts of irrigation. These findings highlight the need to address both variety and irrigation level in pepper production to increase fruit quality. This is what research indicates. The data obtained are in line with other studies carried out in the past, which supports the findings of our previous study [45]. Satisfactory results were also obtained in the context of lower water use, suggesting that the endemic hybrid Kornelya responds very well to lower irrigation conditions.

3.6. Interaction Effect of Fertilization and Irrigation on Sweet Pepper Quality

The effects of the interaction between fertilization and irrigation on several quality parameters in long peppers are presented in Table 4. For most of the compounds determined, fruit quality differs according to nutrients and irrigation, except for protein, for which the values obtained are not significant. The data in the tables highlight that higher values for chlorophyll and lycopene pigments are obtained in the untreated samples and those irrigated with a lower amount of water. β-Carotene is mainly produced by chemical fertilization when more water is used, and a relatively high tannin concentration is obtained in the presence of chemical fertilization and relatively low amounts of water. In general, chemical fertilization results in lower amounts of 15 N in the fruit than organic fertilization does, which stimulates greater amounts of protein.

4. Discussion

The current study investigated the effects of interactions among long pepper cultivars, irrigation regimes and fertilization methods on the quality attributes of fruits. In the current context of restrictive technologies to protect the environment and obtain food safe products, sustainable farming systems demand more restrictions regarding to use of chemical inputs. Significant information for increasing pepper quality was obtained through extensive tests that included antioxidant activity, chlorophyll levels, pigment concentrations, and other compounds with an essential role in human nutrition.
The comparison of three type of cultivars demonstrated the significance of genetic factors affecting sweet pepper quality. Similarly, F1 outperformed the other types in terms of the DPPH antioxidant test results, as well as pigments levels. These findings are consistent with prior research showing genetic diversity in phytochemical composition among different long pepper cultivars [37]. The fact that the highest values for the main pigments are present in Kornelya fruits is a premise that it is possible to obtain high-quality fruits, regardless of fertilization and irrigation. The Napoca cultivar also produces nutrient-rich fruits that are detrimental to the imported variety Kaptur. The data presented in other works show that the Kaptur hybrid results in high yields [42], but its quality suffers mainly. The selection of a cultivar adapted to crops in protected areas guarantees that high-quality fruit can be obtained by choosing the best genotype. Data highlight the positive correlation between pigment content and antioxidant activity. Variations in antioxidant activity and chlorophyll levels could be due to genetic differences across types. This is what research indicates. The quality of fruits is affected by several factors, including their variety [40].
The choice of fertilization method had a significant effect on sweet pepper quality. Compared with organic or biological fertilization, chemical nutrition improves antioxidant activity. This may be due to the higher solubility of nutrients from synthetic fertilizers. These findings support previous research demonstrating the benefits of conventional fertilizers in improving plant physiological growth, nutritional quality, and antioxidant content [46]. The increased antioxidant capacity reported in chemically fertilized peppers suggests a possible mechanism by which conventional farming practices lead to improved nutritional quality and health benefits in agricultural goods. The high level of nutritive compounds in the untreated variant can also be explained by the fact that the species benefit resiliently from nutrients from other previous crops but also in response to nutrient-related antistress factors. In particular, the growth mechanisms of biological species and plants, particularly those subjected to stress, are accelerated as natural impulses [42,47]. Although chemical fertilization accelerates the total pigment content with repercussions on the antioxidant capacity, biological and organic fertilization is one of the most viable nutritive methods to obtain quality products.
The irrigation regime significantly influences pepper quality characteristics. In particular, the application of less irrigation improved the water application rate, resulting in increased antioxidant activity, phytochemical composition, and pigment concentration, and higher correlation between main PCA (Figure S3) The positive relationship between irrigation intensity and quality features emphasizes the importance of water availability in promoting optimal plant physiological processes and nutrient uptake. Water is the main means of nutrient circulation in plants and the deposition of reserve substances in fruits. With the exception of chlorophyll and lycopene, the other compounds studied show small relative differences between the two watering standards, which means that even under slightly lower humidity conditions, the cultivars accumulate important antioxidant compounds [45,48], showing the benefits of precision irrigation, increasing water efficiency and crop quality [48].
Furthermore, the interaction impacts of variety, fertilization and irrigation regime demonstrated the complexity of factors affecting the quality of pepper fruits. Specific combinations had synergistic benefits, increasing the antioxidant activity and chlorophyll concentration. This emphasizes the need to consider several agronomic parameters when developing optimal growing practices.
The data regarding the main analysed compounds determined by the interaction between cultivar and fertilization show that they are positively influenced especially in Kornelya cultivar regardless of the type of fertilization, high values being obtained also in the non-fertilized version. Further the question can be raised: If the plants have not been fertilized, how is it that the main bioactive components are in higher quantity? The answer can be justified physiologically because under stress conditions, plant metabolism changes in the sense that generative activity is more intense than vegetative activity, PCAs being directed to fruits (Figure S3). Data on the increase of pigment content in fruits under nutrient stress have also been presented by Brezeanu et al., 2022.Tha data increased with 31.2% in the case of TPC and 20.2% in the case of ABTS, compared with chemically fertilized Kaptur. Additionally, in the case of the interaction between cultivar and lower fertilization regime, an increasing trend in antioxidant content was observed, mainly due to optimal water consumption, which indicates good adaptation of endemic cultivars. Greater differences are observed for chlorophyll and carotenoid pigments, the same being true for the control variant, which was irrigated with less water. With 15N exception, all PCA increased in Kornelya watering with IR1 and IR2.Under the influence of fertilization and irrigation, the PCA are distributed unevenly, which is why specific technological measures can be taken to improve the quality of pepper fruits. The results obtained under present study regarding the interaction effect on pepper fruit quality are the same as those reported for pepper [1,42] or tomato fruits [47].
Overall, the findings of this study have important implications for sustainable agricultural strategies aimed at increasing sweet pepper quality while reducing environmental effects. The use of ecologically friendly approaches, such as organic and biological fertilization and precision irrigation, appears to be a promising path for increasing crop nutritional content and antioxidant capacity. By explaining the complicated relationship between agricultural practices and sweet pepper quality, this study helps establish sustainable production strategies that benefit both human health and the environment.
These findings highlight the potential of sustainable agriculture to increase both human health and environmental sustainability.
The data from Figure S3 also highlight a positive correlation in the pepper fruit between PCA, which results in higher ABTS and DPPH values. The lower water stress and lack of fertilization for all varieties have led to the accumulation of higher contents of antioxidant compounds, which means that even in the context of organic agriculture and climate change, local long pepper varieties are a viable solution from a nutraceutical point of view.

5. Conclusions

The study of the qualitative features of long pepper varieties grown under various irrigation regimes and fertilization systems has shed light on the intricate interplay between technological factors.
Varieties, irrigation and fertilization measures strongly influence the nutraceutical quality of long peppers. Our study has confirmed that the hybrid Kornelya F1 is reached in contents of total chlorophyll and carotenoid pigments, TPC and antioxidant activity.
Moreover, the control and organic fertilization had positive effects on both the antioxidant activity and the chlorophyll content. With the exception of TPC and protein, where chemical fertilization increased the highest values, organic and biological fertilization ensure the production of nutraceutical-rich fruits, even with a reduced but constant irrigation regime. Additionally, when pepper plants are subjected to hydric and nutrient stress, they can accumulate greater amounts of antioxidant compounds through physiological mechanisms. The study revealed that under the influence of abiotic stress factors, such as irrigation and fertilization, sweet peppers have the ability to accumulate high amounts of antioxidant compounds in fruits. Finally, our study highlights the need for further research on the efficiency of different doses of organic and biological fertilizers to determine their impact on improving pepper fruit quality and production sustainability.

Supplementary Materials

The following supporting information can be downloaded at the website of this paper posted on Preprints.org

Author Contributions

Conceptualization, V.S., S.M.A.E., J.M.M.-R.; methodology, V.S., J.L.O.-D., J-C.M., J.M.M.-R.; software, V.S., G.-C.T., A.C., S.M.A.E. ; validation, V.S., J.L.O.-D., J-C.M., J.M.M.-R.; formal analysis, S.M.A.E., F.N.; investigation, V.S., G.-C.T., A.C., S.M.A.E., F.N.; resources, V.S., J.L.O.-D., J-C.M., J.M.M.E.-R.; data curation, V.S., J.M.E.E.-R.; writing—original draft preparation, V.S.; writing—review and editing, V.S., G.-C.T., J.M.M.-R.; visualization, V.S., G.-C.T., A.C., S.M.A.E., F.N.; bibliography, S.M.A.E., G.-C.T., A.C., F.N.; supervision, V.S., J.L.O.-D., J-C.M., J.M.M.-R. All authors have read and agreed to the published version of the manuscript.

Funding

The authors wish to thank “Ion Ionescu de la Brad” Iasi University of Life Sciences for financial support.

Data Availability Statement

Not applicable.

Acknowledgements

The authors wish to thank “Ion Ionescu de la Brad” Iasi University of Life Sciences (I.U.L.S.), Romania and the Andalusian Institute of Agricultural and Fisheries Research and Training (I.F.A.P.A.) Córdoba, Spain, for the financial support of the experiments. Thanks to Dr. Mihaela Rosca for statistical support.
The authors declare that they have no conflicts of interest.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Table 1. Influence of the experimental treatments on long sweet pepper quality.
Table 1. Influence of the experimental treatments on long sweet pepper quality.
Variable 15N Protein (%) TPC (mg GAE·100 g -1 d.w.) ABTS (mg TE·100 g -1 d.w.) DPPH (mg TE·100 g -1 d.w.) Chlorophyll A (mg·100 g -1 d.w.) Chlorophyll B (mg·100 g -1 d.w.) Lycopene (mg·100 g -1 d.w.) β-Carotene (mg·100 g -1 d.w.) Tannins (mg CE·100 g -1 d.w.)
Variety effects:
Kaptur F1 7.3 9.5b 4.7b 0.98 1.19b 0.82c 0.96b 0.64b 0.56b 0.29b
Kornelya F1 7.2 11.5a 5.4a 1.04 1.30a 1.35a 1.43a 1.10a 0.76a 0.37a
Napoca F1 7.3 9.0b 5.2a 0.99 1.27a 1.04b 0.76c 0.55c 0.51c 0.28b
Signification ns *** *** ns *** *** *** *** *** ***
Fertilization effects:
Chemical 6.6b 10.1 5.3a 1.03a 1.24ab 0.81c 0.84b 0.74b 0.83a 0.33a
Biological 7.5a 9.8 4.8b 0.96a 1.22b 1.23b 0.93b 0.70bc 0.51c 0.27b
Organic 7.4a 10.0 4.9b 0.98a 1.24ab 0.79c 0.83b 0.63c 0.73b 0.32a
Control 7.5a 10.2 5.3a 1.04a 1.32a 1.43a 1.59a 0.98a 0.37d 0.32a
Signification *** ns *** * * *** *** *** *** ***
Irrigation regimes:
IR1 7.2b 9.5b 5.0b 0.99 1.29a 1.27a 1.18a 0.84a 0.56b 0.31
IR2 7.4a 10.5a 5.2a 1.01 1.22b 0.86b 0.92b 0.69b 0.66a 0.31
Signification *** *** * ns ** *** *** *** *** ns
IR1 - 5200 m3·ha-1; IR2 - 7800 m3·ha-1; Within each column, n.s.-no statistically significant difference according to Tukey’s test at p > 0.05, a – higher value for each parameters; * significant difference, values associated with different letters are significantly different according to Tukey’s test at p = (0,01 – 0,05); ** very significant difference, values associated with different letters are very significantly different according to Tukey’s test at p = (0,001 – 0,01); *** extremely significant difference, values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.
Table 2. Influence of cultivar and fertilization regime on long sweet pepper quality.
Table 2. Influence of cultivar and fertilization regime on long sweet pepper quality.
Variable 15N Protein (%) TPC (mg GAE·100 g -1 d.w.) ABTS (mg TE·100 g -1 d.w.) DPPH (mg TE·100 g -1 d.w.) Chlorophyll A (mg·100 g -1 d.w.) Chlorophyll B (mg·100 g -1 d.w.) Lycopene (mg·100 g -1 d.w.) β-Carotene (mg·100 g -1 d.w.) Tannins (mg CE·100 g -1 d.w.)
Kaptur F1 x Chemical 6.6 9.3de 4.8cd 0.94b 1.16bc 0.82e 0.97bc 0.75cde 0.75c 0.29bc
Kaptur F1 x Biologic 7.5 9.4de 4.4d 1.01ab 1.24abc 0.79e 0.89bc 0.57 fg 0.41 g 0.29bc
Kaptur F1 x Organic 7.5 9.5de 4.5d 0.97ab 1.15bc 0.56f 0.73c 0.52 g 0.68cd 0.30bc
Kaptur F1 x Control 7.5 10.0bcde 5.0bcd 1.01ab 1.21bc 1.10cd 1.26b 0.71def 0.42 g 0.27c
Kornelya F1 x Chemical 6.6 11.3abc 5.8a 1.13a 1.27abc 0.82e 0.87bc 0.95b 1.17a 0.39a
Kornelya F1 x Biologic 7.6 11.5ab 5.2abc 0.91b 1.29abc 1.32c 1.08bc 0.92bc 0.70cd 0.32b
Kornelya F1 x Organic 7.3 11.1abcd 4.9bcd 1.04ab 1.32ab 0.93de 0.98bc 0.81bcd 0.96b 0.38a
Kornelya F1 x Control 7.4 12.2a 5.6a 1.09ab 1.33ab 2.33a 2.79a 1.71a 0.22 h 0.39a
Napoca F1 x Chemical 6.6 9.8cde 5.3abc 1.01ab 1.28abc 0.79e 0.68c 0.51 g 0.58de 0.31bc
Napoca F1 x Biologic 7.5 8.5e 4.8cd 0.96ab 1.12c 1.59b 0.83c 0.61efg 0.43 fg 0.21d
Napoca F1 x Organic 7.5 9.6cde 5.4ab 0.94b 1.26abc 0.90de 0.79c 0.55 fg 0.55ef 0.28bc
Napoca F1 x Control 7.6 8.3e 5.4abc 1.03ab 1.41a 0.86e 0.73c 0.51 g 0.47efg 0.30bc
Signification ns * ** * ** *** *** *** *** ***
Within each column, n.s.-no statistically significant difference according to Tukey’s test at p > 0.05, a – higher value for each parameters; * significant difference, values associated with different letters are significantly different according to Tukey’s test at p = (0,01 – 0,05); ** very significant difference, values associated with different letters are very significantly different according to Tukey’s test at p = (0,001 – 0,01); *** extremely significant difference, values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.
Table 3. Influence of cultivar and irrigation regime on long sweet pepper quality.
Table 3. Influence of cultivar and irrigation regime on long sweet pepper quality.
Variable 15N Protein (%) TPC (mg GAE·100 g -1 d.w.) ABTS (mg TE·100 g -1 d.w.) DPPH (mg TE·100 g -1 d.w.) Chlorophyll A (mg·100 g -1 d.w.) Chlorophyll B (mg·100 g -1 d.w.) Lycopene (mg·100 g -1 d.w.) β-Carotene (mg·100 g -1 d.w.) Tannins (mg CE·100 g -1 d.w.)
Kaptur F1 x IR1 7.2bc 9.0 4.7 1.01ab 1.22 0.87d 0.93bc 0.63c 0.49d 0.29b
Kaptur F1 x IR2 7.3ab 10.1 4.7 0.96b 1.16 0.76d 0.99bc 0.65c 0.64c 0.28b
Kornelya F1 x IR1 6.9c 11.3 5.2 0.99ab 1.32 1.66a 1.84a 1.43a 0.95a 0.37a
Kornelya F1 x IR2 7.6a 11.8 5.5 1.10a 1.29 1.03c 1.03b 0.77b 0.57c 0.37a
Napoca F1 x IR1 7.4ab 8.3 5.2 0.98b 1.34 1.27b 0.77c 0.45d 0.24e 0.26b
Napoca F1 x IR2 7.2b 9.8 5.3 0.99ab 1.20 0.80d 0.75c 0.64c 0.78b 0.29b
Signification *** ns ns * ns *** *** *** *** *
IR1 - 5200 m3·ha-1; IR2 - 7800 m3·ha-1; Within each column, n.s. no statistically significant difference according to Tukey’s test at p > 0.05, a – higher value for each parameters; * significant difference, values associated with different letters are significantly different according to Tukey’s test at p = (0,01 – 0,05); *** extremely significant difference, values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.
Table 4. Influence of nutrient system and irrigation regime on long sweet pepper quality.
Table 4. Influence of nutrient system and irrigation regime on long sweet pepper quality.
Variable 15N Protein (%) TPC (mg GAE·100 g -1 d.w.) ABTS (mg TE·100 g -1 d.w.) DPPH (mg TE·100 g -1 d.w.) Chlorophyll A (mg·100 g -1 d.w.) Chlorophyll B (mg·100 g -1 d.w.) Lycopene (mg·100 g -1 d.w.) β-Carotene (mg·100 g -1 d.w.) Tannins (mg CE·100 g -1 d.w.)
Chemical F1 x IR1 6.5e 9.9 5.5a 1.05 1.31abc 0.96cd 0.91bc 0.72bcd 0.64c 0.37a
Chemical x IR2 6.8de 10.3 5.1abc 1.01 1.17c 0.66f 0.77c 0.76bc 1.03a 0.29cde
Biologic x IR1 7.3bc 9.1 4.6cd 0.94 1.24abc 1.53b 0.97bc 0.77b 0.59c 0.26e
Biologic F1 x IR2 7.7ab 10.5 5.0bc 0.98 1.19abc 0.93cd 0.90bc 0.63cd 0.43d 0.29de
Organic x IR1 7.7ab 9.4 4.5d 0.99 1.31ab 0.75ef 0.82c 0.66bcd 0.87b 0.32bcd
Organic x IR2 7.2cd 10.7 5.4ab 0.98 1.18bc 0.84de 0.84c 0.60d 0.59c 0.32bc
Control x IR1 7.1cd 9.7 5.4ab 0.99 1.31ab 1.83a 2.01a 1.19a 0.14e 0.29cde
Control x IR2 7.9a 10.6 5.3ab 1.10 1.32a 1.03c 1.18b 0.77b 0.60c 0.35ab
Signification *** ns *** ns * *** *** *** *** ***
IR1 - 5200 m3·ha-1; IR2 - 7800 m3·ha-1; Within each column, n.s.-no statistically significant difference according to Tukey’s test at p > 0.05, a – higher value for each parameters; * significant difference, values associated with different letters are significantly different according to Tukey’s test at p = (0,01 – 0,05); *** extremely significant difference, values associated with different letters are extremely significantly different according to Tukey’s test at p ≤ 0.001.
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